Geological study of interaction between lithospheric mantle and asthenosphere

这项研究调查了在大陆裂谷和大洋中脊等地球伸展环境中发生的地幔熔融反应。研究领域包括日本北海道东八变质带中的荷罗曼橄榄岩杂岩和阿曼蛇绿岩的地幔剖面。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之间的反应。研究表明，霍罗曼橄榄岩在米尺度上具有高度的非均质性，即使在140米的剖面上也能观察到具有原始地幔成分的肥沃二辉橄榄岩和亏损的方辉橄榄岩。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。另一方面，阿曼蛇绿岩的地幔剖面在10千米的尺度上更加均匀。与霍罗曼橄榄岩140m剖面相比，阿曼地幔剖面25×15 km~2范围内的常量元素和微量元素丰度变化较小。阿曼蛇绿岩地幔剖面的成分变化主要由大洋中脊以下的部分熔融和熔体提取作用解释。然而，这项研究发现，阿曼蛇绿岩的变化比以前所知的要大得多。这些不均质性可能是由于大洋岩石圈地幔在Km尺度上的重熔和参考作用形成的。

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.