Tectonic evolution of the South Altyn, NW China: constraints by geochemical, zircon U-Pb and Lu-Hf isotopic analysis of the Palaeozoic granitic plutons in the Mangya area

The South Altyn Orogenic Belt (SAOB) is one of the most important orogenic belts in NW China, consisting of the South Altyn Continental Block and the Apa-Mangya Ophiolitic Melange Belt. However, its Palaeozoic tectonic evolution is still controversial. Here, we present petrological, geochemical, zircon U-Pb and Lu-Hf isotopic data for the Mangya plutons with the aim of establishing the Palaeozoic tectonic evolution. We divide the Early Palaeozoic magmatism in the Apa-Mangya Ophiolitic Melange Belt into four episodes and propose a plate tectonic model for the formation of these rocks. During 511-494 Ma, the South Altyn Ocean (SAO) was in a spreading stage, and some shoshonite series, I-type granitic rocks were generated. From 484 to 458 Ma, the oceanic crust of the SAO subducted northward, accompanied by large-scale magmatic events resulting in the generation of vast high-K calc-alkaline series, I-type granitic rocks. During 450-433 Ma, the SAO closed, and break-off of the subducted oceanic slab occurred, with the generation of some high-K calc-alkaline series, I-S transitional type granites. The SAOB was in post-orogenic extensional environment from 419 to 404 Ma, and many A-type granites were generated.