Geochronology,Geochemical Characteristics and Geological Significance of Early Paleozoic Mailong Granites in Eastern Section of East Kunlun

Li Bin; Wei Junhao; Gao Qiang; Lai Lianxin; Li Xiaolong; Zhang Shengtao; Du Yumei

doi:10.3799/dqkx.2024.025

Abstract：The Silurian magmatic rocks of the East Kunlun Orogen are of great significance in determining the collisional evolution process of the proto-Tethys Ocean.In this study,the petrographic,chronological,geochemical and Hf isotope analysis were carried out for Mailong granodiorite and monzogranite exposed in the Gouli area of the eastern section of the East Kunlun orogenic belt,and the rock genesis and formation were discussed accordingly construction background.The results show that the zircon weighted mean ages of Mailong monzonite and granodiorite are 438±3 Ma and 426±2 Ma,which indicated it was formed in Early Silurian and Late Silurian.The granodiorite is characterized by high silic,enrichment of alkaline,but depletion in calcium,magnesium,titanium and phosphorus.The A/CNK values range from 1.01 to 1.08.The rock is obviously enriched in large ion lithophile elements(LILE;K,Rb,Sr,U,Th etc.)and depleted in high field strength elements(HFSE;Nb,Ta,Ti etc.),with negative Eu anomalies.The zircon εHf(t)value has a wide range(from-3.54 to-0.56),and the two-stage mode age T2DM(Hf)is 1 805 to 592 Ma.The granodiorite is characterized by high aluminum,high strontium content,high Sr/Y and(La/Yb)N ratio and lower yttrium content.The total amount of rare earth elements in the rock is low,the differentiation between light and heavy rare earth elements is obvious,with positive Eu anomaly characteristics.εHf(t)ranges from-4.9 to-0.7,and the two-stage model age T2DM(Hf)is 1 559 to 1 332 Ma.The monzonite showing characteristics of highly fractionated I-type granites,it is formed by a high degree of separation and crystallization after the mixing of felsic magma in the lower crust and mafic magma in the mantle.But the granodiorite has the characteristics of adakite,it is formed by subsequent crystallization after partial melting of the thickened juvenile lower crust.Combining with new regional studies,the monzonite and granodiorite may have been formed in a syn-collision environment and a transition environment from syn-collision to post-collision extension.It proposes that the East Kunlun area began to enter the syn-collision stage at least in the Early Silurian(440 Ma),experiencing a period of rapid continental collision(440-427 Ma),and due to slab break-off began to transform from the syn-collision stage to the post-collision extension stage between 427 to 425 Ma.