AN: T72A-1228
TI: Multi-Channel Seismic Images of the Mariana Trough: EW0202 Initial Results
AU: Taylor, B
AF: SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822
AU: * Goodliffe, A M
EM: amg@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822
AU: Moore, G F
AF: SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822
AU: Oakley, A J
AF: SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822
AU: Fryer, P
AF: SOEST, University of Hawaii, 1680 East West Road, Honolulu, HI 96822
AB: As the first major phase of a US-Japanese collaborative NSF-MARGINS funded project titled "Multi-scale seismic imaging of the Mariana Subduction factory", we collected 5124 km of multi-channel seismic (MCS) data between 14N and 19N across the Mariana subduction-arc-back-arc system. Using the R/V Maurice Ewing, we deployed a 6-km, 480-channel streamer and shot every 50 m using a 20-airgun array (6817 cu in). Coincident gravity, magnetic, and Hydrosweep DS2 data were collected on all 48 lines. The entire MCS dataset, with a common midpoint interval of 6.25 m, was processed through migration during the 30-day cruise. The resulting geophysical transects extend from the Pacific Plate, across the forearc (including several serpentine mud volcanoes), active arc and rifted margin, and back-arc spreading center to the remnant arc. The margins of the back-arc basin are irregular in plan form and contain arc salients that are almost surrounded by back-arc crust. Well-imaged, normal-fault bounded blocks are commonly juxtaposed against back-arc crust with few resolvable internal reflectors. A boundary of this type, with a prominent magnetic anomaly, is imaged on two MCS lines that cross the active arc south of Anatahan volcano at 16.2N. From the position of this boundary, to the east of the arc line, we infer that Anatahan is built on back-arc crust. This likely results in oceanic crust being sandwiched between arc extrusives and cumulates. Other active arc volcanoes may be built on or through rifted former-arc crust. Near 17.5N, 143.5E, an east-dipping low-angle normal fault (approximately 20 degree dip) is imaged beneath the graben at the boundary between the eastern edge of the West Mariana Ridge remnant arc and the oldest crust of the Mariana Trough. North of DSDP Site 451, on the rifted edge of the West Mariana Ridge, there are reflectors at 10-10.5 seconds two-way travel time that may be from the Moho. The back-arc spreading center has an hourglass-shaped inflated segment at 17N. An axial reflector there may be from a magma lens, but may be from out-of plane ridge flanks.
UR: http://www.soest.hawaii.edu/mariana