Computer Science
Scientific paper
Feb 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006e%26psl.242..272a&link_type=abstract
Earth and Planetary Science Letters, Volume 242, Issue 3-4, p. 272-285.
Computer Science
8
Scientific paper
The Mariana and Izu Bonin arcs in the western Pacific are characterized by serpentinite seamounts in the forearc that provide unique windows into the mantle wedge. We present stable isotope (O, H, S, and C) data for serpentinites from Conical seamount in the Mariana forearc and S isotope data for Torishima seamount in the Izu Bonin forearc in order to understand the compositions of fluids and temperatures of serpentinization in the mantle wedge, and to investigate the transport of sulfur from the slab to the mantle wedge. Six serpentine mineral separates have a restricted range of δ18O (6.5 8.5‰). Antigorite separates have δD values of - 29.5‰ to - 45.5‰ that reflect serpentinization within the mantle wedge whereas chrysotile has low δD values (- 51.8‰ to - 84.0‰) as the result of re-equilibration with fluids at low temperatures. Fractionation of oxygen isotopes between serpentine and magnetite indicate serpentinization temperatures of 300 375 °C. Two late cross-fiber chrysotile veins have higher δ18O values of 8.9‰ to 10.8‰ and formed at lower temperatures (as low as ˜100 °C). Aqueous fluids in equilibrium with serpentine at 300 375 °C had δ18O = 6.5 9‰ and δD = - 4‰ to - 26‰, consistent with sediment dehydration reactions at temperatures < 200 °C in the subducting slab rather than a basaltic slab source. Three aragonite veins in metabasalt and siltstone clasts within the serpentinite flows have δ18O = 16.7 24.5‰, consistent with the serpentinizing fluids at temperatures < 250 °C. δ13C values of 0.1 2.5‰ suggest a source in subducting carbonate sediments. The δ34S values of sulfide in serpentinites on Conical Seamount (- 6.7‰ to 9.8‰) result from metasomatism through variable reduction of aqueous sulfate (δ34S = 14‰) derived from slab sediments. Despite sulfur metasomatism, serpentinites have low sulfur contents (generally < 164 ppm) that reflect the highly depleted nature of the mantle wedge. The serpentinites are mostly enriched in 34S (median δ34Ssulfide = 4.5‰), consistent with a 34S-enriched mantle wedge as inferred from arc lavas.
Alt Jeffrey C.
Shanks Wayne C.
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