中国北方石墨矿床及赋矿孔达岩系碳同位素特征及有关问题讨论  

Carbon isotope geochemistry of graphite deposits and ore-bearing khondalite series in North China: implications for several geoscientific problems

作　　者：陈衍景[1] 刘丛强[2] 陈华勇[1] 张增杰[1] 李超[1] 

机构地区：[1]北京大学地质学系,北京100871 [2]中国科学院地球化学研究所,贵阳550002

出　　处：《岩石学报》2000年第2期233-244,共12页Acta Petrologica Sinica

基　　金：国家九五攀登预选95-预39-04课题;国家自然科学基金! (492 0 3 0 47;495 73 168;49672 119;49972 0 3 5号项目 );教育部跨世纪人

摘　　要：本文综合了中国北方孔达岩系和石墨矿床的碳同位素数据 10 2件 ,发现片麻岩石墨 透辉岩石墨 <大理岩石墨 <石墨大理岩方解石 <大理岩方解石 ;混合岩化岩石中石墨δ1 3C总介于有机碳和无机碳之间 ;不同地体片麻岩石墨δ1 3C极为一致 ,变化于 - 2 2 .8‰～ - 2 1.48‰ ,略低于世界有机质平均值 - 2 6± 7‰ ;大理岩的原岩碳酸盐δ1 3C高于 2‰ ,与2 330～ 2 0 6 0 Ma期间全球性δ1 3Ccarb正向漂移事件一致。地质流体是碳同位素分馏、均一化的重要因素 ,是石墨矿床的 3种主要碳源之一 ,是碳的 5种存在形式之一 ,也是碳循环的重要媒介和方式 ;导致热液矿床δ1 3C=- 5‰左右的因素较多 ,依据δ1 3Ccalcite - 5‰得出成矿物质和流体来自地幔的结论值得怀疑 ;中国北方孔达岩系形成于古元古代 ,可能为 2 30 0～ 2 0 5 0 Ma。A database of 102 analyses of δ 13C(PDB) for graphite deposits and ore-bearing khondalite series in North China clearly shows several regularities: 1) δ 13C gneiss graphite δ 13C diopsidite graphite <δ 13C marble graphite<δ 13C graphite-marble calcite <δ 13C marble calcite; 2) the values of δ 13C migmatite graphite are always between those of organic carbon and inorganic carbon; 3) the averages of δ 13C gneiss graphite for different terrains, ranging from -22.8‰ to -21.48‰, are consistent completely, and slightly lower than the average of -26±7‰ for organic matter from the world; 4) δ 13C for the protolith of marble is estimated over 2‰, which is consistent with the worldwide δ 13C carb positive excursion in the period of 2330~2060 Ma. Conclusions are drawn out as below: (1) geofluid is an important constraint on fractionation and homogenization of carbon isotopes, one of three carbon sources for graphite mineralization, one of five existing forms of carbon, and a key media and style of carbon circulation as well; (2) it is unbelievable that, only stemmed from δ 13C calcite-5‰, ore-forming fluid and material for hydrothermal deposits are derived from mantle, because many factors can cause hydrothermal δ 13C calcite equal to about -5‰; (3) the khondalite series in North China are mainly developed in Paleoproterozoic, most likely, in the period of 2300~2050 Ma.

关 键 词：孔达岩系 石墨矿床 碳同位素 流体作用 赋矿 

分 类 号：P619.262[天文地球—矿床学] P588.3[天文地球—地质学]