Abstract:

Lower Cretaceous volcaniclastic litharentites are widely distributed in the Tethyan Himalaya, while less research was reported about the provenance of these volcaniclastic litharentites. In this paper, we report sedimentray and geochemical characteristics of basalts in Rilang Formation of central-western Tethayan Himalaya. Major and trace element compositions show that these basalts belong to alkaline basalt. They are enriched in LREE relative to HREE, similar geochemically to Ocean Island Basalt (OIB) and intra-plate basalt. The contents of Nb fall between the upper crust and lower crust. These basalts have a relatively low content of Th than that of lower crust and relatively high Th/Nb ratio, low Ce/Pb ratio,which indicates that these basalts suffered variable crustal contamination. Sedimentary and geochemical characteristics of these basalts are apparently different from seamounts basalt in the Yarlung-Zangbo ophiolitic mélange belt. The tectonic setting discrimination diagrams based on trace elements suggest that basalts of the Rilang Formation formed in intracontinental rift environment. Combining the petrology and depositional environments of sedimentary rocks, we conclude that these basalts maybe the one of the provenance of volcaniclastic litharentites of the Rilang Formation.

Key words: Tethyan Himalaya, continental breakup, Rilang Formation basalt, Zhongba County, Tibet