Transcript Archean Plate Tectonics: Isotopic Evidence from Samples of the

Archean Plate Tectonics: Isotopic
Evidence from Samples of the
Lithospheric Mantle to the Upper Crust
Steven B Shirey
Department of Terrestrial Magnetism
Carnegie Institution of Washington
DEPTH
ISOTOPIC DATA
Pb-Pb Array for MORB-OIB
CRUSTAL
EVIDENCE
Sialic rocks with juvenile isotopes
Enriched Os in wet komatiites
O isotopes in magmatic zircon
INFERENCE
OCEANIC SLAB
RECYCLING
OCEANIC ARCS
WITH START OF
CONTINENTAL ARCS
EARLY RELATIVELY
COOL MAGMATISM
MANTLE
LITHOSPHERE
EVIDENCE
Low-T O isotopes in eclogites
C & N isotopes in diamond
+ Os isotopes in sulfide inclusions
MIF sulfur in sulfide inclusions
SUBDUCTION
IMPRINT EVIDENT
Current mantle
heterogeneity,
especially the Pb-Pb
array for MORB-OIB
supports Paleoarchean
mantle recycling.
(Davies, JGR 1984)
(Hart & Gaetani, CMP 2006)
(Davies, EPSL 2002)
QuickTime™ and a
Graphics decompressor
are needed to see this picture.
(Davies, EPSL 2002)
Nd and Hf isotope data
on Archean crustal
rocks used to require
separation on an early
crustal component.
This is no longer the
case.
(Vervoort & Blichert-Toft, GCA 2001)
An Early Depleted
Reservoir (EDR) has
been proposed for the
Earth. All Archean
crust would come from
this reservoir.
(Boyet & Carlson, Science, 2005)
EDR of Boyet & Carlson
(Bennett, Treatise on Geochemistry, 2004; with additions)
(Bennett, Treatise on Geochemistry, 2004)
EDR of Boyet & Carlson
(Bennett, Treatise on Geochemistry, 2004; with additions)
EDR of Boyet & Carlson
CRUSTAL
EVOLUTION
(Harrison et al, Science, 2004; with additions)
Isotopic
heterogeneity
mantle
4.3 Ga
reservoir
(Kamber et al, CMP 2003; with additions)
(Valley et al, CMP, 2005)
(modified from Stachel et al, Elements, 2005)
Peridotite Re-Os shows the
cratonic lithosphere is Archean
Most sulfide inclusions
are late Archean
8.00
6.00
MED IAN PERIDOTITE
Tm a = 3.1 Ga
187
Os/188Os
4.00
MED IAN PERIDOTITE
Trd = 2.7 Ga
2.00
0.00
Kimberley
Jwaneng
Orapa
Koffiefontein
0
100
200
187
(Carlson et al, 1998-2002;
James and Fouch, 2002)
300
Re/188Os
(Shirey et al., GRL, 2001)
400
Re, trace elements and oxygen
correlate with eclogite groups
Oxygen, Re-Os and
REE allow eclogites
to be placed into an
Archean oceanic
lithosphere section
Re-Os whole rock
systematics give a
scattered Archean age
Same for other
localities and some
other isotope systems
(e.g. Nd, Pb)
U-Pb age on zircon
supports Re-Os age
(modified from original fig by Schmitz et al, 2004)
Diamond
Stable
Isotopes
(separate symbols
are E-Types &
fibrous diamonds)
MIF Sulfur
(Mojsis et al., GCA, 2003)
(Farquhar et al., Science, 2000)
An Archean
tracer of
surficial sulfur
Sulfide inclusions in
Orapa diamonds
have surface S
J. Farquhar et al., Science
298, 2369 -2372 (2002)
Eclogitic Sulfides
incident light
Peridotitic Sulfides
Sulfides
incident light
20  m
SE
SE
CL
6a
6b
transmitted
Panda pipe,
Slave Craton
Age = 3520±170 Ma
(Isoplot model 1
MSWD = 0.46)
OsIR =
0.1093±0.0001
(Westerlund, Shirey, Richardson, Carlson, Harris, Gurney, CMP, 2006 in press)
Archean (3.5 Ga) example
Cenozoic example
Mixing of subduction fluids with
peridotite in the mantle wedge
(Westerlund, Shirey, Richardson, Carlson,
Harris, Gurney, CMP in press)
(Widom, Kepezhinskas, and Defant,
Chemical Geology, 2003)
DEPTH
ISOTOPIC DATA
Pb-Pb Array for MORB-OIB
CRUSTAL
EVIDENCE
Sialic rocks with juvenile isotopes
Enriched Os in wet komatiites
O isotopes in magmatic zircon
INFERENCE
OCEANIC SLAB
RECYCLING
OCEANIC ARCS
WITH START OF
CONTINENTAL ARCS
EARLY RELATIVELY
COOL MAGMATISM
MANTLE
LITHOSPHERE
EVIDENCE
Low-T O isotopes in eclogites
C & N isotopes in diamond
+ Os isotopes in sulfide inclusions
MIF sulfur in sulfide inclusions
SUBDUCTION
IMPRINT EVIDENT