Provenance and tectonic setting of Upper Triassic turbidites in the eastern Tethyan Himalaya: Implications for early-stage evolution of the Neo–Tethys

Abstract

Upper Triassic turbidites in the eastern Tethyan Himalaya preserve archives for early–stage evolution of the Neo–Tethys. However, their provenance and tectonic setting remain controversial. Here we report petrographic, detrital zircon U[sbnd]Pb and trace element data of newly discovered sandstones interbedded with layered basalts and whole–rock geochemical data of basalts from the Yumen mélange within Upper Triassic turbidites, and the same types of published data from associated terranes in the eastern Gondwana are compiled for comparison. The interbedded sandstones are dominated by quartz, lithics fragments and plagioclase grains, resembling those of the Langjiexue Group. All samples display similar ranges of detrital zircon U[sbnd]Pb ages, with significant age populations at 280–210 Ma, 650–450 Ma and 1200–800 Ma, comparable to those of the Langjiexue Group and coeval turbidites from Western Myanmar and partly from Central Tethyan Himalaya, implying they should share identical provenance. Trace elements of 300–200–Ma–aged zircons indicate they were derived from a continental magmatic arc. Geochemical data from interbedded basalts display typical within–plate–basalt affinity. Synthesized with regional geological setting, the above observations suggest Upper Triassic turbidites from Eastern and part of Central Tethyan Himalaya, and Western Myanmar were deposited in a marine rift basin of Indian passive continental margin with their primary provenance from Lhasa. However, other contemporaneous turbidites from part of Central Tethyan Himalaya and Australia had distinct primary sources from Indian continent and West Papua, respectively, indicating they may have separate deposystems.