HR: 11:30h
AN: V21F-05    [PDF]
TI: Reconstruction of Pacific-Nazca Plates, Nazca Ridge, and Easter Seamount Chain
AU: * Naar, D F
EM: naar@usf.edu
AF: College of Marine Science, University of South Florida 140 Seventh Avenue South, St. Petersburg, FL 33701 United States
AU: Wilder, D T
EM: dwilder@alaska.net
AF: National Park Service, 201 First Avenue, Fairbanks, AK 99712 United States
AU: Duncan, R A
EM: rduncan@coas.oregonstate.edu
AF: COAS, Oregon State University, Corvallis, OR 97331 United States
AU: Wessel, P
EM: pwessel@hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AU: Harada, Y
EM: harada@soest.hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AU: Mahoney, J J
EM: jmahoney@soest.hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AU: Ray, J S
EM: jsray@soest.hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, HI 96822 United States
AU: Johnson, K T
EM: kevinj@soest.hawaii.edu
AF: Bishop Museum, 1525 Bernice Street, Honolulu, HI 96817 United States
AB: Relative plate motion history since 30 Ma between the Pacific and Nazca (Farallon) plates has been constrained by available seafloor magnetic anomaly data and a two-minute grid of predicted bathymetry. These data are used to create a new plate reconstruction based on finite and stage poles of rotation and radiometric ages along the Easter-Salas y Gomez-Nazca Ridge volcanic lineament. An iterative process of anomaly identifications, pole calculations and anomaly rotations was used to test for self-consistency in the interpretation. The new identified magnetic isochrons (10y, 7y, 6c, 5d, 5b, 5aa, 5o, 4a, and 3a) and the predicted tectonic history provide an improved understanding between chrons 7y (24.73 Ma) and 3 (4.18 Ma). However, the finite poles for 6c and 5d are poorly constrained. Eleven stage poles were calculated using the nine finite poles and two published instantaneous Euler vectors for the 1o and 2a isochrons. The stage poles indicate full-spreading rates increased from about 175 mm/yr to about 205 mm/yr after the break-up of the Farallon plate, and then have slowed to about 145 mm/yr. The tectonic reconstruction indicates two major southward propagating events, the first starting by 28 Ma and terminating by 18 Ma. The second starting in association with breakup of the Farallon plate around 24 Ma and terminating by about 11 Ma. Lithosphere was transferred from Nazca to Pacific during the first event and in the opposite sense during the second. Development of the Mendoza microplate east of the second propagator occurred at about 20 Ma and this dual spreading process appears to have lasted until about 15 Ma. Radiometric ages, geochemical data, relative and absolute motion models presented at the Nice AGU meeting by Duncan et al., Ray et al., Wilder et al., and Harada et al. indicate that since 30 Ma: 1) a hotspot located near Salas y Gomez Island does not require significant motion of the hotspot with respect to the Hawaiian hotspot; 2) that this hotspot has generated similar proportions of OIB vs. MORB end-member compositions in most samples collected east of Salas y Gomez; and 3) that the change of plate motion velocity was primarily accommodated by the combination of propagating rifts and microplate formation, including a rapid clockwise rotation of spreading direction and rapid increase in spreading rate, followed by a subsequent decline until present.
UR: http://imina.soest.hawaii.edu/wessel/drft06rr/
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8155 Plate motions--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting