HR: 1340h
AN: B13A-0177    [Abstracts]
TI: A Recent Volcanic Eruption on a "Magma Starved" Segment of the East Pacific Rise ISS, "10\deg44'N
AU: * McClain, J S
EM: mcclain@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, CA 95616 United States
AU: Zierenberg, R A
EM: zierenberg@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, CA 95616 United States
AU: Voight, J R
EM: jvoight@fieldmuseum.org
AF: Zoology, The Field Museum, 1400 S. Lake Shore Dr, Chicago, IL 60605 United States
AU: Von Damm, K L
EM: kvd@eos.sr.unh.edu
AF: Complex Systems Research Center, EOS, University of New Hampshire, Durham, NH 03824 United States
AU: Rubin, K H
EM: krubin@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East-West Rd, Honolulu, HI 96822 United States
AB: In November 2003, three Alvin dives were made on the East Pacific Rise at 10\deg44'N, (funded by NSF DEB-0072695). We discovered evidence for extremely young lava flows, indicating a recent volcanic eruption. Most of the flow is relatively thin, perhaps only 1 to 2 meters thick, but locally thicker with voids beneath of over 10 meters. The basalts were very glassy, with little devitrification. The pillows were lined with abundant bacterial deposits. We found a number of collapse pits and fissures. Several of these were emitting warm water with bacterial floc, features often referred to as snow blowers. The most prominent collapse feature is a central sinuous feature that extends for several hundred meters, and has a depth of about 10 meters. Initial dating of the basalts is described in an accompanying abstract, and is consistent with a very recent eruption. Global seismicity data do not reveal any events on the EPR at this latitude, and as of this writing, the NOAA (PMEL) hydrophone data for the equatorial Pacific have not yet been recovered. Even the most magma deficient segments of the world's mid-ocean ridge system must undergo magmatism and volcanic activity to produce the basalts that are nearly ubiquitous on the seafloor. Most of the fast spreading East Pacific Rise displays evidence of an abundant magma supply, including the presence of an axial magma chamber (AMC) reflector and an elevated axial high. An exception is the segment of the EPR north of the Clipperton Transform between 10\deg18'N and 10\deg55'N. Along that 70 kilometer length of ridge no AMC reflector was detected in the original survey by Detrick and others in 1985. In contrast, later seismic refraction work indicated anomalously low velocities and high attenuation in the lower crust beneath the axis in this area. Near the Transform, the ridge is narrow and relatively deep ~2800 m). It shoals and widens to the north, suggesting a more abundant magma supply. The 10\deg44'N site lies at the northern end of this magma depleted ridge segment. This suggests either the axial magma chamber has changed over the intervening years, or an AMC reflector is not a necessary condition for magmatic activity on a ridge axis.
DE: 8424 Hydrothermal systems (8135)
DE: 8429 Lava rheology and morphology
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology and bottom photography
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting