Page 376 - Global Tectonics

PRECAMBRIAN TECTONICS AND THE SUPERCONTINENT CYCLE 359

(a) 3.515–3.430 Ga early crust formation
Duffer and Panorama Fms

10 TTG sheeted
Depth (km) 20 sills

30 Basaltic lower crust

(b) 3.410–3.325 Ga volcanism and thermal incubation
Euro Basalt Greenstones Subsiding basin Detachment fault

10
Depth (km) 20 sills and plutons TTG crust Radiogenic heat
Early

30 Conductive heat
Basaltic lower crust

(c) 3.325–3.308 Ga convective overturn – Mt. Edgar Dome
Granitic
Subsiding basin dome
10 Late high-K plutons 10 0 20
800 C
km
800 C
Depth (km) 20 TTG crust greenstone keel Kyanite-bearing rock

30
Basaltic lower crust
Fig. 11.10 Three-stage diapiric model of dome-and-keel provinces in the Eastern Pilbara craton (after Collins
et al., 1998, with permission from Pergamon Press, Copyright Elsevier 1998; the age-spans of the stages are from Van
Kranendonk et al., 2007).

facilitates the extensional collapse of the thickened the gneissic basement. Normal-sense displacements
crust, forming detachment faults (i.e. Mt Edgar shear drop greenstones down between the rising domes.
Zone, Fig. 11.11a) similar to those found in Phanerozoic Emplacement of the domes steepens the detachments
core complexes (e.g. Figs. 7.14b, 7.39c). The density and changes the geometry of the system so that its
inversion created by dense greenstones overlying structure no longer resembles that of Phanerozoic core
buoyant, partially molten basement triggers the rise of complexes (Fig. 11.11c). Steepening during periods of
granitoid domes at 3.31 Ga by solid state fl ow during shortening provides an alternative explanation of the
extension (Fig. 11.11b). This extension is accommo- near vertical sides of the granitoid domes.
dated by displacement on the Mt. Edgar shear zone and The application of both vertical and horizontal
by lateral strike-slip motion in a transfer zone within models to Archean cratons involves numerous uncer-