High-magnesium igneous associations give new insights into geodynamic evolution of the accretionary Central Asian Orogenic Belt

Much controversy exists regarding the evolution and termination of accretionary orogens where typical continent-continent collision features are lacking. The Central Asian Orogenic Belt (CAOB) thus provides a golden opportunity. Precise zircon dating identified two-stage Triassic magmatic events in the southeast CAOB. The Olenekian andesites show typical sanukitoids affinities and yield depleted Hf isotopic compositions and high δ¹⁸O values, indicating that they were originated by partial melting of mantle peridotites with input of 20% terrigenous sediments. The Norian diorites have geochemical characteristics comparable with high-Mg adakites. Their depleted isotopic compositions and high Th/Nb and Ba/Nb ratios conform to an origin that melting of delaminated mafic lower crust subsequently interacted with mantle materials. These two-stage abnormal Triassic high-Mg rocks archive hot slab window triggered by break-off  the Paleo-Asian oceanic slab and lower-crustal delamination related to collapse of the southeast CAOB. This study further benefits the reconstruction of East-Asian blocks in Pangea.