| The East Kunlun Orogenic Belt is located in the western part of the Central Orogenic Belt and is an important part of the Central Orogenic System.The East Kunlun orogenic belt underwent a long process of tectonic evolution related to the Proto-Tethys Ocean and the Paleo-Tethys Ocean.Therefore,the magmatism in the belt is complex and diverse,and magmatic rocks are widespread,especially the Indosinian granitic magmatism related to the evolution of the Paleo-Tethys Ocean.The East Kunlun granite records abundant information of underplating and magmatic mixing.Combining with the coupling relationship between the evolution of the orogenic belt and the magmatism,the study on the petrogenesis of granites in the East Kunlun orogenic belt play a significant role to restore the tectonic evolution of the East Kunlun orogenic belt and discuss crustal growth.In this paper,the granitic pluton and intermediate acid volcanic rocks of the Elashan formation in the Dagele-Zongjia area in the eastern part of the East Kunlun orogenic belt are collected to show the detailed petrology,isotope chronology and geochemistry,then discuss these two magmatic units with their petrogenesis,magma source,tectonic setting and geological significance.The main conclusions are listed as following:1.Dagele granitoid pluton has various rock types,mainly comprising of granodiorite and monzonitic granite,intrusion contact between them.The mainly lithology in this pluton is composed of light gray-white,medium-fine-grained and massive granodiorite,and there are a large number of mafic microgranular enclave enclosed.Zircons U-Pb age of host rocks and mafic microgranular enclave are 261.0±2.8Ma and 261.6±1.6Ma respectively.They are coeval.The granodiorite are characterized by metaluminous medium-high-K calc-alkaline,I-type granite.Trace elements analyses show that the granites are enriched in LREE and LILE,and depleted in HREE and HFSEs(Nb,Ta,etc.).Monzonite is a medium-high-K calcium-alkaline,peraluminous I-type granite;mafic microgranular enclaves in the granodiorite are medium-K calc-alkaline series.Mafic microgranular enclaves are enriched in Fe,Mg,Ca,Ti,etc,with high Mg~#values.Petrogenesis studies show that the mainly body of Dagele granitoid pluton are the products of partial melting of amphibolite in the continental lower crust,with a little the metasandstone involved,but mafic microgranular enclave is the products of rapid chilled of mafic magma injected into the host rock.2.The volcanic rocks types of Elashan Formation in the Polostai area are mainly rhyolitic dacite in compositions.LA-ICP-MS zircon U-Pb isotopic dating show that the age is 233.4±1.3Ma and 234.7±1.5Ma.The rock is a peraluminous,high-K calcium-alkaline series.Trace elements analyses show that the dacite are enriched in LREE and LILE,and depleted in HREE and HFSEs(Nb,Ta,etc.).The rhyolitic dacite of the Elashan formation has enriched Hf isotopic compositions,indicating that its magma originated from crustal melting.Combining with petrogenesis and provenance discrimination,the rhyolitic dacite in the Polostai area is derived from the partial melting of feldspar-rich psammite in the middle and upper crust.The discrimination of the tectonic environment shows that it was formed in the extension environment.3.Combining this research with previous research data,this study subdivides the Indosinian tectonic evolution of the eastern section of the East Kunlun Orogenic Belt into three stages:(1)Buqingshan-A'nemaqen ocean subduction stage(270?240Ma);(2)orogenic stage in the syn-collision(240?235Ma);(3)orogenic stage in the post-collision stage(235?205Ma).This study has preliminarily divided the three-stage evolution of the East Kunlun orogenic belt and constrained the origin of corresponding magmatism. |
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