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991.
Following previous publication of majorminor elementdata, this paper presents rare earth element (REE) data forheterogeneous (chemically zoned) garnets belonging to the peridotitesuite of mantle xenoliths from the Jagersfontein kimberlitepipe, South Africa. The rim compositions of the garnets in thehighest temperaturepressure (deepest) deformed peridotitesshow a typical megacryst-like pattern, of very low light REE(LREE) increasing through the middle REE (MREE) to a plateauof heavy REE (HREE) at c. 20 times chondrite; these compositionswould be in equilibrium with small-volume melts of the mid-oceanridge basalt (MORB) source (asthenosphere). With decreasingdepth the garnet rims show increasing LREE and decreasing HREE,eventually resulting in humped relative abundance patterns.A set of compositions is calculated for melts that would bein equilibrium with the garnet rims at different depths. Theseshow decreasing relative abundance of each REE from La to Lu,and the La/Lu ratio of the melts increases with decreasing depthof formation. Modelling of the effects of crystal fractionationshows that this process could largely generate the sequenceof garnet rim and melt compositions found with decreasing depth,including the humped REE patterns in high-level garnets. Consideringthe behaviour of majorminor elements as well as REE,a process of percolative fractional crystallization is advocatedin which megacryst source melts percolate upwards through peridotitesand undergo fractionation in conjunction with exchange withthe peridotite minerals. The initial megacryst melt probablyincludes melt of lithospheric origin as well as melt from theMORB source, and it is suggested that the process of percolativefractional crystallization may form a variety of metasomaticand kimberlitic melts from initial megacryst melts. Repeatedmetasomatism of the lower lithosphere by such differentiatingmelts is suggested by consideration of garnet core compositions.Such metasomatism would progressively convert harzburgites tolherzolites by increasing their CaO content, and this may accountfor the fact that the Cr-rich diamondgarnet harzburgiteparagenesis is commonly preserved only where it has been encapsulatedin diamonds. KEY WORDS: cratonic lithosphere; garnet zoning; mantle xenoliths; megacryst magma; metasomatic melt 相似文献
993.
994.
山东黄河北煤田岩浆岩特征及其对煤层煤质的影响 总被引:3,自引:0,他引:3
论述了山东省黄河北煤田岩浆岩特性特征、空间分布特点及其对煤层煤质的影响。认为三层岩浆岩是由不同时期从两个方向侵入到本区的,对煤层煤质都有不同程度的影响,形成煤的变质分带。 相似文献
995.
996.
997.
我国主体功能区划的有关理论探讨 总被引:3,自引:0,他引:3
总结了当前国内关于主体功能区划的理论研究、与主题规划的区别及联系、区划的空间尺度效应、国外经验借鉴、区划的方法论等基本问题所取得的最新进展,指出了当前研究的薄弱环节和重点攻破方向.研究认为,区域发展的空间结构理论和人地关系地域系统理论是主体功能区划的核心理论基础,空间均衡模型是该理论基础最为直接的应用,重点深刻解析了空间尺度效应和区域功能属性对于主体功能区划指标因子体系的构建、指标间的优化组合所带来的影响,加强GIS的空间叠置和聚类等空间分析技术在主体功能区划中的应用,可以较好地解决空间尺度与区域功能属性之间的矛盾为区域功能区的定位所带来的影响. 相似文献
998.
喜马拉雅淡色花岗岩带伟晶岩的富铍成矿特点及向更高处找锂 总被引:1,自引:0,他引:1
喜马拉雅淡色花岗岩作为新识别的稀有金属成矿区带,已发现以Be-Nb-Ta(Sn-W)组合为主矿化且已形成大型矿床,如错那洞,但仅在为数不多的几处伟晶岩见到锂辉石,尚未发现工业锂矿床。因此,有必要剖析该区伟晶岩成矿(尤其Be同Li的对比)特点、条件及可能潜力,并与国内其他稀有金属矿带进行对比分析,从而推动喜马拉雅伟晶岩稀有金属矿床尤其是锂矿的发现。该区伟晶岩母体淡色花岗岩与华南稀有金属矿化花岗岩类似,显示高的分异程度但较窄的演化区间,并且熔体具有高的Li浓度。在印亚大陆碰撞带复杂的构造-变质-深熔作用下产生了多期次的岩浆活动,尤其新喜马拉雅期巨量的岩浆可为伟晶岩的形成、远距离迁移分异及成矿提供有利的热和物质基础。基于含Li伟晶岩形成于"远"母体、"高"海拔的特点,提出区域构造层位的上部或更高海拔地区以及淡色花岗岩岩体外侧远端的围岩内将可能是含锂伟晶岩的就位空间与找矿重点地段。 相似文献
999.
Garnet porphyroblasts in sillimanite‐bearing pelitic schists contain complex textural and compositional zoning, with considerable variation both within and between adjacent samples. The sillimanite‐bearing schists locally occur in regional Barrovian garnet zone assemblages and are indicative of a persistent lack of equilibrium during prograde metamorphism. Garnet in these Dalradian rocks from the Scottish Highlands preserves evidence of a range of metamorphic responses including initial growth and patchy coupled dissolution–reprecipitation followed by partial dissolution. Individual porphyroblasts each have a unique and variable response to prograde metamorphism and garnet with mainly flat compositional profiles co‐exists with those containing largely unmodified characteristic bell‐shaped Mn profiles. This highlights the need for caution in applying traditional interpretations of effective volume diffusion eliminating compositional variation. Cloudy garnet with abundant fluid inclusions is produced during incomplete modification of the initial porphyroblasts and these porous garnet are then particularly prone to partial replacement in sillimanite‐producing reactions. The modification of garnet via a dissolution–reprecipitation process releases Ca into the effective whole‐rock composition, displacing the pressure–temperature positions of subsequent isograd reactions. This represents the first report of internal metasomatism controlling reaction pathways. The behaviour of garnet highlights the importance of kinetic factors, especially deformation and fluids, in controlling reaction progress and how the resulting variability influences subsequent prograde history. The lack of a consistent metamorphic response, within and between adjacent schists, suggests that on both local and regional scales these rocks have largely not equilibrated at peak metamorphic conditions. 相似文献
1000.
河南嵩县小南沟金矿床矿体剥蚀深度评价 总被引:4,自引:0,他引:4
河南省嵩县小南沟金矿是产于熊耳群火山岩中的构造蚀变岩型矿床,矿化受控于近南北向断裂构造,工业矿体主要产于其中NE向的含矿断裂中。系统的矿床地质地球化学研究发现,矿体横剖面和纵剖面上的都存在明显的元素分带。纵投影剖面的地球化学反映出Au、Ag、Cu、Pb、Zn、As、Sb和W等元素均形成向上开口的“U”形,含量上高下低,向深部晕的规模逐渐减小,强度减弱,垂向上具有尾晕的地球化学特点。与Au有关的元素 相似文献