Research on interaction between slab melt and mantle peridotite : constraints from natural rocks and high pressure experiments

我们对热洋板块俯冲地区的火成岩进行了调查，并进行了高压实验，以澄清板块熔体与地幔橄榄岩之间的相互作用。主要研究成果如下：(1)在莫霍面深度为1 GPa时，对英安质熔体与橄榄石的相互作用进行了高压实验。用激光消融电感耦合等离子体质谱(LA-ICPMS)分析了运行产物中的微量元素组成。对得到的大于50微米的OPX和CPX晶体进行了分析，测定了约25种元素在辉石和长英质熔体之间的分配系数。到目前为止，OPX对轻稀土等不相容元素对长英质熔体的分配系数通常比对镁铁质熔体的分配系数大。然而，我们得到的值接近于OPX和镁铁质熔体之间的报道。(2)研究了日本西南弧近海沟附近的中新世岩浆活动。该岩浆活动与菲律宾海板块四国盆地的杨氏俯冲作用同时代。阐明了石榴石残渣高压熔融形成的长英质火成岩的区域分布。探讨了海沟附近形成的大量S型花岗岩熔体的成因。(3)研究了安第斯弧南火山带第四纪前缘火山样品的全岩成分沿弧线的变化。发现俯冲沉积流体对岩浆源区的贡献随着俯冲板块年龄的增加而增加。(4)对包括锆石在内的造岩矿物进行了LA-ICPMS分析，获得了微量元素分配系数和放射性年龄的新数据。

We have investigated igneous rocks from the regions where hot oceanic plate subducted, and carried out high pressure experiments, for the purpose of clarifying interaction between slab melt and mantle peridotite. The main results of our research is as follows.(1) We carried out high pressure experiments on the interaction between dacitic melt and olivine at 1 GPa corresponding with the depth of Moho. Trace element composition of run products were analyzed on laser ablation ICP-MS (LA-ICP-MS). Obtained opx and cpx crystals larger than 50 micrometers was analyzed and partition coefficients between pyroxenes and felsic melt on about 25 elements were determined. Partition coefficients of opx for incompatible elements including light REE to felsic melt are usually thought to be greater than those to mafic melt so far. However, we obtained values close to those reported for between opx and mafic melt.(2) Miocene near trench magmatism in the SW Japan arc was investigated. The magmatism was coeval with subduction of young hence hot Shikoku Basin of the Philippine Sea plate. Regional distribution of felsic igneous rocks formed by melting under high pressure with garnet residue was clarified. We also discussed the origin of voluminous S-type granitic melt formed in the region closed to the trench.(3) Along arc variation of whole rock compositions of the samples from Quaternary front volcanoes of the Southern Volcanic Zones in Andean arc was investigated. We found that contributions of the fluid derived from subducted sediment to the magma source increase as the age of the subducted plate beneath the volcano gets older.(4) Microanalysis of rock-forming minerals including zircon on the LA-ICP-MS was carried out, and obtained new data on the trace element partition coefficients and radiometric dating.