Abstract
High-P/T metamorphism of the Franciscan Complex represents evolving subduction-zone processes at depth. Varied peak P-T conditions (100-350°C and 3-10 kbar) promote differences in porosity, permeability, and rheology, potentially impacting fluid mobility and entrainment of seawater. Local-scale isotopic buffering of CaCO3 veins by exchange with adjacent host-rocks obscures assessment of fluid sources (most vein δ13CVPDB = -11.0 to -3.0%, δ18OVSMOW = +12.0 to +18.5‰). Some veins with elevated δ18O (relative to rock-buffered values) may reflect up-dip flow of H2O released at greater depths. Differences in vein δ13C in adjacent coherent greywacke and shaley mélange zones of lower-grade rocks may be due to preferential infiltration of mélange zones by deeply derived CH4-bearing fluids or to vein formation over a range of T. Calculated fluid-δ18O for lower-T veins spans the range of fluids venting in active accretionary prisms and producing forearc serpentinite seamounts. Calcite cement in the Coastal Belt is absent in higher-grade rocks, suggesting that cement is lost to decarbonation reactions like those invoked to elevate fluid alkalinity in Marianas seamounts.
Original language | English |
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Pages (from-to) | 2309-2312 |
Number of pages | 4 |
Journal | Geophysical Research Letters |
Volume | 28 |
Issue number | 12 |
DOIs | |
Publication status | Published - Jun 15 2001 |
Externally published | Yes |
ASJC Scopus subject areas
- Geophysics
- Earth and Planetary Sciences(all)