Geological Study of Partial Melting of Mafic Rock-Bearing Heterogeneous Upper Mantle

本文在野外产状和基性岩中主微量元素丰度的基础上，研究了霍罗曼橄榄岩发生的部分熔融和幔-熔反应。研究结果表明，霍罗曼橄榄岩的ⅰ型基性麻粒岩在约8000万年前经历了重熔事件。基性层中心可能为石榴石斜辉石岩，边缘为与中心平衡的原始熔体。在荷罗曼橄榄岩隆升过程中，两者均变质为基性麻粒岩。在这项研究之后，我在2004-2005年对阿曼蛇绿岩的地幔剖面进行了研究，以了解海洋上地幔部分熔融形成的化学非均质性。对橄榄岩样品进行了详细的矿物成分分析，发现存在与低温剪切带平行的地幔段斜切的高耐火橄榄岩带。认为流体沿剪切带流动导致固相温度降低，重熔锆土形成耐火带。第三，利用ODP第209期14°N ~ 16°N大西洋中脊的橄榄岩样品，直接考察了大洋上地幔的非均质性。对1271 Site B孔钻孔岩心的显微光学观察和矿物组成分析表明，上地幔最浅层的熔融流动和幔-熔反应形成了浸渍灰岩、橄榄辉长岩、辉长岩和橄榄长岩等一系列岩性，是介于灰岩和基性熔体之间的杂岩。

This research investigated the partial melting and mantle-melt reaction occurred in the Horoman peridotite on the basis of field occurrence and major and trace element abudances in mafic rocks. As a result of study, Type I mafic granulite of the Horoman peridotite were experienced remelting event about 80 million years ago. The center of the mafic layer may have been garnet clinopyroxenite while the margin was a primitive melt in equilibrium with the center in terms of trace elements. Both are now metamorphosed into mafic granulite during uplifting of the Horoman peridotite.Following this study, I investigated the mantle section of the Oman ophiolite in 2004-2005 to understand formation of chemical heterogeneity by partial melting of oceanic upper mantle. Detailed analysis of mineral compositions of peridotite samples revealed the presence of highly refractory peridotite zone that obliquely crosscuts the mantle section parallel to the low temperature shear zone. It is advocated that the refractory zone formed by remelting of harzburgite due to reduction of solidus temperature as a result of fluid flow along shear zone.Third, heterogeneity of oceanic upper mantle was directly examined using peridotite samples drilled at Mid-Atlantic Ridge in 14°N〜16°N during ODP Leg 209. Optical investigation under microscope and analysis of mineral compositions for drilled cores from Hole B, Site 1271showed that melt flow and mantle-melt reaction in shallowest upper mantle produced a series of lithologies such as impregnated dunite, olivine gabbro, gabbronorite and troctolite as hybrid rocks between dunite and mafic melt.