Studies On Features Of Granitoids,Tectonic Settings And Fission Track Analysis Of Uplifting And Denudation In Yemaquan Region,Qinghai Province

Yemaquan region is located in west of North-Kunlun zone,Qinghai Province.Yemaquan region underwent complex geological evolution.In Phanerozoic,two stages of granitoid took place in early Paleozoic,late Paleozoic-early Mesozoic,and their petrotectonic assemblages are still not uniform understanding.This paper tried to discuss granitoids petrotectonic assemblages based on geological and geochemical characteristics,study uplifting-denudation history of Yemaquan region based on fission track technology.Some results are concluded as following:Granitoids are mainly types in intrusive rocks in Ymaquan,and they have similar geochemical characteristics.Granitoids are mainly belong to high-potassium calc-alkaline type,with high potassium and high aluminum.Chondrite-normalized REE distribution pattern diagram of all intrusive rocks show negative Eu anomalies,indicating the rocks have similar formation.Granitoids have similar primitive mantle-normalized trace elements spider diagram;enriched in K,Rb,Th,Zr and depleted in Sr,Nb,Ti,P;which reflected that magma was dominated by crustal rocks.w(Rb)/w(Ba)and w(Rb)/w(Sr)in rocks are increased from early period to late period of every stages,showed that magma underwent high evolution.Granitoids are mainly I-type in petrogenesis,have a tendency from A-type to A-type,which record the stage of subduction,syn-collision and post-collision orogenic,reflected that Yemaquan region underwent two tectonic-magmatic event in early Paleozoic and late Paleozoic-early Mesozoic.The formation age of granodiorite and Kaligranite in early Paleozoic are 420.6 ± 2.6 Ma、391 ±3.2 Ma,which are determined by LA-ICP-MS zircon U-Pb isotopic ages;and the formation age of diorite,Kaligranite,granite-porphyry,syeniteporphyry are 240.5 ± 1.7 Ma,232.9 ± 1.5 Ma,229.51 ±0.87 Ma,221 Ma±1 Ma.This paper discuss about uplifting-denudation history of Yemaquan region based on fission track technology,provide geological evolution new evidence of Low-temperature thermochronology.FT data show that AFTA range from 66 Ma to 143 Ma,ZFTA range from 135 Ma to 208 Ma.FTA 213.4 Ma-153.8 Ma show that Yemaquan region was uplifting after orogenic.ZFTA 148.4103.5 Ma and AFTA 120-81 Ma may be related to closing of Bangongco-Nujiang oceanic and collision between the Lhasa and Qingtang blocks.AFTA 67.8-44.4 Ma is distant effects of the India-Eurasia collision.Yemaquan region underwent three periods of geological thermal evolution from about 174 Ma to 0 Ma,with 110 Ma,80 Ma and 15.5 Ma as the dividing lines.The cooling rates were 2.27,0.65,0.16 and 3.39℃/Ma;the uplifting rates were 0.065,0.026,0.004 and 0.097 mm/a;and the uplifting extent were 4.14,0.79,0.29 and 1.5 km.The average cooling rate was 1.35℃/Ma,the average uplifting rate was 0.038mm/a,and the overall extent of uplifting during the four periods was 6.71 km.The uplifting in the first period was due to the closing of Bangongco-Nujiang oceanic and collision between the Lhasa and Qingtang blocks,the uplifting in the fourth period due to the India-Eurasia collision;the geological background was relative calm in the second and the third period.