The origin of mantle wedge carbon

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H04079
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: Hokkaido University
• Principal Investigator: Yamamoto Junji 北海道大学, 総合博物館, 准教授 (60378536)
• Co-Investigator(Kenkyū-buntansha): 鍵 裕之 東京大学, 大学院理学系研究科(理学部), 教授 (70233666) ; 石橋 秀巳 静岡大学, 理学部, 准教授 (70456854)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 炭素 / 同位体 / 流体包有物 / 沈み込み帯 / マントルウェッジ

Outline of Final Research Achievements

Carbon isotope ratio is an important indicator for examining the origin of a material. Organic matters have subducted into the Earth by plate tectonics, and they could have affected carbon reservoir in the Earth’s deep interior. Investigation of carbon isotopic composition of deep-derived materials tells us the material circulation between deep and surface of the Earth.
Carbon has often been observed as CO2 fluid included in minerals, which is called a fluid inclusion. The rocks entrained by ascending magma from mantle also have CO2 fluid inclusions. Adopting a spectrometer with 2000 mm focal length, we established the new measurement method for carbon isotope ratios, which has both high spacial resolution and spectral resolution. This method is applicable to a tiny CO2 fluid inclusion.

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

分光装置を用いた同位体分析法は吸光分析では既に実用化されているが，顕微ラマン分光分析を適用できれば，ナノメートルサイズの物質でも分子振動情報を得ることができる．この特性を利用し，サブミクロンサイズの領域に濃縮固化させた炭素や酸素，硫黄，窒素等の同位体分析にも波及する可能性が考えられる．本研究により，液体二酸化炭素の炭素同位体分析は実用段階に達したが，固体試料や炭素以外の元素への適用には何段階かの工夫が必要である．しかし，この手法の開発に成功すれば，レーザー掘削等で回収した局所物質の同位体分析が可能になるため，環境科学分野全体に浸透していくであろう．