Recognition and tectonic implications of an extensive Neoproterozoic volcano-sedimentary rift basin along the southwestern margin of the Tarim Craton, northwestern China

Abstract

The Tiekelik Belt includes a large outcrop area of Precambrian continental crust, which is exposed along the southwestern margin of the Tarim Craton, NW China. It is characterized by the occurrence of high-grade metamorphic rocks and volcano-sedimentary successions. In this contribution, we present zircon U–Pb results from 10 samples of rocks from these volcano-sedimentary successions for provenance and age determinations, and geochemical analyses on basalts of the bimodal volcanic rocks from the Sailajiazitage Group. Four schist and paragneiss samples from the Ailiankate Group contain numerous zircons with ages of 650–850Ma, suggesting that this group was deposited after the late Neoproterozoic and is not part of the Paleoproterozoic crystalline basement of the Tarim Craton as previously believed. One sample collected from marble of the Bochatetage Formation suggests a depositional age below 773Ma. Three sandstone samples from the Sukuluoke and Qiakemaklike formations contain zircon ranging in ages from 630Ma to 830Ma, suggesting deposition of these formations after the Ediacaran. One andesite clast from the Qiakemaklike conglomerate gave a 206Pb/238U age of 793±5Ma, while a rhyolite from the Sailajiazitage Group gave a 206Pb/238U age of 881±6Ma. The basalts of the bimodal volcanic rocks from the Sailajiazitage Group show enrichment of light rare earth elements (LaN/YbN=4.92–8.51) and high field strength elements (HFSE) (e.g. Nb, Zr and Ti), similar to continental flood basalts (CFB), indicating bimodal volcanism in a within-plate tectonic setting.Our new data, combined with previous sedimentary facies analysis, suggest the presence of a large Neoproterozoic volcano-sedimentary rift basin. This rift basin records the change from a fluviolacustrine to a marine environment along the southwestern margin of the Tarim Craton. The zircon U–Pb ages indicate initial rifting at ∼880Ma, followed by extensive rifting at ∼790Ma. The detrital zircons of the Tiekelik Belt are dominated by four populations of Neoproterozoic (630–670Ma, ca. 740–745Ma, ca. 785Ma, and ca. 800–850Ma), with some Paleoproterozoic and Archean grains (2800–1800Ma). The major detrital zircon populations approximately match the ages of widespread magmatism documented along the northern margin of the Tarim Craton. We consider that sourcing of these components from the northern Tarim could explain the age probability patterns of the Tiekelik Neoproterozoic sediments. We speculate that this process might be linked to far-field tectonics causing uplift and erosion of the northern Tarim rocks and predominantly large-scale southwards transport of sediments over the craton. The rifting environment of the sedimentary basin in the Tiekelik Belt, however, suggests a bidirectional source.