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
Pb-Pb Array for MORB-OIB
Sialic rocks with juvenile isotopes
Enriched Os in wet komatiites
O isotopes in magmatic zircon
Low-T O isotopes in eclogites
C & N isotopes in diamond
+ Os isotopes in sulfide inclusions
MIF sulfur in sulfide inclusions
CRUSTALEVIDENCE
MANTLELITHOSPHEREEVIDENCE
OCEANIC SLABRECYCLING
OCEANIC ARCSWITH START OFCONTINENTAL ARCS
EARLY RELATIVELYCOOL MAGMATISM
SUBDUCTION IMPRINT EVIDENT
ISOTOPIC DATA INFERENCEDEPTH
(Davies, JGR 1984) (Hart & Gaetani, CMP 2006)
Current mantle heterogeneity,
especially the Pb-Pb array for MORB-OIB
supports Paleoarchean
mantle recycling.
(Davies, EPSL 2002)
QuickTime™ and aGraphics 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)
(Boyet & Carlson, Science, 2005)
An Early Depleted Reservoir (EDR) has been proposed for
the Earth. All Archean crust would
come from this reservoir.
(Bennett, Treatise on Geochemistry, 2004; with additions)
EDR of Boyet & Carlson
(Bennett, Treatise on Geochemistry, 2004)
EDR of Boyet & Carlson
(Bennett, Treatise on Geochemistry, 2004; with additions)
EDR of Boyet & Carlson
(Harrison et al, Science, 2004; with additions)
CRUSTAL EVOLUTION
Isotopic heterogeneity
4.3 Ga reservoir
mantle
(Kamber et al, CMP 2003; with additions)
(Valley et al, CMP, 2005)
(modified from Stachel et al, Elements, 2005)
(Carlson et al, 1998-2002; James and Fouch, 2002)
0.00
2.00
4.00
6.00
8.00
0 100 200 300 400
JwanengKimberley
OrapaKoffiefontein
187Re/188Os
MEDIAN PERIDOTITETma = 3.1 Ga
MEDIAN PERIDOTITETrd = 2.7 Ga
187Os/188Os
(Shirey et al., GRL, 2001)
Most sulfide inclusions are late
Archean
Peridotite Re-Os shows the cratonic lithosphere is
Archean
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)
DiamondStable
Isotopes
(separate symbols are E-
Types &fibrous
diamonds)
(Farquhar et al., Science, 2000)
(Mojsis et al., GCA, 2003)
MIF Sulfur
An Archean tracer of surficial sulfur
J. Farquhar et al., Science 298, 2369 -2372 (2002)
Sulfide inclusions in
Orapa diamonds have surface S
Eclogitic Sulfides
20 μm
Peridotitic Sulfides Sulfides
6a
6b
incident light incident light
transmittedCLSESE
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)
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)
Archean (3.5 Ga) example Cenozoic example
Pb-Pb Array for MORB-OIB
Sialic rocks with juvenile isotopes
Enriched Os in wet komatiites
O isotopes in magmatic zircon
Low-T O isotopes in eclogites
C & N isotopes in diamond
+ Os isotopes in sulfide inclusions
MIF sulfur in sulfide inclusions
CRUSTALEVIDENCE
MANTLELITHOSPHEREEVIDENCE
OCEANIC SLABRECYCLING
OCEANIC ARCSWITH START OFCONTINENTAL ARCS
EARLY RELATIVELYCOOL MAGMATISM
SUBDUCTION IMPRINT EVIDENT
ISOTOPIC DATA INFERENCEDEPTH