Uplift Process Of The Western Section Of Yinshan From Mesozoic To Cenozoic Period And Its Geological Implications

The western section of Yinshan is located in the northwest edge of circle-Ordos tectonic belt,a place which is adjacent to plenty of block boundaries.It provides a favorable condition for studying the internal and external dynamic geological effect.Additionally,the study region is a key area to study the northern margin of North China,northern China tectonic framework and landform evolution.Hence,comprehending the uplift process in the western section of Yinshan can theoretically contribute to establish the mechanism and the pattern of mountain formation as well as to study global crust evolution in diverse regions and periods.Meanwhile,it is practical significance to reserve resources,to protect environment and to mitigate hazard.Geochronology,isotope and rock geochemistry of a granite body on the east of Liushuquanzi,eastern Serteng Mountain,were conducted in this paper.The results show that the pluton was composed of biotite monzonitic granite and diorite dike,which are dated in the period of 297 Ma and 292-271 Ma by the method of zircon U-Pb dating,respectively.Among them,the diorite dikes emplaced at 271 Ma were formed by the magma from partially melting of depleted basaltic rocks underplating the lower crust along fissures to shallow crust.Other dikes were originated from basaltic magmas by partial melting from ancient lithospheric mantle,which intruded to the shallow crust after confounding with the acidic magma originating from the ancient crust during rising process.Apatite and zircon fission track analysis were applied to reflect the geothermal history of Serteng Mountain and Langshan.The results indicated that the west section of Yinshan had gone through at least two critical tectonic movement since Mesozoic:i)during the period from late Jurassic to early Cretaceous(161-139 Ma),the western part of Yinshan transformed its pattern from extensional rift-high heat evolution in middle Jurassic to extruding,uplifting and cooling in late Jurassic;ii)the average denudation uplift rate of western Yinshan was 23 m/Ma,while the rate of Langshan was 24.3 m/Ma from early Cretaceous to early Eocene(161-139 Ma),which was a significant uplifting stage.This paper proposed the differential uplifting tilted model of western part of Yinshan and this model also confirmed the pattern by studying the typical fault zone and the piedmont platform.The uplifting process of western Yinshan was proved to be controlled by the strong tension in the northwest Ordos block during late-Cenozoic,whose triggering force was most likely came from the back-arc extension in the Pacific Rim.The denudation mass in the west section of the Yinshan and the Hetao area from the late Cretaceous to Paleocene period was about 1 km via the approaches of apatite fission track and vitrinite reflectance.Furthermore,the regional denudation event of northwestern Ordos was confirmed by the comparison in various regions at that period.On the basis of calculating the amount of denudation mass,the correlation between the mountain uplift and the sedimentation of the Hetao basin in the western part of the Yinshan was further determined by the thermal history simulation of the basin,which provides a theoretical basis for the oil prospecting in the Hetao basin.