http://www.geo.mtu.edu/EHaz/ConvergentPlatesClass/macpherson/martin_etal_2005.pdf

An overview of adakite, tonalite–trondhjemite–granodiorite (TTG), and sanukitoid: relationships and some implications for crustal evolution

Orogenic gold deposits : A proposed classification in the context of their crustal distribution and relationship to other gold deposit types

Orogenic gold and geologic time: a global synthesis

The diversity and evolution of late-Archean granitoids: Evidence for the onset of “modern-style” plate tectonics between 3.0 and 2.5 Ga

Late Archaean (2550–2520 Ma) juvenile magmatism in the Eastern Dharwar craton, southern India: constraints from geochronology, Nd–Sr isotopes and whole rock geochemistry

The Archean Kolar Schist Belt, south India, is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources. The amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago (Ma) along a zone marked by the Kolar Schist Belt. This history of accretion of discrete crustal terranes resembles those of Phanerozoic convergent margins and thus suggests that plate tectonics operated on Earth by 2500 Ma.

http://science.sciencemag.org/content/sci/243/4896/1337.full.pdf

Plate tectonics 2.5 billion years ago: evidence at kolar, South India.

Conspicuous Nd, Sr and Pb isotopic differences exist between the Archean gneiss terranes adjoining the suture at the Kolar Schist Belt, south India. These gneisses, which are the deformed equivalents of plutonic and volcanic rocks, have known or inferred igneous ages of 2630 to 2530 Ma. Initial isotopic ratios of Nd, Sr and Pb suggest that metaplutonic gneisses west of the Kolar Schist Belt were emplaced into, and variably contaminated by, an evolved continental crust that formed prior to 3200 Ma. Felsic metaigneous gneisses that occur as slivers on the western margin of the schist belt have an isotopic character similar to that of the metaplutonic rocks on the same side of the Kolar Schist Belt. On the east side of the Kolar Schist Belt the isotopic evidence suggests that the 2530 Ma granitic gneisses were not derived from or contaminated by an older continental crust. Their source probably evolved with a Nd isotopic composition similar to that of typical Archean mantle, but became light rare earth element enriched after 2900 to 2700 Ma. The inferred tectonic setting for the west side of the Kolar Schist Belt is an Andean continental magmatic arc. For the east side of the Kolar Schist Belt, a possible Phanerozoic analog is an evolved island arc, such as Japan.

Sources of continental magmatism adjacent to the late Archean Kolar Suture Zone, South India: distinct isotopic and elemental signatures of two late Archean magmatic series

Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.

E. J. Krogstad

Papers

Plate tectonics 2.5 billion years ago: evidence at kolar, South India.

Sources of continental magmatism adjacent to the late Archean Kolar Suture Zone, South India: distinct isotopic and elemental signatures of two late Archean magmatic series

U-Pb ages and Sr, Pb and Nd isotope data for gneisses near the Kolar Schist Belt: Evidence for the juxtaposition of discrete Archean terranes