Silurian to Early Devonian tectonic evolution of the southeastern Qilian Orogen inferred from zircon U–Pb dating and geochemistry of intrusive rocks

Abstract

Early to mid-Paleozoic tectono-thermal events in the Qilian Orogen developed during the closure of the Proto-Tethys Ocean and the convergence of microcontinents in the periphery of East Gondwana. In this paper, we present geochronological, geochemical, and Sr-Nd-Hf isotopic data for the granitoid rocks and mafic dykes in southeastern Qilian Orogen. The Liwan (440 Ma), Shixia (434 Ma), and Huchuan (429 Ma) granitoid rocks have metaluminous to weakly peraluminous features, with whole-rock ε Nd (t) values of 1.1 to 1.6, -4.2 to -4.4, and -2.6 to 1.1, and zircon ε Hf (t) values of 0 to 8.9, -6.6 to 1.6, and -4.6 to 2.2, respectively. Geochemical data suggest that the Liwan, Shixia, and Huchuan granitoids are derived from partial melting of the Proterozoic basement with an addition of juvenile material, a felsic crustal basement, and a mafic crustal material, respectively. The Zhangjiayuan mafic dykes (403 Ma) are high-K to shoshonitic with whole-rock ε Nd (t) (-1.1 to -0.9) and zircon ε Hf (t) values (-0.9 to 13.3), derived from an enriched lithospheric mantle. We suggest that these Silurian–Early Devonian intrusive rocks were formed via a complex series of events involving arc-related subduction followed by slab-tearing to post-collisional processes during the Silurian and subsequent lithospheric extension in the Early Devonian. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6693575