Early Neoproterozoic magmatic imprints in the Altun-Qilian-Kunlun region of the Qinghai-Tibet Plateau: Response to the assembly and breakup of Rodinia supercontinent

Abstract

Abstract The Altun-Qilian-Kunlun Mountain (AQK), located on the northeastern margin of the Qinghai-Tibet Plateau, experienced multiple Neoproterozoic magmatic and metamorphic events which are correlated to the Rodinia supercontinent history. Here we present results from a systematic petrologic, geochemical, and zircon U Pb and Hf isotopic study on Neoproterozoic granitoids and mafic rocks from the AQK. In conjunction with a review of the available age data, we divide the early Neoproterozoic magmatism in AQK into two stages: the first stage at ca. 1030–846\xa0Ma and the second stage at ca. 860–660\xa0Ma. The new Lu Hf isotopic data coupled with published Lu Hf and Sm Nd results indicate that the stage 1 mafic rocks were mainly derived from a depleted mantle source with minor contamination with crustal materials or subducted sediments. The stage 2 mafic rocks were mainly derived from the depleted mantle with limited crustal contamination. Combined with whole-rock geochemical compositions and Sr Nd isotopic data, the stage 1 granitic magmas are inferred to have been derived from reworked Paleoproterozoic-Mesoproterozoic crust and the stage 2 granitoid magmas mainly came from reworked continental crust with minor mantle magma input. The AQK experienced arc magmatism in a compressional environment on an active continental margin during the late Mesoproterozoic-early Neoproterozoic (1030–846\xa0Ma), followed by rift-related magmatism in an extensional setting in the middle to late Neoproterozoic (860–660\xa0Ma). Similarities in basement compositions, magmatism and metamorphism between the Qilian block (QL) and surrounding blocks suggest that the AQK was with a composite block at early Neoproterozoic. The assembly of AQK started as early as 1030\xa0Ma with peak convergence at ca. ∼918\xa0Ma. The initial breakup might have started from 860\xa0Ma and lasted until to 660\xa0Ma with the peak at ca. ∼765\xa0Ma. These timings correspond well with those of the assembly and breakup of the Neoproterozoic supercontinent Rodinia. The breakup of AQK from the South China Craton might have occurred in the late Neoproterozoic, not until the opening of the Qilian ocean at around 660\xa0Ma.