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Title :海洋地殻の構成と火成活動
Title alternative :Constitution of Oceanic Crust and Ocean Ridge Magmatism
Authors :宮下, 純夫
前田, 仁一郎
Publisher :東京地学協会
Issue Date :2003
Journal Title :地学雑誌
Volume :112
Issue :5
Start Page :668
End Page :683
ISSN :0022-135X
Abstract :Volumetrically, magmatism at spreading axes occupies more than 60% of present day volcanism, and oceanic crust generated there covers more than two thirds of earth surface. Therefore, studies of the oceanic crust and magmatism at spreading axes yield significant insights to understanding earth evolution. Recent studies on oceanic crust through drilling, submersible surveys, dredging and geophysical exploration indicates that there is considerable variation in lithologic composition and stratigraphic sequences in oceanic crust that is dependent on the spreading rate. Typical ophiolitic stratigraphic sequences are expected to occur at fast-spreading ridges, while complicated and variable stratigraphic successions are encountered at slow-spreading ridges. Mid-Ocean Ridge Basalts (MORBs) are generally regarded as having comparatively uniform compositions. Major element compositions of MORB corrected for low-pressure fractionation show a global systematic variation correlated to axial highs, which can be ascribed to the degree of partial melting. However, the composition of MORB should represent a final product of magmas whose compositions have been greatly modified during ascent through mantle peridotite, by crustal fractionation that produced lower crust (ultramafic to gabbroic cumulates), and by mixing in a melt lens in shallow crust. Therefore, to fully understand MORB petrogenesis it is necessary to study the total magmatic system, which includes surface lavas, dike complexes, plutonic cumulates extracted from melts, and residual mantle. Recent results from the MARK area of the Mid-Atlantic Ridge, the Atlantis bank of the Southwest Indian Ridge and Hess Deep near the East Pacific Rise strongly suggest that source mantle is heterogeneous and that the magmatic system differs significantly depending on the spreading rate.
Keywords :ocean ridge
spreading rate
oceanic crust
Type Local :学術雑誌論文
Language :jpn
Format :application/pdf
URI :http://hdl.handle.net/10191/18247
fullTextURL :http://dspace.lib.niigata-u.ac.jp/dspace/bitstream/10191/18247/1/112_5_668-683.pdf
Appears in Collections:10 査読済論文 = Postprint

Please use this identifier to cite or link to this item: http://hdl.handle.net/10191/18247