Lithospheric Metasomatism

在过去的几年里，通过理论和应用地球物理和地球化学计划，我们对上地幔的理解已经突破了新的领域。虽然上地幔的结构和组成仍然是争论的话题，尽管地球物理和地球化学模型之间仍然存在相当大的差距，但次大陆、次克拉通上地幔的差异正在接近共识，主要是因为模型可能受到上地幔来源的捕虏体套装的直接测量的地球化学限制。确定了将进一步制约上地幔矿物学、岩石学和地球化学的五个研究课题，包括与上地幔碱性和玄武岩岩浆的地球化学模拟有关的大离子亲石元素的源区和储存库。重点是交代成因的钛酸盐矿物和伴生硅酸盐，以及在上地幔交代中演化的榴辉岩和钻石。在非洲、中国、委内瑞拉、西伯利亚和澳大利亚发现了区域岩石圈交代和奇异的钛酸盐。随着钛酸盐作为钻石包裹体的开创性发现，以及涂层钻石中的LILE的发现，需要修订钻石起源的模型。本研究采用的主要技术有光学显微镜和扫描电子显微镜、电子和离子探针以及XRF分析。这些结果将从矿物学、岩石学和地球化学学的角度改进克拉通以下岩石圈的定义。

New frontiers have been broken within the past years in our understanding of the upper mantle through theoretical and applied geophysical and geochemical programs. While the structure and composition of the upper mantle remain topics of debate, and whereas a considerable gap continues to exist between geophysical and geochemical models, discrepancies for the subcontinental, subcratonic upper mantle are approaching consensus, mainly because models can be geochemically constrained by direct measurements of upper mantle-derived xenolith suites. Five research topics are identified that will further constrain the mineralogy, petrology and geochemistry of the upper mantle, including source regions and repositories for large-ion- lithophile-elements relevant to the geochemical modelling of alkali and basaltic magmas in the upper mantle. The emphasis is the titanate minerals and associated silicates of metasomatic origin, and of eclogites and diamonds that have evolved in upper mantle metasomes. Regional lithospheric metasomatism and exotic titanates are recognized in Africa, China, Venezuela, Siberia and Australia. With the seminal discoveries of titanates as diamond inclusions, and of LILE in coated diamonds, revised models for the genesis of diamond are required. Principal techniques to be employed in this study are optical and SEM microscopy, electron and ion-probe, and XRF analyses. The results will provide an improved definition of the subcratonic lithosphere, mineralogically, petrologically and geochemically.//