Geochemistry and geodynamic implications of the Triassic bimodal magmatism from Western Kunlun Orogen, northwest China

Abstract

The Western Kunlun Orogen occupies a key tectonic position at the junction between the Tarim block and the Tethyan domain. However, the late Paleozoic to early Mesozoic, especially the middle to late Triassic tectonic evolution history of the Western Kunlun Orogen remains controversial. This study reports SHRIMP zircon U-Pb ages and geochemical as well as Sr-Nd-Hf isotopic data for middle to late Triassic Taer pluton in Western Kunlun Orogen, Northwest China. The Taer pluton shows a strong bimodal distribution of compositions, with the felsic rocks dominant and the mafic rocks subordinate. Zircon UPb dating reveals that the coexisting mafic and felsic rocks are coeval, both emplacing in a period between 234 and 225 Ma. Most of the studied rocks are potassium rich and can be classified into high-K calc-alkaline to shoshonitic series. They are also strongly enriched in LREE, LILE and depleted in HFSE with strong negative Ti and Nb anomalies, and characterized by enriched Sr-Nd-Hf isotopic signatures. Detailed geochemical and isotopic studies indicate that the Taer pluton was emplaced in a post-collisional extensional setting, with the mafic rocks derived from partial melting of the enriched continental lithospheric mantle in the spinel facies field, and the felsic rocks formed by anatexis of newly underplated basaltic rocks.

Tectonic Switch From Triassic Contraction to Jurassic-Cretaceous Extension in the Western Tarim Basin, Northwest China: New Insights Into the Evolution of the Paleo-Tethyan Orogenic Belt

“…243-227Ma), a mega-magmatic belt of high-K calc-alkaline granitoid belt extending with NW orientation intruded within West Kunlun Mts. (Figure 1B; Liao et al, 2012;Jiang et al, 2013;Wang et al, 2016b;Zhang et al, 2016). And the suture zone along Mazha-Kangxiwa (also called Karakax fault) performed as a ductile shear fault to accommodate the convergence between Qiangtang and Tarim at the end of Triassic (Xu et al, 2007;Ge, 2018).…”

“…Some of Latest Triassic post-collisional magmatism and bimodal magmatism have been reported in West Kunlun and South Tienshan Mts. in recent years (Liao et al, 2012;Jiang et al, 2013;Tang et al, 2017). It indicates the post-orogenic delamination could have occurred.…”

Alternating Extensional and Contractional Tectonics in the West Kunlun Mountains during Jurassic: Responses to the Neo-Tethyan Geodynamics along the Eurasian Margin

“…The Jurassic alkali basalts exhibit enrichment of LREE and HSFEs without obvious crustal signatures (e.g., Nb-Ta depletion; Fig. 7c-d), different from the syn-and post-collisional magmas in the West Kunlun Mountains (Liao et al, 2012;Chen et al, 2021). Their compositions resemble those of intraplate OIBs and could have been generated by low-degree partial melting (~5%) of a garnet lherzolite mantle source (Fig.…”