HR: 0800h
AN: T41D-1248    [Abstracts]
TI: Emplacement and Growth of Serpentinite Seamounts on the Mariana Forearc
AU: * Oakley, A J
EM: aoakley@hawaii.edu
AF: Department of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: Department of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822
AU: Moore, G F
EM: gmoore@hawaii.edu
AF: Department of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822
AU: Fryer, P
EM: pfryer@hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, SOEST, University of Hawaii at Manoa, 1680 East West Rd, Honolulu, HI 96822
AU: Morgan, J K
EM: morganj@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005
AU: Goodliffe, A M
EM: amg@ua.edu
AF: Department of Geological Sciences, University of Alabama, 202 Bevill Building, Tuscaloosa, AL 35487
AB: Seamounts comprised primarily of serpentinite muds are found on the outer forearc of the Izu-Bonin-Mariana subduction system. They represent some of the first material outputs of the recycling process that takes place in subduction zones. Therefore, understanding their evolution is necessary to correctly quantify the flux of material through the subduction system. Serpentinite seamounts have been described as mud diapirs, mud volcanoes, uplifted blocks of mantle material, and a composite of the latter two. Multi-channel seismic (MCS) data collected in 2002 from the outer Mariana forearc imaged, for the first time, the large-scale internal structure of these seamounts. These data, combined with new bathymetry, have provided insight into how the seamounts grow and deform with time and have allowed us to evaluate proposed models for their formation. The serpentinite seamounts rest on faulted and sedimented Mariana forearc basement. Flank flows of serpentinite muds downlap existing forearc substrate, leaving the underlying stratigraphy largely undisturbed. Reflections located 3.5-5 km beneath forearc basement may represent Moho, suggesting that the seamounts are built on anomalously thin forearc crust. A strong reflection at the summit of Big Blue, the largest serpentinite seamount in the Mariana Forearc, represents a collapse structure that has been partially in-filled by younger muds, supporting the idea that serpentinite seamount growth is episodic. Basal thrusts that incorporate forearc sediments at the toe of Turquoise Seamount provide evidence for seamount settling and lateral growth. We are conducting numerical simulations of seamount growth and evolution using the discrete element method (DEM), previously used to examine gravity spreading phenomena in magmatic volcanoes. Simulations employing distinctly low basal and internal friction coefficients provide a good match to the overall morphology of the serpentinite seamounts, and offer insight into their internal structure and dynamics, including the formation of inward-dipping reflections and basal thrust faulting. Although the models do not capture central conduit processes that build the seamounts, they do address flank processes that may explain why some seamounts flow passively over pre-existing sediments while others uplift them.
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 3210 Modeling
DE: 1734 Seismology
DE: 1749 Volcanology, geochemistry, and petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting