【作者】 邓尚贤；

【导师】 朱炳泉； 王江海；

【作者基本信息】 中国科学院广州地球化学研究所 ， 地球化学， 2000， 博士

【摘要】 滇中地区位于扬子、华夏和印支三大块体的结合部位。对该区元古代基底岩群的变质作用和地球化学进行综合研究，不仅对于搞清元古代成矿作用机制和矿产资源的合理利用具有重要的经济意义，而且对于正确认识地球化学急变带的形成机制和确定华南块体在Rodinia古陆中的位置均具有重要的理论意义和科学价值。 通过矿物生长顺序、变质温压条件、石榴石生长环带和~39Ar－~40Ar定年研究，作者在直林群中十字石－蓝晶石等变带内获得了具有逆时针方向演化的P－T－t轨迹。该轨迹的进变质阶段与岛弧地区的岩浆增生过程密切相关，指示元谋地区在中－新元古代期间(1.0～0．85 Ga)存在岛弧构造环境；峰期之后的近等压冷却退变轨迹表明该地区未经历强烈的剥蚀，并可能有深部热流的持续供给。前人和作者对哀牢山－苍山群变质条件的研究表明该变质带内至少存在两期变质作用的叠加：早期为中压型，晚期为低压型。 元素地球化学研究表明，在苍山群和直林群中均存在两类变基性岩：一类为形成于P－MORB环境的变拉斑玄武岩；另一类为形成于板内拉张背景的变碱性玄武质岩墙。Nd-Sr-Pb 同位素体系特征进一步表明，变碱性玄武质岩墙形成于中-新元古代，其源区为 DMM与 EMⅡ端员的混合，反映板块俯冲作用的影响；变拉斑玄武岩形成于古-中元古代，其源区在苍山群为 DMM与 EMⅡ端员的混合，而在直林群为 DMM与 EMⅠ端员的混合，暗示在中元古之前二者分属不同的地球化学块体。 扬子块体西缘元古代基底的对比研究表明该区的变质基底主要形成于古-中元古代（2．0～1．6 Ga),但可能分属不同的块体；中－新元古代(1.0～0．8 Ga)的构造活动可能与Rodinia超级古陆的拼贴和裂解过程密切相关。更多还原

【Abstract】 Systematic studies on metamorphism and geochemistry of the Proterozoicbasements in Central Yunnan in the conjunct area among the Yangtze, Cathaysia andIndochina Blocks are very important not only for interpreting the mechanism of theProterozoic mineralization and using mineral resources but also for understandingthe formation of geochemical steep zones and affirming the location of the SouthChina Block within the Neoproterozoic Rodinia supercontinent.Based on the comprehensive studies of the mineral growth sequence, P-Tconditions of metamorphism, garnet growth zoning and ~39Ar-~40Ar dating, a cunter-clockwise P-T-t path has been reconstructed for a staurolite-kyanite isograde belt inthe Julin Group. The prograde path was related to the magmatic accretion in arcsettings, indicating the existence of an arc setting during the Mesoproterozoic-Neoproterozoic period. The retrograde near-isobaric cooling path after the peakmetamorphism reveals that rapid erosion did not occur and sustained heat suppliesfrom the upper-mantle were maintained after magmatic accretion in the Yuanmouarea. The metamorphic conditions estimated by the author, together with thepublished P-T data for the Ailao Shan-Cang Shan Groups show that al least twoepisodes of metamorphism occurred in this area, i.e., the early episode is themedium-pressure type, and the late episode is low-pressure type.The elemental geochemistry shows that two types of metabasites occurred in theCangshan and Julin Groups. One is the meta-tholeiite formed in a transitional P-MORB and arc tectonic environment, and the other is the meta-alkali basaltic dykeformed in a within-plate extension environment. The characteristics of the Nd-Sr-Pbisotope system further indicate that the meta-alkali basaltic dykes were originat6dfrom a mantle source mixed between two end-members of DMM and EM II sources,indicating that their source was reworked by subduction in the Mesoproterozoic-Neoproterozoic time; and the meta-tholeiites resulted from a mantle source, fOrmedby mixing between the DMM and EM lI end-members for the Cangshan GrouP but theDMM and EM l for the Julin Group in the P a l eo protero zo ic -MesoprotCrozo ic period,indicating that the two Gruops respectively belonged to the different blocks beforethe Mesoproterozoic time.The comparative studies of the Proterozoic basements in the westem margin ofthe YangtZe block show that the metamorphic basements were mainly formed duringthe Mesoproterozoic-Neoproterozoic period (2.0 ~ l.6 Ga) but might belong todiffereni blocks; the tectonic activities during the Mesoproterozoic-Neoproterozicinterval (l.0 ~ 0.8 Ga) may be related to the assembly and breakup of the RodiniasuPercoatinent.更多还原