四川攀枝花铁矿碳酸岩的发现和确认——地质特征、斜锆石U-Pb年龄、C—O同位素组成证据
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本文为中国地质调查局项目(编号:DD20190054,DD20179603,DD20160018- 07,DD20160019)、国家自然科学基金资助项目(编号:41403038,41202067,91855213)和国家重点研发计划重点专项(编号:2018YFA0702605)的成果


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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    摘要:

    碳酸岩是一类稀少但具有重要地质意义的一种岩石类型,且碳酸岩也往往构成大火成岩省岩石序列中的重要组成部分。我国西南地区晚二叠世峨眉山大火成岩省举世闻名,但此前尚未有同期的火成碳酸岩报道。本项目组在四川攀枝花地区开展的地质填图过程中,识别出大规模的碳酸岩,其沿北东—南西向延伸约20千米,可能是我国最大的岩浆型碳酸岩。大量的暗色纯橄榄岩、二辉橄榄岩及煌斑岩地幔捕虏体是认定岩浆型碳酸岩最直接、最重要的野外证据。碳酸岩主体为侵入岩,其次为少量的喷出岩、火山角砾岩及潜火山岩,空间上与侵入碳酸岩紧邻。碳酸岩侵入岩主要由方解石、白云石、橄榄石、斜方辉石及其蚀变而成的蛇纹石组成,并可根据矿物粒度、含量、结构、构造及颜色,划分出不同的碳酸岩类型。碳酸岩喷出岩由方解石、白云石、暗色矿物及气孔构成; 潜火山岩由火山角砾、火山岩玻璃及方解石胶结物构成,方解石胶结物的形成可能与岩浆晚期的少量气液活动有关。拉纳箐矿区粗粒白云石碳酸岩中斜锆石以及与碳酸岩共生的石英二长岩中锆石的加权平均年龄分别为263. 5±3. 2 Ma (MSWD=0. 41, n=20)和260. 2±1. 7 Ma (WSWD=0. 30,n=20)。大规模碳酸岩的识别完善了峨眉山大火成岩省岩浆岩序列。碳酸岩的δ13CPDB(-9. 6‰~+1. 3‰)及δ18OSMOW (+12. 9‰~+21. 3‰)值与其它典型碳酸岩的同位素值接近。攀枝花铁矿区碳酸岩与冕宁—德昌新生代稀土矿化碳酸岩的岩性组合、矿物组合及蚀变类型差异显著,反映了二者具有不同的成因。前者与喜马拉雅造山运动有关,后者形成于与峨眉地幔柱有关陆内裂谷环境,可能为深部地幔低部分熔融的产物,是真正意义上“干的”岩浆成因的碳酸岩。

    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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王生伟,孙晓明,周清,李艳广,付宇,朱斯豹,王坤,郭阳,刘宇杰,马龙,黄景厚.2020.四川攀枝花铁矿碳酸岩的发现和确认——地质特征、斜锆石U-Pb年龄、C—O同位素组成证据[J].地质论评,66(5):1299-1319,[DOI].
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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  • 收稿日期:2019-11-05
  • 最后修改日期:2020-07-05
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  • 在线发布日期: 2020-09-19
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