The Qinghai-Tibet Plateau-Himalayan orogenic belt is the largest continental collision orogenic belt on earth, and its evolution process and uplift history are hot issues in earth science research. There are a lot of post-collision magmatic activities in the Qinghai-Tibet Plateau, including various rock types from the mantle and crust, which is considered as an ideal research object to explore the deep mechanism of plateau uplift. Previous studies on quantitative paleoheight show that the Hoh Xil basin in the northern part of the Qinghai-Tibet Plateau experienced at least 1km surface uplift after Miocene, but there are different understandings about the deep dynamic mechanism that caused the surface uplift. In view of the existence of a large number of Miocene-Pliocene post-collision magmatic rocks in the Hoh Xil Basin, it corresponds to the surface uplift process of the Hoh Xil Basin after Miocene. Therefore, studying the genesis of post-Miocene-Pliocene magmatic rocks in the Hoh Xil basin is helpful to understand the deep dynamic mechanism controlling the uplift of the Qinghai-Tibet Plateau.

Early studies have found that mantle-derived magmatic rocks in the Hoh Xil basin have undergone different degrees of differentiation and evolution or crustal contamination, which cannot fully represent the characteristics of mantle source areas. Dr. Qi Yue and researcher Wang Qiang from Guangzhou Institute of Geochemistry, China Academy of Sciences conducted mineralogical, petrological and geochemical studies on olivine leucite in Hoh Xil Basin 16 Ma (Figure 1a-d). The research shows that the main minerals are (1) olivine, clinopyroxene and leucite (figure 1e, f); (2) The trace elements and O isotope characteristics of olivine indicate that the source region is mainly metasomatic peridotite, and the temperature and pressure conditions of mineral crystallization suggest that the magma quickly erupts to the surface after leaving the mantle source region, with no obvious differentiation and crustal contamination, representing relatively primitive mantle-derived magma (Figure 2); (3) The rocks are alkali-rich, with the characteristics of silicon unsaturation, rich in light rare earth and large ion pro-MagmaElemental, and lack of high field strength elements, showing negative Nb-Ta-Zr-Hf-Ti anomaly. The Sr-Nd isotopic composition is similar to that of the contemporary high Mg mantle-derived magmatic rocks in this area, indicating a relatively uniform enrichment of the mantle (Figure 3).

By comparing the geochemical composition and regional tectonic evolution history of mafic magmatic rocks in different periods in Hoh Xil area, it is considered that the enriched mantle represented by olivine leucite in Hoh Xil was formed in Eocene-Oligocene, and the southward subduction of Qaidam block provided the enriched components of the metasomatic mantle, and the enriched materials were mainly potassium-rich carbonate-silicate mixed melts. Considering that about 75% of the magmatic activities in the Hoh Xil Basin are concentrated between18-1ma, and considering that the lithosphere in the northern plateau is thin, it is considered that the thinning of the lithosphere triggered the partial melting of the mantle and crust of the overlying residual enriched lithosphere, resulting in the Hoh Xil area18-16544.

The research work was supported by the National Natural Science Foundation, the second comprehensive investigation and research project of Qinghai-Tibet Plateau, the key research project of frontier science of Chinese Academy of Sciences, the strategic pilot science and technology project of Chinese Academy of Sciences (Class A) and the project of Guangzhou Institute of Geochemistry 135, and the related research results were published in Petrology Journal.

Figure 1. Geological sketch and petrographic characteristics of olivine leucite in Hoh Xil.

Figure 2. Mineralogical characteristics of olivine leucite in Hoh Xil.

Figure 3. Whole-rock geochemical characteristics of olivine leucite in Hoh Xil.