Early Permian Post-Collisional Extension and Crust-Mantle Magmatism in the Central Tianshan Block,Eastern Tianshan:Constraints from the Study of Porphyritic Monzodiorite
Zhang Weifeng
Deng Xin
Zhang Liguo
Wang Jing
Xie Guogang
Jin Xinbiao
Abstract：As a typical case of the Permian magmatism in the Eastern Tianshan,the porphyritic monzodiorite exposed in the southern margin of the Central Tianshan block.Zircon U-Pb dating on the monzodiorite yields an age of 281.3±1.5 Ma.The monzodiorite shows high-K calc-alkaline and metaluminous affinities,with Na2O+K2O and A/CNK values ranging 5.88‒6.62 wt.%and 0.66‒0.73,respectively.They are characterized by high Fe2O3/FeO ratios(0.66～0.73),and present the assemblage of titanite+quartz+magnetite in the groundmass,suggesting that the monzodiorite formed under a high oxygen fugacity condition.The monzodiorite enriched in LILEs(i.e.Rb,K and Ba),but depleted in HFSEs(i.e.Nb,Ta and Ti)and HREE.In addition,all the study samples have negative εNd(t)(-2.72 to-3.07),high initial 87Sr/86Sr(0.706 46 to 0.706 54)values,and negative zircon εHf(t)(-3.7 to-0.8)values,as well as intermediate Nb/U(10.3 to 10.9)values.These geochemical features indicating that the magmas originated from spinel-garnet lherzolite that metasomatized by subduction-related fluids,and mixed with minor crustal components.Integrating the petrogenesis and other geological evidences,we proposed that the magmatisms in the Central Tianshan block were generated in post-collision extensional setting of slab breakoff during the Early Permian.
Keywords：post-collisional extensionslab breakoffPermianPetrogenesisCentral Tianshan blockgeochemistry
Publication Date：2024-08-15
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：17( 2697-2713 )