Characteristics And Tectonic Significance Of Late Paleozoic Granits Near The Hariaoribuge Weather Station Of Alxa, Inner Mongolia

The study area which is along the border of China and Mongolia locates in thenorth of Alashan， who stands on the suture caused by the collision of Tarim-Sino-Korean plate and Siberian plate. The Engel Usu ophiolite Belt distributes at thesouth of the suture and the Yagan Fault at the northwest.it is a important place forgeologists to understand the tectonic evelution of the Alxa plate. The Granites in thestudy area are displaying extensively，but study on this area is very rare.Through field work，analysing the characteristics of the rocks from the outcrops，drawing the cross sections, collecting appropriate samples so we can obtain theirchemical characteristics and their ages，analysizing the source of the intruves，todiscuss the the tectonic evelution to the rocks，so we can provide some basicgeologicak information for the Hariaoribuge regoin and it is convient for geologis togo on the subsequent in-depth study in the area.Through the study，we can identified three types Granites near the study area,they are adamellite，granodiorite，quartz monzonite diorite. The age of the quartzmonzonite diorite is Carboniferous，the adamellite and granodiorite intruded mainly inEarly Permian.The geochemical characteristics suggest that granitoid plutons are metaluminouscalc-alkaline series or high K calc-alkaline series (mainly) in Hariaobaobuke weatherstation.Carboniferous monzonitic granites a formed in syn-collision tectonicenvironment； early-Permian granodiorites formed in volcanic arc tectonicenvironment.By the LA-ICP-MS zircon U-Pb geochronology test，the weighte ages of theearly-Permian quartz monzobiorites and medium-fine grained granodiorites， are275.9±1.1Ma，272±1Ma.Based on the formation environment of granites and regional tectonic activity，itcan be concluded that the ocean closure time represented by Yagan fault is after the formation of Carboniferous monzonitic granites，the north of Engeerwusu is oceanenvironment before late-Permian.