The Upper Permian volcanic-sedimentary succession in northern Qamdo Block, central Qinghai-Tibet Plateau and its sedimentary, paleogeographic and tectonic significance

Abstract

A combined sedimentological and geochemical study has been carried out on a volcanic-sedimentary succession from a borehole newly drilled in the northern Qamdo Block (QMB, in central Qinghai-Tibet Plateau) in order to improve the knowledge of the sedimentary and tectonic environment. The lithologic data allow to separate four main lithofacies, including massive volcanic lithofacies (LF1), tuffaceous lithofacies (LF2), sandstone lithofacies (LF3) and mudstone lithofacies (LF4). LF1 likely reflects the products of felsic lava flows that were formed during the process of magma ascent onto the seafloor at an earlier stage. LF2 contains two sublifhofacies that respectively represents the proximal and distal accumulation of tuffaceous turbidity flows. LF3 could be the arc-sourced submarine fan deposits, and the sublithofacies LF3a and LF3b represent mid-fan distributaries and interchannel deposits in fan lobes. LF4 is mainly composed of suspension deposits, which represents the sedimentation of post-volcanic activities. Furthermore, the lithofacy associations reveal the evolution of a volcano-sourced submarine fan in the back-arc basin. Geochemically, LF1 and LF2 are characterized by LREE-enriched patterns with negative Eu anomalies, enrichment in large ion lithophile elements (LILEs) and depletion in high-field-strength elements (HFSEs), which correspond with the previously published island arc environment. However, LF2 shows more distinctive patterns, which represents a later evolution stage than that of LF1. This volcanic-sedimentary succession reveals that the sedimentary-tectonic setting could be consistent with the subduction of Jinshajiang oceanic slab in the late Permian period.