HR: 14:55h
AN: S33D-06    [Abstracts]
TI: Slab identification in the lower mantle beneath the Americas from seismic tomography and plate history reconstruction
AU: * Ren, Y
EM: ren@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75005 France
AU: Stutzmann, E
EM: stutz@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75005 France
AU: Van der Hilst, R
EM: hilst@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA02139 United States
AU: Besse, J
EM: besse@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75005 France
AB: We combine results from seismic tomography and published plate motion histories to investigate the structure and evolution of slabs of subducted lithosphere in the lower mantle beneath North- and South America. We constructed models of 3-D variations in propagation speed of P and S waves through travel time inversion. Using broadband waveform cross-correlation, we measured 37,000 differential travel times (P1-P2 and S1-S2) for pairs of stations and 2,000 PcP-P and ScS-S times from single station records. The earthquakes and receivers are located along a wide corridor from Alaska to South America. We invert the data simultaneously to obtain P and S-wave velocity models. Synthetic tests were performed to assess image quality. We interpret slab structures and unravel subduction history by comparing our Vs tomographic images with reconstructed plate motion from present-day up to 100 Ma. Convergence of the Pacific with respect to North and South America is computed using two approaches: (1) by considering the Pacific and Indo-Atlantic hotspot reference frames and (2) by using the plate circuit passing through Antartica, but there is little difference between the two approaches for ages yonger than 80 Ma. In the upper part of the lower mantle we recognize the imprint of the most recent phase of the plate history. Around 800 km depth, four distinctive fast anomalies can be associated with subduction of the Nazca and Cocos plates beneath South and Central America respectively, the Juan de Fuca plate beneath North America, and the Pacific plate beneath the Aleutian islands arc. In the lowermost mantle, the large fast anomalies which is most pronounced in the S-wave models can be associated with Late Cretaceous subduction of the Farallon plate beneath the Aleutian islands and most of the Americas, and perhaps with the Phoenix plate beneath the southern part of South America. Near 2000 km depth, the images record the fragmentation of the proto Farallon plate into the Kula plate in the North and the Farallon plate in the North-East since 80 Ma. Around 1000 km depth, we observe separated fast anomalies interpreted as the Kula-Pacific, the Juan de Fuca, and the Farallon slabs. This interpretation is validated by comparing the volume and length of slabs estimated from the tomographic images and from plate history reconstruction.
DE: 7200 SEISMOLOGY
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8157 Plate motions: past (3040)
SC: Seismology [S]
MN: Fall Meeting 2005