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Cenozoic tectonic history of the Himachal Himalaya (northwestern India) and its constraints on the formation mechanism of the Himalayan orogen

A. Alexander G. Webb1,2,*, An Yin2,3, T. Mark Harrison2, Julien Célérier4, George E. Gehrels5, Craig E. Manning2, and Marty Grove21Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA2Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA3Structural Geology Group, China University of Geosciences Beijing, Beijing 10085, People’s Republic of China4Research School of Earth Sciences, Australia National University, Canberra, ACT 2601, Australia5Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

1013

Geosphere; August 2011; v. 7; no. 4; p. 1013–1061; doi: 10.1130/GES00627.1; 17 fi gures; 4 tables; 7 supplemental fi les.

*[email protected].

ABSTRACT

A central debate for the evolution of the Himalayan orogen is how the Greater Himalayan Crystalline complex in its core was emplaced during the Cenozoic Indo-Asian collision. Addressing this problem requires knowledge of the structural relationship between the South Tibet detachment fault (STD) and the Main Central thrust (MCT) that bound these rocks from above and below. The fault relationship is exposed in the Himachal Himalaya of northwestern India, where they merge in their updip direction and form a frontal branch line that has been warped by subsequent top-to-the-southwest shear deformation. To elucidate how the two major crustal-scale faults evolved in the western Himalaya, we conducted integrated geologic research employing fi eld mapping, pressure-temperature (P-T) analy-ses, U-Pb zircon geochronology, trace and rare earth element (REE) geochemistry, and thermochronology. Our fi eld study reveals com-plex geometric relationships among major thrusts with large-magni-tude shortening within each thrust sheet. Three successive stages of top-to-the-southwest thrust development are recognized: (1) imbri-cate stack development, (2) translation of large thrust sheets along low-angle detachments and backthrusting along the STD, and (3) development of duplex systems via underplating. This kinematic pro-cess can be quantifi ed by our new analytical data: (1) P-T determina-tions show 7–9 kbar and 450–630 °°C conditions across the STD. The lack of a metamorphic discontinuity across the fault is consistent with a backthrust interpretation. (2) U-Pb zircon geochronology yields ca. 830 Ma and ca. 500 Ma ages of granitoids in the MCT hanging wall, ca. 1.85 Ga ages of granitic gneisses in both the MCT hanging wall and footwall, and 8–6 Ma ages of granitic pegmatites in the MCT footwall. These ages help defi ne regional chronostratigraphy, and the youngest ages reveal a previously unknown intrusion phase. (3) Trace element and REE geochemistry of 1.85 Ga, 830 Ma, and 500 Ma gran-itoids are characteristic of remelted continental crust, constraining the protolith tectonic setting. (4) U-Pb geochronology of detrital zir-con reveals that siliciclastic sedimentary sequences above the STD, below the MCT, and between these two faults have similar age spec-

tra with Neoproterozoic youngest age peaks. This result implies that the STD and MCT each duplicated the same stratigraphic section. (5) Th-Pb geochronology of monazite included in MCT hanging-wall garnet yields Paleozoic and early Tertiary ages, indicating Paleozoic and early Tertiary metamorphism in these rocks. (6) The 40Ar/39Ar thermochronology of the K-feldspar from southern MCT hanging-wall rocks evinces cooling below 220–230 °°C ca. 13–19 Ma or later, constraining the thrust development history. We use these results to derive a tectonic model of crustal shortening across the Himachal Himalaya involving early thickening, tectonic wedging emplacement of the Greater Himalayan Crystalline complex between the MCT and STD, and continued growth of the Himalayan thrust wedge by accre-tion of thrust horses from the Indian footwall.

INTRODUCTION

The fi rst-order architecture of the Himalayan orogen is expressed by two major north-dipping faults bounding a high-grade complex in the orogenic core (e.g., Argand, 1924; LeFort, 1996; Yin and Harrison, 2000; DeCelles et al., 2002; Yin, 2006). A central issue with regard to the Ceno-zoic Himalayan development is how the metamorphic core, the Greater Himalayan Crystalline complex, has been emplaced to its current position (LeFort, 1975; Burchfi el and Royden, 1985; Grujic et al., 1996; Nelson et al., 1996; Webb et al., 2007). Resolving this issue requires knowledge of the kinematic history of each bounding fault, i.e., the Main Central thrust (MCT) below and South Tibet detachment (STD) above, and the structural relationship between these faults.

The regional signifi cance of the MCT as a major Cenozoic shorten-ing structure has been recognized since the classic work of Heim and Gansser (1939) (Fig. 1) (see also Le Fort, 1975; Upreti, 1999; Hodges, 2000; DiPietro and Pogue, 2004). In contrast, the STD was discovered much later (Burg et al., 1984; Burchfi el et al., 1992). The STD is gen-erally north- dipping, features alternating top-to-the-south and top-to-the-north shearing, and juxtaposes the largely low-grade Tethyan Himalayan Sequence on top of the Greater Himalayan Crystalline complex (e.g., Patel et al., 1993; Hodges et al., 1996). Excepting the top-to-the-south

Webb et al.

1014 Geosphere, August 2011

shear indicators, these records are consistent with a normal fault inter-pretation. The apparent presence of a major normal fault within the con-tractional orogenic setting of the Himalaya has led to intense debate over the tectonic origin and dynamic role of the STD (e.g., Burg et al., 1984; Burchfi el and Royden, 1985; Yin, 1989; Hodges et al., 1992, 1996; Brown and Nazarchuk, 1993; Patel et al., 1993; Yin et al., 1994, 1999; Lee et al., 2000; Grujic et al., 2002).

Current hypotheses for the emplacement of the Greater Himalayan Crystalline complex offer different solutions to this problem (Fig. 2). Ver-tical wedge extrusion models show the STD as a normal fault at the crust of a Coulomb orogenic wedge (e.g., Burchfi el and Royden, 1985; Grujic et al., 1996). Models of southward middle-crustal channel fl ow interpret the STD as a backstop normal fault allowing the extrusion of channel rocks linked to focused denudation along the Himalayan topographic front (e.g., Nelson et al., 1996; Beaumont et al., 2001). In tectonic wedging models, the STD acts largely as a subhorizontal backthrust off of the MCT, with its top-to-the-north shear surfacing as the Great Counter thrust system (Webb et al., 2007). These competing models for the emplacement of the Greater

Himalayan Crystalline complex make different predictions (Table 1) (Fig. 2). First, the wedge extrusion model (Burchfi el and Royden, 1985) requires local extension over the highest region of the Himalaya and sug-gests that slip may be focused along a preexisting lithologic contact (Burg et al., 1984; Burchfi el and Royden, 1985). Second, both wedge extrusion and channel fl ow models require rapid erosion of the Tethyan Himalayan Sequence and exposure of the Greater Himalayan Crystalline complex during the main motion along the MCT and STD in the Early and Middle Miocene (Nelson et al., 1996; Beaumont et al., 2001; Hodges et al., 2001). In contrast, the tectonic wedging model predicts that the Tethyan Hima-layan Sequence was preserved above the Greater Himalayan Crystalline complex during STD motion. Third, the wedge extrusion model predicts the STD and MCT merge downdip to the north, the channel fl ow model predicts them to be largely subparallel, and the tectonic wedging model predicts them to merge updip to the south.

As the relationship between the STD and MCT is central in differ-entiating these models, fi eld tests must be conducted in regions where their relationships can be established. This requirement motivates our

SHIMLA

KATHMANDU

20oN

90oE80oE

20oN

20oN

N

TIBETAN PL

ATEAU

INDIA

Zanskar shear zone

South Tibet detachment

70°E 80°E 90°E 100°E

30°N

20°N70°E

30°N

Quaternary

Tethyan Himalayan Sequence: < Precambrian - Cambrian < Ordovician - Mesozoic

Late Cretaceous - Tertiary

Greater Himalayan Crystalline complex

Lesser Himalayan Crystalline Nappes (commonly interpreted as frontal Greater Himalayan Crystalline complex)

Lesser Himalayan Sequence

Asian and Indo-Burman plate rocks

Indian Craton

Main Central thrust (MCT)

South Tibet detachment (STD)

Ophiolite / Ophiolitic melange

Great Counter thrust

Figure 3.

Figure 1. Simplifi ed tectonic map of the Himalayan orogen. The dashed line denotes the Indian state of Himachal Pradesh, the box denotes the boundaries of Figure 3. Based on: Academy of Geological Sciences China (1975), Acharyya et al. (1986), Acharyya (1997), Biju-Sekhar et al. (2003), Buick et al. (2006), Deb et al. (2001), Ding et al. (2001), DiPietro and Pogue (2004), Frank et al. (1973, 1995), Fuchs and Linner (1995), Gilley et al. (2003), Jadoon et al. (1994), Johnson et al. (2001), Kapp et al. (2003), Khan et al. (2004), Leloup et al. (1995), Mitchell (1993), Mitchell et al. (2007), Murphy and Copeland (2005), Pilgrim and West (1928), Rao et al. (2000), Robinson (2005), Robinson et al. (2007), Robinson et al. (2006), Socquet and Pubellier (2005), Srikantia and Sharma (1976), Steck (2003), Thakur (1998), Thiede et al. (2006), Upreti (1999), Valdiya (1980), Vannay and Grasemann (1998), Vannay et al. (2004), Webb et al. (2007), Windley (1988), Yeats and Hussain (1987), Yin and Harrison (2000), Yin (2006); see also references cited in Figure 3.

Cenozoic tectonic history of the Himachal Himalaya

Geosphere, August 2011 1015

geologic investigation of the Himachal Himalaya in northwest India (Fig. 1), where contact relationships between the MCT and STD have been proposed and locally tested (Thakur, 1998; Yin, 2006; Webb et al., 2007). This region loosely marks the transition from the western to the central Himalaya, which are in part distinguished by drastically differ-ent preservation of the Tethyan Himalayan Sequence above the STD. In the central Himalaya, the Tethyan Himalayan Sequence has been largely eroded away, leaving the MCT and STD exposed as subparallel structures above and below the Greater Himalayan Crystalline complex (e.g., Hodges et al., 1996; DeCelles et al., 2001). In contrast, the Tethyan Himalayan Sequence is well preserved in the western Himalaya. In the Himachal Himalaya, an along-strike variation of MCT juxtaposition (i.e., from a Greater Himalayan Crystalline complex over Lesser Himalayan Sequence relationship in the east to a Tethyan Himalayan Sequence over Lesser Himalayan Sequence relationship in the west) can be directly observed (Fig. 3) (Thakur, 1998; Steck, 2003; DiPietro and Pogue, 2004). Besides this advantage, the stratigraphic units above and below the MCT are correlative in Himachal (e.g., Miller et al., 2001; Myrow et al., 2003), allowing assessment of the original confi guration of the northern Indian margin before the Cenozoic Indo-Asian collision. This correlative strati-graphic relationship across the MCT in the Himachal Himalaya contrasts strongly with the geology of the central Himalaya of Nepal, where rock units across the MCT differ drastically in age and provenance (Parrish and Hodges, 1996; DeCelles et al., 2000).

In this study we compiled a regional geologic map that combines infor-mation from existing literature and our new geological and analytical data collected via structural, geochemical, thermobarometric, and U-Th-Pb geochronologic and 40Ar/39Ar thermochronologic analyses of key areas and critical samples. We integrate our new results into a tectonic model that shows that the construction of the Himachal Himalaya was mainly accomplished by footwall accretion and vertical thrust stacking of Pro-terozoic strata of the northern Indian passive margin sequence, consistent with a tectonic wedging emplacement of the Greater Himalayan Crystal-line complex.

LITHOLOGIC UNITS

Major lithologic units in the study area include the Cretaceous and Cenozoic Sub-Himalayan Sequence, the Proterozoic and Cambrian Lesser Himalayan Sequence, the high-grade Greater Himalayan Crystalline com-plex, and the Neoproterozoic to Mesozoic Tethyan Himalayan Sequence (Figs. 3 and 4; Table 2). The Lesser Himalayan Sequence, Greater Hima-layan Crystalline complex, and Tethyan Himalayan Sequence are structur-

ally divided as MCT footwall rocks, rocks encased by the MCT below and the STD above, and rocks structurally above the STD, respectively (e.g., Hodges, 2000; Yin, 2006). We describe the lithologic units briefl y herein; for an expanded description, see Appendix 1.

The Sub-Himalayan Sequence consists of lower shallow-marine strata and upper continental deposits separated by an Oligocene unconformity (Table 2). Sub-Himalayan Sequence rocks depositionally overlie rocks of the Lesser Himalayan Sequence and correlative rocks at the base of the Himalayan foreland basin (e.g., Powers et al., 1998).

Four subunits are distinguished within the Lesser Himalayan Sequence: (1) the Neoproterozoic–Cambrian Outer Lesser Himalayan Sequence in the hanging walls of the Krol and Tons thrusts, (2) the Paleoproterozoic–Neoproterozoic Damtha and Deoban Groups in the hanging wall of the Bilaspur thrust and the footwalls of the Tons and Berinag thrusts, (3) the Paleoproterozoic Berinag Group in the hanging wall of the Berinag thrust, and (4) the Paleoproterozoic Munsiari Group, dominantly in the hanging wall of the Munsiari thrust (Table 2) (Figs. 3 and 4).

The Greater Himalayan Crystalline complex is ~7–9 km thick and con-sists of paragneiss, schist, and orthogneiss intruded by minor Tertiary leu-cogranites concentrated mostly in its upper 2–3 km (Table 2). An inverted metamorphic fi eld gradient is observed across a complete section of these rocks along the Sutlej River, progressing from garnet-staurolite–bearing rocks at the base to migmatitic rocks near the top (Vannay and Grase-mann, 1998).

The Tethyan Himalayan Sequence is dominated by the Neoproterozoic–early Cambrian Haimanta Group, early Paleozoic granites, Cambrian Parahio Formation, and overlying Paleozoic–Mesozoic strata (Table 2). Its basement is likely the Paleoproterozoic Baragaon gneiss in the MCT shear zone directly below the unit (Bhanot et al., 1978; Miller et al., 2000; this study). The Haimanta Group is garnet grade across its basal 1–3 km of section, and the grade decreases upsection across the Tethyan Hima-layan Sequence.

REGIONAL TECTONIC FRAMEWORK

First-order structures in the Himachal Himalaya are represented by a stack of northern rooted thrusts, many of which are folded (Fig. 3). The main fault zones and fault systems include, from southwest to northeast, (1) the Main Frontal thrust, (2) the Sub-Himalayan thrust zone, (3) the Bilaspur-Palampur thrust system, (4) the Krol-Mandi thrust system, (5) the MCT, (6) the Tons thrust, (7) the Berinag thrust, (8) the Munsiari thrust, (9) the STD, (10) the Tethyan Himalayan fold-and-thrust belt including the Mata nappe, and (11) the Great Counter thrust system (Figs. 3 and

Wedge extrusionChannel flow / focused denudation

Tectonic wedging

N

TibetITS

ITS

ITS

Tibet

Tibet

N

N

LHS GHC

THS

MainCentral thrust

South Tibetdetachment

Great Counter thrust


MainCentral thrust

LHS GHCTHS

LHS

GHC

THS


MainCentral thrust

Early “tunneling” stage:Eocene-Oligocene

Focused denudation stage:E. Miocene - M. Miocene

(to present?)

E. Miocene - M. Miocene

E. Miocene - M. MioceneFigure 2. Himalayan tectonic models for the emplacement of the Greater Himalayan Crystalline complex (GHC): channel fl ow/focused denu-dation model (e.g., Nelson et al., 1996; Beaumont et al., 2001; Hodges et al., 2001); wedge extrusion model (e.g., Burchfi el and Royden, 1985; Grujic et al., 1996); tectonic wedging model (e.g., Yin, 2006; Webb et al., 2007). THS—Tethyan Himalayan Sequence; LHS—Lesser Himalayan Sequence; ITS—Indus-Tsangpo suture; E.—Early; M—Middle.

Webb et al.


TAB

LE 1

. PR

ED

ICT

ION

S O

F H

IMA

LAYA

N T

EC

TON

IC M

OD

ELS

Mod

els

Hig

h-gr

ade

rock

af

fi nity

Faul

t kin

emat

ics

Exh

umat

ion

hist

ory

Spa

tial d

istr

ibut

ion

of m

etam

orph

ism

Alo

ng-s

trik

e st

ruct

ural

and

/or

stra

tigra

phic

va

riatio

n W

edge

ext

rusi

on

(e.g

., B

urch

fi el

and

Roy

den,

19

85)

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

ro

cks

are

deriv

ed

from

the

Indi

a pl

ate

ST

D to

p-to

-the

nor

th1.

Gre

ater

Him

alay

an C

ryst

allin

e co

mpl

ex

exhu

med

in th

e E

arly

Mio

cene

, syn

-ST

D

mot

ion

2. P

aleo

gene

exh

umat

ion

of T

ethy

an

Him

alay

an S

eque

nce

1. E

xpos

ed m

etam

orph

ic is

ogra

ds

subp

aral

lel t

o ap

prox

imat

ely

plan

ar M

CT,

S

TD

, the

refo

re n

orth

-dip

ping

2.

Inve

rted

met

amor

phis

m d

omin

ates

low

er

5–10

km

of M

CT

han

ging

wal

l

Ear

ly–M

iddl

e M

ioce

ne e

xtru

sion

of t

he G

reat

er

Him

alay

an C

ryst

allin

e co

mpl

ex b

etw

een

the

MC

T a

nd S

TD

at t

he s

urfa

ce r

equi

res

cont

inuo

us e

xpos

ure

of th

is u

nit b

etw

een

the

Less

er a

nd T

ethy

an H

imal

ayan

Seq

uenc

es

alon

g th

e le

ngth

of t

he o

roge

n.

Cha

nnel

fl ow

(e

.g.,

Nel

son

et

al.,

1996

)

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

ro

cks

are

deriv

ed

from

the

Asi

a pl

ate

ST

D to

p-to

-the

nor

th1.

Gre

ater

Him

alay

an C

ryst

allin

e co

mpl

ex

exhu

med

in th

e E

arly

Mio

cene

, syn

-ST

D

mot

ion

2. B

asal

Tet

hyan

Him

alay

an S

eque

nce

exhu

med

prio

r to

the

Gre

ater

Him

alay

an

Cry

stal

line

Com

plex

1. E

xpos

ed m

etam

orph

ic is

ogra

ds

subp

aral

lel t

o ap

prox

imat

ely

plan

ar M

CT,

S

TD

, the

refo

re n

orth

-dip

ping

2.

Inve

rted

met

amor

phis

m d

omin

ates

low

er

5–10

km

of M

CT

han

ging

wal

l

Ear

ly–M

iddl

e M

ioce

ne e

xtru

sion

of t

he G

reat

er

Him

alay

an C

ryst

allin

e co

mpl

ex b

etw

een

the

MC

T a

nd S

TD

at t

he s

urfa

ce r

equi

res

cont

inuo

us e

xpos

ure

of th

is u

nit b

etw

een

the

Less

er a

nd T

ethy

an H

imal

ayan

Seq

uenc

es

alon

g th

e le

ngth

of t

he o

roge

n.M

odifi

ed c

hann

el

fl ow

(e.

g.,

Bea

umon

t et

al.,

2004

)

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

ro

cks

are

deriv

ed

from

the

Indi

a pl

ate

ST

D to

p-to

-the

nor

th;

asym

met

ric th

rust

ex

trus

ion

mod

el

allo

ws

alte

rnat

ing

top-

to-t

he s

outh

and

to

p-to

-the

nor

th S

TD

sh

earin

g (B

eaum

ont

et a

l., 2

004)

1. G

reat

er H

imal

ayan

Cry

stal

line

com

plex

ex

hum

ed in

the

Ear

ly M

ioce

ne, s

yn-S

TD

m

otio

n 2.

Bas

al T

ethy

an H

imal

ayan

Seq

uenc

e ex

hum

ed p

rior

to o

r ap

prox

imat

ely

sync

hron

ousl

y (w

ith a

sym

met

ric th

rust

ex

trus

ion)

with

the

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

1. E

xpos

ed m

etam

orph

ic is

ogra

ds

subp

aral

lel t

o ap

prox

imat

ely

plan

ar M

CT,

S

TD

, the

refo

re n

orth

-dip

ping

2.

Inve

rted

met

amor

phis

m d

omin

ates

low

er

5–10

km

of M

CT

han

ging

wal

l

Ear

ly–M

iddl

e M

ioce

ne e

xtru

sion

of t

he G

reat

er

Him

alay

an C

ryst

allin

e co

mpl

ex b

etw

een

the

MC

T a

nd S

TD

at t

he s

urfa

ce r

equi

res

cont

inuo

us e

xpos

ure

of th

is u

nit b

etw

een

the

Less

er a

nd T

ethy

an H

imal

ayan

Seq

uenc

es

alon

g th

e le

ngth

of t

he o

roge

n.

Tect

onic

wed

ging

(e

.g.,

Yin

, 200

6;

Web

b et

al.,

20

07)

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

ro

cks

are

deriv

ed

from

the

Indi

a pl

ate

Alte

rnat

ing

top-

to-t

he

sout

h an

d to

p-to

-the

no

rth

ST

D s

hear

ing

1. G

reat

er H

imal

ayan

Cry

stal

line

com

plex

ex

hum

ed a

fter

the

Ear

ly M

ioce

ne, p

ost-

ST

D m

otio

n 2.

Bas

al, h

inte

rland

Tet

hyan

Him

alay

an

Seq

uenc

e ex

hum

ed a

ppro

xim

atel

y sy

nchr

onou

sly

with

the

uppe

r G

reat

er

Him

alay

an C

ryst

allin

e co

mpl

ex

1. E

xpos

ed m

etam

orph

ic is

ogra

ds

subp

aral

lel t

o th

e fo

lded

(op

en to

tigh

tly)

MC

T, S

TD

, the

refo

re fo

lded

2.

Inve

rted

met

amor

phis

m s

outh

of M

CT-

ST

D in

ters

ectio

n lin

e do

min

ates

onl

y ~

1–2

km M

CT

zon

e; s

truc

tura

lly h

ighe

r ro

cks

show

rig

ht-w

ay-u

p m

etam

orph

ism

For

elan

d M

CT

str

ands

juxt

apos

e Te

thya

n H

imal

ayan

Seq

uenc

e ro

cks

on to

p of

Les

ser

Him

alay

an S

eque

nce

rock

s; h

inte

rland

M

CT

str

ands

juxt

apos

e G

reat

er H

imal

ayan

C

ryst

allin

e co

mpl

ex r

ocks

ato

p Le

sser

H

imal

ayan

Seq

uenc

e ro

cks.

Loc

ally

, the

le

adin

g ed

ge o

f the

Gre

ater

Him

alay

an

Cry

stal

line

com

plex

rem

ains

bur

ied.

Not

e: S

TD

—S

outh

Tib

et d

etac

hmen

t; M

CT

—M

ain

Cen

tral

thru

st.

Figure 3. This fi gure is intended to be viewed at a size of 11 × 17× 17. To view the full-sized PDF fi le of Figure 3, please visit http://dx.doi.org/10.1130/GES00627.S1. Geological map of the Himachal Himalaya. Lines of cross sections drawn include A-A′ (cross section in Fig. 4A, reconstruction in Fig. 17), A-A′, A′′-A′′′ (sketch cross section in Fig. 4B), and B-B′ (sketch cross section in Supplemental File 11). Red boxes outline the positions of maps in Fig. 6A, 6B, 6C. Figure 3 is based upon our mapping, analysis of LANDSAT images, dis-cussions with A.K. Jain and S. Singh (2004, personal commun.), and previous work by Agarwal and Kumar (1973), Ahmad et al. (1999), Auden (1934), Bassi (1989), Bhargava (1976, 1980), Bhargava et al. (1991), Bhat-tacharya et al. (1982), Célérier et al. (2009a), Choudhuri et al. (1992), Das and Rastogi (1988), Dèzes (1999), Dèzes et al. (1999), Epard et al. (1995), Frank et al. (1973, 1995), Fuchs (1982), Grasemann et al. (1999), Gururajan (1990), Gururajan and Virdi (1984), Jäger et al. (1971), Jain (1972), Jain and Anand (1988), Jain et al. (1999), Kumar and Brookfi eld (1987), Pachauri (1980), Pandey et al. (2003), Pecher and Scaillet (1989), Pilgrim and West (1928), Powers et al. (1998), Raina (1981), Raiverman (2000), Rao and Pati (1980), Rat-tan (1973), Rautela and Thakur (1992), Robyr et al. (2002), Rupke (1974), Schlup (2003), Sch-lup et al. (2003), Shanker and Dua (1978), K.K. Sharma (1977), V.P. Sharma (1977), Singh and Jain (1993), Singh and Thakur (2001), Sri-kantia and Bhargava (1984, 1988), Srikantia and Sharma (1976), Steck (2003), Steck et al. (1998), Tewari et al. (1978), Thakur and Rawat (1992), Thiede et al. (2006), Thöni (1977), Valdiya (1978, 1980), Vannay and Grasemann (1998), Vannay and Steck (1995), Vannay et al. (1999, 2004), Virdi (1979), Wiesmayr and Grasemann (2002), West (1939), Wyss (2000), and Wyss et al. (1999).

1Supplemental File 1. PDF fi le of sketch cross section along profi le B-B′; see text Figure 3. The discontinuous graphitic quartzite marker lithology occurs at two levels in the Chandrabhaga River Val-ley. These occurrences are interpreted as two distinct stratigraphic horizons. Alternatively, these may re-fl ect unrecognized kilometer-scale tight to isoclinal folds. Primary sources for this section are Powers et al. (1998) (sub-Himalayan thrust zone); Srikantia and Sharma (1976) (sedimentary Lesser Himala-yan Sequence units); Frank et al. (1995) [Haimanta Group in the Main Central thrust (MCT) hanging wall]; Thakur (1998), Dèzes (1999), Yin (2006), and Webb et al. (2007) (STD, South Tibet detachment). If you are viewing the PDF of this paper or read-ing it offl ine, please visit http://dx.doi.org/10.1130/GES00627.S2 or the full-text article on www. gsapubs.org to view Supplemental File 1.



Tons R

iver

Pabbar Ri

ver

Sutlej Rive

r

Chandrabhaga River

Spiti

Sutlej

Tso Morari

Beas

River

Yamu

na

Beas Ri

ver

Alaknan

da River

Gang

es R

iver

River

River

Bhila

ngan

a Rive

r

River

Bhagira

thi

Ri

ver

Beas

Riv

er

Parbati River

Yamuna

Ri

ver

KN

TI

Z-CGHC Z-CGHC

Z-CGHC

Z-CGHC

Z-CGHC

Z-CGHC

KG

P-J

P-J

P-J

P-J

O-C

Z-CH

Z-CHZ-CH

Z-CH

Z-CH

Z-CH

Z-CH

Z-CH

Z-CH

Z-CH

Z-CH

Z-CH

XWXJ

XW

XW

XW

C-O

C-O

C-O

C-O

C-O

C-O

C-O

C-O

C-O

ZC

ZC XBA

XBA

XBA

XBE

XBE

XBE

XBE

XBE

X/X

X/X

XD XD

XD

XD

Y-Z

Y-Z

Y-Z

Y-Z

Y-ZD

Y-Z

ZB

ZB

ZB

ZS

ZS

ZS

Z-CK

Z-CK

Z-CH

CT

E/M

K/E

K/E

MLD

MUDMLS

XBA

MMS

M-Q

X/Z

CP

TL

XW

M-Q

M-Q

M-Q

M-Q

M-Q

M-Q

M-Q

MMS

MMS

MMS

MMS

MMS

MLS

MLS

MLS

MLS

MLS

MLS

MLS

K/E

K/E

K/E

K/E

MUD

MUD

MUD

MUD

MUD

CT

CT

P-J

O-C

O-C

P-J

P-J

O-C

O-C

CP

MUD

KG

KG

QQ

Q

Q

QQ

XD?

Y-Z

Z-CH

KN

Kullu

Manali

KhoksarSissu

Keylong

Larji

Patli Kuhl

Manikaran

WangtuRecong Peo

Morang

RampurSangla

Tiuni

Sankri

Harkidun

Tandi

Naura

Chaupal

Narkanda

Mikkim

Muth

Baldar

Tos

Batal

Darcha

Dharmsala

Rohru

Puh

Rohtang La

Mandi

Kangra

Chamba

Kalka

Chandigar Uttarkashi

Bilaspur

Sundarnagar

Gangotri

Rishikesh

Mussoorie

New Tehri

Nahan

Paonta Sahib

Sarchu

SHIMLA

rr

77oE 78oE

79oE

33o N

32o N

31o N

78oE 79oE

33oN

32oN

31oN

30oN

A

A’

Bilaspur thrust

Bilaspur thrust

Main Frontal thrust

Main Frontal thrust

Palampur

Great Counter Great Counter thrust systemthrust system

DEHRA DUN

Chaura thrustChaura thrust

Mata Nappe

Mata Nappe

Main Frontal thrust

Main Frontal thrust



Krol thrust

Krol thrust Tons thrustTons thrust

Berinag thrust

Berinag thrust

Munsiari thrust

Munsiari thrust

Sarchu Normal Fault

Spiti Synclinorium

Spiti Synclinorium

Chamba Synclinorium

Chamba Synclinorium

Tandi Syncline

Tandi Syncline

LeoLeoPargilPargilDomeDome

Phojal Anticline

Phojal Anticline

Main Central thrust

Main Central thrust

Dehra Dun Reentrant

Dehra Dun Reentrant

Mandi

Mandi

Indo-GangeticIndo-GangeticPlainPlain

Nahan beltNahan belt

Kullu

Window

Reentrant

thrust

thrust

thrust

thrust

A’’

A’’’

M

llalall M

a

ma

aaPalal

ma

PalaalalalalPalaal

mam

B

B’Tso Morari UHP dome

Tso Morari UHP dome

Ribil fault

Ribil fault

Spiti Synclinorium

Spiti Synclinorium

Dutung-Thaktote thrust

Dutung-Thaktote thrustParang La thrust

Parang La thrust

NarkandaHalf-Window

Uttarkashi

Half-Window

Zanskar shear zone

Zanskar shear zone

Lansdowne klippeLansdowne klippe

Almora klippeAlmora klippe

50 km0 10 20 30 40

N

Sub-Himalayan Sequence

M-Q Upper Siwalik

Q Active depocenters

MLS Lower Siwalik

MMS Middle Siwalik

MUD Upper Dharamsala

MLD Lower Dharamsala

K/E Singtali / Subathu

E/M Undifferentiated Subathu / Lower Dharamsala

Lesser Himalayan Sequence

Out

er L

esse

r H

imal

aya

Berinag

Mun

siar

iG

roup

XBE

XW

XJ

CT Tal

Z-CK Krol

ZS Simla

ZB Basantpur

Y-Z Deoban

XD Damtha

Wangtu

Jeori

Darla volcanics

Undifferentiated Berinag / DamthaX/X

X/Z

Map Units (described in Table 2)

Tethyan Himalayan Sequence

Sed

imen

tary

Roc

ksIg

neou

s R

ocks

KG

P-J

O-C

CP

XBA

Giumal-Chikkim

Tandi

Thaple-Muth-Lipak

Parahio

Haimanta (with graphitic quartzite marker beds)

Early Paleozoic granite

~830 Ma granite / gneiss

Baragaon granitic gneiss

Z-CH

C-O

Indus Suture Zone

KN Nidar Ophiolite

TI Indus Molasse

Z-CGHC

Tertiary LeucograniteTL

Greater Himalayan Crystalline complex

river

lake

TownSouth Tibet detachment

Overturned South Tibet detachment

Main Central thrust

Munsiari thrust

Berinag thrust

Tons thrust

Krol thrust

Phojal anticline

Geological SymbolsContacts and Folds

Key Structures

Solid: well located; dashed: approximately located; dotted: concealed and inferred

Lithologic Thrust fault

Anticline overturned overturnedSyncline

Normal fault

ZC

overturned synformal anticline

Fig. 6A.

Fig. 6B.

Fig. 6C.

Webb et al.


ZS

ZB

Y-Z XD

XB

E

Y-Z

XD

M-Q

MM

SM

LS

MU

D

K/E

MLD

Z-C

HZ

-CH

ZC

Z-C

H

C-O

Z-C

GH

CX

BA

A

km 5 0 -5 -10

-15

-20

A′ km 5 0 -

5

-10

-15

-20

XW

XJ

P-J

P-J

O-C

CP

KG

K/E

XW/X

J

30 k

m0

1020

no v

ertic

al e

xagg

erat

ion

XB

E

Y-Z

C-O

XW/X

J

Z-C

KK

/E

Bila

spur

thru

st

Kro

l thr

ust

Tons

thru

stB

erin

ag th

rustM

unsi

ari t

hrus

tM

ain

Fron

tal t

hrus

t

Sub

-Him

alay

an th

rust

zon

e

Cha

ura

thru

stM

ain

Cen

tral

thru

stS

outh

Tib

et d

etac

hmen

t

AS

elec

ted

dat

a, c

olo

r-co

ded

: met

amor

phic

con

ditio

ns (

pres

sure

in k

bar,

tem

pera

ture

in °

C),

met

amor

phic

cry

stal

lizat

ion

age

(Ma)

, 40 A

r/39

Ar

mus

covi

te a

ge

(Ma)

, zirc

on fi

ssio

n tr

ack

age

(Ma)

, apa

tite

fissi

on tr

ack

age

(Ma)

. Ref

eren

ces

liste

d in

figu

re c

aptio

n an

d de

note

d by

cap

italiz

ed s

uper

scrip

ts (

e.g.

, 70X

).

6-10

A3-

5A,B

10.5

-12B

0-2A

,C,D

,E2-

3D2-

5B13

-16B

1.7-

2.7B

25-2

15F

10-1

9F

9.7B

15.4

-17.

7B4-

7B,E

13-1

6B,E

16-1

9B,E

23-4

0G27

-34H

(E.)

Pal

eozo

ic, ~

41.5

-28.

5TS

9TS

6-9H

,L,M

580-

660H

,L,M

300N

200N

8M

base

:600

->to

p:75

0Mba

se:6

00->

top:

700B

,I,J,

L,M

7-9T

Sba

se:9

->to

p:7B

,I,J,

L,M

450-

630K

,TS

570T

S

A

km 5 0 -5 -10

-15

-20

-25

A′

A′′

A′′′ km 5 0 -5 -1

0

-15

-20

-25

-30

KG

STD

50 k

m0

1020

3040

no v

ertic

al e

xagg

erat

ion

O-C

Z-C

H

P-J X

W

Z-C

GH

C

KN

TI

KN

KN

Z-C

GH

C (

UH

P)

XB

E

MC

T

MC

TG

CT

Mat

a N

appe

Lada

kh b

atho

lith

(Asi

a pl

ate)

B

Fig

ure

4. (

A)

Cro

ss s

ecti

on o

f th

e H

imac

hal H

imal

aya.

Sec

tion

dra

wn

alon

g lin

e A

-A′ o

f F

igur

e 3.

Uni

ts a

nd s

ymbo

ls a

re a

s in

Fig

ure

3. B

row

n cu

rve

repr

esen

ts E

arth

’s s

ur-

face

, sho

rt b

lack

line

s al

ong

Ear

th’s

sur

face

rep

rese

nt b

eddi

ng a

nd/o

r fo

liati

on a

ttit

udes

. All

faul

ts a

re to

p-to

-the

-sou

thw

est w

ith

the

exce

ptio

n of

the

Sout

h T

ibet

det

achm

ent,

w

hich

dis

play

s re

cord

s of

bot

h to

p-to

-the

-sou

thw

est

and

top-

to-t

he-n

orth

east

mot

ion.

Ref

eren

ces

for

anal

ytic

al d

ata

are:

AT

hied

e et

al.,

200

9; B

Van

nay

et a

l., 2

004;

CJa

in e

t al

., 20

00;

DT

hied

e et

al.,

200

4; E

Thi

ede

et a

l., 2

005;

FSc

hlup

, 200

3; G

E. C

atlo

s, 2

004,

per

sona

l com

mun

.; H

Cha

mbe

rs e

t al

., 20

09;

I Cha

mbe

rs e

t al

., 20

08;

J Cad

dick

et

al.,

2007

; KG

rego

ry, 2

004;

LV

anna

y an

d G

rase

man

n, 1

998;

MV

anna

y et

al.,

199

9; N

Wie

smay

r an

d G

rase

man

n, 2

002;

TS t

his

stud

y. (

B)

Sket

ch c

ross

sec

tion

of

the

Him

acha

l and

Lad

akh

Him

alay

a. M

CT

—M

ain

Cen

tral

thr

ust;

ST

D—

Sout

h T

ibet

det

achm

ent;

GC

T—

Gre

at C

ount

er t

hrus

t sy

stem

; U

HP

—ul

trah

igh

pres

sure

. The

abb

revi

atio

ns a

re t

he s

ame

as

in t

he le

gend

in F

igur

e 3.



TAB

LE 2

. TE

CTO

NO

ST

RAT

IGR

AP

HY

OF

TH

E H

IMA

CH

AL

HIM

ALA

YA

Uni

t nam

e (a

ltern

ativ

e na

me)

Lith

olog

ic d

escr

iptio

nT

hick

ness

(m)

Age

con

stra

ints

Nd,

Sr

isot

opic

co

nstr

aint

s*H

imal

ayan

For

elan

d U

pper

Siw

alik

Fm

†ss

, con

glD

D§

~17

00 -

230

0DD

depo

sitio

n 7

Ma

to P

leis

toce

ne: M

SZ

#N

.D.

Mid

dle

Siw

alik

Fm

ss w

ith m

inor

slts

, sh,

con

glD

D~

1300

- 2

000D

Dde

posi

tion

11 to

7 M

a: M

SZ

#N

.D.

Low

er S

iwal

ik F

msl

ts w

ith m

inor

ss,

shD

D~

700

- 13

00D

D

depo

sitio

n 13

to 1

1 M

a: M

SZ

, AA

#N

.D.

Upp

er D

hara

msa

la F

m (

Kas

auli)

grey

ss,

min

or s

h (fl

uvi

al /

allu

vial

)CC

, TT

~10

00 -

130

0DD

depo

sitio

n 16

.5 to

13

Ma:

MS

AA, c

f. de

trita

l mic

aBB

#N

.D.

Low

er D

hara

msa

la F

m (

Dag

shai

)ss

, slts

, sh,

cal

iche

(fl u

vial

/ al

luvi

al)C

C, T

Tup

to 1

300D

D**

depo

sitio

n 20

to 1

6.5

Ma:

MS

AA, c

f. de

trita

l mic

aBB

, UU

#N

.D.

Sub

athu

Fm

ls, s

h, m

inor

fi ne

gra

ined

ss

(sha

llow

mar

ine)

CC

, TT

up to

200

DD**

, FF,

GG

late

st P

aleo

cene

-M

iddl

e E

ocen

e: fo

ssils

CC

N.D

.S

ingt

ali F

mls

, min

or q

uart

z ar

enite

(sh

allo

w m

arin

e)C

C~

50, d

isco

ntin

uous

CC

Late

Cre

tace

ous

- P

aleo

cene

: fos

sils

CC

††N

.D.

Less

er H

imal

ayan

Seq

uenc

e: O

uter

Les

ser

Him

alay

aTa

l Fm

ss, s

ltsE

EE

, S~

500S

Low

er C

ambr

ian:

trilo

bite

sA, E

EE, R

e-O

s is

ochr

onB

≤ L

PtC

*K

rol G

pdl

, ls

with

min

or s

h, s

ltsR

, FF

F

~15

00 -

220

0HH

, S, F

FF

~59

0-54

3 M

a: fo

ssils

GG

G, R

, EE

E,

13C

shi

ftHH

H≤

LPtM

Shi

mla

Gp

(Cha

ndpu

r +

Nag

that

+

Bla

ini)

sh (

min

or s

late

), s

lts, s

s, w

ith m

inor

gw

, till

ite, c

ongl

CC

C,

FF,

BB

B, D

DD

~38

00 -

410

0II ,

cf.

~33

00F

F<

~62

0 M

a: d

etrit

al U

-Pb

zrcT

S; s

trat

igra

phic

ally

bel

ow K

rol G

pS≤

L P

tE, M

, Y

Bas

antp

ur F

m (

Man

dhal

i)in

terb

edde

d ls

, slts

, sh

(min

or s

late

)FF,

BB

B>

~30

0-64

0S, J

J , cf

.>~

1360

FF

839±

138

Ma:

Re-

Os

isoc

hron

B, N

eo-P

t: st

rom

O, Y

Y≤

L P

tE, M

Less

er H

imal

ayan

Seq

uenc

e: P

arau

toch

thon

Deo

ban

Gp

(Sha

li)dl

, ls

with

min

or s

h, c

hert

, ssS

>~

3000

HH

, II

≥ 2

leve

ls, l

ower

: (la

test

Pal

eo?-

)Mes

o-P

t, up

per:

Neo

-Pt.

stro

m a

nd o

ther

foss

ilsS

, N, O

, P, Q

, WW

, XX

, YY,

ZZ

≥ M

PtM

, Y*

Dam

tha

Gp

(Sun

darn

agar

; Cha

krat

a [lo

wer

mem

ber]

, Rau

tgar

a [u

pper

])

gw, s

lts, s

late

suc

ceed

ed b

y qt

zt, s

l, ba

sic

sills

and

di

kesS

>~

2900

HH

≥ P

aleo

-Pt,

stra

tigra

phic

ally

bel

ow D

eoba

n G

pSN

.D.

Less

er H

imal

ayan

Seq

uenc

e: B

erin

ag th

rust

han

ging

wal

l roc

ks

Ber

inag

Gp

(Ram

pur,

Man

ikar

an)

gree

nsch

ist-

faci

es s

eric

itic

quar

tz-a

reni

te, m

etab

asal

t (s

ills,

dik

es, fl

ow

s), m

inor

slS

, J>

~10

00K

K~

1.85

- 1

.8 G

a: d

etrit

al U

-Pb

zrcM

, TS, U

-Pb

zrc

from

m

etab

asal

tJqt

zt: ≥

M P

tM, Y

, m

eta-

basa

lt: ≤

L

PtJ,

JJJ

, VV

Less

er H

imal

ayan

Seq

uenc

e: M

unsi

ari G

roup

Wan

gtu

gnei

ss (

Ban

dal)

dom

inan

tly g

rani

tic a

ugen

gne

issL

L>

~20

00LL

~1.

85 G

a: R

b-S

r w

hole

roc

kK, J

, U-P

b zr

cJ, L

, M≥

M P

tJ, M

Jeor

i met

ased

imen

tary

roc

kspa

ragn

eiss

, mic

a sc

hist

, min

or m

etab

asite

, qtz

t, gr

aniti

c gn

eiss

LL

unkn

own

som

e la

yers

<~

1.9

Ga,

oth

er l

ayer

s >

~20

68 M

a: d

etrit

al U

- P

b zr

cM, T

S, i

gneo

us U

-Pb

zrcI

II

≥ M

PtJ,

M

Fel

sic

pegm

atite

(cr

oss-

cuts

Wan

gtu

gnei

ss fo

liatio

n)up

to ~

4 m

thic

k di

kes

~8-

6 M

a: U

-Pb

zrc,

Th-

Pb

mon

azite

TS

N.D

.G

reat

er H

imal

ayan

Cry

stal

line

com

plex

para

gnei

ss, s

chis

t, or

thog

neis

s~

4500

-800

0LL

som

e la

yers

you

nger

than

~85

0 M

a: d

etrit

al z

rcM

, TS, 4

95 M

a or

thog

neis

s: R

b/S

rK≤

L P

tM, Y

Leuc

ogra

nite

up to

~10

0’s

m th

ick

~27

-20

Ma:

U-P

b m

onaz

ite, u

rani

nite

H, T

h-P

b m

onaz

iteT

SN

.D.

Teth

yan

Him

alay

an S

eque

nce:

sed

imen

tary

roc

ksG

ium

al-C

hikk

im s

ucce

ssio

nss

, bla

ck s

h, ls

EE

~35

0RR

Cre

tace

ous:

foss

ilsR

RN

.D.

Tand

i Gp

carb

onat

e, s

h, s

lts, q

tztM

M>

~19

20M

MP

erm

ian

- Ju

rass

ic: f

ossi

lsT,

U, V

N.D

.T

hapl

e-M

uth-

Lipa

k su

cces

sion

sh, s

lts, q

tzt,

quar

tz-a

reni

te, c

arbo

nate

, con

glM

M~

1650

MM, c

f. ~

1100

NN

Ord

ovic

ian

- C

arbo

nife

rous

: fos

sils

VN

.D.

Par

ahio

Fm

ss

, sh

(sili

cicl

astic

del

taic

)AA

A

~70

0NN, c

f. >

1350

AA

Aup

perm

ost L

ower

Cam

bria

n-m

iddl

e M

iddl

e C

ambr

ian:

foss

ilsA

,

W, A

AA

N.D

.H

aim

anta

Gp

phyl

lite,

sch

ist,

garn

et s

chis

t, gr

aphi

tic s

chis

t, ps

amm

itic

schi

st, m

inor

car

bona

te, m

inor

met

abas

alt

>~

6250

MM, c

f. ~

2000

-35

00N

N<

~55

0 M

a -

Ear

ly C

ambr

ian:

trilo

bite

sX, c

ross

-cut

ting

igne

ous

ages

E, K

, det

rital

U-P

b zr

cTS

≤ L

PtE

, M, Y

(con

tinue

d)

Webb et al.


TAB

LE 2

. TE

CTO

NO

ST

RAT

IGR

AP

HY

OF

TH

E H

IMA

CH

AL

HIM

ALA

YA (

cont

inue

d)

Uni

t nam

e (a

ltern

ativ

e na

me)

Lith

olog

ic d

escr

iptio

nT

hick

ness

(m)

Age

con

stra

ints

Nd,

Sr

isot

opic

co

nstr

aint

s*Te

thya

n H

imal

ayan

Seq

uenc

e: ig

neou

s ro

cks

Ear

ly P

aleo

zoic

gra

nito

ids

gran

ite, m

inor

mafi

c e

ncla

ves,

min

or a

plite

, loc

ally

gn

eiss

icup

to a

t lea

st ~

2000

OO

Cam

bro-

Ord

ovic

ian:

Rb-

Sr

who

le r

ockD

, U-P

b zr

cE, F

, TS

≤ L

PtE

~83

0 M

a (C

haur

-Bla

ck M

tn)

gran

itegr

anite

, gra

nitic

gne

iss

up to

~30

00Q

Q~

830

Ma:

U-P

b zr

cG, T

SN

.D.

Bar

agao

n gr

aniti

c gn

eiss

myl

oniti

c gr

aniti

od g

neis

sup

to ~

1100

PP

~1.

85 G

a: R

b-S

r w

hole

roc

kI, J

, U-P

b zr

cTS

≥ M

PtJ,

M

Indu

s S

utur

e Z

one

Nid

ar O

phio

lite

ultr

amafi

cs,

gab

bros

, pill

ow b

asal

tsS

S~

2100

-270

0SS

140.

5±5.

3 M

a: S

m-N

d (p

lagi

ocla

se-c

linop

yrox

ene)

SS

N.D

.In

dus

Mol

asse

sh, s

lts, s

s, c

ongl

EE

unkn

own

early

Eoc

eneE

EN

.D.

*Him

alay

an p

re-C

enoz

oic

rock

s pl

ot in

two

larg

ely

dist

inct

gro

ups

in N

d an

d S

r is

otop

ic s

pace

(se

e S

uppl

emen

tal F

ile 2

2 ). T

hese

gro

ups

can

be d

istin

guis

hed

by a

ge: M

iddl

e P

rote

rozo

ic a

nd o

lder

roc

ks y

ield

ε N

d(50

0) <

~-1

4 an

d a

broa

d ra

nge

of 8

7 Sr/

86S

r(50

0) v

alue

s (t

his

grou

p is

abb

revi

ated

as

“ ≥ M

Pt”

in th

e ta

ble)

, whe

reas

Lat

e P

rote

rozo

ic a

nd y

oung

er r

ocks

yie

ld ε

Nd(

500)

> ~

-14

and

a na

rrow

ran

ge o

f 87 S

r/86

Sr(

500)

va

lues

(th

is g

roup

is a

bbre

viat

ed a

s “≤

L P

t” in

the

tabl

e).

† Add

ition

al a

bbre

viat

ions

in th

is ta

ble

are:

Fm

= F

orm

atio

n, G

p =

Gro

up, c

ongl

= c

ongl

omer

ate,

ss

= s

ands

tone

, slts

= s

iltst

one,

sh

= s

hale

, gw

= g

reyw

acke

, ls

= li

mes

tone

, dl =

dol

omite

, qtz

t = q

uart

zite

, N.D

. =

not d

eter

min

ed, M

S =

mag

neto

stra

tigra

phy,

zrc

= z

ircon

, str

om =

str

omat

olite

s, P

t = P

rote

rozo

ic.

§ Cap

italiz

ed, s

uper

scrip

t let

ters

ref

er to

sou

rces

: AH

ughe

s an

d Je

ll, 1

999;

BS

ingh

et a

l., 1

999;

CM

yrow

et a

l., 2

003;

DJä

ger

et a

l., 1

971;

EM

iller

et a

l., 2

001;

FM

arqu

er e

t al.,

200

0; G

Sin

gh e

t al.,

200

2; H

Wal

ker

et

al.,

1999

; ITr

ived

i et a

l., 1

984;

J Mill

er e

t al.,

200

0; K

Fran

k et

al.,

197

7; L

Sin

gh e

t al.,

199

4; M

Ric

hard

s et

al.,

200

5; N

Val

diya

, 196

9; O

Rah

a an

d S

astr

y, 1

982;

PS

rivas

tava

and

Kum

ar, 2

003;

QTe

war

i, 20

03; R

Sin

gh a

nd

Rai

, 198

3; S

Val

diya

, 198

0; T

Pow

ell a

nd C

onag

han,

197

3; U

Srik

antia

and

Bha

rgav

a, 1

979;

VS

rikan

tia a

nd B

harg

ava,

199

8; W

Gar

zant

i et a

l., 1

986;

XH

ughe

s an

d D

rose

r, 19

92; Y

Ahm

ad e

t al.,

200

0; Z

Mei

gs e

t al.,

199

5;

AAW

hite

et a

l., 2

001;

BBN

ajm

an e

t al.,

199

7; C

CN

ajm

an e

t al.,

199

3; D

DP

ower

s et

al.,

199

8; E

ES

teck

, 200

3; F

FS

rikan

tia a

nd S

harm

a, 1

976;

GGR

aive

rman

, 200

0; H

HR

upke

, 197

4; II

Sriv

asta

va a

nd M

itra,

199

4; JJ

Bha

rgav

a,

1976

; KKV.

P. S

harm

a, 1

977;

LL V

anna

y an

d G

rase

man

n, 1

998;

MMW

iesm

ayr

and

Gra

sem

ann,

200

2; N

NV

anna

y an

d S

teck

, 199

5; O

OW

yss

et a

l., 1

999;

PPG

rase

man

n et

al.,

199

9; Q

QS

rikan

tia a

nd B

harg

ava,

198

8;

RRS

teck

et a

l., 1

998;

SSLi

nner

et a

l., 2

001;

TTN

ajm

an a

nd G

arza

nti,

2000

; UUW

hite

et a

l., 2

002;

VVB

hat a

nd L

eFor

t, 19

93; W

WV

enka

tach

ala

and

Kum

ar, 1

998;

XXS

rivas

tava

and

Kum

ar, 1

997;

YYS

inha

, 197

5; Z

ZR

aha,

19

80; A

AAM

yrow

et a

l., 2

006;

BB

BK

umar

and

Bro

okfi e

ld, 1

987;

CC

CP

ilgrim

and

Wes

t, 19

28; D

DDV

aldi

ya, 1

970;

EE

EH

ughe

s et

al.,

200

5; F

FFJa

ing

et a

l., 2

003;

GG

GJa

ing

et a

l., 2

002;

HH

HA

haro

n et

al.,

198

7; II

I Sin

gh e

t al.,

20

06; J

JJB

hat a

nd L

eFor

t, 19

92; T

ST

his

stud

y.# T

he a

ge e

stim

ates

for

the

Mio

cene

and

you

nger

SH

roc

ks la

rgel

y de

pend

on

mag

neto

stra

tigra

phic

cor

rela

tion.

How

ever

, the

you

nges

t 40 A

r/39

Ar

age

of d

etrit

al w

hite

mic

as, w

hich

rec

ord

the

time

at w

hich

the

mic

a co

oled

bel

ow ~

370

°C, p

rovi

de a

max

imum

age

of d

epos

ition

. Det

rital

mic

a ag

es o

f ~22

Ma

at th

e ba

se o

f the

Low

er D

hara

msa

la, a

nd ~

16 M

a in

the

Upp

er D

hara

msa

la (

BB

,UU

) ar

e on

ly c

onsi

sten

t with

the

prop

osed

mag

neto

stra

tigra

phic

age

s if

extr

aord

inar

y co

olin

g ra

tes

are

invo

ked

(see

Yin

(20

06))

. The

you

nges

t whi

te m

ica

ages

obt

aine

d fr

om H

imal

yan

bedr

ock

are

>4 M

a (C

eler

ier

et a

l., 2

009b

), s

o us

ing

~4 m

.y. a

s a

min

imum

lag

time

betw

een

the

cool

ing

age

and

depo

sitio

nal a

ge s

ugge

sts

that

the

mag

neto

stra

tigra

phic

age

s fo

r th

e Lo

wer

and

Upp

er D

hara

msa

la a

re a

t lea

st ~

2 m

.y. t

oo o

ld. A

djus

ting

the

ages

of t

hese

uni

ts

may

als

o af

fect

inte

rpre

ted

ages

of t

he S

iwal

ik s

trat

a.**

Acc

ordi

ng to

the

DDP

ower

s et

al.

(199

8) m

odel

, the

Mai

n H

imal

ayan

Det

achm

ent r

eact

ivat

es th

e on

lapp

ing

depo

sitio

nal c

onta

ct o

f the

Ter

tiary

fore

land

bas

in o

ver

the

Vin

dhya

n G

roup

. In

this

sch

eme,

the

Low

er D

harm

sala

and

Sub

athu

pin

ch o

ut a

long

the

reac

tivat

ed p

ortio

n of

the

cont

act,

and

thus

hav

e 0

thic

knes

s at

the

pinc

h ou

t. T

he e

xpos

ed s

ectio

ns o

f the

se u

nits

hav

e th

ickn

esse

s te

ndin

g to

war

d th

e up

per

thic

knes

s va

lues

giv

en in

the

tabl

e.††

SV

aldi

ya (

1980

) no

tes

that

the

“low

er S

ingt

ali”

may

be

equi

vale

nt to

the

Gon

dwan

as (

i.e.,

late

Pal

eozo

ic-E

arly

Mes

ozoi

c).



4). Excepting the STD and the Great Counter thrust system, all major structures are southwest-directed thrusts. Several large structural culmina-tions are also exposed in the map area due to folding of major thrusts and the development of low-angle detachment faults. We refer to these struc-tures as (1) the Narkanda half-window, (2) the Uttarkashi half-window, (3) the Kullu window, (4) the Leo Pargil dome, and (5) the Tso Morari gneiss dome (Fig. 3). We briefl y describe this regional tectonic framework herein; for an expanded description, see Appendix 2.

MCT Footwall Structures

The Sub-Himalayan thrust zone is bounded by the Main Frontal thrust below and the Krol and Mandi thrusts above (Fig. 3). The Main Frontal thrust places Neogene–Quaternary strata over the modern Indo-Gangetic Plain deposits; the Mandi and Krol thrusts place Lesser Himalayan Sequence rocks over Paleogene–Quaternary strata of the Sub-Himalayan Sequence (Kumar et al., 2006; Srikantia and Sharma, 1976; Powers et al., 1998; Raiverman, 2000).

The Tons thrust, exposed along the Sutlej River near Shimla and across the southern margin of the Uttarkashi half-window, places the Outer Lesser Himalayan Sequence over the Deoban and Damtha Groups (Fig. 3) (e.g., Valdiya, 1980; Célérier et al., 2009a). The Mun-siari thrust can be traced along most of the central Himalayan orogen (e.g., Upreti, 1999; Yin, 2006; Searle et al., 2008; see discussions in Célérier et al., 2009a, 2009b), and is referred to as the MCT I in Nepal (Bordet et al., 1972; Arita, 1981; Harrison et al., 1998). The thrust crops out in the Kullu window and the Uttarkashi half-window, where it places the Munsiari Group (Wangtu and Jeori gneiss) over the Berinag Group (Figs. 3, 4, 6B, and 6C) (e.g., V.P. Sharma, 1977; Valdiya, 1980; Vannay et al., 2004). The Berinag thrust appears in both the hanging wall and footwall of the Munsiari thrust, where it juxtaposes Berinag Group rocks over the Wangtu gneiss and the Damtha Group, respec-tively (Fig. 3) (e.g., V.P. Sharma, 1977; Valdiya, 1980; Vannay et al., 2004; Célérier et al., 2009a).

MCT

The MCT is classically defi ned as the tectonic boundary between the Greater Himalayan Crystalline complex above and the Lesser Himalayan Sequence below (e.g., Heim and Gansser, 1939; Le Fort, 1996; Hodges, 2000; Yin, 2006). This defi nition is uncertain because of debates over which local lithological units should be attributed to which tectonic unit, and it is circular, since the Greater Himalayan Crystalline complex and Lesser Himalayan Sequence are defi ned by their bounding structures (see discussion by Upreti, 1999). Nonetheless, for the Himachal Himalaya most workers share a consensus interpretation of the MCT as a continu-ous, folded, southwest-directed thrust shear zone as much as 2 km thick that was active in the Early and Middle Miocene and has a largely estab-lished map trace (as shown in Fig. 3) (e.g., Thakur and Rawat, 1992; Frank et al., 1995; Steck, 2003; Vannay et al., 2004). This interpretation is based on congruent lithology, strain concentration, metamorphic grade, and ther-mochronologic ages along the mapped shear zone (e.g., Frank et al., 1995; Grasemann et al., 1999; Vannay et al., 2004; Thiede et al., 2005). The MCT hanging-wall rocks show variation; at its northeasternmost trace along the Sutlej River, the MCT underlies a well-established inverted metamorphic sequence that is universally acknowledged as Greater Himalayan Crystal-line complex rocks (Fig. 3) (e.g., Vannay and Grasemann, 1998; Hodges, 2000; Steck, 2003; DiPietro and Pogue, 2004; Yin, 2006). Conversely, it has long been recognized that the MCT hanging-wall rocks to the west of Mandi (i.e., west of ~31°50′N, 77°E) display a right-way-up metamorphic fi eld gradient to chlorite zone conditions and are structurally continuous with the Tethyan Himalayan Sequence to the northeast (Fig. 3) (Frank et al., 1995; Fuchs and Linner, 1995; Thakur, 1998; Steck, 2003; DiPietro and Pogue, 2004; Yin, 2006). Therefore the Himachal region requires a relaxation of the MCT defi nition as the boundary between the Greater Himalayan Crystalline complex and the Lesser Himalayan Sequence.

Based on the change in hanging-wall rocks, we divide the MCT into northern and southern segments. The northern MCT juxtaposes the Greater Himalayan Crystalline complex over the Lesser Himalayan Sequence; the southern MCT places the Tethyan Himalayan Sequence and the Baragaon gneiss over the Lesser Himalayan Sequence (Fig. 3). The intersection line of the STD and the MCT marks the boundary between the two segments of the MCT to the north and south (Thakur, 1998; Yin, 2006; Webb et al., 2007). In subsequent text, we refer to the “MCT zone” if the ~2 km thick-ness of the shear zone is relevant.

In the map area the MCT is folded and displays large full and half- windows and isolated klippes (Fig. 3). Cutoff relationships in the MCT foot-wall suggest that the thrust cuts upsection to the southwest in its transport direction. However, the presence of a large footwall ramp along the MCT in the map area raises the question of whether the Lesser Himalayan Sequence strata in the footwall ramp were horizontal when the MCT was initially cut-ting across them. As Cretaceous–Eocene beds overlie the Shimla Group and Tal Formation of the younger Outer Lesser Himalayan Sequence units in the south and the Deoban-Damtha strata in the north (Srikantia and Sharma, 1976; Valdiya, 1980) (Fig. 3), the Proterozoic–Cambrian sequence of the northern Indian passive margin must have been tilted to the south prior to the emplacement of the MCT hanging wall in the region.

Minimum displacement along the MCT in the map area is ~115 km, determined from the northernmost and southernmost exposures of the fault. Early to Late Miocene activity on the northern segment of the MCT has been inferred from U-Th monazite-inclusion dating, 40Ar/39Ar mus-covite cooling ages, and zircon fi ssion track ages from the Greater Hima-layan Crystalline complex hanging-wall rocks (Fig. 4A) (Walker et al., 1999; Schlup, 2003; Vannay et al., 2004; Thiede et al., 2005). The portion of the MCT across the Kullu and Uttarkashi windows must have ceased

2Supplemental File 2. PDF fi le of 87Sr/86Sr (500 Ma) vs. εNd

(500 Ma) plots for the western and central Himalaya. In the Nepal Himalaya, Nd and Sr isotopic compositions and detrital zircon age distributions are different in the Lesser Hi-malayan Sequence (LHS), Greater Himalayan Crystalline complex (GHC), and Tethyan Himalayan Sequence (THS). It has been proposed that such data can be used to identify the structural setting of Himalayan strata (e.g., Parrish and Hodges, 1996). However, rocks of the same age in the Lesser Himalayan Sequence, Great-er Himalayan Crystalline complex, and Tethyan Himalayan Sequence have the same isotopic compositions and detrital zircon patterns (e.g., Myrow et al., 2003; Richards et al., 2005). This suggests that distinctions from isotopic and detrital zircon signatures in Himalayan rocks cannot be used directly to infer structural setting. Such distinctions are nonetheless valuable for constraining age ranges of Himalayan strata and thus for making stratigraphic comparisons. Neoproterozoic and younger rocks are generally distinguishable from Mesoproterozoic and older rocks in 87Sr/86Sr (500 Ma) vs. ε

Nd (500 Ma) space. (A) 87Sr/86Sr (500 Ma) vs.

εNd

(500 Ma) plot for western and central Himalaya rocks. Data for this plot are divided into three plots to ease tracking of data for individual units. (B) 87Sr/86Sr (500 Ma) vs. ε

Nd (500 Ma) plot for Himachal Himalaya rocks. Data from Bhat

and Le Fort (1992, 1993), Miller et al. (2000, 2001), and Richards et al. (2005). (C) 87Sr/86Sr (500 Ma) vs. ε

Nd (500 Ma) plot for Kumaun and Nepal Himalaya

rocks (Kumaun Himalaya—northwest India Himalaya to the east of Himachal Pradesh). Data from Ahmad et al. (2000), Deniel et al. (1987), France-Lanord et al. (1993), Inger and Harris (1993), and Prince (1999). (D) 87Sr/86Sr (500 Ma) vs. ε

Nd (500 Ma) plot for western Himalayan (Nanga Parbat) syntaxis rocks. Data

from Argles et al. (2003), Foster et al. (2000, 2002), Gazis et al. (1998), George et al. (1993), and Whittington et al. (1999). If you are viewing the PDF of this paper or reading it offl ine, please visit http://dx.doi.org/10.1130/GES00627.S3 or the full-text article on www.gsapubs.org to view Supplemental File 2.

Webb et al.


motion in the Late Miocene when these windows were developed and caused folding of the MCT, as indicated by cooling ages (Vannay et al., 2004; Thiede et al., 2005; Caddick et al., 2007; Chambers et al., 2008). However, the relationship does not preclude the southernmost MCT link-ing younger thrusts in the Lesser Himalayan Sequence to continue its motion after the Middle Miocene.

STD

The STD juxtaposing the Tethyan Himalayan Sequence over the Greater Himalayan Crystalline complex can be traced continuously from the central Himalaya to the northern end of the Kullu window (Figs. 1 and 3) (Burg et al., 1984; Burchfi el et al., 1992; Choudhuri et al., 1992; Thakur, 1998; Dèzes et al., 1999è; Jain et al., 1999; Wyss et al., 1999; Steck, 2003; DiPietro and Pogue, 2004; Yin, 2006). Here the STD is folded and overturned within the southwest-verging Phojal anticline, and the overturned fault trace extends back to the southeast and intersects the MCT on the north and south sides of the eastern Kullu window and at the northwestern rim of the Uttarkashi window (Fig. 3) (Thakur, 1998; Webb et al., 2007). The MCT-STD branch line trends to the northwest, parallel to the strike of the orogen. It is largely buried to the northwest and eroded to the southeast. In the Himachal Himalaya the fault features both top-to-the-northeast and top-to-the-southwest structures, including S-C fabric,

normal drag shear bands, σ-type porphyroclasts, and asymmetric isocli-nal to tight folds, across a 300–600-m-thick shear zone (Choudhuri et al., 1992; Jain et al., 1999; Vannay et al., 2004; our observations).

The Zanskar shear zone represents a possible northwestern extension of the STD (Figs. 1 and 3) (e.g., Searle, 1986; Herren, 1987; Patel et al., 1993; Dèzes et al., 1999; Epard and Steck, 2004). The northwest-trending, northeastern segment of this shear zone has been interpreted as (1) an along-strike continuation of the STD, connected in map view to the right-way-up STD across the Himachal Himalaya (e.g., Searle et al., 1988; Jain et al., 1999), or (2) as part of an STD window (Thakur, 1998; Dèzes, 1999; Yin, 2006). We follow the second interpretation because of the established continuity of the Tethyan Himalayan Sequence from Chamba to the Tso Morari, i.e., weakly deformed rocks cross the path of the proposed STD–Zanskar shear zone map-view connection (e.g., Frank et al., 1995; Fuchs and Linner, 1995). Because the Zanskar STD window is warped but not overturned, it follows that the Phojal anticline is a local structure along the northern margin of the Kullu and Uttarkashi windows that does not extend to the Zanskar region.

The amount of displacement along the STD is diffi cult to determine because rocks above and below the fault share the same protoliths in this region. Also, there is no pronounced metamorphic offset across the fault: metamorphic isograds are subparallel to the STD (Fig. 5). Therefore, despite the signifi cant evidence for shear deformation across the STD

Sillimanite-in isograd

Kyanite-in isograd

Biotite-in isograd

Garnet-in isograd

Ultra-highpressure(UHP) rocks

Isograd minerals occur on the side of each isograd curve marked by a filled semi-circle.

Tso Morari UHP dome

Tso Morari UHP dome UHP

Sillimanite / Andalusite contact

metamorphism

Sillimanite / Kyanite contact metamorphism?

Figure 5. Metamorphic isograd map of the Himachal Himalaya, with (1) largely continuous garnet-in and kyanite-in iso-grads and (2) discontinuous biotite-in and sillimanite-in isograds (due to incomplete metamorphic mapping). Main references are Frank et al. (1973), Epard et al. (1995), and Vannay and Grasemann (1998); see Appendix 1 for additional references.



zone, local lithologic and petrologic information do not constrain the mag-nitude of fault offset. The fault may have initiated in the Eocene as a basal décollement of the Tethyan Himalayan fold-thrust belt (Wiesmayr and Grasemann, 2002). Early to Middle Miocene 40Ar/39Ar muscovite ages in the immediate STD hanging wall and footwall suggest that plastic defor-mation along the STD ceased in that period (Walker et al., 1999; Vannay et al., 2004; Thiede et al., 2005).

Most Tethyan Himalayan Sequence strata northeast of the right-way-up STD are involved in the dominantly top-to-the-southwest Tethyan Hima-layan fold-thrust belt within the Spiti Synclinorium (Figs. 3 and 4B) (e.g., Frank et al., 1995; Fuchs and Linner, 1995; Vannay and Steck, 1995; Steck et al., 1998; Wiesmayr and Grasemann, 2002). Similar relationships also occur across the Chamba Synclinorium in the northwest of our map area (e.g., Frank et al., 1995; Fuchs and Linner, 1995). To the north, Tethyan Himalayan Sequence rocks and suture zone rocks are thrust northeastward over the Indus molasse along strands of the latest Oligocene–Miocene Great Counter thrust system (e.g., Schlup et al., 2003; de Sigoyer et al., 2004). The Great Counter thrust system may represent the northern exten-sion of the STD (e.g., Yin et al., 1994, 1999).

STRUCTURAL GEOLOGY

Thrusting is the dominant expression of contractional deformation in the footwall of the MCT. Although many of these thrusts are well defi ned locally, the relationships among the structures and deformation in individ-ual thrust systems have not been studied in detail. Further issues include: (1) MCT-STD geometric relationships, (2) internal deformation of units to address the assumption of constant bed thickness in line-length balancing, and (3) variable deformation style and strain as functions of both lithology and structural positions relative to nearby faults. To address these issues, we conducted detailed geologic mapping and outcrop-scale observations across the Himachal Himalaya. We summarize the main results of our structural observations in the following.

Mandi-Bilaspur Thrust System Hanging-Wall Structures

Bedding in the Deoban and Damtha Groups is deformed by brittle structures, including dominantly southwest-verging parallel folds and dominantly southwest-directed brittle faults (Figs. 6B, 6D [stereoplots L3, L4, L6, L7], 7A, and 7B). Fold amplitudes range from 50-m-thick schuppen zone comprising 2–15-m-thick horses of quartzite, granitic schist, and granitic gneiss. Gneissic fabric across the Munsiari Group is characterized by a dominantly north-northeast–trending stretching linea-tion (Figs. 6B–6D). Gneissic foliation in the Jeori gneiss unit exposed in the Sutlej River Valley (~15 km northeast of Rampur) is penetratively deformed by kink folds with centimeter- to meter-scale wavelengths and ~90° interlimb angles (Fig. 7H). Along a 10 km stretch of the Sutlej River in the eastern Kullu window (centered on the town of Wangtu), unfoliated pegmatitic granites crosscut the foliation of the Wangtu granitic gneiss (Fig. 7I). The Late Miocene ages of these granites provide a lower limit for the development of the gneissic fabric (see following Geochronology dis-cussion). These granites are the only unit within the Munsiari thrust hang-ing wall, and indeed within the Lesser Himalayan Sequence, for which we did not observe outcrop-scale deformation.

Webb et al.


MCT and Hanging-Wall Structures

We divide the MCT into northern and southern portions based on Greater Himalayan Crystalline complex and Tethyan Himalayan Sequence hanging-wall lithologies, respectively. This division is structurally defi ned by the overturned South Tibet detachment, which is folded with the south-west-verging Phojal anticline. In this interpretation, the southern MCT hanging wall is continuous with the STD hanging wall. Therefore deter-mining the deformation style and strain of the southern MCT hanging wall, the northern MCT hanging wall, and the STD hanging wall provides key tests of the interpretation. We review our main structural observations from each area in the following.

Southern MCT and Hanging-Wall StructuresObservations of deformation in the MCT hanging wall south of the

Kullu window are limited because (1) most preserved rocks are near the

base of the thrust sheet, with structurally high rocks largely eroded away, and (2) despite this knowledge, the undulatory folding of the thrust sheet limits our ability to tightly constrain structural elevation above the MCT base across much of the thrust sheet. This portion of the MCT is defi ned by a 1–2 km top-to-the-southwest shear zone featuring S-C fabrics with northeast-trending stretching lineations defi ned by biotite and feldspar, normal drag shear bands, ultramylonites, σ-type porphyroclasts of feld-spar, brittle-ductile synthetic and antithetic microfaulting of feldspar, and tight to isoclinal folds [Figs. 6A, 6B, 6D (stereoplots TG1, T5, T6, T7, T8), 8A, and 8B]. The base of the shear zone is largely coincident with the garnet isograd within an inverted metamorphic fi eld gradient (Fig. 5). Where the MCT juxtaposes Haimanta rocks directly above Outer Lesser Himalaya rocks (at Narkanda and along the Shimla klippe), mylonitic garnet schist of the MCT zone concordantly overlies pelitic phyllite, chlorite-pyrite schists, and graphitic phyllite, and graphitic schist. Here shear bands and isoclinal folds persist across ~400 m structurally below

Figure 6 (continued on following pages). (A) Geological map of the Upper Beas Val-ley region. (B) Geological map of the central Sutlej River region. Gray structural data are from this study; blue structural data are taken from the literature and were used for cross section construction. (C) Geologi-cal map of the northeastern Sutlej River region. Topographic contours in A, B, and C are from the Shuttle Radar Topography Mission; in some areas these data are dis-torted (e.g., at 32°25′N, 76°50′E). (D) Equal area stereoplots for regions labeled in A, B, and C. The regions were selected on the basis of shared and/or similar structural set-ting and geographic proximity. The regions and stereoplots are labeled with letters and numbers in order to denote different regions (numbers) within different tectonic units (denoted by letters) (e.g., L1—Lesser Himalayan Sequence, area 1; G2—Greater Himalayan Crystalline complex, area 2; T4—Tethyan Himalayan Sequence, area 3). The abbreviations are the same as in the leg-end in Figure 3.



Figure 6 (continued).

Webb et al.






N total = 10n=4 (foliation)n=5 (stretching lineation)n=1 (fold axis)

0°

N total = 11n=1 (bedding)n=6 (foliation)n=2 (stretching lineation)n=2 (fold axis)

0°

N total = 55n=27 (foliation)n=22 (stretching lineation)

n=3 (axial plane)n=2 (fold axis)

n=1 (R1 shear)

0°


0°


0°


0°

N total = 17n=4 (bedding)n=6 (foliation)

n=5 (fault)n=1 (fold axis)

n=1 (stria)

0°


n=9 (fault)n=1 (stria)

n=2 (axial plane)n=4 (fold axis)

n=1 (R1 shear)

n=9 (stretching lineation)

0°


0°


n=3 (axial plane)n=9 (fold axis)n=4 (S Plane)n=3 (C plane)

n=1 (fault)

0°

N total = 60

n=28 (foliation)n=21 (stretching lineation)

n=1 (bedding)

n=3 (fault)n=2 (axial plane)n=5 (fold axis)

0°


n=4 (fold axis)n=2 (axial plane)

n=2 (C plane)n=2 (S plane)

n=1 (Extensional shear band)

0°


0°


0°


n=3 (axial plane)

n=1 (C plane)n=3 (fold axis)

0°

N total = 16n=8 (bedding)n=6 (fold axis)n=2 (fault)

0°

N total = 92

n=13 (fold axis)



n=1 (C plane)n=1 (S plane)

0°


n=35 (fold axis)n=6 (S plane)n=11 (C plane)

n=3 (R1 shear)


n=5 (axial plane)

0°

N total = 37n=18 (foliation)n=14 (stretching lineation)n=4 (fold axis)n=1 (fault)

0°

N total = 52n=26 (foliation)n=21 (stretching lineation)n=3 (fold axis)n=2 (axial plane)

0°

N total = 36n=24 (foliation)n=9 (stretching lineation)n=2 (fold axis)n=1 (axial plane)

0°

N total = 24n=4 (bedding)

n=2 (fault)

n=1 (fold axis)n=1 (axial plane)


n=1 (stria)

0°


n=8 (fold axis)n=10 (stretching lineation)

n=3 (fault)n=1 (R1 shear)

n=1 (axial plane)

0°

T1 T3T2

T4 T6T5

T7 T9T8

GT1 G2G1

L1 L3L2

G3 G5G4

L4 L6L5

L7 L8

D

Webb et al.


AA

cover

Southwest

1 m

Southwest

1 m

10 m

Southwest

MCT

DeobanGroupcarbonates

Baragaon gneiss

Southwest

MCT

10 m

BB

Southwest

5 cm

Southwest

5 cm

Quartzvein

CC

Northwest

10 cm

coverDD



30 cm

N

150 cm

300 cm

260 cm

Total restored bed lengthis 560 cm

Final bed length

Horizontal shortening strain = (150-560)/560 = -73%

S1

S1

S0

E

Figure 7 (continued on following pages). Field photographs of the Main Central thrust (MCT) footwall (locations marked in Figs. 6A, 6B, 6C). All photographs were taken in the Sutlej River Valley except for 6D, which was taken along the Shimla-Narkanda Road. (A) Thrust fault system within the Deoban Group with associated folds. (B) Folding and duplexing of Deoban carbonates beneath the MCT. Here the base of the MCT is a brittle fault, with fractures interpreted as Riedel shears. (C) Tight similar folds in Deoban carbonaceous schist within the MCT zone. (D) Tight folding of Shimla Group rocks. (E) Folding of Shimla Formation rocks with preserved S0, shortening estimate. (F) Cross-bedding preserved in Berinag Group quartzites. (G) Tight to isoclinal folds in Berinag Group quartzites, same site as F. (H) Kink folds of Jeori

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