Cambrian and Cryogenian tectonothermal events in the Amdo microcontinent, Central Tibet: Implications for paleogeographic reconstruction and tectonic evolution of northern Gondwana

Abstract

The Early Paleozoic paleogeographic locations of the Tibetan terranes in Gondwana remain poorly constrained. This study reports petrology, zircon LA-ICP-MS U-Pb ages, whole-rock major and trace element compositions, and Sr-Nd-Hf isotopic data for the gneissic granites in the Amdo microcontinent, central Tibetan Plateau. LA-ICP-MS zircon U-Pb dating yielded Cambrian ages of ca. 500 Ma for the granites. A Cryogenian age of ca. 800 Ma was recognized from inherited zircons. Geochemical data indicate that these granites belong to high-K calc–alkaline I-type granitoids. They mostly exhibit negative values of zircon εHf(t) (−7.1 to +0.1) and whole-rock εNd(t) (−5.9), as well as old zircon Hf model ages (TCDM = 1718–1472 Ma) and whole-rock Nd model ages (TCDM = 1771 and 1777 Ma). These granites can be interpreted as resulting from partial melting of ancient crustal materials that have been modified by mantle-derived magmas. Integrating previous magmatic studies with the data presented in this contribution, we suggest that the Amdo microcontinent was linked to the Indian Gondwanan margin and recorded the arc-related magmatism along the proto-Tethyan margin.