HR: 1330h
AN: V12C-0602    [PDF]
TI: Tectonic and Geologic Characterization of the Incipient Rift, east of the East Pacific Rise at 2o40'N
AU: * Klein, E M
EM: ek4@duke.edu
AF: EOS; Duke Univ., 108 Old Chem., Durham, NC 27708-0227 United States
AU: Smith, D K
EM: dsmith@whoi.edu
AF: Woods Hole Oc. Inst., MS 22, Woods Hole, MA 02540 United States
AU: Williams, C M
EM: clare@whoi.edu
AF: Woods Hole Oc. Inst., MS 22, Woods Hole, MA 02540 United States
AU: Hanna, H
EM: heather.hanna@duke.edu
AF: EOS; Duke Univ., 108 Old Chem., Durham, NC 27708-0227 United States
AU: Zhu, W
EM: wzhu@whoi.edu
AF: Woods Hole Oc. Inst., MS 22, Woods Hole, MA 02540 United States
AU: Rudnicki, M
EM: mrudnick@duke.edu
AF: EOS; Duke Univ., 108 Old Chem., Durham, NC 27708-0227 United States
AU: Cheney, R
EM: crc3@duke.edu
AF: EOS; Duke Univ., 108 Old Chem., Durham, NC 27708-0227 United States
AU: Vancouver Leg01 Scientific Party, .
EM: ek4@duke.edu
AF: EOS; Duke Univ., 108 Old Chem., Durham, NC 27708-0227 United States
AB: The "Incipient Rift" (IR), first identified by P. Lonsdale and co-workers, is located immediately east of and orthogonal to the East Pacific Rise (EPR) at 2o40'N. The IR is a slowly diverging (approx. 15 mm/yr full-rate) spreading center separating the Cocos and Galapagos plates. Interest in the IR stems, first, from the fact that because it is adjacent and orthogonal to the robust EPR, it may tap less pooled magmas produced within the wide melting regime feeding the EPR; and second, because it is a sparsely explored limb of the complex plate boundary surrounding the Galapagos microplate. In August, 2002, we mapped and sampled a broad area centered on the IR, including its intersection with the EPR and apparent termination approx.75 km to the east. Data sets collected included complete Seabeam 2000 bathymetric and side-scan (amplitude) coverage, sea-surface magnetics,14 camera tows (WHOI Towed Camera), rock sampling (53 dredges, 5 wax cores) and hydrothermal surveying (MAPR and CTD). Based on these data, the IR can be divided into three distinct tectonic and magmatic provinces from west to east: a)"The Linking Ridge," following Lonsdale's demarcation, from EPR to 101o59'N, a zone of robust magmatism; b) "The Magmatic Gore," from 101o59'W to 101o53'W, transitional between the Linking Ridge and the Faulted Gore to the east; and c) "The Faulted Gore" from 101o53' to the undisturbed N-S EPR-parallel abyssal hills at 101o26'W. The Faulted Gore is a highly tectonized zone of rifting, with EPR parallel abyssal hills extensively stretched with faults oriented in E-W. Recent magmatism in the Faulted Gore was found to be confined to a narrow zone that runs through the southern portion of the Rift, just north of the faults that define its southern boundary. In general, sediment cover and tectonism (faulting) increase, and the quality of fresh glass decreases, with distance from the EPR. However, photographic evidence of recent magmatism (e.g., fissures erupting lava over sedimented terrain) in areas far east of the EPR axis, as well as a high in magnetization, support the idea that sporadic, recent magmatic activity occurs along the length of the IR (geochemistry: Hanna et al., 2003). No evidence of hydrothermal activity was found along the IR, although a hydrothermal plume was detected in the water depth over the adjacent EPR, and photos on the Linking Ridge show old hydrothermal deposits. A brief SeaBeam survey of the area northeast of the Incipient Rift during our transit revealed the probable existence of a second, perhaps larger propagating rift (Smith et al., 2003), which further emphasizes the complicated nature of the microplate boundaries in this region.
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting