Underplating mechanism of Triassic granite of magma mixing origin in the East Kunlun orogenic belt

Abstract：Triassic granites of magma mixing origin are widespread in the East Kunlun orogenic belt. They have the following common features： the composition of granites varies greatly; granites contain abundant mafic microgranular enclaves (MME); and different rock types tend to show gradational relationships. Particularly, these rocks co-exist with low-grade metamorphic rocks representing the lower crust without exception, implying that the magma was emplaced in the deep crust. In addition, basic intrusive rocks are widely developed in the area. They either occur in high-grade metamorphic rocks or occur together with granites of magma mixing origin, suggesting that partial melting of the lower crust and formation of the granites of magma mixing origin are probably related to underplating of basic magma. Take for example the Jialuhe granite—a typical granite intrusion of magma mixing origin in the East Kunlun area, the authors studied in detail its petrological, geochemical and isotope geochemical characteristics. It is concluded that the mantle-derived magma underplating was the direct cause of the formation of such granites and played an important role in the Triassic crustal growth and tectonic evolution in the East Kunlun orogenic belt. Furthermore, the genetic relation between the mantle-derived magma underplating and granites of magma mixing origin is discussed and a model of breaking-off-underplating-mixing-delamination in the setting of the thickened continental crust is constructed.