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Geochemical Journal, Vol. 46 (No. 3), pp. e21-e26, 2012

EXPRESS LETTER

Estimation of sulfur, fluorine, chlorine and bromine fluxes at Mid Ocean Ridges using a new experimental crushing and extraction method

Takanori Kagoshima,1 Naoto Takahata,1 Jinyoung Jung,1 Hiroshi Amakawa,2 Hidenori Kumagai3 and Yuji Sano1

1Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8564, Japan
2Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan
3Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan

(Received February 28, 2012; Accepted April 7, 2012; Online published May 10, 2012)

Abstract: We measured helium-3 (3He), sulfur (S), fluorine (F), chlorine (Cl) and bromine (Br) concentrations in vesicles of Mid Ocean Ridge Basalts (MORBs) and Back-Arc Basin Basalts (BABBs). The aim of this study was to characterize the MORB-source composition and to estimate the fluxes of S, F, Cl and Br from the mantle. A newly developed gas extraction method called the "Frozen Crushing Method" was applied. Measured concentrations in vesicles were (4-31) × 10-15 mol/g of 3He, (20-420) × 10-9 mol/g of S, (60-5000) × 10-9 mol/g of F, (160-450) × 10-9 mol/g of Cl and (10-1300) × 10-9 mol/g of Br. We estimated global fluxes of S, F, Cl and Br at Mid Ocean Ridges using the molar ratio of each element on the 3He in the samples and the known mantle 3He flux of 527 mol/yr. Estimated fluxes using element concentrations measured in vesicles are (1.2 ± 0.7) × 1010 mol/yr of S, (1.4 ± 1.0) × 1011 mol/yr of F, (1.4 ± 0.5) × 1010 mol/yr of Cl and (3.1 ± 2.8) × 1010 mol/yr of Br. In addition, fluxes calculated on the basis of estimated concentrations in the bulk basalts are (1-26) × 1010 mol/yr of S, (2-120) × 1011 mol/yr of F, less than (2-120) × 1010 mol/yr of Cl and (4-240) × 1010 mol/yr of Br.
Key words: degassing flux, sulfur, halogen, helium, Mid Ocean Ridge basalts


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