贵州遵义下寒武统黑色岩系型Ni,Mo矿床Rb-Sr同位素测年与示踪研究  

STUDY ON THE ISOTOPE DATA TRACING AND ISOTOPIC CHRONOLOGY IN THE BLACK-ROCK-SERIES-TYPE Ni-Mo DEPOSITS IN THE LOWER CAMBRIAN IN HUNAN AND GUIZHOU PROVINCES

作　　者：江永宏[1] 李胜荣[1] 

机构地区：[1]岩石圈构造与深部过程及探测技术教育部重点实验室中国地质大学

出　　处：《矿物岩石》2005年第1期62-66,共5页Mineralogy and Petrology

基　　金：国家自然科学基金(40073012);国家重点基础研究发展规划(G1998040800);国土资源大调查(199910200264;20001020223023;200313000068-02)

摘　　要：　湘、黔地区张家界、遵义一带分布有黑色岩系型Ni-Mo-PGE矿床,对Re-Os同位素研究发现张家界和遵义两地矿床虽相距400km,但它们是同一期矿化作用的产物,其等时线年龄(542Ma±11Ma)为金属矿物生成年龄,也为矿化年龄,接近前寒武纪和寒武纪的分界时限,而铷-锶测年一般被认为是反映后期构造热事件年龄,研究发现Rb-Sr等时线年龄大约为277Ma±37Ma,相当于石炭与二叠界线年龄(290Ma),属于海西晚期。Rb-Sr同位素体系与Re-Os同位素体系有显然不同的物质来源。Re,Os同位素显示它们是同一期矿化作用的产物,而187Os/186Os=16.355～96.664(平均62.081),不仅高于陨石和地幔的相应值,也高于海洋沉积物的比值,其下限值与地壳的均值较为接近,体现了陆相壳源特征,显然黑色岩系的物质来源多样,不限于海水。87Sr/86Sr为0.7120±0.0020,明显高于玄武岩的值(0.704),而比陆源硅酸盐的值(0.720)偏低,表明为陆源物质和深源物质的混合物,而且深源物质对87Sr/86Sr的影响大于来自于岛弧间浅海陆棚地区的陆源物质。因为后生期构造热变质事件与有机质的热解过程或热演化史相关,所以该过程应影响了成矿早期富集的PGE元素在后生期,伴随着热变质事件而出现在富烃有机质流体中的活化、迁移以及再次富集。The Black-Rock-Series-Type Ni-Mo-PGE deposits are located in the Zhangjiajie of Hunan province and Zunyi of Guizhou province. The Re-Os isotopic research reveals that the deposits were produced in the ore-forming process, although the localities are 400 km apart. The Re-Os isochron age of 542 Ma±11 Ma is both the mineralization age and the forming age of the metallic minerals, which is close to the boundary age of the Cambrian and the Precambrian. Generally,the Rb-Sr isotopic age is thought to be the late stage structural thermal event. During this study, it is close to 277 Ma±37 Ma, equivalent to the boundary age of Carbonaceous and Permian(290 Ma).It is found that the Rb-Sr isotopic system is different from the Re-Os isotopic system with respect to different material supply. Rb-Sr isotopic study indicates the same product of the mineralization,whereas the value ()^(187)Os/()^(186)Os=16.355 to 96.664(average as 62.081)is not only higher than the range of meteorite and mantle,but also than that of oceanic sediments.The lower limit of which is close to the average value of the crust, featuring like the continental crust-derived source and to be remarkably different from marine source or just from a diverse varieties of source. The initial data of ()^(87)Sr/()^(86)Sr is equal to 0.712 0±0.002 0,which is higher than that of basalt (0.704)and is lower than that of the continent-sourced silicate (0.720), typical of the blend of deep-derived materials and crust-derived materials.Moreover,the deep-derived materials had a stronger effect on the value ()^(87)Sr/()^(86)Sr than the continent-sourced material from the island-arch neritic-shelf.The structural thermal event of the catagenesis is correlated with the pyrolysis and the thermal evolutional history, this process is deemed to be influential to the PGE enriched by the early mineralization stage and has caused them to be activated, migrated and re-enriched in the rich-hydrocarbon fluid, which was accompanied by the thermal metamorphism during the catagenesis.

关 键 词：黑色岩系 SR同位素 测年 物质来源 等时线年龄 陆源物质 矿床 有机质 遵义 变质 

分 类 号：P618[天文地球—矿床学] P736[天文地球—地质学]