Recycling of water, carbon, and sulfur during subduction of serpentinites: A stable isotope study of Cerro del Almirez, Spain

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• 作者：Jeffrey C. Alt^a ; ^{jalt@umich.edu} ; Carlos J. Garrido^b ; ^{carlos.garrido@csic.es} ; W.C. Shanks III^c ; ^{pshanks@usgs.gov} ; Alexandra Turchyn^d ; ^{avt25@cam.ac.uk} ; José ; Alberto Padró ; n-Navarta^e ; ^{padron@ugr.es} ; Vicente Ló ; pez Sá ; nchez-Vizcaí ; no^b ; ^f ; ^{vlopez@ujaen.es} ; Marí ; a Teresa Gó ; mez Pugnaire^b ; ^e ; ^{teresa@ugr.es} ; Claudio Marchesi^b ; ^{claudio@iact.ugr-csic.es}
• 关键词：subduction ; stable isotopes ; serpentinite ; volatiles ; geochemical cycling
• 刊名：Earth and Planetary Science Letters
• 出版年：2012
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：15 April, 2012
• 卷：327-328
• 期：Complete
• 页码：50-60
• 文件大小：1270 K

摘要

We use the concentrations and isotope compositions of water, carbon, and sulfur in serpentinites and their dehydration products to trace the cycling of volatiles during subduction. Antigorite serpentinites from the Cerro del Almirez complex, Spain, contain 9-12 wt.%H₂O and 910 卤 730 ppm sulfur, and have bulk 未¹⁸O values of 8.6 卤 0.4鈥? 未D = 鈭?#xA0;54 卤 5鈥? and 未³⁴S = 5.0鈥? consistent with serpentinization at temperatures of ~ 200 掳C by seawater hydrothermal fluids in a seafloor setting. The serpentinites were dehydrated to chlorite-harzburgite (olivine + orthopyroxene + chlorite) at 700 掳C and 1.6-1.9 GPa during subduction metamorphism, resulting in loss of water, and sulfur. The chlorite-harzburgites contain 5.7 卤 1.9 wt.%H₂O, and have bulk 未¹⁸O = 8.0 卤 0.9鈥? and 未D = 鈭?#xA0;77 卤 11鈥? The rocks contain 650 卤 620 ppm sulfur having 未³⁴S = 1.2鈥? Dehydration of serpentinite resulted in loss of 5 wt.%H₂O having 未¹⁸O = 8-10鈥?and 未D = 鈭?#xA0;27 to 鈭?#xA0;65鈥? and loss of 260 ppm sulfur as sulfate, having 未³⁴S = 14.5鈥? The contents and 未¹³C of total carbon in the two rock types overlap, with a broad trend of decreasing carbon contents and 未¹³C from ~ 1300 to 200 ppm and 鈭?#xA0;9.6 to 鈭?#xA0;20.2鈥? This reflects mixing between reduced carbon in the rocks (210 ppm, 未¹³C 鈮?#xA0;鈭?#xA0;26鈥? and seawater-derived carbonate (未¹³C 鈮?#xA0;鈭?#xA0;1鈥?. Our results indicate: 1) Serpentinized oceanic peridotites carry significant amounts of isotopically fractionated water, carbon and sulfur into subduction zones; 2) Subduction of serpentinites to high P and T results in loss of water, and sulfur, which can induce melting and contribute to ¹⁸O, D, and ³⁴S enrichments and oxidation of the sub-arc mantle wedge; and 3) Isotopically fractionated water, carbon, and sulfur in serpentinite dehydration products are recycled deeper into the mantle where they can contribute to isotope heterogeneities and may be significant for volatile budgets of the deep Earth.