Petrogenesis and tectonic significance of the late Devonian‐early Carboniferous Jianxiashan pluton in the western domain of the eastern Kunlun Orogen, northern Tibetan Plateau

Abstract

The Eastern Kunlun arc activities were interrupted by repeated continent–continent collision followed by ocean opening along the older suture zones previous created in the Neoproterozoic. The first report of the later Devonian‐early Carboniferous arc magmatism has played a vital role in constraining the evolution of the Eastern Kunlun Orogen. We undertook zircon U–Pb dating, Hf isotopic compositions, whole‐rock geochemical and Nd–Sr isotopic analyses of the Jianxiashan pluton in the western end of the Eastern Kunlun Range. The pluton is composed of tonalite, granodiorite, and monzogranites. Our new data suggest that the pluton formed during the late Devonian‐early Carboniferous with ages of 339–358 Ma. These rocks have high A/CNK = 1.06–1.30, with 1.11–3.80% of normative corundum and are characterized by negative Eu anomalies and strong depletion in Ba, Nb, and Sr elements. The zircon Hf isotopic analyses give predominantly negative εHf(t) values (−9.25 to −2.80), whereas the values of inherited zircons are various from −25.84 to +8.80. The U–Pb age and Hf isotopic data of these inherited zircons are similar to the widespread meta‐sediments of Kuhai Group basement. The peraluminous granitoids have negative εNd(t) values (−7.1 to −5.1) and relatively high initial 87Sr/86Sr ratios (0.71009). These isotopic compositions suggest that the Kuhai Group could possibly be the source rocks of these peraluminous granitoids. We suggest the tonalite and granodiorite are I‐S transition type, whereas the monzogranite is highly fractionated S‐type formed in a back‐arc extensional tectonic setting, which was possibly related to the northern subduction of the Paleo‐Kunlun oceanic lithosphere.