Discovery and identification of the carbonatites in Panzhihua iron deposit, Sichuan——Eviedences of geological characteristics, U-Pb ages of baddeleyite and C—O isotopic composition
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    Abstract:

    Objectives:Carbonatite is rare, but an important rock type which usually constitutes the significant part of magmatic rock series in large igneous province(LIP). The late Permian Emeishan LIP in southwest China was extensively investigated by previous researchers, however, no contemporaneous carbonatite bas been reported. Methods: In the course of geological mapping in field, we identified a large scale carbonatite which distributed NE—SW about 20 kilometers on southeast of V—Ti—Fe orebodies in Panzhihua iron deposit, and might be the largest carbonatite in china. Numerous xenoliths of dunite, lherzolite and lamprophyre in the carbonatite are the most important and direct field evidences of magmatogene. The carbonatites are composed mainly of intrusive plutons, and secondly of eruptive, volcanic breccia and subvolcanic rocks which are closed to the plutons in space. The intrusive carbonatites consist of calcite, dolomite, olivine, orthopyroxene and altered minerals, e.g. serpentine, and they can be divided into different types according to texture and colour of carbonatite, and the granularity, content and structure of the rock- forming minerals. The eruptive carbonatite are composed of calcite, dolomite, dark minerals and hole. The few subvolcanic carbonatite consists of volcanic breccia, volcanic glass and calcite cement which probably crystallized in the stage of late slightly magmatic gas—liquid activities. Results: The weight mean U- Pb age of baddeleyite in coarse dolomite—carbonatite and zircons in paragenetic adamellite are 263.5±3.2 Ma(MSWD=0.41, n=20) and 260.2±1.7 Ma (WSWD=0.30, n=20) respectively. Identification of the large- scale late Permian carbonatite in Panzhihua iron deposit make up for the magmatic rock series of Emeishan LIP. The δ13CPDB(-9.6‰~+1.3‰) and δ18OSMOW(+12.9‰~+21.3‰) are similar to those of the main typical carbonatites elsewhere in the world. Conclusions: Magmatic rock and mineral associations, alteration types of Panzhihua carbonatite are greatly different from those of the Cenozoic REE- mineralized carbonatite in Mianning—Dechang area, implying different petrogenesis of two different carbonatites. The former were related to Himalayan orogeny, and the later were the result of low partial melt in deep mantle and were real sense of dry and magmatogenic carbonatite which formed from intracontinental rift environment caused by Emei mantle plume.

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WANG Shengwei, SUN Xiaoming, ZHOU Qing, LI Yanguang, FU Yu, ZHU Sibao, WANG Kun, GUO Yang, LIU Yujie, MA Long, HUANG Jinghou.2020. Discovery and identification of the carbonatites in Panzhihua iron deposit, Sichuan——Eviedences of geological characteristics, U-Pb ages of baddeleyite and C—O isotopic composition[J]. Geological Review,66(5):1299-1319.

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History
  • Received:November 05,2019
  • Revised:July 05,2020
  • Adopted:
  • Online: September 19,2020
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