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

抄録

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.