希ガス同位体比とマグマ源の特性 : 現状と課題

概要

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Since noble gases are chemically inert and include both radiogenic (+ nucleogenic) and stable isotopes, they are quite useful to identify the characteristics of magma sources, which were established on global scale and affected mainly by time-integrated effects through the history of the Earth. Based on noble gas isotope signatures, at least four different components have been classified: M (MORB) source, P (plume) source, A (atmospheric) component and C (crustal) component. Other types such as island arc type source (Ac) can be explained by the mixture of them. However, there remain problems concerning their definite values which are significant to evaluate their distribution quantitatively in the Earth's interior. To infer those values, it is essential to evaluate the secondary effects properly which occur during magma transportation and extrusion and affect their primary signatures. In this paper, examples of secondary contamination by groundwater and sea water on the noble gas signatures are shown for volcanic lavas of the Unzen Volcano and a MORB glass, respectively. Further, coupled or decoupled characteristics are discussed among each isotope systematics.
特定非営利活動法人日本火山学会の論文
1997-04-25