Late Paleozoic-Early Mesozoic Tectono-Magmatic Evolution of the Northern Qaidam Block: New Constraints from Granitoid and Gabbro Intrusions in the Damenkou Area

These geochemical signatures indicate derivation from partial melting of igneous protoliths in a magmatic arc setting. Zircon U-Pb weighted mean ages span 431.7 to 232.5 Ma, defining multiple magmatic pulses at ca. 432 Ma, 381 Ma, 369 Ma, 362 Ma, 269 Ma, 258 Ma, and 233 Ma. Most samples yield positive εHf(t) values (+3.89 to +13.99) with two-stage depleted mantle model (TDM2) ages of 1055-376 Ma, indicating contributions from Neoproterozoic and Ordovician juvenile crustal sources.

In contrast, the Early Silurian granodiorite (431.7 Ma) shows negative εHf(t) values (-7.68 to -5.08) with TDM2 ages of 1914-1748 Ma, suggesting reworking of the Paleoproterozoic continental crust. Our results demonstrate that the granitoid and gabbro intrusions in the northwestern NQB record two subduction-post-collision tectono-magmatic cycles during the Late Paleozoic to Early Mesozoic, corresponding to the closure of the Proto- Tethys Ocean and the Paleo-Tethys Oceans, respectively.

This study provides new constraints on the spatial extent of the Tethyan arc system and the prolonged tectonic transition of the Tethyan domain in the northern QXP.