Provenance of Xigaze fore-arc basin clastic rocks (Cretaceous, south Tibet)

摘要: The Xigaze Group of south Tibet was deposited in a fore-arc basin produced by northward subduction the Neotethys under Eurasia during middle Cretaceous time. Clasts andesite from Gangdese magmatic belt to north and limestone clasts shelf rimming are near exclusive detrital components eastern part studied region older (Albian) deposits west. Younger (Cenomanian–Coniacian) western central parts show increasing amounts tonalite pebbles conglomerates, quartz sand. These trends reflect differential arc uplift erosional dissection, with higher rates Some arenites evidence for sediment contribution an additional source, probably orogen Lhasa Block. presence this indicates that crustal thickening is not restricted Cenozoic times. Belt apparently lacked acid volcanic rocks. This suggests low degree contamination and/or differentiation primitive magma, because crust beneath area thin. A thin accordance elevation arc, deduced continuous carbonate production on marine excursions beyond arc. Magma eruption estimated volume, were (≈7.5 km 3 /km segment per million years), but within range modern arcs. varying compositions may be typical front continental lack correlation composition fining-upward sedimentary supercycles taken as favor eustatic cycle control.