扬子地块西缘天全新元古代过铝质花岗岩类成因机制及其构造动力学背景  

Petrogenesis and tectonic implication of the Neoproterozoic peraluminous granitoids from the Tianquan area,western Yangtze Block,South China

作　　者：赖绍聪[1] 秦江锋[1] 朱韧之 赵少伟[1] 

机构地区：[1]西北大学大陆动力学国家重点实验室,西北大学地质学系,西安710069

出　　处：《岩石学报》2015年第8期2245-2258,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41372067);国家自然科学基金重大计划项目(41190072);国家自然科学基金委创新群体(41421002);教育部创新团队(IRT 1281)联合资助

摘　　要：四川西部天全地区花岗岩属于扬子地块西缘岩浆岩带,是"康滇地轴"北段的重要组成部分。岩石形成年龄为851±15Ma(MSWD=0.7),属于新元古代花岗岩,与扬子地块西缘和北缘大量的中酸性侵入体和火山岩具有相近的形成年龄。火夹沟花岗闪长岩为过铝质、低Si O2、具有相对亏损的Sr-Nd-Pb同位素地球化学组成,结合岩石低的Al2O3/Ti O2和高的Ca O/Na2O比值,其应是在镁铁质岩浆底侵的条件下,成熟度较低的杂砂岩部分熔融形成的过铝质熔体,岩石较低的Si O2含量表明其同化了部分镁铁质熔体。而角脚坪花岗岩具有高的Si O2含量,为过铝质、富Na的熔体,而且具有极度亏损的Sr-Nd同位素组成,表明其应是亏损的玄武质岩石(洋壳或是与地幔柱有关的玄武岩)在H2O饱和条件下发生低程度部分熔融形成的过铝质熔体。结合扬子西缘其它新元古代火成岩的地球化学特征及区域构造资料,我们认为天全地区的Na质花岗闪长岩-花岗岩组合代表在高地温梯度条件下,玄武质岩石在H2O饱和条件下发生部分熔融形成的过铝质花岗岩。The Neoproterozoic per-aluminous granitoids in the Tianquan area, western margin of the Yangtze Block have crystallization age of 851 ± 15Ma（ MSWD = 0. 7）,which was identical with the Neoproterozoic intrusive-volcanic rocks from the western and northern margin of the Yangtze Block. The Huojiagou granodiorites have low Si O2 contents,peraluminous,and relatively depleted Sr-Nd-Pb isotopic compositions. And in combination with their low Al2O3/ Ti O2 and high Ca O / Na2 O ratios,we suggest that the Huojiagou granodiorites were derived from partial melting of greywackes under H2 O saturation condition,which may be generated by underplating of mafic melts from mantle. The Jiaojiaoping granites have higher Si O2 contents,sodic-rich,peraluminous,and extremely depleted Sr-Nd-Pb isotopic compositions,these features indicate that the Jiaojiaoping Na-rich granites were derived from partial melting of depleted basaltic rocks（ MORB or mantle plume-related basalts） under H2 O saturation condition. In combination with other Neoproterozoic intrusive-volcanic rocks in the western margin of the Yangtze Block,we argued that the Na-rich,peraluminous granodiorite-granite association from the Tianquan area were formed by partial melting of basaltes and greywackes under H2 O saturation and high geothermal gradient.

关 键 词：钠质花岗岩 过铝质 地球化学 新元古代 扬子地块西缘 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]