【作者】 陈振宇；

【导师】 陈毓川； 王登红；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2008， 博士

【摘要】 金红石、磷灰石、绿帘石等矿物是中国大陆科学钻探（CCSD）主孔岩心及苏鲁.大别超高压变质岩中常见的副矿物,主孔岩心的脉体中还存在许多特殊的脉体矿物,它们不仅是超高压变质过程即大陆深俯冲—折返过程的重要“见证”矿物,而且是超高压变质岩中一些重要的微量元素如高场强元素（HFSE）、稀土元素（REE）、挥发性组分（F、Cl、OH）及Sr、U、Th、Pb等大离子亲石元素（LILE）的重要载体。对这些副矿物和脉体矿物的研究,对超高压变质岩的矿物学、元素地球化学和变质流体演化具有重要意义,是认识板块俯冲和折返过程地球动力学的一个重要窗口。然而,目前对这些矿物的相关研究还都比较薄弱。本论文工作选择以CCSD主孔及苏北.大别地表超高压变质岩中的这些副矿物和脉体矿物为主要研究对象,通过详细的岩相学、岩石化学、矿物化学等研究,对这些副矿物在超高压变质作用及大陆深俯冲—折返过程的指示意义进行了较为深入的探讨,在以下几个方面取得新的认识:1.在矿物学方面,首次较为系统地研究了超高压变质岩中的金红石、磷灰石、绿帘石等副矿物,并通过详细的岩相学和矿物化学研究,首次在苏鲁-大别超高压变质岩中发现了一些具有特殊成分/结构的矿物或矿物组合,如在榴辉岩金红石中发现了刚玉、菱镁矿、高钛黑云母和石榴石矿物包裹体,在片麻岩中发现了Nb-Fe金红石和具有自形环带结构的高Si-Y磷灰石,在榴辉岩和片麻岩中发现了具有类似岩浆成因的自形生长环带结构的绿帘石/褐帘石,在片麻岩的脉体中发现了大量富含稀土元素REE（包括Y）、高场强元素HFSE（Nb、Ta、Zr、Ti）、大离子亲石元素LILE（K、Th、U、Sr、Ba）,以及挥发性组份（CO₂、F、P、S）的特殊矿物,丰富并提升了超高压变质岩的矿物学研究。2.在元素地球化学方面,通过对金红石、磷灰石、绿帘石、脉体矿物等详细的矿物化学研究,提出榴辉岩金红石中的Cr含量与其全岩的MgO含量成正比,而与其原岩是否为堆晶岩无必然关系;认为流体参与下的扩散作用和退变质作用是苏鲁-大别榴辉岩中金红石Zr含量温度普遍偏低的主要原因,金红石中的Zr含量记录的是再平衡后的温度而不是峰期变质温度。指出LILE和LREE在退变质流体作用下表现出较大的活动性,而HREE和HFSE在挥发性元素/基团大量存在时,也可具有较强的活动性。这些认识加深了对HFSE、REE、LILE及挥发性组分在超高压变质过程中地球化学行为的理解。3.在变质流体演化上,通过系统地统计、分析了CCSD主孔5000m岩心中脉体的数量、产出和分布特征,并据此提出超高压变质的不同阶段存在不同程度和不同方式的流体活动。通过对副矿物和脉体矿物的分析,提出榴辉岩的退变质流体很可能是一种含NaCl和硅酸盐的水溶液,片麻岩退变质过程中存在富含REE、HFSE、挥发性组分及Ba、Sr、Th、U等LILE的特殊流体;提出变质流体在进变质-峰期-退变质过程中的氧逸度状态可能经历了从氧化-还原-氧化的复杂变化。从而深化了对超高压变质过程中流体活动方式及性质的认识。4.在矿床学上,在前人的研究基础上,指出榴辉岩型金红石矿床的最主要控矿因素为原岩性质和超高压变质作用。与新元古代裂谷岩浆作用有关的富钛基性原岩是榴辉岩型金红石矿床形成的物质基础,三叠纪高压—超高压（＞1.5GPa）区域变质作用是苏鲁榴辉岩型金红石矿床形成的必要条件。更多还原

【Abstract】 Rutile, apatite and epidote are common accessory minerals in Ultra-high pressure metamorphosed (UHPM) rocks from Chinese Continental Scientific Drilling (CCSD) main-hole and Sulu-Dabie terrene, besides, there are some special vein minerals in various veins in CCSD drill core, these accessory minerals and vein minerals are not only the "witness" of UHPM and continental subduction-exhumation, but also the most important carrier for some significant trace elements, such as High Field Strenth Elements (HFSE), Rare Earth Elements (REE), some Large Ion Lithophile Elements (LILE, eg. Sr, Ba, Th, U, Pb) and volatile elements (eg. F, Cl, S, C, P, OH). Therefore, study on these accessory minerals and vein minerals will have significant implication to mineralogy, elemental geochemistry, and the evolution of metamorphic fluid. However, there are few related studies about these minerals up to date. This dissertation focus on rutiles, apatites epidotes and vein minerals from CCSD drill core and outcrops of Sulu-Dabie UHPM rocks, by detailed study of petrography, petro-chemistry, and mineral-chemistry, the implication of these minerals to UHPM and continental subduction-exhumation were discussed. Major conclutions from this study can be summarized as following:1. On mineralogy, rutiles, apatites, epidotes and vein minerals from UHPM rocks were firstly and systematically studied, by detailed petrography and mineral-chemistry investigation, some mineral or mineral assemblage with special composions or texture were firstly found in UHPM rocks from Sulu-Dabie, for example, corrudum, magnesite, high-Ti biotite and garnet were found as inclusions in rutiles from eclogites, Nb-Fe rutile and zoned Si-Y apatite were found in gneiss, epidote / allanite with euhedral zones like magmatic genesis were found in elogites and gneiss, a lot of minerals with high REE, HFSE, LILE and volatiles were found in veins of gneiss. These founds enrich and improve the mineralogy study in UHPM rocks.2. On elemental geochemistry, the understanding of geochemical behavious of REE, HFSE, LILE and volatiles during UHPM were deepened by detailed mineral-chemistry study of rutiles, apatites epidotes and vein minerals. It is pointed out that Cr content of rutile in eclogite is positively related to the MgO content of bulk rock, and the protolith of rutiles with high Cr content is not necessarily meta-cumulates. It is considered that diffusion and retrogression with retrograde fluid are responsible for the lower of Zr content of rutile in eclogites from Sulu-Dabie, and the Zr-in-rutile recorded temperatures of re-equilibium but not peak metamorphism. LILE and LREE show high activity in retrograde fluid, however, HREE and HFSE will also show activity only if there are abundance of volatiles dissolved in fluid.3. On the evolution and characteristics of metamorphic fluid, the number, occurrence and distribution of veins in CCSD drill core were systematically counted and analyzed to deduce that the fluid activaty at various stage have various extents and manners. By analyzing the accessory and vein minerals, it is point out that the retrograde fluid in eclogites may be hydrous solution with NaCl and silicate, and the retrograde fluid in gneiss are rich in REE, HFSE, LILE and volatiles. The redox state of metamorphic fluid may experienced oxidation→reduction→oxidation during prograde-peak→early retrogration→amphibolite facies.4. On metallogeny, based on previous study, it is point out that the most important factors that control the mineralization of eclogitic type rutile deposit are protoliths property and UHPM. Ti-rich basaltic protoliths related to the rift magmatism in neoproterozoic are the material foundermatal for rutile deposit, high to ultra-high pressure (>1.5GPa) are prerequisite for this ore type.更多还原