Geochemical Effects of Deep Subduction of Oceanic Crust: An Experimental Study of 4-20 GPa

9706517 RAPP这项关于大洋地壳深俯冲的地球化学效应的实验研究包括两个部分。第一个方面是对英云闪长岩-奥长花岗闪长岩深成和克拉通化相互关联的过程施加实验限制。在900-1200oC的压力范围内，对含水的天然玄武岩进行了一系列多锤实验，以补充现有的1-3 Gpa的实验数据。目的包括确定这一范围内的玄武岩湿固相线，确定含水熔体-榴辉岩RESITE组合中的物相组成，估计微量元素矿物-熔体分配系数，以约束部分熔融榴辉岩残留物的地球化学特征。该提案的第二个方面旨在研究洋壳在从岛弧体制俯冲到过渡带时所经历的地球化学变化，同样是通过在多砧板装置中对含水玄武岩进行相平衡实验。这方面将通过定义P-T范围为4-20 Gpa和900-1300oC的含水玄武岩的一般相关系来解决，然后重点研究石榴石、单斜辉石及其在天然玄武岩成分中的固溶体中的微量元素系统学作为压力的函数。

9706517 Rapp This experimental study on the geochemical effects of deep subduction of the oceanic crust has two parts. The first aspect is to place experimental constraints on the linked processes of tonalite-trondhjemite granodiorite plutonism and cratonization. A series of multi-anvil experiments on hydrous natural basalts will be conducted in the pressure range 4-8 GPa at 900-1200oC, to complement existing experimental data at 1-3 GPa. Objectives include defining the wet basalt solidus in this range, determining the compositions of the phases in the hydrous melt-eclogite restite assemblage, and estimating the trace element mineral-melt partition coefficients in order to constrain the geochemical characteristics of eclogite residues of partial melting. The second aspect of the proposal aims to examine the geochemical changes oceanic crust undergoes as it subducts beyond the island arc regime into the transition zone, again by conducting phase equilibria experiments on hydrous basalt in the multi-anvil apparatus. This aspect will be addressed by defining the general phase relations for hydrous basalt in the P-T range 4-20 GPa and 900-1300oC, and then focusing on trace element systematics in garnet, clinopyroxene, and their solid solutions in natural basalt compositions as a function of pressure.