HR: 08:15h
AN: T31F-02    [Abstracts]
TI: Synchronous changes in the rift-margin San Jose Island basin and initiation of the Alarcón spreading ridge: implications for rift to drift transition in the Gulf of California
AU: * Umhoefer, P J
EM: paul.umhoefer@nau.edu
AF: Northern Arizona University, Geology 4099, Flagstaff, AZ 86011, United States
AU: Sutherland, F
EM: fionahsutherland@gmail.com
AF: SIO, University of California San Diego, La Jolla, CA 92037, United States
AU: Kent, G
EM: gkent@ucsd.edu
AF: SIO, University of California San Diego, La Jolla, CA 92037, United States
AU: Harding, A
EM: aharding@ucsd.edu
AF: SIO, University of California San Diego, La Jolla, CA 92037, United States
AU: Lizarralde, D
EM: danl@whoi.edu
AF: Woods Hole, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Fletcher, J
EM: jfletche@cicese.mx
AF: CICIESE, CICESE, Ensenada, BC 22860, Mexico
AU: Holbrook, W
EM: steveh@uwyo.edu
AF: Univesity of Wyoming, Geology and Geophysics, Laramie, WY 82071, United States
AU: Axen, G
EM: gaxen@ees.nmt.edu
AF: New Mexico Institute of Mining and Technology, Earth and Environmental Sciences, Socorro, NM 87801, United States
AU: González-Fernández, A
EM: mindundi@cicese.mx
AF: CICIESE, CICESE, Ensenada, BC 22860, Mexico
AB: The rift to drift hypothesis is widely cited, but it well known in detail. The low sedimentation rate and recent rifting of the Gulf of California provides insight into the rift-to-drift process. Lizarralde et al. (2007) showed that the style of rifting, based on crustal structure, varies significantly between the central and southern Gulf of California, and this combined with the analysis of sedimentary basins shows the small-scale (~15 km) complexities of the rift-to-drift transition. The shut off of rifting on the eastern side of the plate boundary occurred at ca. 2 – 3 Ma (Aragon-Arreola etal, 2005, Aragon-Arreola & Martin-Barajas, 2007; our unpublished data). Many studies have shown that the western side of the Gulf is still active despite sea-floor spreading occurring on the Alarcón and other short spreading centers since 2 - 3 Ma. At the mouth of the Gulf, magnetic anomalies on the eastern side of the Alarcón rise show that it appears to have changed to seafloor spreading as early as 3.7 Ma. But comparatively, on the eastern side, magnetic anomalies do not indicate the formation of new oceanic crust until 2.5 Ma, so spreading was first fully established at 2.5 Ma. The San Jose Island basin (Umhoefer et al., 2007) began at approximately 4- 6 Ma; the basin had its most rapid subsidence, with faulting accompanying marine sedimentation, from 3.6 ± 0.5 Ma (Ar tuff age) to 2.5-2.4 Ma (forams). Basin margin faulting died and moved east (offshore) shortly after 2.5-2.4 Ma. Late Quaternary marine terraces suggest that faulting rates slowed by 1-2 orders of magnitude since the fault reorganization at 2.5 Ma. These observations suggest that the rift – drift transition started, but is not yet finished, on the western side of the Gulf of California, with low rates of faulting (<1? mm/yr) continuing on the continental margin for reasons that are not well understood. Our work highlights the importance of combining onshore field and MSC data and analyzing entire conjugate rifted margins to accurately assess rifting processes.
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8150 Plate boundary: general (3040)
DE: 8169 Sedimentary basin processes
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting