Geochemical characteristics and the constraints on paleoenvironment, provenance, and tectonic setting of Precambrian Xifangshan Formation in the northwestern Tarim Basin, NW China

Abstract

Combining geochemistry and petrology to clarify paleoenvironment, provenance and tectonic setting is the most reliable approach. Few studies have been conducted on the Xifangshan Formation, a set of turbidite deposits from the Precambrian in the northwestern Tarim Basin, NW China. The tectonic setting during this period is not clear. This study reports the petrological characteristics and geochemical data of the Xifangshan sandstones, aiming to constrain the paleoclimate, paleoredox conditions, paleoweathering, provenance, and finally establish the tectonic development pattern of this period. Xifangshan Formation is mainly composed of litharenite and feldspathic litharenite. Most of the trace elements (Rb, Sr, Pb, U, Y, Sc, V, Cr, Cu, Co, Ni, Zn) are depleted relative to the upper continental crust. And, the rare earth elements show a slight negative Eu anomaly. The sandstones were first-cycle, displaying immaturity of composition and structure. The major element composition and low chemical index of alteration indicate that the sandstones have experienced weak weathering during transportation. Multiple geochemical indicators show that the Xifangshan Formation was deposited in an oxic-suboxic marine environment with moderate salinity and semiarid climate. Based on the geochemical and petrographic characteristics of the rock fragments, the source of the Xifangshan Formation has a felsic provenance, and the parent rock is predominantly acidic magmatic rocks, with a small amount of intermediate magmatic rocks. Influenced by the subduction of the ancient oceanic plate, the blueschist-bearing Aksu Group and the continental margin magmatic arc were formed. This magmatic arc provided the source for the Xifangshan Formation sandstones.