Statistics – Computation
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.t71f..11k&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #T71F-11
Statistics
Computation
3660 Metamorphic Petrology, 5480 Volcanism (8450), 7230 Seismicity And Seismotectonics, 8450 Planetary Volcanism (5480)
Scientific paper
Metamorphic devolatilization in subduction zones is essential to arc magmatism, seismicity and volatile recycling. Our premise is that realistic modeling of metamorphic devolatilization of subducted lithologies is only possible for chemical systems that closely approximate actual bulk compositions. Volatile components are introduced into subduction zones by three contrasting lithologies: marine sediments, and hydrothermally altered mantle ultramafic rocks (serpentinites) and oceanic metabasalts. Using free energy minimization (Perplex programs: erdw.ethz.ch/~jamie/perplex), phase equilibria were computed to 6 GPa (~160 km) to quantify the evolution of CO2 and H2O by prograde metamorphism of marine sediments and oceanic metabasalts entering the Izu-Bonin-Mariana (IBM) subduction system. Major oxide compositions for these protoliths (from sites 801 and 1149 ODP cores) were utilized as input for our computations. Assuming that the IBM system is a relatively cool subduction zone, we quantified devolatilization for the P-T path along the top of the subducted slab. Major dehydration of pelagic clays in sites 801 and 1149, and volcaniclastic turbidites in site 801, are predicted to occur in the subarc. The subjacent hyrothermally altered basalts in sites 801 and 1149 will undergo little devolatilization for cool geotherms. With the unsubstantiated assumption that serpentinites exist in the upper mantle of the subducted slab, this lithology would also provide a significant subarc H2O source. With serpentinite included in the subducted slab, and assuming a fluid-assisted embrittlement mechanism for earthquakes, metamorphic dehydration could account for the distribution of hypocenters along the top of the subucted slab of the IBM system. Serpentinite as a major H2O source for the Isu arc is compatible with the strong depletion in trace element concentrations of the arc volcanics [1]. Trace element signatures in the Mariana arc magmas [2] are consistent with subducted volcaniclastic turbidites as a H2O source. [1] Plank, T., et al., 2000, Proc. ODP Init. Repts. 185, 1-63; [2] Elliott, T., et al., 1997, J. Geophys. Res. 102, 14,991-15,019.
Connolly James
Kerrick David
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