期刊
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
卷 14, 期 10, 页码 4370-4391出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/ggge.20269
关键词
chlorine; stable isotope; fluid-assisted mass transfer; high pressure; subduction
资金
- NSF [EAR-0911669]
Chlorine isotope compositions of high-pressure (similar to 2.3 GPa) serpentinite, rodingite, and hydrothermally altered oceanic crust (AOC) differ significantly from high- and ultrahigh-pressure (> 3.2 GPa) metasedimentary rocks in the Aosta region, Italy. Texturally early serpentinites, rodingites, and AOC have bulk delta Cl-37 values indistinguishable from those of modern seafloor analogues (delta Cl-37 = -1.0 to +1.0%). In contrast, serpentinites and AOC samples that recrystallized during exhumation have low delta Cl-37 values (-2.7 to -0.5%); Cl-37 depletion correlates with progressive changes in bulk chemistry. HP/UHP metasediments have low delta Cl-37 values (median = -2.5%) that differ statistically from modern marine sediments (median = -0.6%). Cl in metasedimentary rocks is concentrated in texturally early minerals, indicating modification of seafloor compositions early in the subduction history. The data constrain fluid sources during both subduction and exhumation-related phases of fluid-rock interaction : (1) marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction. (2) No pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial. (3) Localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel. Most samples, however, preserved protolith signatures during subduction to near-arc depths.
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