HR: 13:55h
AN: T43C-02 INVITED    [Abstracts]
TI: Crustal growth deduced from seismic structure of the Mariana arc-backarc system
AU: Takahashi, N
EM: narumi@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: * Klemperer, S L
EM: sklemp@stanford.edu
AF: Stanford University, Mitchell Building 353, 397 Panama Mall, Stanford, CA 94305-2215, United States
AU: Kodaira, S
EM: kodaira@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Tatsumi, Y
EM: tatsumi@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Calvert, A J
EM: acalvert@sfu.ca
AF: Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
AU: Kurashimo, E
EM: ekura@eri.u-tokyo.ac.jp
AF: Earth Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AB: We obtained a seismic velocity model of the Mariana arc-backarc system (MABS) based on active-source seismic profiling under the umbrella of the MARGINS program: US-JAPAN collaborative research multi-scale seismic imaging of the Mariana subduction factory. A 2D profile across the Mariana arc (MA), Mariana Trough (MT), West Mariana Ridge (WMR), and the Parece Vela Basin (PVB) was complemented by a 3D refracion study across the MA and a 2D profile along the arc, The major structural characteristics are (1) crustal thickness variations across the MABS (~20 km in the MA, ~17 km in the WMR, ~6 km in the MT and PVB); (2) of the presence of at least some middle crust with velocity of 6 km/s beneath arc regions (MA and WMR); (3) uneven distribution of lower-velocity lower crusts (6.7–6.9 km/s, LVLC) beneath the volcanic front and adjacent to the MT; (4) slow velocities of less than 8 km/s in the upper mantle, under the arc regions; (5) deep reflectors in the mantle with slow velocity of < 8km/s beneath the arc regions, and (6) a high-velocity lower crust (7.2–7.4 km/s) at the boundary regions between the MA and MT. (7) Crustal thickness beneath the MT axis is a few kilometers thicker than that of the surrounding trough region and the clear reflector distributes beneath the axis. Although the bulk composition of the MA and WMR is still basaltic, simple petrologic modelling of our 2D profiles based on an anatexis model suggests that the volume of lower crustal restites and olivine cumulates after extraction of mid-crustal andesite should be significantly larger than observed, suggesting that part of the lower crust, especially cumulates, is seismically part of the mantle. The LVLC, which may indicate advanced crustal growth, located adjacent to the MT suggests that the backarc opening promoted crustal growth and differentiation. The distribution of the low mantle velocities and the deep reflectors, especially beneath the extinct WMR, suggest that their origin could be explained by transfer of lower crustal residues to the seismically defined mantle across the Moho. In addition, the high-velocity lower crust beneath the arc-backarc transition zone is likely composed of mafic/ultramafic materials created by extensive partial melting of mantle peridotites or last stage of the arc magmatism rather than serpentinized peridotites. The crustal thickening and the deep reflectors beneath the MT axis suggests underplating of basaltic magmas and existence of the low velocity region in the upper mantle.
DE: 0930 Oceanic structures
DE: 3025 Marine seismics (0935, 7294)
DE: 7205 Continental crust (1219)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting