【作者】 苏犁；

【导师】 周鼎武；

【作者基本信息】 西北大学 ， 构造地质学， 2004， 博士

【摘要】 华南板块新元古代中期（～800 Ma）各种类型火成岩的广泛分布目前已引起地学界的普遍关注，这一时期岩浆活动的构造环境是地幔柱还是大陆边缘弧，在Rodinia超大陆构建、我国华南等陆块在Rodinia再造模型中的位置，以及Rodinia超大陆裂解事件的动力学机制等重要地质问题的讨论中至关重要。本文选择秦—祁—昆大陆造山带及两侧地块中的三个重要、且著名的镁铁—超镁铁岩体为解剖对象，在详细的野外地质工作基础上，通过岩石学、地球化学、矿物学、包裹体地质学和SHRIMP锆石U—Pb定年等综合研究和分析，探讨各岩体的成岩作用、成岩构造环境和成岩年龄，进而对比分析了相关古陆块的区域古构造背景及它们对新元古代构造岩浆事件性质和Rodinia超大陆裂解事件的示踪意义。主要研究进展如下： 1、通过元素地球化学分析，认为赋存超大型铜镍矿床的金川橄榄岩体的成岩作用受橄榄石的结晶所控制，现存岩体可能是上部岩石单元被剥蚀后的结晶于岩浆房底部的超镁铁质岩石单元。主量、微量和Nd同位素组成反映与岩体伴生的辉绿岩脉与金川超镁铁岩岩体的母岩浆为同源、不同成分的幔源熔浆，均源于富集地幔源区（εNd（t）≈—3），但金川超镁铁岩体显示了更强烈的地壳物质混染性，这一特征可能由其母岩浆具有的高温、富镁特性所造成。金川岩体中铬铁矿成分也反映TiO₂含量高，指示成岩环境为大陆板块内部。利用SHRIMP锆石U—Pb年代学分析技术，获得了含超大型铜镍硫化物矿床的金川橄榄岩体和伴生辉绿岩脉的确切成岩年龄分别为827±8 Ma和827±4 Ma，在误差范围内完全一致。据此提出，出露于龙首山隆起区的金川橄榄岩体等镁铁／超镁铁岩可能是与Rodinia裂解时期（约825 Ma）地幔柱岩浆作用（Li Z X，1999；Li X H，2003）相关的高镁苦橄质拉斑玄武岩浆结晶形成的深成侵入体。 2、通过详细的构造—岩相学分析，揭示扬子板块北缘汉南基性杂岩是一由超镁铁岩带、辉长岩带、辉长闪长岩带组成的大型层状堆晶杂岩体，并特别指出杂岩体底部有稳定的橄长岩类岩石堆晶层位，反映其母岩浆为非岛弧环境产生的“干”的玄武质熔浆，成岩作用表现为纯橄岩—橄长岩—橄榄辉长岩—辉长岩的斜长石优先结晶趋势。不同层位岩石元素地球化学对比研究发现，造成汉南层状基性杂岩被认为具有Zr、Hf负异常等似岛弧玄武岩成分特征的主要原因是由于杂岩体下部堆晶岩系中橄长岩、浅色辉长岩中斜长石的过量堆积所造成。同时发现，汉南基性杂岩辉长岩中斜长石、单斜辉石、斜方辉石及钛铁矿等矿物内普遍存在矿物出溶现象，且首次在斜长石中首次发现钛铁矿的出溶现象，表明其结晶于高温富钦熔浆。这些新的观察和研究，以及其中大型钒钦磁铁矿矿床（毕机沟钒钦磁铁矿床）的产出等，一致地反映汉南层状基性杂岩体是由地慢柱源高温、富Ti“干”熔浆结晶分异形成的层状基性杂岩体，而非形成于大陆边缘的岛弧低Ti“湿”熔浆结晶形成的深成岩体。 3.对倍受关注的北秦岭松树沟地区松树沟纯橄岩体和其周围石榴辉石岩和其退变质的（石榴）斜长角闪岩等深变质岩，以及富水杂岩体等的研究认为这些岩石并非“中新元古代蛇绿岩”的不同岩石单元。主要依据（1） 51刃又压尸错石U一Pb定年揭示，石榴辉石岩的变质年龄为501士10 Ma，富水基性杂岩体的成岩年龄为490士10 Ma，同为早古生代秦岭洋俯冲一闭合事件的产物。（2）石榴辉石岩/（石榴）斜长角闪岩等深变质岩与松树沟岩体的接触关系表现为似包裹状，而不呈构造岩片关系。（3）首次在松树沟纯橄岩体橄榄石等矿物中发现典型岩浆包裹体，同时其岩石组合表现出的特殊性（岩体出露面积95%以上为纯橄岩）、岩石结构构造、元素地球化学特征都显示出与蛇绿岩底部残留地慢岩不同的特征，进而提出该岩体是形成于大陆岩石圈壳慢过渡带的渗滤成岩纯橄岩体，其球粒陨石标准化的LREE富集分布形式等显示渗滤熔体为地慢柱源高镁熔体，依岩体内部巨晶辉石40Ar/39Ar高温坪年龄834士3 Ma（陈丹玲，2002），推测其也与约825 Ma的地慢柱源岩浆作用相关。 4、出露于扬子地块北缘、龙首山隆起和北秦岭构造块体的上述3个镁铁、超镁铁岩体研究表明:（1）.它们的成岩年龄在误差范围内基本一致:819士1 OMa、827士SMa和834士4Ma;（2）.虽从岩石组合、成因类型看它们存在明显差异，但成岩（矿）作用过程、元素地球化学指标等反映他们均不具有岛弧富挥发份“湿”熔浆结晶岩石的特征，而都显示母岩浆是地慢柱源的高温“干”熔浆。因此，中国中西部这3个重要（著名）的镁铁一超镁铁岩体均可能与Rodinia超大陆裂解早期（⁸25 Ma）强烈的岩浆活动（如华南板块等）相关，是地慢柱构造背景下产生的大量岩浆，短时期内上涌分别在壳慢过渡带渗滤改造地慢橄榄岩形成的纯橄岩体，以及侵入于深地壳和上部岩浆房结晶形成的深成侵入体。这些近同时形成的不同类型镁铁灌镁铁岩体的被识别，对示踪新元古代中期岩浆作用性质和Rod而a超大陆裂解的动力学机制等提供了新的、重要依据。更多还原

【Abstract】 The various igneous rocks of the middle Neoproterozoic (~ 800 Ma) that are well developed in the South China Platform have been received a great deal of attention to many researchers over the world. The nature of magmatic activities in this period, whether in mantle plume or in island arc of continental margin, directly constrains the re-construction and breakup of Rodinia supercontinent, as well as the location of the South China platform in the re-constructed model of Rodinia supercontinent. On the basis of field investigations, three Neoproterozoic mafic and ultramafic intrusions in Qinling-Qilian-Kunlun orogenic super-belt and adjacent areas were selected for comprehensive studies on petrology, geochemistry, mineral structures, melt and fluid inclusions and SHRIMP zircon U-Pb dating in this paper. Rock-forming processes and environments of the three intrusions have been analyzed. These studies play important roles in comparing analysis and exploring the regional tectonic settings in the Neoproterozoic era and in tracing information for tectono-magmatism associated with breakup of the Rodinia Supercontinent. Some achieves are as following:1. Jinchuan Cu-Ni-ore-bearing ultramafic intrusion occurs as lensoid or dyke-like bodies in NW direction in the Longshushan Rise, the south margin of Alax block. It consists of dunite, lherzolite, plagioclase lherzolite and olivine-pyroxenite. Zircon U-Pb SHRIMP analyses yield precise magmatic crystallization ages of 827? Ma for the ultramafic body and 828? Ma for the accompanied dykes. Petrological and geochemical studies reveal that the parental magma of Jinchuan Cu-Ni ultramafic body is high-Mg picritic tholeiite, and mafic dykes within or outside the body are also the products of tholeiitic intrusion from the same parental magma. Nd isotope, REE and trace elements reveal that this body and mafic dykes were sourced from a long-term enriched mantle (eNd(t) < -3). The results suggest that Jinchuan ultramafic body and the accompanied dykes are deep-seated intrusions related to within-plate mantle plume magmatic activity.2. Based on detailed tectono-petrographic investigations, this paper demonstrates that Hannan Complex is a large layered cumulate hybrid body that consists of ultramafic zone, gabbro zone and gabbro-diorite zone from the bottom to the top. Troctolite layers that steadily occur in the basal part of the complex reflect that theparental magma generates in a "dry" environment rather than the "wet" island arc, which is characterized by crystallization of plagioclase earlier than that of pyroxenes and shows a cumulate sequence of dunite-troctolite-olivine gabbro-gabbro from bottom to top. The negative anomaly of Zr and Hf in some rocks can be readily explained as excessive cumulation of plagioclase in troctolite and light-colored gabbro in the low part of the cumulate sequence, because Kd of Zr and Hf between plagioclase and melt is much lower than that between pyroxene and melt. Discovery of ilmenite exsolution lamellae in plagioclase suggests that minerals crystallized from a high-T and Ti-rich parental magma. Combining all aspects of fact, for instance, the LREE-enriched patterns of all rocks, the E-MORB-affinity trace element spidergram shown by most cumulate gabbro and gabbroic diorite, and occurrence of the large ore deposit of V-bearing titanic magnetite, we can conclude that Hannan complex crystallizes from a high-temperature magma at an environment of mantle plume.3. Songshugou dunite body and accompanied garnet-pyroxenite and amphibolite and Fushui complex body in north Qinling Orogenic Belt have received a great deal of attention. Using CL and ion microprobe (SHRIMP) techniques, this study obtains a high-pressure metamorphic age at 501+ 10 Ma for garnet pyroxenite (Sm-Nd isochron age is 1030+46Ma for the protolith) near Songshugou dunite body and a magmatic age at 490+10 Ma for Fushui island-arc gabbro-diorite complex. The two concordant ages constructed the Early Paleozoic tectonic pattern of plate subduction and collision in the North Qin更多还原