滇东南猛洞岩群构造环境:变质碎屑岩地球化学约束

发布时间：2019-07-26 08:45

【摘要】：猛洞岩群位于滇东南文山-麻栗坡断裂与红河断裂带之间的老君山-Song Chay变质核杂岩核部,由一套经历过多期变质-变形的杂岩体组成。变质碎屑岩地球化学特征显示,主、微量元素平均组成与大陆上地壳相似,且SiO_2/Al_2O_3、K_2O/Na_2O比值显示该套变质沉积岩具有相似的成熟度,但片岩类样品可能遭受过强烈的风化作用;稀土元素特征与变质岩原岩恢复图解显示,片岩类原岩为黏土岩及泥质岩,片麻岩类原岩为砂岩、杂砂岩。化学蚀变指数(CIA)、成分变异指数(ICV)、斜长石蚀变指数(PIA)反映了片岩类原岩形成后经历过较强的风化作用,但副片麻岩类原岩经历的风化作用较弱,反映了副片麻岩类主要来源于不成熟的物源区,显示出活动构造环境沉积物的特征。Rb/Sr和Th/U比值判别结果表明该套碎屑岩经历了较复杂的沉积演化过程;La/Th-Hf图解和砂岩-泥岩套的物源区判别图解表明变质碎屑岩样品以石英岩沉积物源区为主,混合少量中性火成岩物源区;ThSc-Zr/10和La-Th-Sc图解表明猛洞岩群可能沉积于大陆岛弧环境。综上所述,猛洞岩群变质碎屑岩原岩为一套泥质岩-砂岩(杂砂岩),这套碎屑岩经历了较强风化作用及复杂的沉积演化过程,主要沉积于与大陆岛弧环境相关的盆地,推测猛洞岩群的物质来源与昆阳群有关,可能与扬子地块具有较强的亲缘关系。
[Abstract]:The Mengdong rock group is located in the core of the Laojunshan-Song Chay metamorphic core complex between the Wenshan-Mailipo fault and the Honghe fault zone in southeastern Yunnan, and is composed of a set of complex bodies that have experienced many stages of metamorphism and deformation. The geochemical characteristics of metamorphosed clastic rocks show that the average composition of trace elements is similar to that of the upper continental crust, and the SiO_2/Al_2O_3,K_2O/Na_2O ratio shows that the metamorphosed sedimentary rocks have similar maturity, but schist samples may have suffered strong weathering. The rare earth element characteristics and the restoration diagram of metamorphic rock source rock show that the schist source rock is clay rock and mudstone, and the gneiss source rock is sandstone and complex sandstone. The chemical alteration index (CIA), composition variation index (ICV), plagioclase alteration index (PIA) reflects the strong weathering after the formation of schist source rocks, but the weathering of accessory gneiss protolith is weak, which reflects that the accessory gneiss mainly comes from immature provenance areas. The characteristics of sediments in active tectonic environment are shown. The discriminant results of RB / Sr and Th/U ratios show that the clastic rocks have experienced a complex sedimentary evolution process. The La/Th-Hf diagram and the source region discrimination diagram of sandstone-mudstone suite show that the metamorphosed clastic rock samples are dominated by quartz sedimentary source area and mixed with a small amount of neutral igneous source area, while ThSc-Zr/10 and La-Th-Sc diagrams show that the Mengdong rock group may be deposited in the continental island arc environment. To sum up, the metamorphosed clastic rock source rock of Mengdong Group is a set of mudstone-sandstone (complex sandstone). This set of clastic rocks has experienced strong weathering and complex sedimentary evolution process, which is mainly deposited in basins related to continental island arc environment. It is speculated that the material source of Mengdong rock group is related to Kunyang Group and may have a strong genetic relationship with Yangtze block.
【作者单位】：成都理工大学地球科学学院;中国地质科学院矿产综合利用研究所;中国科学院地球化学研究所矿床地球化学国家重点实验室;
【基金】：国家“973”项目(编号G2007CB411408) 国家自然科学基金项目(编号40302026、40972129、41603034) 矿床地球化学国家重点实验室自主选题项目(编号KCZX20090106)资助的成果
【分类号】：P584;P588.3

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