マントルウェッジ炭素の起源を考える  [in Japanese] The possible origin of carbon in mantle wedge  [in Japanese]

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Author(s)

Abstract

The occurrence of subduction-related fluid in mantle wedge is responsible for various geological phenomena in subduction zone. Identification of the fluid will especially constitute a valuable contribution to the interpretation of geophysical observations regarding subduction-related events. As a way to identify the fluid, it is effective to analyze fluid within peridotite xenoliths collected at subduction zone. We frequently observe fluid in the peridotite xenoliths as tiny fluid inclusions, which are composed of various volatiles. Though water or brine has been supposed as a dominant fluid composition in mantle wedge, the occurrence of CO<sub>2</sub> fluid is prominent above all. Density of CO<sub>2</sub> fluid in shallower mantle wedge is around 1.1 g/cm<sup>3</sup>, which is far lower than that of surrounding rocks, resulting in upward flow of the CO<sub>2</sub> fluid. That is, the CO<sub>2</sub> fluid within mantle wedge is an allochthonous component. Further studies on the distribution and origin of the CO<sub>2</sub> fluid would clarify circulation system of the fluid in mantle wedge. Here, we review studies examining geochemical aspects and the origin of the CO<sub>2</sub> fluid in peridotite xenoliths. Assuming an oxygen fugacity and temperature, carbon in shallower mantle wedge should exist as CO<sub>2</sub> fluid, which is fairly consistent with the observation of the peridotite xenoliths. Carbon isotopic composition of the CO<sub>2</sub> fluid suggests the possible occurrence of subduction-related carbonic fluid in mantle wedge. To make better elucidation of the origin of the fluid inclusions, it is necessary to combine it with any other isotopic indices such as nitrogen isotopes. Determination of the origin of the fluid will enhance our understanding on the mechanism of geological events in subduction zone.

Journal

  • Chikyukagaku

    Chikyukagaku 46(4), 243-255, 2012

    The Geochemical Society of Japan

References:  77

Codes

  • NII Article ID (NAID)
    110009577763
  • NII NACSIS-CAT ID (NCID)
    AN00141280
  • Text Lang
    JPN
  • Article Type
    REV
  • ISSN
    0386-4073
  • NDL Article ID
    024226032
  • NDL Call No.
    Z15-645
  • Data Source
    CJP  NDL  NII-ELS  J-STAGE 
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