庐山玉京山岩体成因及其对构造体制转换的约束  

Petrogenesis for the Yujingshan Pluton in Lushan Area, and Its Constraints on Tectonic Regime Transformation

作　　者：王嘉玮 王东升[1] 王刚[1] 武昱东[1] Wang Jiawei;Wang Dongsheng;Wang Gang;Wu Yudong(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,CAGS,Beijing 100037,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地球科学》2024年第12期4369-4384,共16页Earth Science

基　　金：地调项目(No.DD20230564);中央级科研院所基本科研业务费(No.KK2217);国家重点研发计划(No.2016YFC0600202)。

摘　　要：对庐山核部的玉京山二长花岗岩开展了系统性分析.结果显示该岩体形成于125±1 Ma,其锆石εHf(t)值为-6.5~-2.0,二阶段模式年龄为1.6~1.3 Ga,表明岩浆源于中元古代地壳的部分熔融.岩体属过铝质高钾钙碱性花岗岩(A/CNK=1.10~1.15;K_(2)O/Na_(2)O=1.01~1.45),稀土总量较低(48.54×10^(-6)~80.32×10^(-6)),轻重稀土元素分馏不明显((La/Yb)N=2.91~4.32),具Eu负异常(σEu=0.19~0.28),富集Rb、Sr、Th、U、K,亏损Nb、Ti.岩体εNd(t=125)值为-10.1~-8.9,指示出它们来源于古老地壳物质的重熔.综上所述,岩石形成过程中经历了结晶分异,属高分异S型花岗岩.岩体形成于早白垩世古太平洋板块北西向俯冲时,陆壳从挤压向伸展的构造转换阶段,随后于晚白垩世遭受了糜棱岩化.结合区域资料,表明华南板块构造体制转换发生于晚中生代,区域伸展作用可持续至早白垩世晚期.In this paper,systematic analysis of the Yujingshan monzogranite is conducted to investigate its petrogenesis and source.The results show that the crystallization age of the monzogranite is 125±1 Ma.TheεHf(t)values of zircons are between-6.5 and-2.0 and the two-stage model ages(tDM2(Hf))are 1.6-1.3 Ga,which suggests that the magma was derived by partial melting of Mesoproterozoic crust.Geochemically,the Yujingshan pluton belongs to peraluminous and high K calc-alkaline series with A/CNK=1.10-1.15 and K_(2)O/Na_(2)O=1.01-1.45.TheΣREE of the Yujingshan pluton is relatively low(ΣREE=48.54×10^(-6)~80.32×10^(-6)).LREE and HREE fractionation is not significant((La/Yb)N=2.91-4.32),but there is a negative Eu anomaly(σEu=0.19-0.28).The samples are enriched with large ion lithophilic elements(Rb,Sr,Th,U,K)and depleted in high field strength elements(Nb and Ti).The enriched Sm-Nd isotopic composition[εNd(t=125)of-10.1 to-8.9]indicates that the magma originated from remelting of ancient crustal materials.Comprehensive analysis shows that the Yujingshan monzogranite was generated by the partial melting of Mesoproterozoic argillaceous rocks and experienced fractional crystallization.The magma belongs to highly differentiated S-type granites,which formed in a tectonic regime transformation process going from compression to extension during the northwest subduction of the paleo-Pacific plate.Subsequently,ductile shearing occurred during the Late Cretaceous,resulting in mylonitization of the Yujingshan pluton.This research,combined with regional magmatic and structural geology data,suggests that the tectonic regime transformation in the South China block occurred at Late Mesozoic,and that regional extension continued until the late Early Cretaceous.

关 键 词：二长花岗岩 锆石U-PB年龄 Nd-Hf同位素 庐山 地球化学 岩石学 

分 类 号：P595[天文地球—地球化学]