HR: 09:00h
AN: T11G-05    [Abstracts]
TI: A Small Ocean Rift Leads to a New View of the Galapagos Microplate: the Incipient Rift at 2 Degrees North, East of the East Pacific Rise
AU: * Klein, E M
EM: ek4@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, 103 Old Chemistry Building, Durham, NC 27708 United States
AU: Smith, D K
EM: dsmith@whoi.edu
AF: Woods Hole Oceanographic Institution, MS 22, Woods Hole, MA 02543 United States
AU: Williams, C M
EM: clare@whoi.edu
AF: Woods Hole Oceanographic Institution, MS 22, Woods Hole, MA 02543 United States
AU: Schouten, H
EM: hschouten@whoi.edu
AF: Woods Hole Oceanographic Institution, MS 22, Woods Hole, MA 02543 United States
AB: The Galapagos microplate (GMP) shares a complex plate boundary configuration with the surrounding Cocos, Nazca and Pacific plates. While the configuration of the microplate's southern boundary with the Nazca plate is relatively well understood, the nature of its northern boundary with the Cocos plate has remained more elusive. Work by Lonsdale and co-workers (1988; 1992) identified an "incipient" spreading center east of and orthogonal to the East Pacific Rise (EPR) at 2deg40minN, forming a portion of the northern boundary of the GMP. They described this spreading center as a slowly diverging, westward propagating rift, verging toward the EPR. In 2002, we mapped and sampled a broad region centered on the IR, extending ~140 km east of the EPR. Various geological, geophysical and rock sampling tools were used, including Seabeam2000 bathymetry and side-scan (amplitude); towed magnetometer; bottom photography (14 camera tows using the WHOI camera system); water column hydrothermal surveying and rock sampling. Our recent analysis of the bathymetric, side-scan and magnetic data suggests that the IR forms a lozenge-shaped feature, which tapers both westward toward the EPR and eastward, away from the EPR. Within the eastern half of the lozenge, there is a sinuous trough that trends ~100ø to the southeast, along which reflection amplitudes indicate high-reflectivity consistent with relatively sparse sediment cover. The eastern end of this trough clearly cuts north-south-oriented abyssal hills and then dies out in the vicinity of 101deg29minW. The photographic results show sparsely sedimented lavas, often with delicate ornamentation and basaltic glass, with local in-filling of sediment between pillows. In a number of photographs, particularly along the eastern portion of the IR, lavas appear to emanate from local fissures with southeast-northwest orientations. Taken together, these data suggest that the IR is magmatically active along its length and has propagated eastward to the current location of its eastern rift tip. We suggest that continued spreading leads to pivoting of lithosphere about this rift tip, with important implications for the integrity and kinematics of the GMP to its south (see abstract by Schouten et al).
DE: 3005 Geomagnetism (1550)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting