Geochemical Characteristics And Tectonic Environment Of Magmatic Rocks In The Area Of Hami Da Nanhu Of Xinjiang

Da Nan Hu is located in the southeastern margin of the Turpan-Hami Basin.A large area of magmatic rocks is developed in this area,including intermediate-basic volcanic rocks and intermediate-acid intrusive rocks.In this study,the petrology and geochemical characteristics of magmatic rocks were analyzed to discuss the tectonic environment and tectonic evolution of the southeastern margin of the Turpan-Hami Basin during the Paleozoic.The ore-forming prospects in the study area were analyzed and the specific results and understanding are as follows:(1)Various types of Carboniferous intermediate-basic volcanic rocks developed in the southeastern margin of the Turpan-Hami basin in the eastern Tianshan Mountains of Xinjiang,which have homologous characteristics.The rocks have high aluminum(Al2O3=15.95%—17.14%)and high calcium(Ca O=7.83%).-9.89%)is characteristic of calc-alkaline rocks,and the evolution of magma is controlled by plagioclase.The fractionation of LREE elements in rock is obvious,but the degree of fractionation is not high,and the relative loss of HREE element fractionation is not obvious.The Eu anomaly is not obvious,?Eu=0.89-1.09,which shows that the early magma plagioclase crystallization is not obvious,and the standardization curve of the rock rare earth element chondrite is slightly tilted to the right,and the slope is not large.The morphology is similar to that of the continental rift basalt in eastern China.In a similar manner,rocks enrich for K,U,Rb,Ba,Sr,and Y elements,and deplete Ta,Th,Nb,Ti,P,and Yb elements,and have relatively obvious negative TNT(Ta-Nb-Ti)anomalies.The magma is formed by partial melting of the mantle metasomatism,suggesting that the magma originated from the lithosphere mantle and the rocks formed in the continental rift tectonic setting.The geochemical characteristics of the rock show that it does not have typical oceanic basalt features,indicating that there is no oceanic environment in the southeastern margin of the Turpan-Hami basin in the Carboniferous,and the ancient Asian Ocean was closed before the Carboniferous.(2)A large area of Devonian granodiorite complex is developed in the southeastern margin of the Turpan-Hami basin in the eastern Tianshan Mountains of Xinjiang.There is a significant difference in the degree of aluminum saturation in rocks,with A/CNK = 0.77-1.89.The basicity of rock is different,the Liteman index is ? = 0.15-3.68,and the alkalinity rate is AR=1.76-4.93.Part of the quartz diorite is of type "S" the characteristics of granite,other granite characteristics of "I" type granite.The rocks are enriched with light rare earth elements,and light and heavy rare earths are clearly fractionated.The normalization curve of the rare earth element chondrite was generally tilted to the right,with a significant negative Eu anomaly(?Eu=0.31-0.8),and no significant Ce anomaly(?Ce=0.94-1.07).The rocks are rich in K,U,Rb,Ba,La,Ce,Zr,Hf,and Y elements,depleting Ta,Th,Nb,Ti,P,and Yb elements,and have relatively obvious negative TNT(Ta-Nb-Ti)anomalies.It shows that the magma originated from the island arc structure.The Th/U values of rocks are quite different,Th/U=1.4-4.29,showing that the rocks have different source magma characteristics.The rocks are produced in the island arc structure of the active continental margin.Different rocks represent two different in the same tectonic setting the tectonic evolution phase: the pre-collision phase and collision phase.(3)The tectonic evolution of the study area is as follows: continental subduction of the Ordovician,development of intra-ocean arcs in the Silurian,early collisions of the Devonian,collisions in the mid-Devonian,and end of collisions in the late Devonian,Ocean Completely closed;Carboniferous entered the post-collision extension phase early and developed a continental rift or fault-depressed basin.(4)Rock isotopic geochronology shows that the granitoids developed in the study area are Devonian rock masses.Among them,the monzonitic granites are Early Devonian granites with a 206Pb/238 U age of 394±21 Ma,Quartz diorite are Late Devonian granites had a 206Pb/238 U age of 371.8±7 Ma.(5)The basic volcanic rocks of the Carboniferous in the study area were produced in the post-collision extension stage.They have similar tectonic features with the typical mines in the eastern Tianshan Mountains,and have certain ore-forming prospects.