formation and evolution of the earliest felsic crust
TRANSCRIPT
Formation and evolution of the earliest felsic crust
Stephen J. Mojzsis University of Colorado [email protected]://isotope.colorado.edu ESF Archean Environment Workshop 2009
Special thanks to: O. Abramov, W. Bleeker, M. Harrison, M. Hopkins, D. Trail, B. Watson, N. CatesNASA Exobiology Program, NASA Lunar Science Institute, European Science Foundation
Outline of the presentation
• Origin of the first “felsic” crust(s)
• Nature of the oldest known granitoid gneisses
• The oldest zircons of probable(?) granitic origin
• Problems that we have to ‘fess up to
BTW, My samples do not have the gustatorial quality of Judy and Cris’ stroms
Figure courtesy Eric Gaidos (University of Hawaii)
A timeline of key events
The “darkest” of the Dark Ages
“Terrestrial” (silicate) worlds:Mercury – Venus – Earth + Moon – Mars - Asteroids
Earth has granitic crust while others (apparently) do not.
Why? What do we know of their different compositions? (little, actually)
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75
1022
1023
1024
1025
mas
s (1
024 k
g)
AU
When did the crust form?General hypotheses of origin
• Early from late accretionary veneer of more volatile elements?– Crust should be very old and volatile rich
• Early by crystallization of a magma ocean?– Crust should be very old and rich in incompatible
elements (and volatile depleted)• Magmatism through time
– Crust should be relatively young and rich in incompatible elements
Composition of crust
• Crust is rich in some (moderately) volatile elements (alkalis: Na, K, Rb), but these are incompatible.
• Crust is clearly enriched in incompatible elements.
• Crust compositions point to a magmatic origin.
1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.97510-1
100
101
102
103
Upper Continental Crust
N-MORB
CI n
orm
aliz
ed a
bund
ance
ionic radius (Å)
Orgueil (CI chondrite)
1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.97510-1
100
101
102
103
Upper Continental Crust
N-MORB
CI n
orm
aliz
ed a
bund
ance
ionic radius (Å)
Orgueil (CI chondrite)
1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.97510-1
100
101
102
103
Bulk Mars (model)
Earth's Crust + hydrosphere
bulk Moon (model)
CI n
orm
aliz
ed a
bund
ance
ionic radius (Å)
Ultramafic rocks
1.175 1.150 1.125 1.100 1.075 1.050 1.025 1.000 0.97510-1
100
101
102
103
ALH84001
Earth's Crust + hydrosphere
Shergotty
CI n
orm
aliz
ed a
bund
ance
ionic radius (Å)
Bulk Mars (model)
The Moon and Mars are VASTLY different from Earth.
Early on, solar-system-wide processes setthe stage for subsequent expression of thesedifferences.
Conventional Sm-Nd and common-Pb “ages”of the continental crust are
relatively young (e.g. 2.5 Ga); but do theseages represent the time the crust was
created or simply the last time iswas partially or wholly recycled?
Before we go in to this issue, we must address special problems of the “Early Earth”
Crustal recycling processes “frozen in time”
…planets form hot.
Whole Earth melting (magma ocean) –conditions
• conditions after planetary formation were hot
• Earth-Moon impact enough to vaporize the planet
• Moon-forming impact supplied ~4 x 1031 J (or ~7 x 106 J kg-1) to the proto-Earth
• Low P heat of vaporization of rock is 6 – 14 x 106 J kg-1 (depending on rock type)
• Latest estimates place this event at ~4.51 Ga
• This event effectively hit the planet’s RESET button
Physical parameters from Sleep et al. (2001)
Moon-forming impact (consequences)
• Silicate vapor atmosphere
• Impact energy radiated back to space (Teff = 2300 K)
• Eventual condensation of rock vapor atmosphere
Cooling of the first crust…
• Dissipation of optically-thick atmosphere needed
• Surface heat flow = 1.6 x 106 W/m2
• At this rate of cooling = atm. collapse in <2000y
• CO2 and H2O (supercritical) atm. remained
• Heat transfer from mantle to atmosphere to space controlled by molten crust. Once this is solidified, the situation changes dramatically (cooling is slowed)
• A magma ocean has a solid surface (except at the very start)
Already discussed by Jeroen & Nick this morning
Formation of a cool rind…• Of initially ultramafic composition?
• Provided a potentially habitable surface at this time
• Convection became “sluggish” because of the establishment of an effective “lid”
• Collapse of an ultra-greenhouse helped in cooling
• 2.7 Myr? to reach clement surface (30ºC)
• Volatile exchange between atm., crust and hydrosphere was enormous
• Planetary hydrothermal system formed with hot water + hot rock on a global scale
• Substantial H2 and CO followed by methane generated from hydrothermal alteration of the first crust?
Image by Don Dixon
10 100 1000100
101
102
103
1
2
Sola
r Win
d, X
-ray
flux
, EU
V (re
lativ
e to
pre
sent
)
time (Myr after solar system formation)
solar wind x-ray EUV
Solar lum
inosity (relative to present)
Greenland
BIFs
solar luminosity
Hadean
Moon-forming
event
Archean
Expanded and based on compilation by Zahnle (2007)
Low luminosity but high UV
Evolution of the Sun in time
MASSIVE abioticMethane source?
methanogens
What are melts that might form under hot, wet conditions
on the early Earth?
An exploration of “TTGs”tonalites – trondhjemites- granodiorites
Errr, Nick already gave this part of the talk for me!
Primer on Archean “TTGs”• The most typical of the so-
called Archean “grey/gray gneisses”
• Preserve highly fractionated REEs that require amphibole, garnet (or both) as the residuum during magma generation
• Dehydration melting (at subduction) from H2O released from the breakdown of amphibole ! dissolves into H2O-undersaturated silica liquid (P. Wyllie and coworkers)
Qtz (10-20%), alkali-feldspar (Ca-rich Plag), Px, Hbl, Bio and accessory Zrc,Ap, Ti-phases (aTi > 0.6). (Right, Zircon becomes important in this talk).
Primer on Archean “TTGs”• Yields liquid compositions that
correspond well to the Archean TTGs through a range of P and T
• As pointed out by Wyllie, Wolf and Van der Laan (1997) and others there is a limited area in P-T space of the lithosphere where garnet and amphibole will co-exist on the liquidi. (residual amphibole requires moderate temperatures but high H2O; residual garnet needs depths >50 km, lower H2O and higher temperatures than for residual amphibole).
The occurrence of hornblende and biotite is important because they prove that the magma was H20-bearing! These are HOT (950°C) magmas with ~140 ppm Zr.
Zr (SiO4) - what is it made of, why does it survive?
Courtesy: E.B. Watson
Courtesy: E.B. Watson
Courtesy: E.B. Watson
Cherniak and Watson (2001)Cherniak et al. (1997a,b)Watson and Cherniak (1997)
Courtesy: E.B. Watson
Where are the oldest zircons found?
Ion probe analysis of detrital zircons demonstrates Hadean origins
Zircons from Jack Hills range from 3.9 to 4.38 Ga and are the oldest minerals yet found on Earth
Mojzsis et al. (2001) Wilde et al. (2001)
E.B. Watson
Quantity of crust in the Hadean
Lu/Hf studies - concepts
εHf denotes deviations in 176Hf/177Hf fromBulk Earth (in parts per 104)
176Lu decays to 176Hf with t½ = 37 Ga
Conventionally expressed relative to epsilon
On-going collaborations with J. Blichert-Toft and F. Albarède (ENS Lyon)
Lu/Hf studies
εHf denotes deviations in 176Hf/177Hf fromBulk Earth (in parts per 104)
176Lu decays to 176Hf with t½ = 37 Ga
Lu/Hf studies
... .. .. .. .... .
mantle evolution
conti
nenta
l evol
ution
Zircons have extremely low Lu/Hf, thus they record initial 176Hf/177Hf at time of formation established by Pb ages
Lu/Hf studies
Zircons have extremely low Lu/Hf, thus they record initial 176Hf/177Hf at time of formation established by Pb ages
3200 3400 3600 3800 4000 4200 4400
-10
-5
0
5
10
Bulk Earth
Amelin et al. (1999)
εε εε Hf
Age (Ma)
Continentalevolution
‘Depletedmantle’
We have long assumed that continents didn’t emerge until ca. 4 Ga, but earlier depletions may have been remixed
3200 3400 3600 3800 4000 4200 4400
-10
-5
0
5
10
Bulk Earth
Amelin et al. (1999)
εε εε Hf
Age (Ma)
Lu/Hf studies
176Lu177Hf = 0.08
176Lu177Hf = 0
Harrison TM, Blichert-Toft J, Muller W, Albarede, F, Holden, P, Mojzsis, SJ Heterogeneous Hadean hafnium: Evidence of continental crust at 4.4 to 4.5 Ga SCIENCE 310 (5756): 1947-1950 DEC 23 2005
New Jack Hills initial 176Hf/177Hf data indicate very large negative ANDpositive eHf deviations from Bulk Earth
Formation of continental crust by ~ 4.4 Ga
Further evidence
Existence of live terrestrial 146Sm
Live 146Sm (a decays to 142Nd with t½ of 103 Ma) present during solar system formation
Evidence of 146Sm should be preserved in continental crust if differentiation began early and produced high Sm/Ndreservoirs.
Reports of small (0.03‰), 142Nd excess in >3.7 Ga rocks (and younger materials; hidden reservoir).
Crustal evolution paradigm
Resolving whether 146Sm effects have been preserved in the crust is key to understanding earliest differentiation history of the Earth as this is potentially the most sensitive indicator.
Continental growth history
(i) The paradigm long favored by isotope geochemists is that continental growth began after ~4 Ga and was ~80% of present mass by 2.5 Ga
(ii) A less popular but persistent viewpoint is that continents have maintained equivalent (or greater!) mass to today since the early Hadean
176Hf/177Hf results are consistent with this latter (ii) viewpointFrom this we might infer that plate recycling mechanisms were operating
Yep, Nick and Jeroen showed this one too.
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Amelin et al. 1999 (TIMS)Harrison et al. 2005 (LA-ICPMS)Harrison et al. 2005 (sol n ICPMS)Harrison et al. 2008 (LA-ICPMS)
Blichert-Toft and Albarède 2008 (soln ICPMS)
3.4 3.6 3.8 4.0 4.2 4.4Age
0
+5
-5
+10
+15
-10
Bulk SilicateEarth
εHf(T)
From Blichert-Toft and Albarede (2008)
Hadean zircon data
Mafic rocks
Hf values strongly resemble TTGs;OBVIOUSLY WE NEED TO PAY ATTENTIONTO ROCKS BETWEEN 3.6 AND 4.1 Ga
Mineral inclusion chemistry and Ti thermometry seems to point to the
role of liquid water in crustal processes (more about this later).
From Cherniak and Watson (2007)
Closure temperatures
Ti is retentive
4.2 Ga Jack Hills zircon
25 calculated temperatures yield 725±35°C
Courtesy: E.B. Watson
From Hopkins, Harrison and Manning (2008)
Low temperature, high pressure conditions.
Consistent with subduction
Hadean zircon inclusions
The chemical fingerprints of subduction-related volcanism
• Volcanism almost always occurs above subductinglithospheric plates– Most likely due to
dehydration of subducting ocean crust
• When subduction occurs along a (proto-)continental margin, the magmas add to the volume of continental crust (e.g. Andes)
What could the rocks have been that shed the ancient zircons?
Trace elements and their partition into Hadean zircons can
shed light on this.
Distribution Coefficients• D = Ratio of concentration of an element
between two phases
• concentration (c)• component (i)• two phases (α and β) α
βαβ
i
ii c
cD =−
Distribution Coefficients• Depend on the radius and charge on the ion (i), also on the structure of the
mineral.
• Each mineral has one or more optimum D-values, corresponding to the radius of each structure site.
• Away from a maximum the vs. ri relationship approaches linearity.
• log varies with the square of the radius difference between the ion and the ‘size’ of the site.
• Major elements in the mineral do not necessarily plot at the peak of the curve
• Curves of this kind can be used to estimate an unmeasured for an element, just by knowing its ionic radius and valence.
meltsolidiD −
meltsolidiD −
meltsolidiD −
Lattice strain theory• Onuma (1968); Blundy and Wood (1994); Beattie (1994)
))(31)(
2(4ln 32
aiaiaa
a
i rrrrrRTEN
DD −+−−= π
Olivine-melt partition coefficients for divalent and trivalent cations, measured at 1100°C, shown with curves through points calculated using the Lattice Strain Theory (Beattie, 1994).
0.7 0.8 0.9 1.0 1.1 1.210-4
10-3
10-2
10-1
100
101
102
103
Hf
Zr
LuTm
HoY
Dy
Gd
EuSm
Ce+3
Nd
Pr
La
Na
Ga
Sc
Nb
Ti
Ce4+
V4+
Mg
Li
Ionic radius (Å)
U+4
U+4
(inferred)Pu+4 (inferred)
Pu+3
(inferred)
1+
2+3+4+5+
Blundy and Wood (2003)
Th+4
Par
titio
n C
oeffi
cien
t
A case study to belabor the point…
A simple test of mafic sources…
0.975 1.000 1.025 1.050 1.075 1.100 1.125 1.150 1.17510-4
10-3
10-2
10-1
100
101
102 Coogan and Hinton (2006)
147-894G-9R3 70-76zircons 1,2,3
147-894G-9R3 70-76 (1)
147-894G-9R3 70-76 (2)
147-894G-9R3 70-76 (3)
parti
tion
coef
ficie
nt
ionic radius (Å)
…passes the test
0.975 1.000 1.025 1.050 1.075 1.100 1.125 1.150 1.17510-4
10-3
10-2
10-1
100
101
102
Pedersen et al. (1996)
147-894G-9R3 80-83Gabbronorite
Peck et al. (2001) ~4.4 Ga zircon W74/2-36
m2-13 m2-14 m2-17 m2-30 m2-31
147-894G-9R3 70-76 (1)
parti
tion
coef
ficie
nt
ionic radius (Å)
Hadean zircons fail the test
0.95 1.00 1.05 1.10 1.151E-4
1E-3
0.01
0.1
1
10
100
1000 MORB Tonalite trondhjemite granodiorite granite syenite anorthosite adakite
parti
tion
coef
ficie
nt
ionic radius
ONLY felsic sources pass
0.95 1.00 1.05 1.10 1.151E-5
1E-4
1E-3
0.01
0.1
1
10
100pa
rtitio
n co
effic
ient
ionic radius (Å)
magmatic zircon
"hydrothermal" zircon
Figure 5c of Trail et al. (2007) in G3
sample BP42, (Hoskin et al., 2000; Hoskin 2005)
So, there appears to have been granitoid crustaround in the Hadean
Something out of the ordinary appears to have happened to the inner solar system about 3.9 billion years ago that must have modified these early crusts and is therefore germane to discussions of surface processes.
“There is no physics in this figure!” (Hal Levison)
Ryder, 1990, 2002
Moon MarsGomes et al. 2005
“Nice Model”
Four stages of a medium-scale, lunar surface Cratered Terrain Evolution Model run using the main asteroid belt impactor population derived by Bottke et al. [2005] This run has a pixel-scale of 307.9 m, and depicts 1/100 of the Lunar surface area. Richardson et al. (submitted). THIS WOULD BE THE EARTH.
Trail et al. (2007)
Correspondence between 238U/206Pb & 235U/207PbTrail et al. (2007)
• Hadean zircons which preserve narrow 3.93-3.97 Ga zones record massive Pb-loss in those domains, which are not metamict (damaged by radiation)
• Diffusive Pb-loss distances in these zircons are 2-4 µm, far smaller than the spot size of conventional 2-D SIMS analysis. They would be missed.
• What physical process(es) could cause this?
Closure Temperature(Tc)
typical grainsize range
Courtesy D. Cherniak
• At peak T>Tc a mineral is theoretically not retentive of a diffusing species.
T-Tc (SUB-closure behavior)• At peak T>Tc a mineral is theoretically not retentive of a diffusing species.
• However, for T≤Tc considerable diffusional exchange still occurs.
500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 180010-4
10-3
10-2
10-1
100
101
102
103
1y10y
100y1 Myr0.1My10ky
1ky
1s
1h1d
Pb d
iffus
ion
in z
ircon
x
(µm
)
Temperature (°C)
What is the oldest preserved continental crust?
• Oldest known rocks are from the Slave Province (Northwest Territories), and are 4.03 Ga.
3960 to 4050 Ma gneisses4020 xenocrystic zircon
Transposed mid-crustal rocks Leucogabbros Tonalites
Survey, Map, use mapping to guide sampling, micro-sampling, chemistry
1: 4.02 Ga2: 3.96 Ga (discordant)3: ~3.7 Ga4: ~3.3 – 3.5 Ga5: ~2.9 Ga
In situ analyses & mineral separate work
From Manning et al. (2006)
3830 Ma orthogneisses West GreenlandItsaq Gneiss Complex (the first time we see paragneisses)
From Cates and Mojzsis, 2006
From Manning et al. (2006)
These enclose the metamorphic equivalentsof marine sediments, so they are at least 3.83 Ga
From Manning et al. (2006)
Age:3830 Ma
Ortho-GNEISS
This used to be tonalite
Amphibolite(mafic schists)
This used to be Basalt
Granitoid dikes crosscut the supracrustal
packages during magmatic evolution
NormalSupracrustal“stratigraphy”
From Cates & Mojzsis (2006)
Other 3800 Ma gneisses
From Cates & Mojzsis (2006)
Other 3800 Ma gneisses Innersuartuut, West Greenland
From Cates & Mojzsis (2006)
Garnet-biotite schists
Amphibolite
Ages:Ca. 3800 Ma
From Cates & Mojzsis (2006)
These zircons are from tonalites
AFM diagram (boundary of Irvine and Baragar, 1971) showing tholeiitic affinity of Am-type units in Akilia association.
Normalized trace element plots. Least altered amphibolites from the ISB (dark field) and the AA] (light field). (A) Chondrite normalized REE plot of amphibolites. (B) Primitive mantle normalized multi-element plot of amphibolites. (C) Chondrite normalized REE plot of orthogneisses. (D) Primitive mantle normalized multi-element plot of orthogneisses.
from:Cates and Mojzsis (2006, 2007)
Typical tholeiitic compositions for the Akilia amphibolites
TTGs
Tectonic discrimination diagram of ISB (triangles and circles) and Akilia association (squares) mafic rocks. Fields of Pearce and Cann (1973). (1) Polat et al. (2003); (2) Polat et al. (2002); (3) Polat and Hofmann (2003); (4) Manning et al. (2006); (5) McGregor and Mason (1977); (6) Nutman et al. (1996).
These tholeiites most resemble Island Arc types
Tectonic discrimination diagram of ISB (triangles and circles) and Akilia association (squares) mafic rocks showingoceanic arc affinity for Akilia association amphibolites. Fields of Pearce (1983).
3750 Ma gneisses northern Québec
Inukjuak (Nuvvuagittuq supracrustal belt)
•Excellent exposure
•As elsewhere, reduced collection of rock types, deformed and metamorphosed
From GEOTOP, 2001
The Nd Story
Are there 4.28 Ga volcano-sedimentary rocks in Northern Quebec?
The Nd StoryO’Neil et al. Science
vol. 321, 2008Neodymium-142 Evidence for
Hadean Mafic Crust
Geochemistry: Amphibolites
The Nd Story
The Nd Story
Ultramafic to Gabbroic Sill Banded Amphibolite
Cummingtonite-amphibolite 147Sm-143Nd age: 3819±270 Ma (MSWD 5.5)
Maximum age of the NSB is likely to be 3.78 Ga
Nuvvuagittuq
• Gneisses• Amphibolites• Ultramafics• Sedimentary rocks
– Chemical sediments(BIFs)
– Detrital sediments(quartz-biotite schists)
Cates and Mojzsis (2007, 2009)
Geochemistry: NSB Orthogneisses
Geologic Map of the Tuk-Tuk siteNuvvuagituk Belt, Nunavik (Québec)
scale 1:50
From Cates and Mojzsis, 2007
3784 Ma
These are trondhjemitegneisses and the ages arenot inherited
Zircon saturation considerations
0.98 1.00 1.02 1.04 1.06 1.08 1.10
10-2
10-1
100
101
102
103
104
Lu Yb Er Dy Gd Sm Nd
3
4
2
1
6
5
Par
titio
n co
effic
ient
Cation radius (Å)
IN05003_18
rims
core
It turns out that there are lots of preserved (typical) marine volcanosedimentary successions from the Eoarchean.
BIFs Pillow basalts TTGs Detrital sediments
Detrital sediments
BIF
Aqa
Aqa
AqaBIF
Amb
Ag
Chemical sediments
Putting it all together
What we see is reminiscent of what’s occurring in the Western Pacific
ODP Leg 193 Preliminary Report:Anatomy of an Active Felsic-HostedHydrothermal System, Eastern Manus Basin (2001)
Example: Manus Basin
ODP Leg 193 Preliminary Report:Anatomy of an Active Felsic-HostedHydrothermal System, Eastern Manus Basin (2001)
Example: Manus Basin
ODP Leg 193 Preliminary Report:Anatomy of an Active Felsic-HostedHydrothermal System, Eastern Manus Basin (2001)
Example: Manus BasinLooks a little like what Kurt showed
Key points for the Hadean-Eoarchean Earth
• Granitoid crust and perhaps granite present by ~4.4 Ga (I don’t know if there were emergent landmasses).
• Hydrosphere in place and rock cycle – established by 4.38 Ga (I don’t know if there was more or less water)
• Plate recycling processes were operative – perhaps early on and likely at diffuse plate boundaries (I don’t know if there were rigid plates)
• The problem remains: How do we warm the Hadean Earth? (We are so far from resolving this problem)
Figure modified from one that appeared in Cassell’s “Atlas of Evolution” (2001)
Hypothesis:
Abundant small proto-continental masses, akin to immature-to-mature island arcs at ocean-ocean subduction zones and plume-related edifices.
Paul’s Steve’s conceptual model of the Eoarchean Earth
“reality often astonishes theory”
- Car Talk
0 500 1000 1500 2000 2500 3000 3500 4000 45001200
1400
1600
1800
2000
2200
2400
2600Change in mantle temperature with time
Tmantle initial = 2500oC Tmantle initial = 2000oC terrestrial secular cooling curves (Richter, 1988)
T ( o C
)
t (Ma)Discussed by Jeroen can Hunen at this meeting
0 500 1000 1500 2000 2500 3000 3500 4000 450010-11
10-10
10-9
10-8
planetary accretion & lunar formation
Crustal Heat Production (A) through time
tholeiitic basalt alkali basalt granodiorite granulite
A (W
kg-1
)
t (Ma)
( ) ( ) zzhkA
kqTT c
msz 2
1−++= ρ