HR: 1340h
AN: V43B-1587    [Abstracts]
TI: Submarine volcanism in the north Loreto subbasin, Baja California Sur, Mexico
AU: * Skinner, L A
EM: lisa.skinner@nau.edu
AF: Northern Arizona University, PO Box 4099 Northern Arizona University, Flagstaff, AZ 86011 United States
AU: Umhoefer, P J
EM: paul.umhoefer@nau.edu
AF: Northern Arizona University, PO Box 4099 Northern Arizona University, Flagstaff, AZ 86011 United States
AB: The remnants of a group of submarine to subaerial, mid- (?) to late-Pliocene, calc-alkaline, rhyolitic-to-dacitic lava domes are preserved in the southeastern sector of the north Loreto subbasin, Baja California Sur, Mexico. We studied lithological characteristics and sedimentation patterns of volcanic, volcaniclastic, and sedimentary rocks in this dome field in order to characterize the eruptive history of San Basilio dome and determine the depositional environments of the north Loreto subbasin. Foraminifera analyses, facies descriptions, and stratigraphic correlations across the dome field indicate that the original depth to the top of San Basilio dome was ~110m plus or minus 10m. We delineate and describe three stages of evolution for San Basilio dome. First, effusive eruptions produced a small-volume, polyhedral- and columnar-jointed dome edifice surrounded by a hyaloclastite breccia. Second, explosive hydromagmatic or partially pyroclastic activity ensued, perhaps because the dome surface was elevated to a shallow water depth. During this phase, explosive eruptions or the collapse of over-steepened dome flanks resulted in the emplacement of at least one small-volume block-and-ash flow deposit. Wave action, bottom-currents, tidal currents, bedload transport, and/or gravitational sliding simultaneously reworked ash and pumice deposits on the dome flanks. During the third and final stage, volcanic activity ceased, turbulent water currents continued to rework fallout, and hyaloclasts were re-sedimented down slope. The eruptive history of San Basilio lava dome is similar to the evolution of a rhyolite dome-top tuff cone in the Bunga Beds, southeastern Australia, as well as the modern eruptions of Rumble IV and Rumble V volcanoes, southern Kermadec Arc. However, a significant difference exists between these silicic submarine eruptions and those we document in north Loreto subbasin in that there is no remaining evidence that San Basilio dome underwent significant sector-collapse, possibly because the dome had a relatively small volume or because those deposits were subsequently eroded or buried. Additionally, San Basilio dome is unique because it is a Pliocene submarine volcanic succession where paleo-water depths can be constrained.
DE: 8425 Effusive volcanism
DE: 8427 Subaqueous volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005