滇中扬子西南缘戛洒地区大红山岩群高压榴闪岩的发现及厘定

    Discovery and determination of high-pressure garnet-amphibolite in Dahongshan Group in Gasa area, southwest margin of central Yangtze, Yunnan Province

    • 摘要: 通过野外地质调查,在滇中新平县戛洒的浅部熔岩铁矿地区原划分的大红山岩群红山组内部,新发现了一套变质强烈的变质岩。岩相学研究表明,该变质岩为榴闪岩类,退变质作用强烈,仅保留有部分俯冲−折返的矿物学记录,未见岩石早期变质及峰期变质阶段的矿物组合,且矿物世代具顺时针变质轨迹特征。据电子探针测试结果,通过GBP(石榴子石−黑云母−斜长石)平均温压计法,其记录的最大变质压力达1.52 GPa;角闪石单矿物温压计法获得角闪石记录的最大变质压力为0.66 GPa,表明榴闪岩为高压变质级。结合大红山岩群的成岩时代、变质时代、岩石地球化学特征等,认为大红山岩群成岩于Columbia 超大陆裂解期,是古元古代晚期洋盆的岩石组分;主期变质作用形成于Rodinia 超大陆拼合−裂解过程的俯冲−折返作用;大红山岩群可能是一套不完整的蛇绿混杂岩,代表了古元古代晚期洋盆的残迹。

       

      Abstract: In the course of field geological investigation, a new set of metamorphic rocks with strong metamorphism was discovered in the Hongshan Formation of Dahongshan Group in the shallow lava iron ore area of Jiesa, Xinping County, central Yunnan Province. Petrographic studies show that the metamorphic rocks are eclogite amphibolites with strong retrometamorphism and only partial subduction−reentrant mineralogical records. There is no mineral association in the early metamorphic and peak metamorphic stages of the rocks, and the mineral generations have the characteristics of clockwise metamorphic tracks. According to the results of electron probe test, the maximum metamorphic pressure recorded by GBP (Garnet−Biotite−Plagioclase) average temperature manometer is 1.52 GPa. The maximum metamorphic pressure of hornblende recorded by temperature manometer method is 0.66 GPa, which indicates that the eclogite in this study is of high pressure metamorphic grade. According to the diagenetic age, metamorphic age and geochemical characteristics of Dahongshan Group, it is believed that Dahongshan Group was formed in the cracking period of the Columbia supercontinent and is a rock component of the Late Paleoproterozoic ocean basin. The main−stage metamorphism was formed by the subduction−reentrant process of the Rodinia supercontinent, and the Dahongshan Group may be an incomplete set of ophiolitic melanomics, representing the remnants of the Late Paleoproterozoic ocean basin.

       

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