Zircon U-Pb Dating And Geochemistry Of The Kudong Amphibole Gabbro From Central Tianshan In Xinjiang And Its Tectonic Significance

The research area of this paper is located in the northern part of the middle section of the Central Tianshan.After detailed field geological survey work on the hornblende gabbro in the study area,the geochemical and zircon U-Pb dating and Lu-Hf isotope were studies in the Kudong hornblende gabbro.The results show that the zircon in the hornblende gabbro exhibits a typical magma rhythm zone and a strip structure between light and dark,the Th/U ratio is 0.37¹.35,which is a typical magmatic origin zircon,and its ²⁰⁶Pb/²³⁸U age-weighted average is 314.8 Ma±6.4 Ma,indicating that the rock mass was formed in the Late Carboniferous.Zircon has a uniform Hf isotope composition,the initial ratio of ¹⁷⁶Hf/¹⁷⁷Hf is 0.282847⁰.282963,the corresponding?_Hf?t?value is 9.6¹3.1,and the single-stage Hf mode age is 452⁷16Ma.The rock is characterized by low SiO₂?46.55%⁴8.61%?,rich MgO?6.25%⁸.18%?,poor Na₂O?1.96%².79%?and K₂O?0.56%¹.06%?and Na₂O/K₂O greater than 1.85.And shows a weak Eu positive anomaly??Eu=1.01¹.1?,enriching large ion lithophile elements such as Rb,Ba,K,Sr,etc.,and losing high field strength elements such as Nb,Ta,Ti,etc.Weak Zr and Hf losses.The degree of fractionation between light rare earth elements and heavy rare earth elements is slightly stronger.The fractionation of light and heavy rare earth elements is weaker.The Mg^#value of rock mass is higher,ranging from 66.9 to 68.4,and the average value is 67.7.Comprehensive research shows that the rock mass is formed in an island arc environment,and the magma source area is a mantle affected by the enriched components,but the degree of influence is small.Combined with the regional geological background,some of the rock masses in the southern part of the Central Tianshan are not obviously affected by the subduction plates.The magmatic rocks in the northern Jurassic tectonic belt of the Central Tianshan have obvious subduction plate mixing.The signs suggest that the Late Carboniferous of the ancient oceanic crust has a southward subduction polarity.