formation and evolution of the earliest felsic crust

Formation and evolution of the earliest felsic crust

Stephen J. Mojzsis University of Colorado mojzsis@colorado.eduhttp://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

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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

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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

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101

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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