Late Triassic lithium pegmatites in Northwest China: A response to continental collision during Paleo‐Tethys Ocean closure

Abstract

Spodumene‐bearing pegmatite dyke swarms have recently been discovered in the Chaqiabeishan area, at the northeastern margin of the Qinghai‐Tibet Plateau in northwest China. In order to elucidate the connection between the Chaqiabeishan lithium pegmatites and Triassic magmatism and mineralization within the West Kunlun – Songpan ‐Garzê rare‐metal belt, this study presents new columbite‐group mineral and monazite U–Pb dating results, mineral chemistry, monazite in situ Nd isotope analyses and gamma‐ray spectrometric measurements. Magmatism and mineralization at Chaqiabeishan mainly occurred ca. 216 Ma, and the mineralized pegmatites (Mn‐rich columbite‐group minerals, highly evolved monazite compositions and high effective uranium contents in the gamma‐ray survey) were generated from the high degree of the fractional crystallization in a volatile‐rich granitic magma. The source material of the Chaqiabeishan lithium pegmatites (εNd(t) values from −14.4 to −12.8) was more enriched than that of other pegmatite‐type lithium deposits (Jiajika and Bailongshan) in the West Kunlun – Songpan – Garzê rare‐metal belt and is ascribed to melting of ancient crustal materials in the basement. These late‐Triassic mineralizing events were closely related to the collision‐related tectonic setting at the northeastern margin of the Tibetan‐Qinghai Plateau, a product of Paleo‐Tethys Ocean closure.