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引用本文:田康志,季长军,伊海生,谭梅,金峰,范立顺. 南羌塘坳陷扎仁地区中侏罗统布曲组晶粒白云岩成因分析[J]. 中国地质, 2019, 46(2): 398-406.
TIAN Kangzhi,JI Changjun,YI Haisheng,TAN Mei,JIN Feng,FAN Lishun. Origin of grained dolomite from the Buqu Formation of Zaring area in southern Qiangtang depression[J]. Geology in China, 2019, 46(2): 398-406(in Chinese with English abstract).
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南羌塘坳陷扎仁地区中侏罗统布曲组晶粒白云岩成因分析
田康志1, 季长军2,3,4, 伊海生1, 谭梅5, 金峰6, 范立顺6
1.成都理工大学沉积地质研究院, 四川 成都 610059;2.中国地质科学院地质力学研究所, 北京 100081;3.自然资源部古地磁与古构造重建重点实验室, 北京 100081;4.中国地质科学院页岩油气调查评价重点实验室, 北京 100081;5.重庆自然博物馆, 重庆 400700;6.甘肃勘探者地质矿产有限公司, 甘肃 兰州 730000
摘要:
以青藏高原南羌塘坳陷扎仁地区中侏罗统布曲组晶粒白云岩为对象对其进行成因的研究。通过显微镜观察、流体包裹体数据以及碳氧同位素分析,认为研究区白云岩可分为细粉晶白云岩、中晶白云岩以及粗晶白云岩,在裂隙附近还广泛发育晶粒较粗大的鞍形白云石。白云石中流体包裹体均一温度在150.2~216.0℃,盐度均值达到了24.5% NaCl,远高于方解石包裹体均一温度与盐度,表明白云石的形成经历了高温高盐度的过程。白云石碳氧同位素分析显示其δ13CPDB值为-0.01‰~3.43‰,δ18OPDB值为-11.17‰~-7.68‰,通过白云石-水氧同位素分馏方程得到白云化流体的δ18OSMOW值为4.82‰~12.85‰,δ13CPDB对比认为白云石受寄主灰岩环境的影响。通过碳氧同位素数据对比以及前人的研究结果,认为研究区白云岩为相对封闭环境下受岩浆活动加热的高盐度流体对寄主灰岩交代的产物,高盐度流体由于镁离子的消耗导致流体对方解石过饱和,继而沉淀了高温的方解石。因此,热液活动对研究区中侏罗统布曲组白云岩的发育具有重要意义,值得加强对这一方向的探索研究。
关键词:  流体包裹体  碳氧同位素  白云石  布曲组  扎仁地区
DOI:10.12029/gc20190216
分类号:P588.24+5
基金项目:中国地质调查局项目"羌塘盆地隆鄂尼-鄂斯玛地区油气地质构造调查"(121201010000150014)资助。
Origin of grained dolomite from the Buqu Formation of Zaring area in southern Qiangtang depression
TIAN Kangzhi1, JI Changjun2,3,4, YI Haisheng1, TAN Mei5, JIN Feng6, FAN Lishun6
1.Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, Sichuan, China;2.Institute of Geomechanics, Chinese Academy of Geological Sciences. Beijing 100081, China;3.Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources, Beijing 100081, China;4.Key Lab of Shale Oil and Gas Geological Survey, Chinese Academy of Geological Sciences, Beijing 100081, China;5.Chongqing Natural Museum, Chongqing 400700, China;6.Gansu Kantanzhe Geology and Mineral Resources Co., Ltd., Lanzhou 730000, Gansu, China
Abstract:
The genetic mechanism of dolomite of the Middle Jurassic Buqu Formation in the Qiangtang depression was studied by using microscopy, fluid Inclusion data, and carbon and oxygen isotope analysis. The results show that the dolomites in the study area can be divided into fine-powdery dolomite, medium dolomite and coarse dolomite according to grain size. Dolomite generally has a fogged center and clear margin structure, in the cracks near the extensive development of grained saddle dolomite. Fluid inclusions in the dolomite have homogenization temperature ranging between 150.2 and 216.0℃ and average salinity of 24.5%NaCl, much higher than the homogenization temperature and salinity of fluid inclusions in calcite, indicating a high temperature and high salinity diagenetic environment. The isotopic analysis shows that δ13CPDB values vary from-0.01‰ to 3.43‰, and δ18OPDB values vary from-11.17‰ to -7.68‰; according to the dolomite-fluid oxygen isotope fractionation equation, the δ18OSMOW values of dolomitization fluid are in the range of 4.82‰-12.85‰, It is believed that the matrix dolomite and the saddle dolomite that are filled in the pores in the study area are the products of host limestone altered by the high salinity fluid heated by the magma activity in a close environment, while the high salinity fluid due to the consumption of magnesium ions led to over-saturation of fluid calcite and then to the precipitation if high-temperature calcite. Therefore, hydrothermal activity was very significant for the development of dolomite of the Middle Jurassic Buqu Formation in the study area.
Key words:  fluid inclusion  carbon and oxygen isotope  dolomite  Buqu Formation  Zaring area