HR: 1330h
AN: T32A-0911    [PDF]
TI: Variability in Mineralogy of Mariana Serpentinite Mud Volcanoes: Source Compositions and Relationships to Fluid Release From the Subducted Slab
AU: * Gharib, J J
EM: jgharib@soest.hawaii.edu
AF: SOEST/University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Fryer, P
EM: pfryer@soest.hawaii.edu
AF: SOEST/University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Ross, K
EM: kross@soest.hawaii.edu
AF: SOEST/University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Mottl, M
EM: mmottl@soest.hawaii.edu
AF: SOEST/University of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AB: Sediments from active serpentinite mud volcanoes on the Mariana forearc reveal considerable variability in mineralogy across and along strike, as well as with time. This suggests a complexity in source material and possibly in eruptive processes. As shown previously, several seamounts are bringing up high-pressure, low-temperature lithic clasts. Others lack these lithics, however, and even within individual seamounts some mud flows contain these mafic components while others lack them. This indicates variable sources for the muds even within a given seamount. The variability in mud composition contrasts with a more regular pattern of composition of slab-derived pore fluids at active seeps on the seamounts. It has been established that there are systematic changes in slab-derived fluid composition (Mottl et al., this volume) with distance from the trench and thus with depth to slab. Carbonate alkalinity is lower near the trench, but is higher farther away. Ca concentration is higher nearer the trench. As alkalinity increases Ca is removed via CaCO3 precipitation. Authigenic carbonate (e.g., aragonite, calcite, sjogrenite group minerals), formed by the interaction between seawater and upwelling slab-derived fluids, were collected by coring and ROV sampling in the shallow subsurface of several serpentinite mud volcanoes at various distances from the trench. Both spatial and temporal variability in the pore fluid composition may play a part in the isotopic concentrations of d13C and d18O in these carbonates. The muds erupting from the seamounts probably derive from varying sources beneath the edifices through time; in contrast the compositional snapshot presented by the active seeps suggests that the extraction of fluids from the slab is depth controlled. The range of isotopic concentrations of the carbonates suggests that there may be factors controlling the release of fluids from the slab that vary with time. Recent sea-floor mapping with the DSL-120 high-resolution sidescan sonar system and detailed sea-floor observations with the Jason 2 ROV indicate a far greater degree of complexity in the processes of formation of these seamounts than previously observed (see Fryer et al., this volume).
DE: 1050 Marine geochemistry (4835, 4850)
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3660 Metamorphic petrology
DE: 3675 Sedimentary petrology
SC: Tectonophysics [T]
MN: 2003 Fall Meeting