[S-MP25] Supercontinents and Crustal Evolution

[SMP25-05] The structural and stratigraphic framework of the western Dharwar craton: some vital clues to the Archean tectonics

*Sreehari Lakshmanan¹ (1.Department of Earthscience, Shimane University, Shimane.)

キーワード：Archean, Plate tectonics, Dharwar craton

The Dharwar Craton (DC) is the largest Archean craton in India and is divided into the Western Dharwar Craton (WDC), Central Dharwar Craton (CDC), and Eastern Dharwar Craton (EDC). Among these the WDC preserves the oldest fragments of the DC and consists of two generations of volcano-sedimentary sequences, –older Sargur Group (>3.0 Ga), younger Dharwar Supergroup (<3.0 Ga)– and multiple generations of granitic rocks ranging from 3.3 to 2.5 Ga. Detailed structural and stratigraphic investigations into the volcanosedimentary sequences in the WDC is carried out. Especially in the Chitradurga Schist Belt (CSB), Bababudan Schist Belt (BSB), and Shimoga Schist Belt (SSB). Six stages of deformation events were identified from the study area; among those two events (D2 and D3) were regional-scale deformations. D2 event represents reverse faults and upright folds while D3 event is a strike-slip sinistral fault. Schist belts are dominated by volcano-sedimentary rocks and boarded by granitic gneisses. The contact between schist belts and basement gneiss is marked by the presence of conglomerate with oversized quartzite pebbles in amphibole-rich matrix. In some locations, the conglomerate is oligomict with quartz pebbles in a sandy matrix. The boundary between schist belts is also dominated by D2 reverse faults. sedimentary rocks in the schist belts show the dominance of shallow marine indicators and slump folding structures. Most of the rock formation in the WDC is folded during the D2 event and the intensity of the folding increases from the west to east. Tightly folded sequences are present in the CSB, that is the eastern margin of WDC. The unfolding of the layers shows that the schist belts are narrow, short-lived basins typically resembling aborted-rift settings in the Phanerozoic. Folded layers seem to be sandwiched between reverse faults (D2) in the margin of the schist belts, which in total represent a fold-and-thrust belt. The overall structural architecture of WDC suggests that the schist belts probably represent multiple stages of failed rifts later amalgamated during regional-scale deformation. Present-day structures in the schist belts of the DC possibly represent an inverted failed rift basin. Sediments and volcanic rocks were deposited in basins formed by rifted granitic basement and several immature basins were formed in different parts of the WDC. More geochronological and geochemical evidence is required to clarify the spatial and temporal relation between these intracratonic basin formation processes.