Geochronology,Petrogenesis Of The Intermediate Basic Dykes From The Kawabulak Area,Central Tianshan And Its Dynamic Significance

The Central Tianshan plays a major role of Central Asian orogenic belt.And play a significant role in tectonic-magmatic evolution.Late Paleozoic is a key period,in this time,an active continental margin arc setting caused by the norward subduction of the South Tianshan ocean.Paleozoic igneous rocks are widely exposed and intruded by subsequent intermediate and mafic dykes in the Kawabulak area,Central Tianshan.The formation age,magma source characteristics,petrogenesis and dynamic significance of the typical intermediate basic dykes are investigated on the base of zircon U-Pb geochronology,major and trace elements geochemistry and Hf isotopes.Solutions presented in this thesis can be summarized as follows:1.The intermediate basic dykes from Kawabulak area in Central Tianshan extend in north and east,north and west,north and south directions and intrudeinto the Early Carboniferous K-feldspar granites and monzonitic granites.2.LA-ICP-MS zircon U-Pb dating yielded a weighted mean ²⁰⁶Pb/²³⁸U ages of296.1±2.5Ma?MSWD=1.4?and 299.5±2 Ma?MSWD=1.07?for diorite and gabbro dykes,respectively.3.Geochemically,the dykes are characterized by enrichment of LILEs?Rb,U,Th?,LREE and depletion of HFSEs?Nb,Ta,Ti?.Intermediate and mafic dykes?50?REE varies from 69.19×10^-6234.62×10^-6,while LREE/HREE changes from3.97¹1.18.(¹⁷⁶Hf/¹⁷⁷Hf)values of zircons from diorite dyke vary from0.280618⁰.283329,with corresponding?_Hf?t?values between-14.57⁺25.06.The available data show that parental magma of studied dykes was mainly derived from a depleted mantle and experienced fractional crystallization as well as significant crustal contamination during magma emplacement.4.Field geological characteristics and geochemical analysis,integrated with regional data from the literature,show that the dykes were likely formed in post-collision extensional environment,indicating that South Tianshan Ocean closed prior to Early Permian in Kawabulak area.The inherited zircons with Precambrian ages captured by Late Paleozoic dykes from the Kawabulak area show that the Central Tianshan has experienced multiphase tectonic thermal events.