扬子地块西缘新元古代泸沽A型花岗岩成因与变泥质岩熔融

发布时间：2018-02-23 20:43

本文关键词： 新元古代扬子地块 A型花岗岩岩浆起源俯冲造山作用　出处：《中国地质》2017年01期 　论文类型：期刊论文

【摘要】：前人对扬子地块西缘新元古代I型和S型花岗岩开展了深入的研究工作,但有关A型花岗岩的研究则鲜有报道,其岩石成因及大地构造意义仍存较大争议。文章选择最新发现的泸沽A型花岗岩体为研究对象,开展系统的LA-ICP-MS锆石U-Pb年代学、岩石学和地球化学研究,探讨其成因机制和地质意义。泸沽花岗岩由钾长花岗岩和二长花岗岩组成,LA-ICP-MS锆石U-Pb年代学分析显示其结晶年龄分别为(806±5)Ma和(815±5)Ma,属新元古代岩浆活动产物。岩石具有高硅(SiO_2=71.2%~76.1%)、高碱(K_2O+Na_2O=6.73%~8.95%)、高K_2O/Na_2O比值(1.89~3.60)和强过铝质(A/CNK=1.07~1.49)的特征。[FeO~T/(FeO~T+Mg O)]-SiO_2和[(Na_2O+K_2O)-CaO]-SiO_2图解均指示泸沽花岗岩为铁质碱钙性A型花岗岩。泸沽花岗岩具有较高的稀土元素含量(∑REE=221×10~(-6)~387×10~(-6)),具有轻稀土富集而重稀土亏损的特征((La/Yb)N=3.42~9.69),具有明显Eu的负异常(δEu=0.10~0.34)。泸沽花岗岩具有较高的Zr、Nb、Ce和Y含量,具有较高的Ga/Al、Y/Nb、Yb/Ta和Ce/Nb比值,显示出典型的A2型花岗岩特征。综合元素地球化学及区域地质资料,文章提出泸沽新元古代铝质A2型花岗岩起源于新元古代早期俯冲造山过程中的变泥质岩熔融。
[Abstract]:Previous studies on Neoproterozoic I-type and S-type granites in the western margin of the Yangtze block have been carried out, but there are few reports on A-type granites. The petrogenesis and tectonic significance are still controversial. In this paper, the newly discovered Lugu A-type granite body is selected as the research object, and LA-ICP-MS zircon U-Pb geochronology, petrology and geochemistry are systematically studied. The genetic mechanism and geological significance of the Lugu granite are discussed. The U-Pb geochronology analysis of the Lugu granite is composed of potash feldspar granite and monzomorphic granite. The zircon U-Pb geochronology analysis shows that the crystallization ages of the Lugu granite are 806 卤5 Ma and 815 卤5 Ma, respectively, which belong to the product of Neoproterozoic magmatic activity. The rocks have the characteristics of Neoproterozoic magmatism. High SiO21.2 / 76.1C, high alkali-K2O Na2O-6.73K / 8.95g, high K _ 2O / Na2O-Na2O ratio 1.893.60) and strong peraluminite A / CNK _ (1.07N) 1.49). [FeO~T/(FeO~T MgO] -SiO2 and [Na2OK2O-CaO] -SiO2 diagram show that Lugu granite is A type A granite with alkali calcium type A granite. Lugu has a high content of REE=221 脳 10 ~ (10) (-6387x 10 ~ (10)) ~ (-) ~ (6). The characteristics of LREE enrichment and heavy REE depletion are Lap / YbN ~ (3.42) ~ (9.69), with a negative anomaly of EU (未 EU ~ (0.10) ~ (0.10) ~ (0.34)). The Lugu granite has a high content of ZrNbCe and Y. It has a high ratio of Ga / Alb / Y / NB / Yb / Ta and Ce/Nb, which shows the typical characteristics of A2 type granites, and synthesizes element geochemistry and regional geological data. The authors suggest that the Lugu Neoproterozoic A2-type granite originated from the melting of argillaceous rocks during the early Neoproterozoic subduction orogeny.
【作者单位】：四川省地质调查院;中国地质大学地球科学学院;
【基金】：中国地质调查局项目“龙门山—滇中成矿带通安和宁蒗地区地质矿产调查”(121201010000150016)资助~~
【分类号】：P588.121

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