扬子板块北缘光雾山地区钾长花岗岩年代学、地球化学特征及构造意义  

ZIRCON U-Pb AGE, GEOCHEMICAL CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF THE K-FELDSPAR GRANITE IN GUANGWUSHAN AREA,NORTHERN MARGIN OF YANGTZE PLATE

作　　者：魏国安[1] 邹光富[2] 潘伟奇 罗茂金 马志鑫 毛琼[4] 余学磊 WEI Guoan;ZOU Guangfu;PAN Weiqi;LUO Maojin;MA Zhixing;MAO Qiong;YU Xuelei(Henan Vocational and Technical College of Architecture,Zhengzhou 450000,China;Chengdu Center China Geological Survey,Chengdu 610081,China;College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;Huabei Oilfield Institute,Renqiu 062552,China)

机构地区：[1]河南建筑职业技术学院,河南郑州450000 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]成都理工大学,四川成都610059 [4]华北油田研究院,河北任丘062252

出　　处：《矿物岩石》2019年第2期14-24,共11页Mineralogy and Petrology

基　　金：中国地质调查局项目(121201010000150016);四川省南江地区1∶5×104关坝-南江-朱家坝幅矿产地质调查项目

摘　　要：为了限定扬子板块北缘地区新元古代岩浆活动事件的准确时间及和探讨岩石成因,本文对出露于四川省南江县光雾山钾长花岗岩进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学研究。结果表明光雾山地区钾长花岗岩锆石U-Pb年龄为836.3Ma±8.3Ma,属于新元古代花岗岩。岩石具有高w(SiO2)(72.68%~78.10%),w(K2O)(4.26%~5.32%),w(Na2O)(1.68%~3.38%),相对富钾(K2O/Na2O=1.12~2.54),高碱(w(Na2O+K2O)=7.64%~8.99%),低P2O5含量等特征,铝饱和指数A/CNK=0.99~1.49,光雾山花岗岩属于过铝质高钾钙碱性花岗岩。岩石具有轻稀土元素相对富集,重稀土元素亏损的特征,具有明显Eu负异常,δEu为0.48~0.73。光雾山花岗岩微量元素表现出Rb,Th,K,Nd,Sm元素富集,Ba,Nb,Ta,Sr,P,Ti元素亏损的特点。地球化学研究表明,光雾山钾长花岗岩主要以粘土岩部分熔融为主及少部分含粘土的变质杂砂岩部分熔融形成的。岩浆可能来源于本区结晶基底新太古界-古元古界后河岩群和褶皱基底中-新元古界火地亚群中深变质岩为代表的地壳物质的部分熔融产物,为壳源成因类型,具有岛弧型花岗岩特征,形成于岛弧构造环境。光雾山钾长花岗岩的形成是新元古界时期扬子板块与华北板块之间的俯冲碰撞、岛弧形成构造演化过程中使区域地壳不断加厚和地壳深融作用的响应。扬子陆块北缘南江地区约836Ma同碰撞岛弧型钾长花岗岩的发现,表明该地区在约836Ma时为Rodinia超大陆汇聚形成阶段,此时期该区Rodinia超大陆尚未进入大陆裂解阶段。The chronology and geochemistry of Guangwushan K-feldspar granites in the northern margin of the Yangtze block are studied by means of LA-ICP-MS zircon U-Pb dating and geochemical analysis techniques so as to constrain the precise emplacement time and genesis of the Neoproterozoic igneous rocks in the Nanjiang County of Sichuan Province. The zircon LA-ICP-MS dating reveals that the Guangwushan K-feldspar granites were formed in the Neoproterozoic period with an emplacement age of 836.3 Ma±8.3 Ma. Geochemical analyses show that the Guangwushan K-feldspar granites have medium content of w(SiO2)(72.68%~78.10%),high K(K2/Na2O=1.12~2.54) and peraluminous ratio(A/CNK)=0.99~1.49) and belong to k black to high-K calc-alkaline peraluminous S-type granites, similar to calc-alkaline rocks of island arc or active continental margin. The ΣREE of granites ranges from 158.85×10^-6 to 304.26×10^-6 with rightward incline pattern and obvious negative Eu abnormity(δEu=0.48~0.73).Rb,Th,K,Nd and Sm are enriched and Ba,Nb,Ta,Sr,P and Ti depleted,also similar to calc-alkaline rocks in island arc or active continental margin. It is proposed that the original rocks of the granites are greywacke and mudstone and the magma source is probably derived from partial melting of the Neo Archean Houhe Rock Group and Paleoproterozoic to mid-Proterozoic Huodeya Group metamorphosed basement.Based on the geochemical characteristics,it is considered that the Neoproterozoic K-feldspar granites were in an island arc and syn-collision environment and formed in a transitional tectonic setting from the compression system to the island arc system.The tectonic-magmatic movement in northern margin of Yangtze block is intimately related to the subduction and collision between the Yangtze plate and North China plate,and the granites were resulted from the thickening and deep melting of the regional crust in the geological process.

关 键 词：钾长花岗岩 锆石U-PB定年 地球化学 光雾山 扬子板块北缘 

分 类 号：P597.3[天文地球—地球化学]