Geological study of interaction between lithospheric mantle and asthenosphere

本研究探讨了发生在地球伸展环境中的地幔熔融反应，如大陆裂谷和洋中脊。研究领域包括日本北海道日高变质带的霍罗曼橄榄岩杂岩和阿曼蛇绿岩的地幔部分。根据地幔橄榄岩及其组成矿物中稀土等微量元素的空间变化，定量模拟了岩石圈地幔与上升软流圈熔体的反应。研究表明，霍罗曼橄榄岩在米尺度上具有高度的不均匀性，即使在140米的剖面上也观察到具有原始地幔成分的肥沃二辉橄榄岩和亏损的辉橄榄岩。不相容元素的变化更加复杂，反映了软流圈熔体流动的交代作用。而阿曼蛇绿岩地幔剖面在10千米尺度上更为均一。阿曼地幔剖面25 × 15km^2范围内常量和微量元素丰度的变化小于霍罗曼橄榄岩140m剖面。阿曼蛇绿岩地幔剖面的成分变化主要是由洋中脊下的部分熔融和熔融萃取作用所解释的。然而，这项研究发现阿曼蛇绿岩的变化比以前所知的要大。这些不均匀性可能是由千米尺度的大洋岩石圈地幔重熔和再肥化作用形成的。

This research investigated the mantle-melt reaction that occurs at Earth's extensional environments such as continental rift and mid-ocean ridge. The studied fields includes the Horoman peridotite complex in the Hidaka Metamorphic Belt, Hokkaido, Japan and the mantle section of the Oman ophiolite. On the basis of spatial variation of trace elements such as rare earth elements in the mantle peridotites and in their constituent minerals the reaction between lithospheric mantle and ascending asthenospheric melt was quantitatively modeled. The study showed that the Horoman peridotite are highly heterogeneous in a meter scale so that even in the 140 meters section fertile Iherzolite with primitive mantle composition and depleted harzburgite are observed. The variation of incompatible elements are further complicated thereby showing the metasomatism by asthenospheric melt flow. On the other hand, the mantle section of the Oman ophiolite are more homogeneous in the scale of ten kilo meters. Abundances of major and trace element in the area of 25 x 15km^2 in the Oman mantle section are less variable than those in the 140m section of the Horoman peridotite. Compositional variations in the mantle section of the Oman ophiolite are mainly explained by partial melting and melt extraction beneath mid-ocean ridge. However, this research found greater variations in the Oman ophiolite than it has been known before. These heterogeneities may have formed by remelting and refertilization of oceanic lithospheric mantle in a scale of km.