deep structure of the armorican basin (bay of biscay): a review of norgasis seismic reflection and...

$: Deep structure of the Armorican Basin (Bay of Biscay): a review of Norgasis seismic reflection and refraction data$
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1

Deep stof Norg Thinon1, L

11BRGM-CDG

22Centro de G

33IUEM-UBO,

44Départemen

55IFREMER, D

Received 30

AbstractThe Bay o

Western A

considered

succession

is abrupt. T

profiles tog

important re

the Armoric

layer (7.4–

occurs exc

observed o

the North B

than a long

Keywords:

IntroducFrom the W

continental

wide (e.g. M

et al. 1985

Sibuet et a

deep boreh

tructuregasis se

L. Matias2

G/MA, 3 avenu

Geofisica, Rua

UMR6538 du

nt de Sismolog

DRO-GM, BP

July 2002; re

t of Biscay is

Approaches

this margi

n of tilted blo

This paper e

gether with

esult is the

can Basin (

–7.5 km s–1)

clusively und

only at the b

Biscay Ridg

g ridge elong

: Bay of Bis

ction West Iberia

crust and t

Montadert e

; Ginzburg

al. 1992). M

holes have

e of theeismic r

, J.P. RÉh

ue Claude Gui

da escola Po

u CNRS, Place

gie, UA195 CN

70, Place Nic

evised typesc

s bounded

and Armo

in typical o

ocks benea

examines th

new multich

discovery o

a deep sed

) overlain b

der the nar

base of the

e is a large

gated off th

scay, passiv

a margin to

typical ocea

et al. 1979a

et al. 1985

More recent

indicated th

Armorireflectio

hault3, A. H

illemin, BP 600

litecnica 58, 1

e Nicolas Cop

NRS, IPG, 4 p

olas Copernic

cript accepted

to the nor

orican seg

f a non-vol

ath which oc

he Armorica

hannel refle

of a 80 km w

dimentary ba

by sediment

rrow contine

continenta

e oceanic pl

e whole No

ve margins,

the Goban

anic crust w

a; Avedik et

5; Boillot et

tly, off the

hat this con

ican Baon and r

Hirn4, L. Fi

09, 45060 Orl

1200 Lisbon, P

pernic 29280 P

place Jussieu,

c 29280 Plouz

d 27 August 2

rth by the

ments. In

lcanic pass

ccurs the S

an segment

ection and r

wide ocean

asin). It is c

ts. The oth

ental slope;

al slope in t

lateau pres

orth Biscay m

transition z

n Spur mar

was first pro

t al. 1982; D

al. 1987a;

West Iberia

ntact may in

asin (Barefractio

idalgo-Go

léans cedex 2

Portugal

Plouzané, Fran

75252 Paris 0

zané, France

2002

North Bisc

the 1970s

sive margin

S reflector a

t and is bas

refraction s

–continent

characterize

her results a

; (2) the tilt

he narrow d

sent only off

margin.

zones, rifting

rgin, the zo

oposed as a

Derégnauco

Whitmarsh

a non-volca

nvolve a wi

ay of Bison data

nzÁlez3,5 &

, France (e-m

nce

05, France

ay margin,

s and 198

: it is chara

nd the cont

sed on a stu

eismic data

transition zo

ed by a high

are: (1) the

ed blocks a

domain call

f the NW Ar

g, crustal th

one of trans

a sharp tran

ourt & Boillo

et al. 1990

anic margin

der (30–120

scay): a

& F. Aved

mail: i.thinon@b

, which com

80s, most

acterized b

tinent–ocea

udy of all e

a (Norgasis

one that co

h-velocity lo

e main crus

and the S r

led the ‘nec

rmorican m

hinning.

sition betwe

nsition, less

ot 1982; de

0; Pinheiro

n, seismic

0 km) zone

a review

ik3,5

brgm.fr)

mprises the

researchers

by a striking

an boundary

arly seismic

s cruise). An

oincides with

ower-crusta

stal thinning

reflector are

ck area’; (3

margin rathe

een thinned

than 10 km

Graciansky

et al. 1992

profiles and

e referred to

w

e

s

g

y

c

n

h

al

g

e

)

r

d

m

y

2;

d

o

hal-0

0647

845,

ver

sion

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n 20

12Author manuscript, published in "Journal of the Geological Society of London 160 (2003) 99-116"

DOI : 10.1144/0016-764901-103

http://dx.doi.org/10.1144/0016-764901-103

http://hal-brgm.archives-ouvertes.fr/hal-00647845/fr/

http://hal.archives-ouvertes.fr

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69

70

2

as the ocea

exhumed c

with a very

much lower

Reflection

(between 4

velocities o

dipping seis

et al. 1995

between 7.

1999), whic

measured

common fe

velocity low

interpreted

mantle (Wh

basic comp

(Srivastava

suggested

exhumed a

et al. 1980

1999; Whit

Greenland

Basin (Reid

been suppo

Iberia penin

al. 1994; W

From these

during prol

Although th

some non-v

they would

(Skogseid

margins pr

considerab

margin.

an–continen

continental m

y quiet mag

r than those

profiles sho

4.5 and 6.0

of 7.2–7.6 k

smic reflect

5, 1999, Lo

.2 and 7.6 k

ch are lowe

within the

eature of th

wer-crustal l

variously a

hitmarsh &

position; (2

a & Roest 19

for the Ne

and variably

, 1987b; G

tmarsh et a

margins (C

d 1994), an

orted by geo

nsula (e.g. B

Whitmarsh e

e examples

longed per

he 7.2–7.6

volcanic rift

represent

et al. 1992

resented b

ly thicker th

nt transition

mantle (Wh

netic zone

e of the wel

ow that the

km s–1), an

km s–1 and

tors (Pickup

ouden & C

km s–1 (e.g.

er than that

oceanic lay

is and othe

layer (Loud

as one of th

Miles 199

2) thin, tect

995; Srivas

wfoundland

y serpentiniz

irardeau et

al. 2001). T

Chian & Lou

nd the SW

ological dat

Boillot et al

t al. 1998) a

s, there is g

riods of ext

km s–1 velo

ted margins

underplatin

2; White 19

by White (

han normal

(e.g. Picku

itmarsh et a

(Whitmarsh

l-known Cre

upper bas

nd are unde

by a comp

p et al. 1996

hian 1999)

Whitmarsh

t measured

yer 3 or w

er ocean–co

en & Chian

he following

95), which m

tonized oce

tava et al. 2

d Basin and

zed upper m

al. 1988; S

This last int

uden 1994;

Australia m

ta obtained

. 1987b, 19

and by dred

general agr

tension wit

cities are c

s, they are a

g gabbros o

992a). One

1992a, 199

off a volcan

up et al. 199

al. 2001). T

h et al. 199

etaceous M

sement rock

erlain by a

plex reflecti

6). This zon

). The deep

h et al. 199

d within nor

within lower

ontinent tra

n 1999). Cu

: (1) thinne

may repres

eanic crust

2000); (3) te

d Flemish C

mantle, as s

Sawyer et a

terpretation

Chian et a

margin (Nic

by dredgin

988; Beslier

dging off the

reement for

th little or

characteristi

also observ

or a lower c

of the diffe

92b) conce

nic margin

96; Whitmar

he ocean–c

90) whose m

Magnetic Qu

ks are very

lower base

ivity includi

ne has a lac

pest basem

90; Chian &

rmal mantle

continenta

nsition zon

rrently, oce

ed continent

sent transiti

produced

ectonized u

Cap margin

suggested f

al. 1994; W

is also va

al. 1995; Ch

cholls et al.

g, drilling a

et al. 1988

e Australian

r an ocean–

no melt ge

ic of the oc

ved beneath

continental

erences be

erns the a

and is thinn

rsh & Sawye

continent tra

magnetic an

iet Period.

y thin, with

ement layer

ng both lan

ck of Moho

ment layer

Louden 19

e (8 km s–1)

al crust (6.5

es and is re

ean–contine

tal crust intr

ional contin

by ultraslo

nderplated

ns (Keen &

for the Wes

Whitmarsh et

lid for the

halmers 199

. 1981). Th

nd using su

; Girardeau

margin (Ni

–continent t

enerated fro

cean–contin

h volcanic p

crust intrud

etween volc

djacent oc

ner than nor

yer 1996) or

ansition zon

nomaly am

typically lo

r characteriz

ndward- an

reflections

has seism

994; Chian

), and highe

5–7 km s–1

referred to a

ent transitio

ruded by m

nental crust

ow sea-floo

gabbros, a

& De Voogd

st Iberia ma

t al. 1998;

Labrador a

97), the Ne

his last hyp

ubmersible o

u et al. 1988

icholls et al

transition z

om the up

nent transitio

passive mar

ded by maf

canic and n

ceanic crus

rmal off a n

r the zone o

ne coincides

plitudes are

w velocities

zed by high

nd seaward

(e.g. Chian

ic velocities

et al. 1995

er than tha

). This is a

as the high

n zones are

melt from the

t with more

r spreading

s previously

d 1988); (4

argin (Boillo

Chian et al

and western

ewfoundland

othesis has

off the Wes

8; Sawyer e

. 1981).

zone formed

per mantle

on zones o

rgins, where

ic intrusions

non-volcanic

st, which is

non-volcanic

of

s

e

s

h

-

n

s

5,

at

a

-

e

e

e

g

y

)

ot

l.

n

d

s

st

et

d

e.

of

e

s

c

s

c

hal-0

0647

845,

ver

sion

1 -

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n 20

12

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72

73

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79 80

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99

100

101

102

103

104

105

3

This paper

to the ocea

the bounda

crustal thin

constraints

thinning, th

study is the

domains.

RegionaThe Bay of

the North

segments:

northern (N

morphology

Western Ap

boundary o

Canyon an

continental

to the west

The relativ

1996) durin

with the op

Biscay and

al. 1979b)

Late Aptian

sediments

Chron 33 (8

ceased afte

Biscay is s

(80–35 Ma

led to the p

The Trevel

formed dur

Thinon et a

Armorican

examines

anic crust. T

aries betwe

ning and to

are neces

he initiation

e discovery

al settingf Biscay (se

Biscay mar

the Weste

N110°) and

y of the Nor

pproaches

of the Wes

nd linked by

slope of th

by the Trev

e moveme

ng Early Cre

pening of th

the age of

mark the b

n) and the

consist of J

80 Ma, Cam

er Chron 34

strongly link

) convergen

partial closi

lyan Seam

ring the Py

al. 2001). Re

Basin is ve

the Armoric

The principa

een oceanic

o determine

ssary for m

of oceanic

y of a wide

g ee Fig. 1) is

rgin and th

ern Approa

southern (N

rth Biscay m

domain co

stern Appro

y the abrup

e Armorican

velyan–Mer

nts betwee

etaceous tim

he North At

the synrift s

beginning o

beginning

Jurassic (15

mpanian) ha

4 (Fig. 2; W

ked to the P

nce of the

ing of the B

ount (see

yrenean co

ecent studie

ry weakly a

can segmen

al aims of th

c and contin

the crustal

modelling t

c accretion,

e transitiona

s a triangula

he North Ib

ches marg

N140°) com

margin, disr

llinear with

aches marg

pt eastern

n margin, w

riadzek com

en the Nort

me induced

tlantic Ocea

sediments d

f rifting dur

of oceanic

50–140 Ma

as not been

Williams 197

Pyrenean o

Iberia penin

Bay of Bisc

Fig. 1) and

mpressive

es of the Py

affected by

nt of the No

he study re

nental crus

structure o

he process

and kinem

al domain b

ar oceanic

beria margin

gin (oriente

mponents. A

rupted only

the NE–SW

rgin with th

termination

we distinguis

mplex and to

th American

d the format

an. The ab

drilled on th

ring the Ea

c accretion

a, Kimmerid

n recognize

75). The lat

orogenic ph

nsula towar

cay and ma

d the Dôm

phase (De

yrenean pha

the Pyrene

orth Biscay

eported here

sts, to deter

f the whole

ses of con

matic recons

between the

domain bo

n. The Nor

d N110°)

steep linea

by the Mer

W axis of t

e Armorica

n of Meriad

sh a deep b

o the east b

n, Europea

tion of the B

bsence of m

he Western

rly Cretace

in Late Ap

gian to Por

d, the ocea

ter post-rift

ases induc

rds Europe

ajor deforma

e Gascogn

byser et al

ase emphas

an compres

margin from

e were to id

rmine the lo

margin. Su

tinental bre

structions. T

e typical co

unded by tw

rth Biscay

and the Ar

ar continent

riadzek Ter

he English

an margin is

dzek Terrac

basin, the A

by the Dôme

an and Iber

Bay of Bisca

magnetic Ch

Approache

ous (140–1

ptian–earlies

rtlandian) pl

anic accretio

structural e

ced by the C

. This conv

ation of the

ne are large

l. 1971; Fra

size a partic

ssive deform

m the conti

dentify more

ocation of

uch data an

eak-up and

The main re

ontinental a

wo conjuga

margin com

rmorican m

tal slope do

rrace promo

Channel R

s near the

ce. At the b

Armorican B

e Gascogne

rian plates

ay, contemp

hron M0 in

es margin (M

110 Ma, Ne

st Albian ti

latform carb

on of the Ba

evolution of

Campanian

vergent mov

e North Iber

e structura

rappa & Va

cular charac

mation pha

nental shel

e accurately

the zone o

d geometric

d of crusta

esult of this

and oceanic

ate margins

mprises two

margin, with

ominates the

ontory in the

Rift. The SE

Black Mud

base of the

asin, limited

e structure.

(e.g. Olive

poraneously

the Bay o

Montadert e

eocomian to

ime. Pre-rif

bonates. As

ay of Biscay

f the Bay o

n–Oligocene

vement also

rian margin

l inversions

aillant 1972

cteristic: the

se, which is

lf

y

of

c

al

s

c

s,

o

h

e

e

E

d

e

d

et

y

of

et

o

ft

s

y

of

e

o

n.

s

2;

e

s

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

106

107

108 109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

4

intense onl

structures a

BackgroThe Bay o

Montadert

Barbier 198

Avedik et a

The North

margin (e.

Derégnauc

Pichon & B

margin acro

first observ

these obse

that the We

striking suc

pattern of

margin is c

(Fig. 3b; L

Barbier et

Armorican

slope to the

new seismi

The Armori

Resting on

km s–1 (Bac

morphology

et al. 1973;

1971; Grau

synrift form

been interp

al. 2002). T

attributed to

1973) or to

al. 1974), t

km) contine

ly at its oce

are today pr

ound of Biscay w

et al. 1971,

87). Ocean

al. 1996; Thi

Biscay mar

g. Montad

court & Boill

Barbier 198

oss the Me

ved a strong

rvations, m

estern Appr

ccession of

the Armori

haracterize

e Pichon &

al. (1986)

margin, and

e oceanic d

ic dataset, w

ican Basin

the basem

con et al. 1

y and acous

Montadert

u et al. 1973

mation of the

preted as a

This unit re

o the top o

the S refle

the substrat

ental crust

eanic and c

reserved on

was survey

, 1974, 197

nographic s

inon 1999).

rgin is usua

dert et al.

lot 1982; G

7). From th

eriadzek–Tre

g reflector b

ost workers

roaches ma

tilted fault b

can margin

ed by signific

& Sibuet 19

applied th

d proposed

omain, by a

we verify th

is a thick se

ment, Unit 3

969) to 4.6

stic facies,

et al. 1974

3); (3) pre-r

e Western A

sedimentar

ests on a s

of the basem

ctor (Barbie

tum of the A

(Fig. 3b an

continental

n the North

yed extensi

79; Derégna

urveys beg

ally conside

1974, 197

inzburg et a

he few scatt

evelyan com

below the ti

s (e.g. Aved

argin from t

blocks bene

n is controv

cant crustal

981). More

he global s

that the Ar

a successio

is crustal pa

edimentary

B, a seism

6 km s–1 (Av

Unit 3B was

; Derégnau

ift Cretaceo

Approaches

ry body emp

subhorizonta

ment (Mont

er et al. 198

Armorican

nd c; Grau

domain bo

Biscay mar

ively in the

aucourt & B

gan again in

ered to be

79b; de C

al. 1985; Ba

tered seism

mplex (Mon

ilted blocks

dik & Howar

the shelf to

eath which o

versial. Firs

l necking un

recently, u

structural p

rmorican ma

on of tilted b

attern.

basin (5–7

ically transp

vedik & How

s interprete

ucourt & Boi

ous sedimen

s margin (M

placed by s

al layer wit

tadert et al.

86). Rather

Basin is tho

et al. 197

oundaries (f

rgin and in t

e 1970s an

Boillot 1982;

n 1994 and

a typical ex

Charpal et

arbier et al

mic profiles

ntadert et a

, which the

rd 1979; Mo

the true oc

occurs the S

st, on the

nder the slo

using the S

pattern of

argin was c

blocks over

km thick),

parent unit

ward 1979)

ed as: (1) ev

illot 1982); (

nts (Barbier

Montadert 1

lumping at

th high-amp

. 1971, 197

than being

ought to co

3; Avedik &

fig. 5 of Th

the Parentis

nd 1980s (

; Barbier et

d 1997 (e.g

xample of a

al. 1978;

. 1986; Wh

shot off the

al. 1971), de

y called the

ontadert et

ceanic crus

S reflector (

basis of su

ope and by t

SNEAp seis

Montadert

characterize

the S reflec

discovered

characteriz

, is present

vaporites (S

(2) basaltic

r et al. 1986

1984). More

the end of r

plitude and

74; Sibuet e

a typical oc

onsist of an

& Howard 1

hinon et al.

s Basin (see

(Debyser e

t al. 1986; L

g. the Norg

a non-volca

Avedik e

itmarsh et a

e Western A

e Charpal e

e S reflecto

al. 1979b) h

st is charact

(Fig. 3a). Th

ubsidence

the lack of

smic reflect

et al. (197

ed, from the

ctor (Fig. 3c

byBacon e

zed by velo

t (Fig. 4). B

Sibuet et al.

rocks (Mon

6); (4) equiv

e recently, U

rifting phase

continuous

et al. 1971;

ceanic crust

extremely

1979; Mont

2001). Rif

e Fig. 1).

et al. 1971

Le Pichon &

gasis cruise

anic passive

t al. 1982

al. 1986; Le

Approaches

et al. (1978

or. Following

have shown

terized by a

he structura

history, the

tilted blocks

ion dataset

79b) to the

e continenta

c). From ou

et al. (1969)

cities of 4.4

Based on its

1971; Grau

ntadert et al

valent to the

Unit 3B has

e (Thinon e

s reflections

Grau et al

t (Limond e

thinned (<4

tadert et al

ft

;

&

e;

e

2;

e

s

)

g

n

a

al

e

s

t,

e

al

r

).

4

s

u

l.

e

s

et

s

l.

et

4

l.

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163 164

165

166

167

168

169

170

171

172

173

174

175

176

177

5

1979b; Le

about the n

Basin, the

was: (1) cr

result of a l

1) (Derégna

Bay of Bisc

seismic ref

so as to un

The northe

less than 1

Ginzburg e

1971; Grau

that this bo

crossed on

strong, line

& Le Mouë

margin (see

show using

unlikely to

Bay of Bisc

Seismic The structu

seismic pro

1979b; Va

processed

Société Na

provide a s

the North B

Armorican

seismic refl

The Norgas

using a sin

(Avedik et

17 s TWTT

continental

Pichon & S

nature and

nature of i

reated along

ate Triassic

aucourt & B

cay (Debys

fraction and

derstand its

rn continen

0 km in wid

et al. 1985;

u et al. 197

oundary is

nly by the O

ear and neg

l 1970; Fig.

e Fig. 2a; M

g our new

extend alon

cay of a wid

data acqural analys

ofiles acquir

illant 1988

stacked mu

tionale ELF

shallow to d

Biscay mar

margin do n

lection and

sis seismic

ngle bubble

al. 1993, 19

T recording

shelf, slop

Sibuet 1981

the age of

its substrat

g a strike-s

c extension

Boillot 1982

er et al. 19

d reflection

s origin.

nt–ocean bo

dth (de Cha

Whitmarsh

73; Montade

associated

OC17 seism

ative magn

. 2a), this b

Montadert e

seismic da

ng the entir

e ocean–co

quisitionis presente

red between

). They in

ultichannel

F (Barbier e

eep crustal

rgin and of

not reach th

refraction d

c reflection

e array with

996). Twen

provides d

pe and the

; Derégnau

f Unit 3B ha

um and its

slip fault sy

al phase (li

; Olivet 199

971; de Cha

data, we he

oundary of t

arpal et al. 1

et al. 1986

ert et al. 19

d with a ba

mic profile (

netic anoma

basement hi

et al. 1979b

ata and pro

re North Bis

ontinent tran

n and proed in this p

n 1969 and

clude a re

seismic ref

t al. 1986).

l seismic im

f the Armor

he oceanic d

data collecte

profiles wer

h 8–10 air

nty-four-fold

eep crustal

true ocean

ucourt & Bo

ave led to

origin. Diff

ystem of the

ke the Engl

96); (3) form

arpal et al.

ere describ

the Bay of

1978; Aved

6). Most wo

974, 1979b;

asement hig

(Figs 3b an

aly observed

igh was infe

b; Derégna

ocessed ma

scay margin

nsition zone

ocessingpaper is m

d 1981 (Fig.

ectangular

flection prof

These last

mage (10–12

rican Basin

domain. Th

ed during th

re acquired

guns and

coverage w

l seismic im

ic areas. T

oillot 1982; B

controversy

fferent hypo

e Hercynian

lish Channe

med during

1978; Le P

be the deep

Biscay was

ik et al. 198

orkers (e.g.

; Le Pichon

gh called t

d 4). On th

d on the tot

erred to ext

ucourt & Bo

agnetic data

n. We will a

e.

g ainly based

1; e.g. Deb

net of 650

files (with a

lines (SNE

2 s TWTT (

n. Unfortuna

ese data ar

he Norgasis

d with a 96-

a generato

was availab

mages of th

The Norgasi

Barbier et a

y about the

otheses pos

n Orogeny

el Rift and th

the Early C

Pichon & Sib

structure o

s previously

82; Derégna

Bacon et a

n & Sibuet

he North B

he evidence

tal magnetic

end along t

oillot 1982)

a that the

also discuss

d on a rein

byser et al.

00 km of i

a 24-fold re

Ap), which

(two-way tra

ately, the S

re complete

s cruise.

-channel st

or capacity

ble with a 5

e Armorica

is seismic r

al. 1986). U

e age of the

stulated tha

(Ziegler 19

he Parentis

Cretaceous

buet 1981).

of the Armo

y assumed t

aucourt & B

al. 1969; De

1981) have

Biscay Ridg

e of the con

c field map

the entire N

). In this pa

North Bisca

s the occurr

nterpretatio

1971; Mon

industry ac

ecording sys

we have re

avel time) re

SNEAp pro

ed by new m

treamer (25

from 804

50 m shot in

an margin in

refraction d

Uncertainties

e Armorican

at the basin

982); (2) the

s Basin (Fig

rifting of the

. Using new

orican Basin

to be sharp

Boillot 1982

ebyser et al

e postulated

ge, which is

ntinuity of a

(Le Borgne

North Biscay

aper, we wil

ay Ridge is

rence in the

n of all the

ntadert et al

cquired and

stem) of the

einterpreted

ecording) o

files off the

multichanne

5 m interval

to 1230 in

nterval. The

ncluding the

data (Fig. 1

s

n

n

e

g.

e

w

n

p,

2;

l.

d

s

a

e

y

ll

s

e

e

l.

d

e

d,

of

e

el

)

n3

e

e

)

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

6

were acqui

by the LOB

providing a

were digitiz

matching t

crustal stru

algorithm o

vertical inc

refractors s

layer veloc

later). The

positions w

gradients o

method of

model, pres

mainly from

of the spac

strike profi

Norgasis 14

The details

some of th

interpreted

critical are

uncertainty

obtained by

seismic ref

The density

of 0.2 km s

computed f

crustal laye

(phase PHP

3B (5.2 km

reflections,

f). Refracte

5d). The str

3 (P3) (see

identificatio

red using a

BS Laborat

large set o

zed at a 100

he observe

ucture of t

of Zelt & S

cidence pro

so that thei

cities were a

deeper lay

were later

of the differe

Zelt & Elli

sented for t

m record se

cing of instru

les and the

4 model rep

of the anal

he most rele

travel time

as of the

y. The layer

y Ludwig et

fraction mod

y of the hig

s–1 in its orig

free-air ano

er are cons

P) and its b

m s–1) and

as illustrat

ed arrivals f

ructure of th

e Fig. 5c).

on of both P

an array of

tory (Kanas

of long and s

0 Hz sampli

ed and com

he in-line

Smith (1992

ofiles were

r location m

allowed to

yers are be

compared

ent layers w

s (1988), w

he Norgasis

ections obta

uments (abo

e parallel p

presents a s

lysis of the

evant featu

e curves (F

model. Tra

r densities

t al. (1970)

del had to

h-velocity lo

ginal velocit

omalies is

strained by

base (phase

the high-v

ted by the o

from the up

he oceanic

Here the p

PHP and PM

20 ocean-b

sawa & Sh

short profile

ng rate. Wh

mputed prim

profiles wa

2). The mai

e found to

measured i

vary. This

tter constra

with the v

were refined

which is ba

s 14 profile

ained from s

out 20 km),

profile near

synthesis of

seismic refr

ures are pre

Fig. 5a) sho

avel time r

were estim

and a 2D g

be slightly

ower-crusta

ty (from 7.2

3.0 mGal.

refracted a

e PMP) (see

velocity low

observation

per mantle

crust is ded

presence of

MP arrivals t

bottom seis

hiobara 199

es together

hen necess

mary and f

as obtained

in horizons

correspon

n TWTT w

restriction a

ained by the

vertical inci

d by the use

ased on as

(see Fig. 7

seven ocea

, many featu

r seismic l

f the interpr

raction data

esented in

ows that th

residuals a

mated from t

gravity mode

modified in

al layer was

2 to 7.4 km

The veloci

arrivals (ph

e Fig. 5d an

wer-crustal l

s and mode

(phase Pn

duced from

f the high-v

that are con

smometers d

94). The ins

with many o

sary, the ins

first multiple

d using the

identified

nd to signi

was kept fixe

applied also

e ocean-bo

idence data

e of synthet

symptotic ra

7c, below) a

an-bottom s

ures of the

ine OC17

retation of th

a will be pre

Figure 5. T

he deep str

are less tha

the P-wave

el was obta

n the uncon

s also reduc

s–1). The r.m

ty and thic

hase PH) a

nd e). The h

layer (7.4

elled by sy

) are also o

refracted a

velocity low

nspicuous o

developed

struments r

off-line sect

trument loc

e water-wa

e joint inve

in the sedi

ficant wide

ed during t

o to the MS

ottom seism

a. The thic

tic seismog

ay theory. T

nd discusse

seismomete

velocity mo

(see Fig. 6

he whole da

esented in a

The ray tra

ucture is w

an 0.1 s,

e velocity m

ained (Fig. 5

strained pa

ced, corresp

m.s. misfit b

kness of th

and reflecte

igh velocity

km s–1) pro

nthetic seis

observed in

arrivals from

er-crustal la

on several o

at Hokkaid

recorded co

tions. The s

cation was c

ave arrivals

ersion and

imentary co

e-angle ref

the inversio

S and S ho

mometer da

ckness, ve

grams comp

The seismi

ed in the te

ers. Howeve

odel are cle

6, below).

ataset.

a forthcomin

acing that m

well constra

the estima

model using

5b). Near th

art to obtain

ponding to

between ob

he high-vel

ed arrivals f

y contrast b

oduces hig

smograms (

some reco

m layer 2 (P2

ayer is infe

other record

o University

ontinuously

seismic data

corrected by

. The initia

ray-tracing

over on the

flectors and

on. Only the

orizons (see

ta and thei

locities and

puted by the

ic refraction

xt, was buil

er, because

arest on the

In fact, the

ng paper bu

matches the

ained in two

ated picking

g the curves

he coast the

n a good fit

a difference

bserved and

ocity lower

from its top

etween Uni

h-amplitude

(Fig. 5e and

ordings (Fig

2) and laye

erred by the

d sections.

y

y,

a

y

al

g

e

d

e

e

r

d

e

n

lt

e

e

e

ut

e

o

g

s

e

t.

e

d

r-

p

it

e

d

g.

r

e

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

215

216

217

218

219

220

221

222 223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

7

More recen

on board th

10 knots w

TWTT reco

software w

complete a

across this

InterpretFrom our d

domains (I,

(IV), which

through a z

V (Fig. 7).

The Armor

The contine

(around 3 s

8). At its ba

and low fre

profiles acr

about 30–3

lower crust

The contine

simple and

narrower in

(<4°) in its

escarpmen

constitutes

upper part

slope, no c

the lower c

inherent fe

areas. It co

intra-crusta

Faulted and

the contine

ntly, we ma

he R.V. l'At

with a six-ch

ording. A co

was applied

and homoge

non-volcan

tation ata, we hav

, shelf; II, s

does not

zone we cal

rican conti

ental crust

s TWTT thic

ase (at 10–

equency. We

ross the co

32 km thick

(Avedik & H

ental slope

d steep slop

n its lower

s upper pa

nt, which is

the oceanw

of the slop

conspicuous

continental

ature of the

ould also re

al fluid circu

d tilted con

ental slope,

de a multib

talante (Fig.

hannel stre

onventional

d to the N

eneous dat

nic passive

ve divided t

lope) to the

present any

ll the ‘neck

inental mar

of the she

ck) that disp

–11 s TWTT

e interpret i

ontinental s

with velocit

Howard 197

e exhibits a

pe (30 km

part (15 km

rt. The sei

s exposed

ward flank o

pe (Fig. 8)

s tilted fault

crust is st

e acquisitio

eflect the r

lation).

tinental blo

and corres

beam surve

. 1). During

eamer, two

l seismic pr

orgasis an

aset (18 00

margin.

he Armorica

e oceanic do

y character

area’ (III). T

rgin (doma

lf comprise

plays horizo

T depth), th

it as the Mo

shelf (Cazes

ties of 5.8–

79).

variable m

wide, with

m wide with

smic profile

or covered

of a horst, w

or marks t

ted blocks h

rongly atten

on and proc

ifting proce

ocks are res

ponding to

ey of this zo

g this cruise

Generator

rocessing s

d Zee-Gas

00 km) prov

an margin i

omain (V).

ristics of th

The Norgas

ains I, II and

es a non-re

ontal, high-a

ere is a thr

oho reflectio

s et al. 19

–6.1 km s–1 f

morphology

a dip of 7°

h an averag

es show th

d by thin s

which eithe

the edge of

have been

nuated on

cessing of

ess (tectonic

stricted to a

the ‘neck a

one during t

e, seismic re

injector gu

scheme (sta

scogne refl

vides new i

nto five dom

They are s

e others an

sis14 profile

d III)

eflective cru

amplitude a

ree-phase r

on, following

88; Dymen

for the uppe

(Fig. 1). Its

°). The Sou

ge dip of 7

hat the stee

ediments (

r bounds a

f the shelf

observed. U

all seismic

seismic pro

c and therm

a deeper 30

area’ (zone

the Zee-Ga

eflection pro

ns (105 in2

ack, migrat

ection data

information

mains (Fig.

eparated by

nd which pa

extends fro

ust lying on

and low-freq

eflection wi

g a compar

nt 1989). Th

er crust and

s northern

uth Armoric

°), and wid

ep slope c

Figs 8 and

hanging se

(Fig. 9). Be

Under the s

c lines (Fig.

ofiles in ste

mal events

0 km wide d

III, Fig. 6).

ascogne cru

ofiles were 2 each), an

tion) using

a (Thinon

on the dee

6) from the

y a transitio

asses to th

om domain

a layered

quency refle

ith very hig

rison with ot

he continen

d 6.6–7.0 km

segment c

can slope is

der and wea

coincides w

d 9). This

edimentary

eneath the

slope, the r

. 8). This c

eeply dippin

and conse

domain, at

This is the

uise in 1997

acquired a

d with 10 s

the ProMax

1999). This

ep structure

e continenta

onal domain

he slope (II

I to domain

lower crus

ections (Fig

h amplitude

ther seismic

ntal crust is

m s–1 for the

onstitutes a

s steep and

akly dipping

with a majo

escarpmen

basin in the

continenta

eflectivity o

could be an

ng sea-floo

equences o

the base o

last domain

7

at

s

x

s

e

al

n

)

n

st

g.

e

c

s

e

a

d

g

r

nt

e

al

of

n

r

of

of

n

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

8

oceanward

several hor

tilted blocks

(Figs 8 and

less than 2

on a portion

exhibits a h

crust blocks

is identified

(6.2–6.8 km

observed b

foot of the

11). The to

reflection th

at 10 s TW

wedged ou

deep-layere

vertical velo

6.8 to 6.9 k

and seems

under the

continental

Transitiona

Along the A

transitional

amplitude m

eastern par

its substrat

Substratum

an acoustic

frequencies

systematica

situated at

large wave

that the bul

in which re

rsts, which

s (two succ

d 9). These

0 km wide.

n of the cru

horst with ve

s in the ‘ne

d as the S r

m s–1; Fig. 7

between the

continental

op of this de

hat deepens

WTT (Figs 8

ut above its

ed unit is th

ocity distrib

km s–1, simil

s to also hav

shelf. The

crust of the

al domain

Armorican m

domain (z

magnetic an

rt exhibits s

um has neit

m of transitio

c reflector,

s that were

ally truncate

depths of

length bulg

lges formed

emnants of

can create

cessive blo

e blocks are

The tilted b

st (Figs 9 a

elocities fro

eck area’. Th

reflector (Fig

b). We emp

e S reflecto

l slope, the

eep-layered

s landward

8 and 11). T

base, whic

hus sandwic

bution (Fig.

ar to those

ve no direc

nature of

e shelf, a ne

(domain IV

margin, the

zone IV, Fig

nomalies, w

some discre

ther the cha

onal domain

the MS ref

e in the p

es the dippi

8–9.5 s TW

ges (Fig. 13

d just before

f the contin

relief at the

cks at mos

e uncommo

blocks inclu

and 10). The

om 5.4 to 6.

he blocks a

gs 7a and 1

phasize that

r and any s

Norgasis r

d unit coinci

, evolving fr

The interna

ch we have

ched betwee

7b) shows

of the lowe

t seismic re

this deep-

ew layered c

V)

continental

g. 6), assoc

without linea

ete, strong a

aracteristics

n. Througho

flector that

past consid

ng reflector

WTT (Figs

), generally

e deposition

nental crust

e foot of th

st, Figs 10

on, relatively

de a very im

e refraction

2 km s–1 tha

are tilted on

10) and coi

t on all seis

structure or

reflection da

ides with th

from a singl

al reflections

e attributed

en the S ref

that this d

er continent

elation with

layered un

continental

l and ocean

ciated with

arity, simila

and positive

s of the con

out the tran

gives rise

dered to re

rs (DR) in th

7 and 12).

y independe

n of the first

have been

he slope (Fi

and 11) an

y small in s

mportant pr

model alon

at confirms

a strong, c

ncides with

smic lines n

r reflector w

ata show a

he S reflecto

e reflection

s character

to the crus

flector and

eep-layered

tal crust. Th

the layered

it remains

crust, or ot

nic domains

a magnetic

r to a very

e magnetic

tinental cru

nsitional dom

to reflectio

epresent th

he underlyin

Its regiona

ent of the o

post-rift se

n observed.

gs 1, 4 and

d some sh

size, 2 s TW

e-rift unit (1

ng the Norga

the presenc

continuous

h a sharp se

o direct sei

within the co

deep-layer

or. Its base

n at 9 s TWT

izing this u

t–mantle bo

the shallow

d unit has v

he unit vanis

d lower cont

open: it co

her materia

s are separa

c signature

quiet magn

anomalies.

st nor those

main, the to

ons with hig

e S reflec

ng material

al topograp

verlying str

diments (Fi

. This doma

d 7a), as w

hapeless fau

WTT thick a

1–2 s TWTT

asis 14 prof

ce of upper

seismic ho

eismic veloc

ismic relatio

ontinental s

red unit (Fi

is marked

TT to a trip

nit are trun

oundary (Fi

w top of the

velocities ra

shes towar

tinental cru

ould be thi

al.

ated by an

characteriz

netic zone (

The acous

e of the oce

op of the su

gh amplitud

ctor. The M

(Figs 7, 8 a

hy is chara

ructures. Th

igs 4, 7 and

ain contains

ell as a few

ulted blocks

at most, and

T thick) lying

file (Fig. 7b

r continenta

rizon, which

city contras

on has been

slope. At the

gs 7, 8 and

by a strong

ple reflection

ncated by o

ig. 11). This

mantle. The

anging from

d the ocean

st observed

inned lowe

80 km wide

zed by low

(Fig. 2b). Its

stic facies o

eanic crust.

ubstratum is

des and low

MS reflecto

and 12). It is

acterized by

his indicates

d 12).

s

w

s

d

g

)

al

h

st

n

e

d

g

n

r

s

e

m

n

d

r

e

w-

s

of

s

w

r

s

y

s

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

9

The MS re

zone, unde

indirectly b

Norgasis da

(5.0–5.2 km

7b) called

velocity low

coincides w

lower-crust

DR reflectio

by the MS

be a functi

bulges (Fig

The overly

overlying th

zone, is a s

with a posi

reflector) a

appears ge

which pinch

showed tha

because of

Western Ap

Armorican

reflection (

amplitude.

permit us to

Along the o

directly by

sediments

important b

represent a

and the ba

high and po

off the Wes

1988; Sawy

eflection is g

er Unit 3C

by the upw

ata, acquire

m s–1 v. 7.4 k

the high-ve

wer-crustal c

with a veloc

tal is associ

ons are hig

reflection. T

on of the to

gs 7b and 13

ying materia

he MS refle

seismic unit

itive velocit

re continuo

enerally as

hes out tow

at Unit 3B i

f its emplac

pproaches

transitional

Fig. 12b) a

On the Loi

o identify th

oceanic dom

a set of

(e.g. Deré

bodies (2 s

a pre-Pyren

asement rid

ositive mag

st Iberia ma

yer et al. 19

generally co

, where it

ward termin

ed in the we

km s–1), at t

elocity lowe

corresponds

city contrast

iated with th

gh-amplitud

Their distrib

opography

3).

als. The lan

ector (Figs 6

t with low r

ty gradient,

ous and sm

a half-lens

wards the o

is a sedime

cement bet

margin. Un

domain (F

and at its ba

re Maritime

e nature of

main, in the

conformabl

gnaucourt

s TWTT thi

ean erosion

ges may b

gnetic anom

argin (e.g. B

994; Whitma

ontinuous a

is discontin

ations of t

estern part,

he top of a

er-crustal la

s to a deepe

t (7.5 km s

he upper pa

e, low–med

bution and

of the subs

ndward tran

6 and 12). U

eflectivity (F

and a thic

mooth seism

s with a hor

ocean (Fig.

entary body

tween the b

nit 3C is ob

ig. 6). It is

ase by the

e 2 profile (

Unit 3C.

oceanward

e seismic

& Boillot 1

ick) that pr

n surface (F

e volcanic

malies (Fig. 2

Boillot et al.

arsh et al. 1

and smooth

nuous with

the dipping

the MS ref

3–4 km thi

yer by Lou

er and disc

s–1 v. 8.0 km

art of the su

dium-freque

their orienta

stratum, as

nsitional do

Unit 3B, ob

Figs 7 and

ckness of 0

mic horizons

rizontal bas

9). From th

y emplaced

break-up u

bserved exc

bounded at

MS reflect

Fig. 12c), U

d transitiona

reflectors

1982; Thino

resent conic

Figs 6 and 1

ridges, con

2). Alternat

1980, 1987

998).

h (Fig. 12a)

h a low am

g underlying

flector coinc

ck layer wit

uden & Chia

ontinuous r

m s–1) under

ubstratum c

ency, dippin

ation, which

they are m

omain is ch

bserved in t

12a). It has

0–3300 m (

s. On the s

se (Fig. 12a

he seismic

by slumpin

nconformity

clusively in

t its top by

tion, which

Unit 3B see

al zone, the

interpreted

on 1999). I

cal to ridge

14). The con

nsistent with

ively, they c

7b, 1988; B

), except in

mplitude or

g reflectors

cides with a

th velocities

an (1999).

reflector we

rlying the M

containing t

ng seismic

h includes c

more import

haracterized

he western

s velocities

Fig. 7b). Its

eismic refle

a), or a thic

correlations

ng at the en

y and the s

the landwa

a strongly

is here dis

ems to onla

MS reflect

as Aptian–

It is locally

e shapes w

nical structu

h the prese

could be pe

eslier et al.

n the easter

is suggest

s (DR) (Fig

a clear seism

s of 7.4–7.5

The base

call the Mn

Moho. The h

the DR refle

reflections,

constant di

tant on the

d by Units

n Armorican

from 4.6 to

s top and

ection profil

ck ‘incompe

s, Thinon e

nd of the ri

synrift form

ard area of

refractive a

scontinuous

ap 3C. Our

tor is genera

–Cenoman

y interrupte

with flat top

ures may be

ence of som

eridotite ridg

1988; Gira

rn landward

ted to exis

g. 12b). On

mic contras

km s–1 (Fig

of the high

n reflector. I

high-velocity

ections. The

interrupted

ps, seem to

side of the

3B and 3C

transitiona

o 5.3 km s–1

bottom (MS

les, Unit 3B

etent’ body

et al. (2002

fting phase

ation of the

the eastern

and irregula

and of low

data do no

ally covered

ian post-rif

d by a few

ps that may

e volcanoes

me discrete

ges as seen

ardeau et al

d

st

n

st

g.

-

t

y

e

d

o

e

C

al

,

S

B

y,

)

e,

e

n

r

w

ot

d

ft

w

y

s

e,

n

l.

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

10

Other struc

conical and

TWTT thick

sedimentar

sedimentar

uppermost

Boundaries

transitional

block of the

(Figs 7, 8 a

between th

deep-layere

The relatio

oceanic do

(Fig. 7). He

with seism

basement

Background

basement h

Compared

(Fig. 7), wi

was initiate

spreading p

margin whe

significant

velocity low

plateau.

True ocean

Apart from

domain is

strongly dif

seismic vel

6.2–7.0 km

model indic

(6–8 km). T

North Atlan

ctures, calle

d ridge stru

k. The top is

ry unit (Un

ry series o

oceanic cru

s of the tra

domains a

e ‘neck are

and 11). Fig

he M reflec

ed unit).

onship betw

omain is aty

ere, it under

ic velocitie

high would

d section).

high forms

with the w

th no Aptia

ed before th

phase. This

ere underp

erosion of

wer-crustal

nic domain

m the large

8.5–9 s TW

ffractive and

locities is a

m s–1 layer 3.

cates that t

This last o

ntic continen

ed ST, are

ctures desc

s only sugg

it 3). From

r volcanic

ust (White 1

ansitional do

are well ima

ea’ correspo

gure 11c sh

ctor (contine

ween the tra

ypical, as lo

rplates a lar

s in the ra

d coincide

Contrary

a large pla

whole ocean

an–Cenoma

he Paleocen

s local ocea

lated low-d

its sedimen

could hav

n (domain V

oceanic p

WTT deep,

d irregular,

also represe

. The depth

he oceanic

bservation

ntal margins

also obser

cribed abov

ested by th

m acoustic f

extrusive r

1992b).

omain. The

aged on th

onds appro

hows that t

ental Moho

ansitional d

ocally the h

rge baseme

ange of 4.5

with the

to the initi

teau, only o

nic domain,

anian sedim

ne to Oligo

anic structu

ensity mate

ntary cover

e produced

V)

plateau des

shallower

similar to t

entative of

h of the base

c crust is 3–

agrees with

s (Ginzburg

rved on a

ve. They ha

e interruptio

facies, this

rocks. Its v

e geometric

he Norgasis

oximately to

the MS refle

) and S re

domain of

high-velocity

ent high (8 s

5–7.0 km s

North Bisc

ial hypothe

off the nort

this basem

ments (Unit

ocene Pyren

ure can be

erials have

r (Skogseid

d a relative

scribed abo

than that o

that of an o

typical oce

e of the cru

–5 km thick

h other sei

g et al. 1985

disrupted M

ave a ‘chao

on of the re

feature m

velocity is

c relations

s lines (Fig.

o the junctio

ector lies o

flector (bas

the Wester

y lower-cru

s TWTT de

s–1 that we

cay Ridge

esis, our ne

h segment

ment high h

3). This ob

nean comp

compared w

induced th

et al. 199

e and loca

ove, the ac

of the ocea

oceanic cru

anic crust w

ust is 10 s T

k, thinner th

smic meas

5; Whitmars

MS reflecto

otic’ acousti

eflectors bel

ay be inte

too high (6

between th

. 11). The o

on of the S

n the prolo

se of tilted

rn Armorica

stal penetra

ep, 60 km w

interpret a

defined in

ew seismic

of the Arm

has a reduc

servation s

ression, ce

with that de

he uplift of

2). The un

al uplift of

coustic bas

an–continen

st. The ver

with a 4.4–

TWTT. The

han average

surements a

h et al. 199

or (Fig. 7b)

ic facies an

longing to th

erpreted as

6 km s–1, F

he continen

oceanward

S, M and M

ongation of

blocks and

an Basin a

rates the oc

wide and 1

as oceanic

n the 1970

c data sho

morican mar

ced sedime

suggests tha

rtainly durin

escribed on

the oceani

derplating

the observ

sement of t

nt transition

rtical distrib

–5.0 km s–1

well-contro

e normal oc

along the n

90; Pinheiro

around the

nd are 0.2 s

he overlying

a volcano

Fig. 7b) fo

ntal and the

continenta

S reflectors

the junction

d top of the

nd the true

ceanic zone

00 km long

crust. This

0s (see the

ow that this

rgin (Fig. 6)

entary cove

at this relie

ng the early

n the Vöring

ic crust and

of the high

ved oceanic

the oceanic

n zone. It is

bution of the

layer 2 and

olled velocity

ceanic crus

non-volcanic

et al. 1992

e

s

g

-

r

e

al

s

n

e

e

e

)

s

e

s

).

r

ef

y

g

d

-

c

c

s

e

d

y

st

c

2;

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381 382

383

384

385

386

387

388

389

390

391

11

White 1992

continent–o

floor spread

The magne

are similar

Chron M0 (

To a first a

sharp ocea

(Fig. 1). Mo

Sibuet 198

negative m

signature o

and 4). On

magnetic a

IV (the very

that the No

Compariso

domain and

magnetic g

between th

This shift co

ESE and si

strong mag

Discuss The ocean

The main c

allowed us

previously c

80 km) that

characteris

signature, o

existence o

overlies a

reflectors).

2a, 1992b),

ocean trans

ding.

etic anomal

to those of

(Macnab et

approximatio

an–continen

ost workers

81; Derégna

magnetic an

of a baseme

n the map

anomaly doe

y quiet mag

rth Biscay R

n of the s

d the transit

gradient (Fig

he limits of

oincides wit

ituated in th

gnetic signa

ion

n–continent

characterist

to image t

considered

t coincides w

tics of oth

occurrence

of a subho

complex re

However,

, which sho

sition. White

ies of this d

f the North

al. 1995), w

on, our inte

nt boundary

(e.g. Bacon

aucourt & B

nomaly obs

ent ridge, th

of magnet

es not exist

gnetic zone

Ridge is not

eismic and

tional doma

gs 2 and 6

the oceani

th the prese

he western

ture that inf

t transition

tics of the A

the ocean–

as a sharp

with the Arm

her ocean–

of shallow

rizontal and

eflectivity zo

the Armo

ow an abno

e (1992a, 19

domain hav

Atlantic Oc

which chara

erpretation o

y of de Cha

n et al. 1969

Boillot 1982

erved on t

he North Bis

tic anomali

t, but a stro

). This obse

t a baseme

d magnetic

ain identified

). However

c domain d

ence of the

prolongatio

fluences the

n zone

Armorican o

–continent tr

p contact (D

morican Bas

–continent

high-veloc

d smooth b

one includin

orican ocea

ormally thin

992b) sugg

ve high amp

cean betwee

acterizes the

of the begin

arpal et al.

9; Grau et a

2; Barbier

he total ma

scay Ridge

es reduced

ong magnet

ervation ag

nt ridge but

data show

d on the se

r, off the ea

deduced fro

ST bodies

on of the Dô

e oceanic li

ocean–conti

ransition zo

Derégnauco

sin (Fig. 6).

transition

city material

basement s

ng both lan

an–continen

n oceanic c

ested that t

plitudes and

en the mag

e Cretaceou

nning of the

(1978) and

al. 1973; Mo

et al. 1986

agnetic fiel

, observed

d to the po

ic gradient

grees with th

t a large and

ws that the

ismic profile

astern Armo

om seismic

and some

ôme Gasco

mit drawn fr

inent transi

one along t

ourt & Boillo

. This transi

zones sur

ls (high-velo

surface (MS

ndward- and

nt transition

crust immed

the cause m

d a weakly

gnetic Chron

us Magnetic

e oceanic d

d Derégnau

ontadert et

6) have pos

d map (Fig

only on the

ole (Fig. 2b

separates d

he new seis

d local plate

boundary

es coincides

orican marg

data and m

basement r

gne. These

rom the ma

ition zone. T

the Armoric

ot 1982), is

itional doma

rveyed: a

ocity lower-

S reflector)

d seaward-

n zone sh

diately adja

might be ver

marked lin

n 34 and th

c Quiet Per

domain agre

ucourt & Bo

al. 1979b; L

stulated tha

g. 2a) is th

e OC17 pro

b), this larg

domain V f

smic data,

eau (Fig. 6)

between t

s globally w

gin, a small

magnetic da

ridges, orien

e elements

agnetic data

The seismic

can margin.

in fact a w

ain shares t

very ‘quiet

-crustal laye

), which sy

-dipping ref

hows some

acent to the

ry slow sea

earity. They

he magnetic

riod.

ees with the

oillot (1982

Le Pichon &

at the large

he magnetic

file (Figs 3b

ge negative

rom domain

which show

).

the oceanic

with a strong

l shift exists

ata (Fig. 6)

nted WNW–

may have a

a.

c data have

. This zone

ide zone (c

the principa

t’ magnetic

er), and the

ystematically

flectors (DR

e distinctive

e

-

y

c

e

)

&

e

c

b

e

n

w

c

g

s

).

–

a

e

e,

c.

al

c

e

y

R

e

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428 12

features in

Moho reflec

volcanic bo

crustal laye

velocity low

oceanic cru

Nature and

velocities (

greater tha

Various int

section of

(Srivastava

surface of

magnetic a

possibly br

asthenosph

this case th

layer, could

thinned co

throughout

could be m

other volca

Abyssal Pla

Bank area

the top of t

high-velocit

Iberia mar

serpentiniza

induced by

This last in

which pres

landward- a

with those

geographic

comparable

that found

to that of th

comparison

ctions (Mn

odies in pro

er, which is

wer-crustal l

ust.

d origin of t

(7.4–7.5 km

an those me

erpretations

this paper)

a et al. 200

oceanic cru

anomalies (

roken up,

heric upwel

he DR refle

d represent

ntinental cr

the Armor

mafic magm

anic rifted m

ain non-vol

(Girardeau

he mantle.

ty lower-cru

rgin. In this

ation, and t

a volume in

nterpretation

sents some

and seawa

described i

cal position

e with those

off the Wes

he Enigmati

n with other

reflector) b

oximity to th

covered dir

ayer penetr

the high-vel

m s–1) lower

easured wit

s of the hig

). It could

00). Howeve

ust, the vel

(Fig. 2b). S

continental

ling, as sug

ectors, whic

t traces of

rust (<4 km

ican Basin,

mas underpl

margins (S

canic marg

et al. 1998

Our data c

ustal layer a

s case, th

the bulges

ncrease as

n of the hig

characteris

ard-dipping

n the West

against th

e of the We

st Iberia ma

c Terrane d

r ocean–co

beneath the

he oceanic d

rectly by sed

rates the oc

locity lower

r than thos

thin oceani

gh-velocity

be oceanic

er, the smo

locities of t

Second, thi

l crust und

ggested by

ch character

the volcan

m thick), w

, seems to

lated during

kogseid et

gin (Cornen

), where a 5

annot exclu

as an abnor

he DR refle

of the subs

a result of s

h-velocity lo

stics compa

reflectors (

t Iberia ocea

he contine

st Iberia ma

argin: Unit 3

described o

ntinent tran

e ocean–con

domain and

diments an

ceanic dom

r-crustal lay

e measure

c layer 3 o

lower-crust

c material,

ooth charac

the baseme

s material

derplated a

Whitmarsh

rize the sei

nic intrusion

ith a smoo

us unlikely

g the rifting

t al. 1992;

n et al. 199

5 km thick b

ude such an

rmal hydrate

ectors (Fig

stratum (Fig

serpentiniza

ower-crusta

arable with

(DR reflecto

an–contine

ntal slope,

argin. The o

3B (Figs 9 a

on Galicia B

nsition zone

ntinent tran

d by particu

d overlies M

ain, where

yer. The hig

d within th

or the lower

tal layer ha

produced

cter of the

ent are too

could repre

and intrude

et al. (199

smic facies

ns. Howeve

oth surface,

y. Third, the

g period, as

White 199

6, 1999) an

by 80 km lo

n origin. An

ed mantle t

g. 12) may

g. 13) may

ation (Recq

al layer is s

other ocea

ors) under

nt transition

its width

overlying m

and 12a) ex

Bank by Boil

s. It is mark

nsition zone

ularities of t

Moho reflect

it underplat

gh-velocity l

e normal m

r continenta

ve been fo

by ultraslo

MS reflecto

high and t

esent an e

ed by parti

0) for the T

s of the high

er, the exist

without co

e high-veloc

s shown by

2a), but al

nd, further

ong gabbro

other possi

hat extends

y represent

correspond

q et al. 1996

upported b

an–continen

the MS ref

n zone by P

and its m

aterial can

xhibits a sim

llot et al. (1

ked by the

e, by the oc

the high-vel

ctions. Loca

tes the thin

lower-crusta

mantle (8 k

al crust (6.5

ormulated (s

ow sea-floo

or is not ty

this area ha

extremely th

al melt ge

Tagus Abys

h-velocity lo

tence of an

onspicuous

city lower-c

y underplati

so beneath

south, in th

body was d

ibility is to c

s along the

t faults, im

d to serpent

6).

by its seism

nt transition

flector are

Pickup et al

magnetic sig

also be com

milar seism

995). Also,

presence o

ccurrence o

locity lower

lly this high

Cretaceous

al layer has

km s–1), and

5–7 km s–1)

see the firs

r spreading

ypical of the

as no linea

hinned, and

enerated by

sal Plain. In

ower-crusta

n extremely

s structures

crustal laye

ing beneath

h the Iberia

he Gorringe

described a

consider the

entire Wes

mportant fo

tinite diapirs

ic structure

n zones: the

comparable

l. (1996). Its

gnature are

mpared with

mic signature

the seismic

of

of

r-

-

s

s

d

).

st

g

e

r

d

y

n

al

y

s,

r

h

a

e

at

e

st

r

s

e,

e

e

s

e

h

e

c

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

456

457

458

459

460

461

462

463

13

image of U

basement (

the rifting in

The nature

The ‘neck a

where struc

blocks are

They could

crust. There

Western Ap

The blocks

lower-crust

normal prod

al. (1979b)

rate calcula

blocks obse

consider th

margin. In t

area’ would

continental

therefore g

continent d

A similar de

the foot of t

some smal

This deep-

continental

seismic dat

layered low

possibly un

would be th

Previous in

transition w

from the G

1989); (3)

nit 3C (Fig.

(see Fig. 16

n the Bay of

e of the ‘ne

area’ (zone

ctural elem

restricted t

d also repre

e are very f

pproaches m

s overlie va

tal layer (Fi

duct of the

and Chene

ated from th

erved off th

at these blo

this case, t

d represent

break-up)

give, apart

omain.

eep-layered

the West Ib

l tilted block

-layered un

crust, as it

ta that allow

wer continen

nderplated d

he locus of t

nterpretation

within contin

alicia marg

an intra-c

12b) exhib

6b, below; P

f Biscay too

eck area’ an

e III, Fig. 6)

ments attribu

to this area

esent a few

few tilted bl

margin (e.g

ariable crus

gs 8 and 1

stretching p

et et al. (198

he tilted bloc

e Armorican

ocks repres

he tilted blo

t a ‘glide blo

would be

from rare

d unit obser

beria contin

ks resting o

nit could co

displays si

w us to con

ntal crust of

during the

the continen

ns of the S

nental crust

gin; (2) a de

crustal deta

bits numero

Pickup et al

ok place, at

nd its signi

is the last

uted to the

a. They com

w fragments

locks along

. Montadert

tal material

1). If we fo

phase of th

83), who wo

ck geometry

n margin ha

sent gravity

ocks are un

ock area’ a

situated at

exceptions

rved on the

ental slope

on a highly

orrespond t

milar seism

nfirm a gene

f the shelf. A

rifting phas

ntal break-u

S reflector s

(de Charpa

etachment f

achment fa

us similariti

l. 1996). If th

least initial

ificance

domain oce

continenta

mprise a lo

s of the mo

g the Armor

t et al. 1979

ls, such as

ollow the co

e continent

orked on the

ry is too low

ave a simila

slide struct

ninvolved in

nd the true

t the base

s, a good

Norgasis p

: the IAM 9

reflective m

to a part o

mic facies an

etic relation

Alternatively

se. In the la

up.

suggested

al et al. 197

fault that pe

ult (Sibuet

ies with ima

his last inte

ly, with little

eanward, at

al crust hav

ow crustal t

ore superfic

ican margin

9b; Whitmar

s the deep-

onventional

tal crust. Ho

e Western A

w to justify a

ar involveme

tures related

the proces

e limit of the

of the slo

approximat

profiles (Fig

9 profile (see

material inclu

of the thinn

nd velocities

nship betwe

y, this deep

atter case,

that it corre

78; Le Picho

enetrates th

1992); (4

ages from th

rpretation is

e or no mag

t the foot of

ve been obs

hickness an

cial part of

n (five at mo

rsh et al. 19

layered cru

hypothesis

owever, acc

Approaches

n overall cr

ent. An alte

d to the flex

sses of crus

e continenta

pe. The co

ion of the

s 7, 8 and

e Fig. 16c,

uding landw

ned and st

s. However

een the dee

-layered cru

the base o

esponds to

on & Barbie

he entire lith

) a detach

he Iberia Ab

s correct, it

gmatic activi

f the contin

served. The

nd a thick

f the upper

ost) compa

986; Fig. 2a

ust or the h

s these bloc

cording to M

s margin, th

rustal thinni

rnative imp

xural subsid

stal thinning

al domain (

ontinental s

precise ex

11) is obse

below) inde

ward-dippin

tretched lay

r, we do not

ep-layered u

ust could be

of the contin

o: (1) the br

er 1987), or

hosphere (B

hment betw

byssal Plain

implies tha

ity.

nental slope

e rare tilted

pre-rift unit

continenta

red with the

a).

high-velocity

cks reflect a

Montadert e

he extension

ng. The few

lication is to

dence of the

g. The ‘neck

the locus o

slope would

xtent of the

rved also a

eed exhibits

g reflectors

yered lowe

t have direc

unit and the

e new crust

nental slope

rittle–ductile

as deduced

Boillot et al

ween uppe

n

at

e,

d

t.

al

e

y

a

et

n

w

o

e

k

of

d

e

at

s

s.

r

ct

e

t,

e

e

d

l.

r

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

14

continental

a complex

(6) an abru

lower-crust

only off the

of tilted fau

faulted bloc

(1982) and

The lack o

excludes th

continuatio

Sibuet 199

reflection a

velocity low

seismic refl

surface of t

either the d

et al. 1996;

reflector ha

reflector ha

in the crust

The thinnin

Our data d

area that c

the crustal

less than 1

escarpmen

the crustal

behaviour o

a result of

The domai

displays so

are conside

represents,

Conclus

crust mate

boundary w

upt transitio

tal layer (Lo

e continenta

ult blocks. I

cks have m

Barbier et

of relationsh

he hypothe

n of a ‘brea

92; Reston

and refractio

wer-crustal l

lection data

tilted blocks

deep-layere

; Manatscha

as no direct

as restricted

tal thinning

ng of the c

demonstrate

corresponds

thickness d

10 km at th

nt, which bre

thinning is

of the layere

the reflectiv

n immediat

ome faulted

ered here

, as a first a

sions

erial and ser

with features

n between

ouden & Ch

al slope, in t

t therefore

oved and ro

al. (1986) o

hip betwee

esis that th

akaway’ as

1996; Rest

on data, the

layer that co

aset, it appe

s, and evol

ed crust or t

al & Niever

t seismic re

d influence w

processes.

continental

e that crust

s to the con

decreases u

he foot of t

eaks the up

thus only a

ed lower co

vity loss, bu

tely at the f

blocks sep

to be grav

approximatio

rpentinized

s (3) and (4

the faulted

ian 1999). A

the ‘neck a

correspond

otated. This

on the West

n these str

e S reflect

s often sugg

ton et al. 1

e S reflecto

orresponds

ears that the

ves toward

the upper m

gelt 1997; L

elationship w

within the z

crust

al thinning

ntinental slo

under the c

the slope (

pper crust a

very small

ontinental cr

ut the steep

foot of the c

arated from

vity slide st

on, the locu

upper man

4) (Boillot e

upper cont

Along the A

rea’. Its occ

ds most clo

s interpreta

tern Approa

ructures an

tor is the t

gested (Ba

996; Mana

or appears t

s to the MS

e S reflecto

s the ocea

mantle (Boil

Louden & C

with the loc

zone of tilted

of the Arm

ope, of 15–

continental s

(Fig. 8b). T

above a str

amount of

rust beneath

p rise of the

continental

m a deep-lay

tructures. W

us of the init

ntle (Boillot e

t al. 1995; R

tinental crus

Armorican m

currence alw

osely to a d

tion is in ag

aches margi

nd the fault

trace of a

rbier et al.

atschal & N

to be the pr

reflector (F

or correspon

n into interf

llot et al. 19

Chian 1999)

cation of cru

d blocks an

morican mar

50 km widt

slope from

The crustal

riking Moho

extension i

h the slope

e mantle im

slope corre

yered unit b

We conside

tial continen

et al. 1989;

Reston 199

st and the t

margin, the

ways coinc

écollement

greement w

n.

ts of the up

long, low-a

1986; Boill

ievergelt 19

rolongation

Fig. 11). On

nds to an in

faces betwe

987a, 1995

). Off the Ar

ustal thinnin

d seems to

rgin is restr

h. The seis

about 35 km

thinning is

rise. The a

n the upper

is not well i

mplies its dis

esponds to

by the S refl

r thus that

ntal break-u

Chian et a

96; Reston e

top of the h

S reflector

cides with th

t surface, o

with that of A

pper contin

angle detac

lot et al. 19

997). On th

of the top

the basis o

ntra-crustal

een faulted

; Reston 19

rmorican m

ng. We thin

o have had a

ricted to a v

smic profile

m at the sh

s underlain

apparent ex

r continenta

imaged by

sappearanc

the ‘neck a

lector. The

t the contin

up.

al. 1995); (5

et al. 1996)

high-velocity

is observed

he presence

n which the

Avedik et al

nental slope

chment, i.e

987b, 1989

he Norgasis

of the high

of our whole

detachmen

blocks and

996; Reston

argin, the S

k that the S

a minor role

very narrow

s show tha

helf break to

by a majo

xpression o

al crust. The

our data, as

ce (Fig. 8a)

area’, which

tilted blocks

nental slope

)

);

y

d

e

e

l.

e

e.

9;

s

-

e

nt

d

n

S

S

e

w

at

o

r

of

e

s

).

h

s

e

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

499

500

501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

520

521

522

523

524

525

526

527

528

529

530

531

532

533

15

Integration

oceanic do

Interpretatio

that define

continental

the ‘neck a

of the Armo

The main c

(1) The oce

continent tr

Basin. It s

magnetic s

layer, 7.4–

complex re

Armorican

other ocea

the ocean–

and by par

Compared

oceanic cru

normal oce

transition zo

(2) The No

but instead

due to loca

(3) Contine

corollary th

that the cru

to less than

in the uppe

the contine

break-up.

(4) The S r

base of the

data show

of the new

omain, high

on of the en

es five ma

domain (th

rea’. We kn

orican marg

conclusions

ean–contine

ransition zo

shares the

signature, o

–7.5 km s–1

flectivity zo

ocean–con

n–continent

–continent t

rticularities

with the ot

ust immedi

eanic crust

one could r

rth Biscay R

d is part of a

l underplati

ental crustal

hat the cont

ustal thickne

n 10 km at

er continent

ental slope

reflector an

e continent

the followin

w seismic

hly constra

ntire seismi

in domains

he slope), t

now now the

gin that sum

are as follo

ent bounda

one of 80 k

main chara

occurrence

) and of a

one includin

ntinent tran

t transition

ransition zo

of the high

ther non-vo

ately adjac

t. The high

represent an

Ridge, as d

a large plat

ng of the hi

thinning is

tribution of c

ess decreas

the foot of

tal crust sup

represents

d extension

al slope in

ng features.

reflection a

ains the sh

c dataset h

s: the une

he oceanic

e 3D crusta

mmarizes the

ows.

ry, previous

km width. T

acteristics

of shallow

a subhorizo

g both the l

sition zone

zones. It is

one, the ex

h-velocity lo

olcanic pass

cent to the

h-velocity l

n abnormal

defined in th

teau situate

igh-velocity

restricted t

crustal stre

ses under th

the slope. C

perimposed

s, as a first

nal structure

the narrow

(a) A deep

and refract

hallow and

has resulted

extended co

c domain, a

al geometry

e observatio

sly propose

This zone c

of other oc

w high-veloc

ontal basem

landward- a

e does sho

s marked b

xistence of v

ower-crusta

sive North

Biscay co

ower-crusta

mantle con

he 1970s, d

ed off the N

lower-crus

to the narrow

etching was

he continen

Crustal thin

d on a steep

t approxima

es such as

w domain c

p-layered cr

tion data, f

deep stru

d in a struct

ontinental

a wide trans

of the Arm

ons made is

ed to be a s

coincides w

cean–contin

city materia

ment surfac

and seawar

w some di

by the prese

volcanic bo

al layer, wh

Atlantic ma

ntinent–oce

al layer of

nstituted by

oes not exi

orth Armor

tal layer un

w continent

very limite

ntal slope fro

ning is exp

p shallowin

ation, the g

tilted block

called the ‘n

rust is sque

from the co

ucture of th

ural map of

domain (th

sitional zone

orican marg

s given in F

harp contac

ith a major

nent transit

al (the high

ce that sys

d-dipping re

stinctive fe

ence of Mo

dies close

ich is overl

argins (Whi

ean transitio

the Armo

serpentiniz

st along the

ican margin

der the oce

tal slope (15

d. The new

om about 35

ressed alon

g of the ma

geometry of

ks are obse

neck area’.

eezed betwe

ontinental s

he Armoric

f the Armor

he shelf), t

e and a do

gin. A struc

Fig. 15.

ct, is in fact

r part of the

tion zones:

h-velocity lo

stematically

eflectors. H

eatures com

oho reflectio

to the ocea

lain by the

ite 1992a,

on is thinn

rican ocea

zed peridotit

e North Bis

n. This plate

eanic crust.

5–50 km wi

w seismic pr

5 km at the

ng a major

antle. We c

f the initial

erved exclus

The Norga

een the S r

shelf to the

can margin

rican margin

the thinned

omain called

ctural sketch

t an ocean–

e Armorican

: very quie

ower-crusta

y overlies a

owever, the

mpared with

ons beneath

anic domain

sediments

1992b), the

er than the

an–continen

tes.

scay margin

eau may be

de) with the

rofiles show

e shelf break

escarpmen

onsider tha

continenta

sively at the

asis seismic

eflector and

e

n.

n

d

d

h

–

n

et

al

a

e

h

h

n

s.

e

e

nt

n,

e

e

w

k

nt

at

al

e

c

d

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

534

535

536

537

538

539

540

541

542

543

544

545

546

547

548

549

550

551

552

553

554 555

556

557

558

559

560

561

562 563 564 565

566 567 568

16

the Moho.

crust or as

restricted to

of tilted blo

the deep-la

structures.

In comparis

The Labrad

Cap margin

the loci of t

The crustal

margin, wh

upper mant

This paper

geometry o

of the West

Armorican

Numerous

wide ocean

the North B

AcknowThe first au

this study,

are gratefu

constructive

helpful for

processing

collected du

ReferencAvedik, F., Ho

Bay of Biscay

Printing Office

Avedik, F., C

reflection stud

Royal Society

It could be

a crust und

o the zone

ocks that ev

ayered crus

We conclud

son with oth

dor, West G

ns present s

he main cru

l geometry

hich also ex

tle uprising

has examin

of the Armo

tern Approa

margin has

questions r

n–continent

Biscay marg

wledgemeuthor thanks

and Ifreme

l to D. Nee

e discussio

the final

of the ma

uring the Ze

ces oward, D. , ET

y. In: Montade

e, Washington

Camus, A.L., G

dy of the con

y of London, 3

e explained

derplated or

of tilted blo

volves towa

st or the upp

de that the

her diverge

Greenland,

some very s

ustal thinnin

of the Armo

xhibits a na

as exempli

ned only on

rican margi

aches marg

a wide oce

remain: wh

t transition

gin, the Wes

ents s J.-L. Olive

er and Instit

edham, J. G

ons, and rev

manuscript

agnetic data

ee-Gascogn

T AL., 1979. P

ert, L. & Robe

n, DC, 1015–1

Ginzburg, A.,

ntinent–ocean

305, 5–25.[Cro

as a part

r intruded d

cks. It seem

ards the oce

per mantle.

‘neck area’

ent margins,

Orphan Ba

similar featu

ng (see Kee

orican marg

arrow contin

fied by the

ne segment

n seems ve

in (Avedik &

ean–contine

at are the g

zone along

stern Appro

et and D. As

tut Universi

Girardeau a

viewers are

t. C. Truffe

a. R. Le Su

ne and Séd

Preliminary res

erts, D.G. (ed

1023.

Montadert, L.

transition be

ossRef]

of the thinn

during the ri

ms to corres

ean into an

. (c) The tilt

represents

, we consid

asin, Southe

ures: they a

en & Dehler

gin (Fig. 15

nental slope

IAM 9 profi

t of the Nort

ery different

& Howard 1

ent transitio

geodynami

g the Armor

oaches marg

slanian for t

itaire Europ

nd G. Corn

e gratefully

ert (BRGM

uavé and G

ifan cruises

sults of a seis

ds) Initial Repo

., Roberts, D.

eneath the no

ned and str

fting phase

spond to an

n interface b

ted blocks a

s a ‘glide blo

der that the

ern Grand

all have nar

r 1997; Loud

) can also b

e linked to

le (Fig. 16).

th Biscay m

t from the p

979; Monta

n zone and

c processe

rican margi

gin and the

their interes

péen de la

nen for critic

acknowled

M) provided

G. Auffret g

s, respective

smic refraction

orts of Deep-S

G. & Whitmar

orth Biscay m

retched lay

. (b) The S

n intra-crust

between fau

are conside

ock area’.

Armorican

Banks, Nov

rrow contine

den & Chia

be compare

a sharp es

.

margin, the A

published st

adert et al. 1

fewer tilted

s that perm

n? Why are

Armorican

st and help

Mer (IUEM

cal reviews

ged for the

much ap

gave us fre

ely.

n study in the

Sea Drilling P

rsh, R.B. 198

margin. Philoso

yered lower

reflector ha

tal detachm

ulted blocks

ered to be g

margin is n

va Scotia a

ental slopes

n 1999, p. 7

ed with the

scarpment,

Armorican m

tructural int

1979b). In c

d blocks.

mitted the c

e the two s

margin, so

during the

) for their s

of the man

eir pertinent

ppreciated h

ee access

Meriadzek–T

Project, 48. US

82. A seismic

ophical Trans

r continenta

as influence

ment surface

s and eithe

gravity slide

not atypical

and Flemish

s, which are

745; Fig. 1)

West Iberia

and a high

margin. The

erpretations

contrast, the

creation of a

segments o

different?

evolution o

support. We

nuscript and

t comments

help in the

to the data

Trevelyan area

S Governmen

refraction and

sactions of the

al

e

e

r

e

l.

h

e

).

a

h

e

s

e

a

of

of

e

d

s

e

a

a,

nt

d

e

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

569 570

571 572

573 574

575 576 577

578 579

580 581 582

583 584 585

586 587

588 589 590

591 592 593

594 595 596 597

598 599

600 601 602

603 604 605 606

17

Avedik, F., Re

366–382.

Avedik, F., Hi

perspectives f

Bacon, M., G

Letters, 6, 377

Barbier, F., D

mécanisme d

Société Natio

Beslier, M.O.,

continentale p

Boillot, G., G

continent bou

Letters, 48, 23

Boillot, G., Re

drilling result

Science][Geo

Boillot, G., W

103. Ocean D

Boillot, G., Gi

mantle rocks

Results, 103.

Boillot, G., M

Tankard, A.J.

Association o

Boillot, G., Be

from the crust

G.B. & Tudh

Geological So

Cazes, M., Bo

Institut França

Chalmers, J.A

volcanic marg

Science][Geo

Chenet, P., M

northern Bisc

Drake, C.L. (e

716.

enard, V., Alle

irn, A., Renar

for lithospheri

Gray, F. & Mat

7–385.[Web o

Duvergé, J.,

de rifting et de

nale d'Elf Aqu

, Girardeau, J

passive de la G

Grimaud, S., M

undary off the

3–34.[CrossR

ecq, M. , ET A

ts (ODP Le

oRef]

Winterer, E. L.,

Drilling Program

irardeau, J., K

on the seaflo

Ocean Drilling

Mougenot, D.,

. & Balkwill,

f Petroleum G

eslier, M.O., K

tal structure a

hope, A.W. (e

ociety, London

ois, Ch. & Dam

ais du Pétrole,

A., 1997. The

gin. Journal o

oRef]

Montadert, L.,

ay continenta

eds) Studies in

enou, J.P. & M

rd, V., Nicolich

ic exploration.

tthews, D.H. 1

of Science][Ge

Le Pichon, X

e formation de

uitaine, 10, 105

J. & Boillot, G

Galice (Espag

Mauffret, A.,

e Iberian marg

Ref][Web of Sc

AL., 1987a. Te

eg 103, W.

Meyer, A. W

m, College Sta

Kornprobst, J.

oor. In: Boillot,

g Program, Co

Girardeau, J.

H.R. (eds) Ex

Geologists Mem

Krawczyk, C.M

nd segmentat

eds) The Tec

n, Special Pub

motte, B. 1988

, Institut Natio

e continental

of the Geolog

Gairaud, H. &

l margins: imp

n Continental

Morvan, B. 199

h, R., Olivet, J

Tectonophysi

1969. Crustal s

eoRef]

X. 1986. Stru

e la marge con

5–121.

G. 1988. Litho

gne). Comptes

Mougenot, D

gin: a serpent

cience][GeoRe

ectonic denud

Galicia mar

W., et al. (eds)

ation, TX.

. et al. 1988.

, G. & Wintere

ollege Station,

& Winterer, E

xtensional Te

moir, 46, 353–

M., Rappin, D.

tion of the dee

ctonics, Sedim

blications, 90,

8. Principales

onal des Scien

margin off so

gical Society.

& Roberts, D.

plications for e

Margin Geolo

93. Single-bub

J.L. & Sachpa

ics, 267, 57–7

structure stud

ucture profond

ntinentale. Bu

ologie et struc

s Rendus de l'

D., Kornprobst

tinite diapir w

ef]

dation of the up

rgin, Spain).

) 1987b Proce

Rifting of the

er, E.L. (eds)

, TX, 741–756

E.L. 1989. Rif

ectonics and

–355.

& Reston, T.

ep Galicia mar

mentation an

71–91.

Acquisitions S

nces de l'Unive

outhern Green

London, 154

1983. Extens

evolution mod

ogy. American

bble airgun ar

azi, M. 1996.

71.[CrossRef][

dies in the Bay

de de la mar

ulletin du Com

cture des péri

'Académie des

t, J., Mergoil-

west of the Ga

pper mantle a

Tectonophys

eedings of the

e Galicia marg

Proceedings

6.

fting processe

Stratigraphy o

J. 1995. The

rgin, Spain. In

d Palaeocean

Scientifiques o

ers, CNRS et

nland: along-s

4, 571–576.[A

sion ratio mea

dels of passive

Association o

rray for deep e

‘Single-bubble

[Web of Scien

y of Biscay. E

rge Nord Gas

mité de Recher

idotites à plag

s Sciences, 30

-Daniel, J. &

alicia Bank. Ea

along passive

sics, 132, 3

e Ocean Drillin

gin: crustal thi

of the Ocean

es on the Wes

of the North A

formation of p

: Scrutton, R.A

nography of

ou Intérêt Indu

SNEA, Paris,

strike transitio

Abstract/Free F

asurements on

e continental m

of Petroleum G

exploration. G

e’ marine sou

nce][GeoRef]

Earth and Plan

scogne. Impli

erche et de Pr

gioclases bor

06, 373–380.

Torrent, G.

Earth and Plan

margins: a m

335–342.[Cros

ng Program, I

inning and em

n Drilling Prog

st Galicia mar

Atlantic Marg

passive margin

A., Stoker, M.

the North At

ustriel. Progra

1, 223–249.

on from an am

Full Text][Cros

n the Galicia,

margins. In: W

Geologists Me

eophysics, 38

rce offers new

netary Science

ications sur le

roduction de la

rdant la marge

1980. Ocean–

netary Science

model based on

ssRef][Web o

Initial Reports

mplacement o

gram, Scientific

rgin, Spain. In

gins. American

ns: constraints

S., Shimmield

tlantic Region

amme ECORS

magmatic to a

ssRef][Web o

Portugal, and

Watkins, J.S. &

moir, 34, 703–

8,

w

e

e

a

e

–

e

n

of

s,

of

c

n:

n

s

d,

n.

S.

a

of

d

&

–

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

607 608

609 610

611 612 613

614 615 616

617 618

619 620

621 622

623 624

625

626 627

628 629

630 631

632 633 634

635 636

637 638

639 640

641 642

18

Chian, D. & L

Geophysical R

Chian, D., Lo

formation of n

Chian, D., Lo

southern Iber

Journal of Ge

Cornen, G., B

transition in th

the Ocean Dr

Cornen, G., G

the West Iber

Debyser, J., L

Français du P

de Charpal, O

Biscay. Natur

de Graciansky

Printing Office

Derégnaucou

Dyment, J., 1

la Société Gé

Frappa, M. &

Géologie du B

Ginzburg, A.,

the northern c

Girardeau, J.,

of continental

Drilling Progra

Girardeau, J.

Portugal). Com

Grau, G., Mo

and Ireland, fr

Kanasawa, T

and Planetary

Keen, C.E. &

Atlantic exam

ouden, K.E. 1

Research, 99,

uden, K.E. &

non-volcanic c

ouden, K.E., M

ria Abyssal P

eophysical Res

Beslier, M.O. &

he Iberia Abys

rilling Program

Girardeau, J. &

rian margin. M

Le Pichon, X.

Pétrole, I et II.

O., Guennoc, P

re, 275, 706–7

ky, P. C., Paog

e, Washington

urt, D. & Boillot

989. SWAT e

éologique de F

Vaillant, F.X.

Bassin d'Aquit

Whitmarsh, R

continental ma

, Evans, C.A.

l rifting: hole 6

am, Scientific

, Cornen, G.

mptes Rendus

ntadert, L., D

from seismic d

T. & Shiobara,

y Science Join

& Dehler, S.A

mples. Tectonic

1994. The con

9117–9135.[

Reid, I. 1995

continental ma

Minshull, T.A.

Plain from sei

search, 104, 7

& Girardeau, J

ssal Plain. In:

m, Scientific Re

& Monnier, C.

Mineralogy and

& Montadert,

P., Montadert,

711.[CrossRef]

g, C. W., et al

n, DC.

t, G. 1982. Str

t les bassins c

France, 8, 477–

. 1972. Prolon

taine, 12, 101–

R.B., Roberts,

argin of the Ba

& Beslier, M.O

637A, ODP LE

Results, 103.

et al. 1998.

s de l'Académ

elteil, R. & W

data. Tectonop

H. 1994. New

nt Meeting.I11

A. 1997. Exten

cs, 16, 744–75

tinent–ocean

[CrossRef][Ge

. Crustal struc

rgins. Journal

& Whitmarsh,

ismic refractio

7443–7462.[Cr

J. 1996. Petro

: Whitmarsh, R

esults, 149. Oc

1999. Basalts

d Petrology, 67

L. (eds) 1971

L. & Roberts,

f][Web of Scien

l. (eds) 1985 I

ructure géolog

celtiques: rela

7–487.

ngation vers l

–121.

D.G., Montad

ay of Biscay. A

O. 1988. Struc

EG 103 on th

Ocean Drilling

Premiers rés

mie des Scienc

Winnock, E. 19

physics, 20, 31

w ocean botto

, P82–341.

nsional styles

54.[CrossRef][

crustal transit

eoRef]

cture of the La

l of Geophysic

, R.B. 1999. D

on profiles: O

rossRef][GeoR

ologic characte

R.B., Sawyer,

cean Drilling P

s, underplated

7, 111–142.[C

1 Histoire Stru

, D.G. 1978. R

nce]

Initial Reports

gique du golfe

ations avec la

'ouest des str

dert, L., Camu

Annales Geop

ctural analysis

he Galicia mar

g Program, Co

sultats des p

ces, 326, 247–

973. Structure

19–339.[Cross

om seismome

s and gravity

[Web of Scien

tion across the

abrador Sea c

cal Research,

Deep structure

Ocean Drilling

Ref]

eristics of the

D.S., Klaus,

Program, Colle

d gabbros and

CrossRef][Web

ucturale du Go

Rifting, crustal

s of the Deep

de Gascogne

croûte hercyn

ructures du go

us, A. & Avedi

hysicae, 3, 49

s of plagioclase

rgin. In: Mazz

ollege Station

plongées du N

–254.

of the Europe

sRef][Web of S

ter system for

anomalies at

nce][GeoRef]

e southwest G

conjugate mar

100, 24239–2

e of the ocean

Program (Le

ultramafic roc

A. & Masson,

ege Station, T

d pyroxenites

b of Science][G

olfe de Gasco

attenuation a

Sea Drilling P

e. Bulletin du B

ienne, néoform

olfe de Gasco

k, F. 1985. Th

99–510.[GeoR

e-bearing peri

zullo, E.K. (ed

, TX, 209–223

Nautile sur le

ean continenta

Science][GeoR

r a dense surv

t rifted contin

Greenland mar

rgin and impli

24253.[CrossR

n–continent tr

egs 149 and

cks from the oc

, D.G. (eds) P

TX, 377–396.

record the rift

GeoRef]

ogne. Publicati

and subsidenc

Project, 80. U

BRGM, 1, 149

rmation du Mo

ogne. Bulletin

he deep seism

Ref]

idotites empla

d.) Proceeding

3.

e Banc de Go

tal margin bet

Ref]

rvey. Abstracts

nental margins

rgin. Journal o

ications for the

Ref]

ransition in the

173) transect

cean/continen

Proceedings o

ting process o

ion de l'Institu

ce in the Bay o

S Governmen

9–178.

oho. Bulletin de

de l'Institut de

mic structure o

aced at the end

g of the Ocean

orringe (Oues

ween Portuga

s, Japan Earth

s: some North

of

e

e

t.

nt

of

of

ut

of

nt

e

e

of

d

n

st

al

h

h

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

643 644

645 646

647 648

649 650

651 652

653 654

655 656

657 658

659 660

661 662 663

664 665

666 667

668 669 670

671 672

673 674

675 676 677

19

Keen, C.E., D

deep seismic

Le Borgne, E

l'Académie de

Le Pichon, X.

of Biscay mar

Le Pichon, X.

3720.[GeoRe

Limond, W.Q.

and Planetary

Louden, K.E.

of the Royal S

Ludwig, W.J.,

53–84.

Manatschal,

Switzerland).

Montadert, L.,

(eds) Les Mar

Montadert, L.,

de Gascogne

CNEXO, Paris

Montadert, L.

Burk, C.A. & D

Montadert, L.

Printing Office

Montadert, L.

margin of the

48. US Gover

Nicholls, I.A.,

of Australia. E

Olivet, J.L., 1

Aquitaine, 20,

Pickup, S.L.B

transition of

1082.[Abstrac

De Voogd, B.

reflection stud

E., Le Mouël

es Sciences, 2

& Barbier, F.

rgin. Tectonics

. & Sibuet, J.C

f]

., Gray, F., Gr

y Science Lett

& Chian, D. 1

Society of Lon

, Nafe, J.E. &

G. & Nieverg

Eclogae Geol

, 1984. Segm

rges Continen

, Damotte, B.,

e. In: Debyser

s, II, VI.14.1–V

, Winnock, E.

Drake, C.L. (e

, Roberts, D.

e, Washington

., Roberts, D.

e Bay of Bisca

rnment Printin

Ferguson, J.,

Earth and Plan

1996. La ciném

, 131–195.

B., Whitmarsh

ff West Ibe

ct/Free Full Te

1988. The con

dies. Tectonic

l, J.L. 1970.

271, 1167–117

. 1987. Passiv

s, 6, 133–150.

C. 1981. Pass

rau, G., Fail, J

ters, 23, 357–3

1999. The dee

don, 357, 767

& Drake, C.L.

gelt, P. 1997.

logicae Helvet

entation morp

ntales Actuelle

, Fail, J.P., De

r, J., Le Pich

VI.14.42.

, Delteil, J.R.

eds) Publisher,

G., et al. (ed

n, DC.

G., De Charp

ay. In: Montad

g Offic, Wash

, Jones, H., M

netary Science

matique de la

h, R.B., Fowle

eria from a

ext][CrossRef][

ntinent–ocean

cs, 7, 107–124

Cartographie

70.

ve margin form

.[Web of Scien

sive margins:

J.P., Montade

358.[CrossRe

ep structure of

7–805.

1970. Seismi

A continent–

tiae, 90, 3–27

phologique et s

es et Fossiles a

elteil, J.R. & V

hon, X. & Mon

& Grau, M. 1

, Town, 323–3

ds) 1979a Ini

pal, O., Guen

dert, L., Rober

ington, DC, 10

Marks, G.P. &

e Letters, 56, 3

a plaque ibériq

er, C.M.R. &

a deep mu

][Web of Scien

n boundary at

4.[CrossRef][W

e aéromagnét

mation by low

nce][GeoRef]

a model of fo

ert, L., Patriat,

ef][Web of Scie

ff non-volcanic

ic refraction. I

–ocean transi

7.[Web of Scie

structurale. In

autour de la F

Valery, P. 197

ntadert, L. (e

974. Continen

341.

itial Reports o

nnoc, P. 1979

rts, D.G. et al.

025–1060.

Mutter, J.C. 1

362–374.[Cro

que. Bulletin d

Reston, T.J.

ultichannel s

nce][GeoRef]

the rifted mar

Web of Science

tique du Gol

w-angle faulting

ormation. Jour

Ph. 1974. A

ence][GeoRef]

c rifted contine

In: Maxwell, A

ition recorded

nce]

n: Boillot, G., M

France. Masso

71. Structure g

eds) Histoire S

ntal margins o

of the Deep S

9b. Rifting and

. (eds) Initial R

1981. Ultrama

ssRef][Web o

du Centre de

1996. Insight

seismic refle

rgin off eastern

e]

fe de Gasco

g within the up

rnal of Geoph

seismic study

]

ental margins.

A.E. (ed.) The

d in the Err a

Montadert, L.,

on, Paris, 82–1

géologique de

Structurale du

of Galicia–Port

Sea Drilling P

d subsidence

Reports of the

fic blocks from

f Science][Ge

Recherches

t into the natu

ection profile

rn Canada: ne

ogne. Compte

pper crust: the

hysical Resear

y in the Bay of

. Philosophica

e Sea. Publish

and Platta nap

Lemoine, M.,

121.

la plaine aby

u Golfe de G

rtugal and Bay

Project, 48. US

of the northe

e Deep Sea D

m the ocean fl

eoRef]

Exploration–P

ture of the oc

e. Geology,

ew results from

es Rendus de

e northern Bay

rch, 86, 3708–

f Biscay. Earth

al Transactions

her, New York

ppes (Eastern

Biju-Duval, B

yssale du Golfe

ascogne. IFP

y of Biscay. In

S Governmen

ern continenta

Drilling Project

floor southwes

Production Elf

cean–continen

24, 1079–

m

e

y

–

h

s

k,

n

B.

fe

P-

n:

nt

al

t,

st

f-

nt

–

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

678 679 680

681 682

683 684

685 686

687 688 689

690 691

692 693 694

695 696 697

698 699

700 701 702

703 704 705

706 707 708

709 710 711

712 713

20

Pinheiro, L.M

Iberia—II. Cr

Science][Geo

Recq, M., Wh

l'ouest du Ban

Reid, I., 1994

99, 15161–15

Reston, T.J.,

International,

Reston, T.J.,

depth migrati

8091.[CrossR

Sawyer, D. S

149. Ocean D

Sibuet, J.C.,

margins. Jou

Science][Geo

Sibuet, J.C.,

Europe) from

Trends in Geo

Sibuet, J.C., M

Sciences, 318

Sibuet, J.C.,

sismique. In:

l'Institut Franç

Skogseid, J.,

Talleraas, E.

Society Speci

Srivastava, S

location of the

95–120.

Srivastava, S

during the fo

76.[CrossRef]

Thinon, I. 199

Brest Univers

M., Whitmarsh,

rustal structur

oRef]

hitmarsh, R.B

nc de Galice (

4. Crustal stru

5180.[CrossRe

1996. The S

127, 230–244

Krawczyk, C

ion for detach

Ref][GeoRef]

S., Whitmarsh,

Drilling Program

1992. New c

urnal of the

oRef]

Louvel, V. &

m gravity data

ophysical Res

Monti, S. & Pa

8, 615–625.

Pautot, G., L

Debyser, J., L

çais du Pétrole

Pedersen, T

(eds) Structu

ial Publication

S.P., Roest, W

e ocean–conti

S.P., Sibuet, J.

ormation of t

f][Web of Scien

99 Structure p

sity.

R.B. & Miles,

re in the Tag

B., Sibuet, J.C

(Ouest Ibérie).

cture of a non

ef]

S reflector we

4.[Web of Scie

C.M. & Klaesc

hment faultin

R. B., Klaus,

m, College Sta

constraints on

e Geological

Dyment, J.

and deep se

search, Resea

autot, G. 1994

Le Pichon, X.

Le Pichon, X.

e, II, VI.10.1–V

T. & Larsen, V

ural and Tecto

n, 1, 55–82.

W.R. 1995. Nat

inent boundary

.C., Cande, S

the Newfound

nce][GeoRef]

rofonde de la

, P.R. 1992. T

gus Abyssal

C., White, R.S

Comptes Ren

n-volcanic rifte

st of Galicia:

ence][GeoRef]

hen, D. 1996

g during con

, A., et al. (ed

ation, TX.

n the formatio

Society. Lo

1992. Crustal

eismic profiles

rch Trends, S

4. New bathym

1971. Interp

& Montadert,

VI.10.31.

V.B. 1992. Vö

onic Modelling

ture of thin cr

ry. In: Banda, E

S., Roest, W.R

dland and Ib

marge Nord G

The ocean–co

Plain. Geoph

S. & Lyness, D

ndus de l'Aca

ed margin eas

the seismic

f]

6. The S refle

ntinental break

ds) 1994 Proc

on of the non

ondon, 149,

l structure of

s: constraints

Sreekanteswar

metric map of t

prétation struc

, L. (eds) Hist

öring Basin: s

g and its App

rust across th

E. et al. (eds)

R. & Reid, I.D.

berian margin

Gascogne et d

ontinent bound

hysical Journ

D. 1996. Struc

démie des Sc

st of Newfoun

signature of a

ector west of

k-up. Journal

ceeding of the

n-volcanic con

829–840.[Ab

the Celtic Se

on the forma

ram, Trivadrum

the Bay of Bis

cturale du Go

toire Structura

subsidence an

plication to Pe

e Southwest

Rifted Ocean

. 2000. Magne

ns. Earth and

du bassin Arm

dary off the we

al Internation

cture sismique

iences, 322, 5

dland. Journa

a detachment

Galicia (Spain

of Geophysi

e Ocean Drillin

ntinental Galic

bstract/Free F

ea basins and

ation of contin

m, India, 1, 17

cay. Comptes

lfe de Gasco

le du Golfe de

nd tectonic ev

etroleum Geo

Greenland ma

n–Continent Bo

etic evidence

d Planetary S

moricain (golfe

estern contine

nal, 109, 106

e de la ride d

571–578.

al of Geophys

t fault. Geoph

n): evidence f

ical Research

ng Program,

cia–Flemish C

Full Text][Cros

d Goban Spu

nental basins

73–201.

s Rendus de l

ogne à partir

de Gascogne.

volution. In: L

ology. Norweg

argin and its b

oundaries. Pu

for slow seaf

Science Lette

e de Gascogne

ental margin o

6–124.[Web o

de péridotite à

sical Research

hysical Journa

from pre-stack

h, 101, 8075–

Initial Reports

Cap conjugate

ssRef][Web o

ur margin (NW

and margins

'Académie des

des profils de

Publication de

arsen, R.M. &

gian Petroleum

bearing on the

ublisher, Town

floor spreading

ers, 182, 61–

e). PhD thesis

of

of

à

h,

al

k

–

s,

e

of

W

s.

s

e

e

&

m

e

n,

g

–

s,

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

714 715

716 717 718

719 720

721 722

723 724

725 726

727 728 729

730 731

732 733

734 735 736

737 738

739 740

741 742

743 744

745 746

747

748

21

Thinon, I., Fid

Comptes Ren

Thinon, I., Ré

du Bassin Arm

Géologique d

Vaillant, X. 19

géodynamiqu

Verhoef, J., R

the Arctic and

White, R.S.,

Society, Lond

White, R.S.,

(eds) Magmat

Whitmarsh, R

deduced fro

3806.[CrossR

Whitmarsh, R

Iberia—I. Cru

Whitmarsh, R

of Biscay. Ge

Whitmarsh, R

continental-rif

Ocean Drilling

Whitmarsh, R

Reports, 173.

Whitmarsh, R

seafloor sprea

Williams, C.A

Planetary Scie

Zelt, C.A. &

amplitude forw

Zelt, C.A. &

International,

Ziegler, P.A.,

dalgo-Gonzále

ndus de l'Acad

éhault, J.P., Fi

moricain (Golf

de France, 273

988 L'extrémit

ues. PhD thesi

Roest, W. R.,

d North Atlanti

1992a. Crusta

don, 149, 841–

1992b. Magm

tism and the C

R.B. & Miles, P

m surface

Ref][GeoRef]

R.B., Miles, P.

stal structure

R.B., Avedik, F

ophysical Jou

R.B., Sawyer,

fting to seafloo

g Program, Ini

R. B., Beslier,

Ocean Drillin

R.B., Manatsch

ading. Nature,

A., 1975. Sea

ence Letters,

Ellis, R.M. 1

ward modellin

Smith, R.B.

108, 16–31.[W

1982. Geolog

ez, L., Réhaul

démie des Scie

idalgo-Gonzál

fe de Gascog

3, in press.

té de la marge

is, Brest Unive

Macnab, R., A

ic Oceans and

al structure a

–854.[Abstract

matism during

Causes of Con

P.R. 1995. Mo

and deep-to

R. & Mauffre

at 40°30'N. G

F. & Saunders,

urnal of the Ro

D.S. , ET A

or-spreading p

itial Reports, 1

, M. O., Wall

ng Program, C

hal, G. & Mins

, 413, 150–15

a-floor spread

24, 440–456.[

988. Practica

g. Canadian J

1992. Seism

Web of Scienc

gical Atlas of W

lt, J.P. & Oliv

ences, 332(9)

lez, L. 2002. L

ne) à Partir d

e Nord Gascog

ersity.

Arkani-Hamed

d Adjacent Lan

and magmatism

t/Free Full Tex

and after con

ntinental Break

odels of the d

ow magnetic

t, A. 1990. Th

eophysical Jo

, M.R. 1986. T

oyal Astronomi

L., 1996. The

processes. In:

149. Ocean Dr

lace, P. J., et

College Station

shull, T.A. 200

4.[CrossRef][G

ding in the Ba

[CrossRef][We

al and efficien

Journal of Exp

mic traveltime

ce][GeoRef]

Western and C

vet, J.L. 2001.

), 561–568.

La Couverture

de Nouvelles D

gne: contexte

d, J. & Memb

nd Areas. Geo

sm of North A

xt][CrossRef][

ntinental break

k-up. Geologi

development o

anomalies.

he ocean–con

ournal Internat

The seismic st

ical Society, 8

e ocean/conti

Sawyer, D.S.

rilling Program

t al. (eds) 19

n, TX.

01. Evolution

GeoRef]

ay of Biscay

eb of Science]

nt ray tracing

ploration Geop

inversion for

Central Europe

Pyrenean de

e Sédimentair

Données de S

stratigraphiqu

bers of the Pro

ological Survey

Atlantic contine

[Web of Scienc

k-up. In: Store

cal Society, Lo

of the West Ib

Journal of

ntinent bounda

tional, 103, 50

tructure of thin

86, 589–602.[W

inent transitio

, Whitmarsh,

m, College Sta

998 Proceedin

of magma-po

and its relati

][GeoRef]

g in two-dimen

physics, 24, 16

r 2-D crustal

e.. Shell, The H

eformation in t

e Syn-rift de l

Sismique Réfle

ue, structural e

oject Team, 1

y of Canada.

ental margins

ce][GeoRef]

ey, B.C., Alab

ondon, Specia

beria rifted co

Geophysical

ary off the we

09–531.[Web o

nned continen

Web of Scienc

n beneath the

R.B. & Klaus,

ation, TX, 713–

ng of the Oce

or continental

ionship to the

nsional media

6–34.[GeoRef]

velocity struc

Hague.

the northern B

la Marge Nord

exion. Bulletin

et cinématiqu

996 Magnetic

s. Journal of t

baster, T. & P

al Publications

ontinental mar

al Research,

estern contine

of Science][Ge

ntal crust in the

ce][GeoRef]

e Iberia Abys

A. (eds) Proc

–733.

ean Drilling P

l margins from

e North Atlan

a for rapid tr

f]

ucture. Geoph

Bay of Biscay

d Gascogne e

n de la Société

e. Implications

c Anomalies o

the Geologica

Pankhurst, R.J

s, 68, 1–16.

rgin at 40°30'N

100, 3789–

ental margin o

eoRef]

e northern Bay

ssal Plain and

ceedings of the

Program, Initia

m final rifting to

ntic. Earth and

ravel time and

hysical Journa

y.

et

é

s

of

al

J.

N

–

of

y

d

e

al

o

d

d

al

hal-0

0647

845,

ver

sion

1 -

5 Ja

n 20

12

749

750 751 752 753 754 755 756 757

758 759 760 761 762

22

FIGURES

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m. Mercator p(DSDP); petroCantabria Seamargin

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total field maetic anomaliesmagnetic dataThe structura

n map. Isobatshowing locatek Terrace; TEnglish Chan

agnetic anomas reduced to pa has been mal zones (blue

th interval of ttions of the deT, Trevelyan Snel Rift; NBM

alies (numericpole, from the ade with surfe

e line, oceanic

he bathymetryeep drillholes Seamount; BMM, North Biscay

cal magnetic d

total field mager and gmipac

c limit from se

ry (Sibuet et a(Deep Sea Dr

MC, Black Muday margin; NIM

data collected gnetic data ofck software in

eismic data; re

l. 1994) is 200rilling Programd Canyon; CsM, North Iberia

by Verhoef ef Verhoef et aln collaborationed line, limit o

0 m s, a

et l. n

of

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763 764 765 766 767

768 769 770 771 772 773 774 775 776

777 778 779 780 781 782

23

the lcontiRidg

from (198(198

S, S

last continentainental slope;

ge.

Fig. 3. P

Avedik & Ho1). NBR, Nort7).

Fig. 4. Oreflector; 3B,

al blocks) andIII, ‘neck area

Published struoward (1979) ath Biscay Ridg

OC17 seismic enigmatic uni

d the OC17 sa’; IV, ocean–c

uctural schemaand Montaderge. (c) The Ar

profile (for locit; 1, 2 and 3 a

seismic refleccontinent trans

a of the Northrt et al. (1979rmorican marg

cation, see Figare post-rift se

tion profiles asition zone; V,

h Biscay marg9). (b) The Armgin from Barb

g. 6) from Debediments.

are reported h true oceanic

gin. (a) The Wmorican margier et al. (198

byser et al. (19

here. I, contindomain; NBR

Western Approgin from Le Pi86) and Le Pic

971). CC, Con

nental shelf; IIR, North Biscay

oaches marginichon & Sibuechon & Barbie

ntinental crust

I, y

n et er

t;

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783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800

24

deepreflectransmodelowethe sblockoceadepephasoceafrom of noseismsecti

Fig. 5. (per layers (onlcted and divisformation of el geometry w

er-crustal layersame layer, thks is the consan-bottom seisendent gain anses are overlaanic layer 3; P

the high-veloormal mantle.mometer, usinion were used

(a) Structural ly one ray in eing waves. (bP-wave veloc

was slightly mor above normahe model is dsequence of stsmometers P0nd a bandpassain. InterpretePHP, reflectedocity lower-cru. (f) Syntheticng a Ricker wd.

model for proevery four is p

b) Observed cities to densiodified in the ual mantle was

divided into bltrong heteroge05, P15 and Ps filter (6–18 H

ed phases: P2d arrival from ustal layer; PMc seismogramwavelet as so

rofile Norgasisplotted). The () and compuity using the dunconstraineds reduced. To locks separateeneity. (c), (dP17, respectivHz) have been2, refracted athe top of the

MP, reflected ams computed ource function

s 14 with the velocities (seeuted free-air data from Lud

d part near the account for la

ed by verticald) and (e) showvely, plotted wn applied. Therrival from oc

e high-velocityarrival from the

by asymptoti. Same gain

ray paths thae Fig. 7b) andgravity for the

dwig et al. (19coast and the

ateral velocityl boundaries. w examples owith 7 km s re computed tra

ceanic layer 2y lower-crustale Moho; Pn, ric ray theory and plotting p

at were usedd depths are c

he Norgasis 1970). To impre density of thy or density vaThe large nu

of seismic refreduction velocavel times for 2; P3, refractel layer; PH, rerefracted arriva

for the P17 parameters a

d to define theconstrained by

14 profile afterove the fit thee high-velocityariations withinumber of theseraction data focity. An offsetthe interpreteded arrival fromefracted arrivaal from the topocean-bottom

as for the data

e y

er e y n e

or t-d m al p m a

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801 802 803 804 805 806

807 808 809 810 811 812 813 814 815 816

25

figure

faultemajoconti2 prunco

Fig. 6. Sres is shown. ○

Fig. 9. Sed block, com

or escarpmeninental blocks rofile (LM2) isonformity.

Structural map○, ocean botto

Stacked SNEAmposed of the

t that definess and the bases reported he

p of the Armorom seismomet

Ap reflection pupper contine

s the continenement of oceaere. 3B, Alloc

rican margin. ters used for t

profile (for locaental crust (Cntal slope. Un

an–continent trchthonous sy

The location the refraction m

ation see Fig. C) and a thicknit 3B coversransition zone

ynrift unit; BU

of cross-sectimodels along

6) across the k pre-rift unit (s the autochthe. The intersecU, break-up un

tion (green linthe Norgasis

e North Armori(5), is tilted athonous synrifction with the

unconformity;

e) included as14 profile.

ican margin. At the base of aft unit (4), theLoire MaritimeD1, Pyrenean

s

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817 818 819 820 821 822 823 824

26

shelfrefraNorgrepor

Fig. 7. (f to the ocea

action model cgasis 14 reflecrted here. D1,

(a) Time-migranic domain a

computed by ction profile (fo, Pyrenean un

ated reflectionacross the ocL. Matias and

for location senconformity (E

n profile (Norgcean–continend A. Hirn from

ee Fig. 6). TheEocene time); M

gasis 14) acront transition zom Norgasis oce intersection M, Moho refle

oss the North one; (b) line cean-bottom swith the Loirections.

Armorican mdrawing of th

seismometer de Maritime 2 (

argin from thehis profile; (cdata along the(LM2) profile is

e c) e s

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825 826 827 828 829 830 831 832

833 834 835 836 837 838 839

27

Fig.

margin; (b) inbasement of continental cr

Armosedimreflec

8. (a) Time-nterpreted prothe OCT zone

rust; ds, deform

Fig. 10. orican ‘neck aments; 5, pre-ctions; CC, co

migrated reflefile; (c) synthee; DR, dippingmed sediment

Section of sarea’. 3B, Alloc-rift sedimentsontinental crus

ection profile etic depth secg reflectors; Sts.

stacked AB64chthonous syns; MS, basemst

(Norgasis 23;ction without vS, S reflector;

40 SNEAp renrift unit; D1, P

ment of the oce

; for location vertical exagg; M, Moho ref

eflection profiPyrenean uncean–continent

see Fig. 6) aeration. D1, P

flections; 3C,

ile (for locatioonformity; 3, pt transition zo

across the SoPyrenean uncoenigmatic sei

on see Fig. post-rift sedim

one; S, S refle

outh Armoricanonformity; MSismic unit; CC

6) across thements; 4, synrifector; M, Moho

n S, C,

e ft o

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840 841 842 843 844 845 846 847 848

849 850 851 852 853 854 855 856 857

28

Fig. betwbasetop o

of thtruncdiffer(Fig. unco

Fig. 11. 6) across the

ween the S, Mement of the oof the normal m

Fig. 12. he western Acates the dipprent seismic c6). (c) Interp

onformity; MS,

(a) Line drawSouth Armori

MS and M refocean–continemantle; 3C, en

(a) Enlargemermorican oce

ping reflectorscharacter of Upreted section basement of

wing of time-mican margin; (flectors; (c) in

ent transition znigmatic seism

ent of SNEA pean–continent

beneath. (b) Unit 3C obsers of Loire Mathe ocean–co

migrated reflec(b) enlargementerpretation ozone; S, S reflmic unit; CC, c

profile (for loctransition zoEnlargement

rved only in tharitime 2 profilontinent transi

ction profiles (ent showing thof the enlargeflector; M, Mohcontinental cru

cation see Fig.ne (Fig. 7). t of SNEA prohe eastern Arle (LM2). 3B, tion zone; DR

(Norgasis N20he deep layereement. D1, Pho reflections;ust; CO, ocean

6) showing thUnit 3B coveofile (for locatirmorican oceaallochthonous, dipping refle

0 and N21; foed unit and th

Pyrenean unco; DR, dipping nic crust.

the typical seisers the MS reion see Fig. 6

an–continent ts synrift unit;

ectors.

or location seee relationshipsonformity; MSreflectors; Mn

smic characteeflector, which6) showing thetransition zoneD1, Pyrenean

e s

S, n,

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858 859 860 861 862 863 864 865

866 867 868 869 870

29

of thseismconti

see body

Fig. 13.

he digitized Mmometers. Thinental blocks

Fig. 14. Fig. 6). D1, P

y.

Morphology aMS reflector hahe magnetic (d

(red line) are

An SNEAp APyrenean unc

and depth (kmas been convdouble black lshown.

B640 seismicconformity; M

m) of the subsverted to depline) and seism

c reflection proMS, basement

tratum of the pth (km) with mic (bold blue

ofile across thof the ocean

transitional dothe velocities

e line) oceanic

e body with an–continent tra

omain. The tims of Norgasis c limits and th

a conical shapransition zone

me (TWTT (s)ocean-bottom

he limits of the

pe (for locatione; Vo, volcanic

)) m e

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878 879 880 881 882

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BiscaBasenorm

Fig. basement of ttilted blocks, dipping reflec

Fig. 15. ay margin. (aement of the omal mantle of t

16. (a) Reintethe ocean–conat the base otors; S, S refle

Schematic illua) Synthetic ocean–continethe Armorican

erpreted sectintinent transiti

of the continenector; CO, oce

ustrations of atime section.

ent transition zBasin; HVLC

on of IAM 9 prion zone (Pickntal slope. MSeanic crust.

rchetypal crus. (b) Synthetzone; M, Moh

C, high-velocity

rofile across tkup et al. 1996S, Basement

stal section actic depth sec

ho; DR, dippingy lower-crustal

the West Iberia6). (c) Enlargeof the ocean–

cross the Armoction without g reflectors; Sl layer; NBR, N

a margin. (b) Eement of the d–continent tran

orican segmevertical exag

S, S reflector; North Biscay R

Enlargement

deep-layered cnsition zone;

nt of the Northggeration. MS

Mn, top of theRidge.

of the acousticcrust under theM, Moho; DR

h S, e

c e

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deep structure of the armorican basin (bay of biscay): a review of norgasis seismic reflection and...

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