HR: 08:30h
AN: T31F-03    [Abstracts]
TI: The Sills of Guaymas Basin, Gulf of California: Implications for Crustal Melt Distribution and Thermogenic Carbon Flux
AU: * Lizarralde, D
EM: danl@whoi.edu
AF: Woods Hole Ocng Inst, Dept Geology and Geophysics, Woods Hole, MA 02543, United States
AU: Soule, S A
EM: ssoule@whoi.edu
AF: Woods Hole Ocng Inst, Dept Geology and Geophysics, Woods Hole, MA 02543, United States
AU: Seewald, J S
EM: jseewald@whoi.edu
AF: Woods Hole Ocng Inst, Dept Geology and Geophysics, Woods Hole, MA 02543, United States
AU: Kent, G M
EM: gkent@ucsd.edu
AF: Scripps Inst Ocng, IGPP, La Jolla, CA 92037, United States
AU: Harding, A J
EM: gkent@ucsd.edu
AF: Scripps Inst Ocng, IGPP, La Jolla, CA 92037, United States
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: Univ Wyoming, Dept Geology and Geophysics, Laramie, WY 82071, United States
AU: Umhoefer, P J
EM: paul.umhoefer@NAU.EDU
AF: N Arizona Univ, Dept Geology, Flagstaff, AZ 86011, United States
AU: Axen, G J
EM: gaxen@ees.nmt.edu
AF: New Mexico Tech, Dept Earth and Evn Sci, Socorro, NM 87801, United States
AU: Fletcher, J M
EM: fletche@cicese.mx
AF: CICESE, Dept Geologia, Ensenada, BC 22860, Mexico
AU: F, A G
EM: mindundi@cicese.mx
AF: CICESE, Dept Geologia, Ensenada, BC 22860, Mexico
AB: Multi-channel (MCS) and wide-angle seismic data acquired in 2002 reveal the distribution of igneous sills emplaced into sediments and their relationship to the deeper crustal structure of Guaymas Basin, a young (<6 m.y.), heavily sedimented rift basin. The transition from extended continental to oceanic crust is abrupt across the basin's margins, and most of the crust underlying Guaymas Basin is new igneous crust that is essentially oceanic. However, as a consequence of high sedimentation rates (1-2 km/m.y.), it does not have a typical oceanic Layer 2, but instead has an upper layer of intercalated sediments and igneous intrusions. The MCS data reveal shallow (i.e. recent) sills up to 50 km away from the ~200-m-deep seafloor grabens that delineate the two spreading segments of Guaymas Basin, with no systematic relationship between sill depth and distance from the grabens. For example, sills 42 km away from the graben (1.75 m.y. spreading age) lie beneath only 50 m (or 50 k.y.) of undisturbed sediments. Thus, ongoing sill emplacement is distributed over tens of km relative to the kinematic plate boundary, and the grabens do not mark the locus of focused shallow magmatic emplacement. This implies that the distribution of deeper melt is correspondingly broad, consistent with the deeper velocity structure. Magmatic emplacement in this and perhaps other young, sedimented rift system is thus substantially different from that of unsedimented mid-ocean ridges, where hydrothermal circulation tends to focus magmatic accretion to within <10 km of the ridge axis. The MCS data also reveal 50- to 150-m-thick regions of intense sediment disruption above intruded sills. These regions probably indicate induration from alteration processes accompanying sill intrusion, including the release of thermogenic methane and carbon dioxide. New sills appear to be emplaced at the boundary between high porosity uppermost sediments and the more dense indurated sediments. Active sill intrusion over a much broader region than previously thought greatly increases the predicted carbon flux into the ocean and atmosphere from this and similarly sedimented rift basins.
DE: 3025 Marine seismics (0935, 7294)
DE: 7220 Oceanic crust
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting