湘东地区锡田印支期花岗岩的地球化学特征及其构造意义  

Geochemical characteristics and tectonic significance of the Xitian Indosinian granites in eastern Hunan Province,South China

作　　者：何苗 刘庆 孙金凤 牛睿[2] HE Miao;LIU Qing;SUN JinFeng;NIU Rui(CAS Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Henan Rock and Mineral Testing Center,Zhengzhou 450012,China)

机构地区：[1]中国科学院地球动力学重点实验室中国科学院大学地球与行星科学学院,北京100049 [2]河南省岩石矿物测试中心,郑州450012

出　　处：《岩石学报》2018年第7期2065-2086,共22页Acta Petrologica Sinica

基　　金：国家重点研发计划‘深地资源勘查开采’重点专项(2016YFC0600401);国土资源部公益项目(201211024-04);国家自然科学基金项目(41273046);中国科学院大学校部教师与研究所科研合作专项基金(Y552012Y00)联合资助

摘　　要：华南印支期花岗岩分布较为分散,其构造背景长期存在争议。湘东地区的锡田印支期花岗岩位于扬子板块和华夏板块的结合带中部,主要由黑云母花岗岩和黑云母二长花岗岩组成,二者均含有较高的SiO_2(67.6%~76.8%)和全碱含量(ALK=K_2O+Na_2O,6.8%~10.7%),呈过铝质的特征(A/CNK值范围为1.0~1.2),分异指数D.I值为84~93;微量元素显示出Rb、Th、U富集和Ba、Nb、Sr、P、Ti亏损的特征,稀土元素配分图呈右倾海鸥状,轻重稀土分馏明显,指示岩体经历了高度的分异演化;P_2O_5和微量元素比值随着分异程度变化的特征,表明岩石过铝质的特征是由高度的分离结晶作用造成。锡田印支期花岗岩的ε_(Hf)(t)值为-11.3^-4.34,δ^(18)O值分布范围为6.9‰~10.8‰,O同位素分布较为分散,主要是记录了源岩与流体的不同特征。Hf同位素的二阶段模式年龄为1.6～2.2Ga,反映其源区主要为中元古-古元古代的华夏基底;Hf-O同位素呈现出良好的线性关系,同时未蚀变的花岗岩明显偏离源岩为沉积岩的大容山花岗岩,表明锡田花岗岩的形成受到了幔源岩浆的底侵作用。结合邻区邓阜仙岩体和王仙岭岩体的研究成果,显示研究区在印支期就处于伸展的构造背景,可能与古太平洋板块的俯冲作用有关。Indosinian granites are widespread in South China and their tectonic setting has been in dispute for a long time. The Xitian Indosinian granites in eastern Hunan are located in the middle of the suture zone between Yangtze block and Cathay block. They are mainly composed of biotite granites and biotite monzogranites. Both of them contain high contents of SiO2（ 67. 6% - 76. 8%） and total alkali（ ALK = K2 O ＋ Na2 O,6. 8% - 10. 7 %）,showing peraluminous（ A/CNK range from 1. 0 to 1. 2）. Trace elements of all these rocks are enriched in Rb,Th,U and depleted in Ba,Nb,Sr,P,Ti. The REE pattern curves show a right-leaning seagull shape,indicating an obvious REE fractionation. Combined with the D. I index（ 84 - 93）,the characteristics of trace element indicate that the Xitian Indosinian granites have undergone highly differentiated evolution. P2O5 and trace element ratio with the degree of differentiation changes,indicating that the characteristics of peraluminous is due to the high degree of separation-crystallization. ε（Hf）（ t）values range from-11. 3 to-4. 34,and the δ-（18） O values range from 6. 9‰ to 10. 8‰. O isotopes are more dispersed on account of the difference between protolith and fluid. With a two-stage model age of 1. 6 - 2. 2 Ga,it reflects that the source of the Xitian Indosinian granites are Mesoproterozoic-Paleoproterozoic basement. The Hf-O isotope of the Xitian Indosinian granites show a good linear relationship,and unaltered granite,were obviously deviated from the Darongshan granite which is the representative granites of sedimentary source,indicating mantle magma underplating affected the forming of the Xitian Indosinian granites. Accompanying with the geochemical characteristics of Dengfuxian pluton and Wangxianling pluton in the adjacent area,the results reveal that research area was in an extensional tectonic setting. It may be controlled by subduction of the ancient Pacific plate.

关 键 词：印支期花岗岩 HF-O同位素 构造背景 华南 

分 类 号：P588.121[天文地球—岩石学]