Characteristics And Formation Mechanism Of The Late Jurassic Granitic Rocks In The Middle Of Yilehuli Mountains

In this paper,the petrographic,chronological and geochemical tests of the granitic rocks in the middle of the Yilehuli mountains in the northern part of the Greater Khingan Range were analyzed.The geochemical characteristics of granitic rocks in the study area were analyzed and their formation times were determined.This paper mainly discusses the magmatic source and source region,rock formation and tectonic setting,which provide new information for the activity time and tectonic evolution of the late Jurassic intrusive rocks in the Greater Khingan Range.By testing and analyzing the samples to determine the lithology of the granitic rocks in the middle of Yilehuli mountains is mainly quartz monzodiorite diorite and monzogranite.The LA-ICP-MS U-Pb zircon age was measured for samples with better zircon crystal morphology.The results showed that the age of the samples was 163.1±0.6Ma,162.5±IMa,158.1±0.7Ma,belonging to the late Jurassic early.The geochemical analysis of the three lithologic samples of the granitic rocks in the study area is closer,SiO2 content is 59.42%?75.32%(average 67.53%),K2O content is 2.75%?5.19%,iron deficiency TFe2O3,the content was 3.18%?5.02%,and the MgO was 0.18%?2.88%,and TiO2 was 0.19%?1.44%,The total alkali content was 7.18%?9.87%,and the CaO content was 0.54%?4.95%,more aluminum-rich Al2O3,the content was 12.5%?16.5%,belonging to high potassium calcine alkaline type ? granite;The ratio of Al2O3/(Na2O+K2O)is 1.25?2.19,the aluminum saturation index is 1.19?1.6,belong to quasi-aluminum-weakly peraluminous.The total amount of rare earth elements is not high,?REE=109.54×10-6?312.73×10-6,rare earth distribution curve of light rare earth enrichment right,heavy rare earth is relatively flat.The LREE/HREE heavy rare earth elements ratio=5.37?18.62,(La/Yb)N?6.57?62.81(average 29.01),light and heavy rare earth element fractionation is stronger,with rich LREE,HREE relative loss.?Eu=0.29?1.27(average 0.85),showing a weak Eu negative anomaly.Trace element spidergrams for the Yilehuli mountain area granitoids indicate enrichments in LILE(K,Rb),and depletion in HFSE(Ta,Nb).The chronological and geochemical characteristics indicate that the middle of the Yilehuli Mountains granitic rocks are belong to the ?-type granite.Compared with the geochemical characteristics,the granitic rocks in the study area have characteristics similar to those of the C-type adakites.The original magma originates from the thickening of the underlying crust material.Through the discussion of the background,it is speculated that the formation of granite rock in the study area is related to the continental-continental collision orogenic late environment in the closure process of the Mongolian-Okhotsk suture zone,the formation time also limit the closing time in Northern Greater Khingan Range range Yilehuli mountain area of the Mongolia Okhotsk ocean for late Jurassic early.