Download Volume II Accomplisments (28 Mb pdf). - IRIS

A Slab Remnant beneath the Gulf of California
Hanneke Paulssen (Utrecht University), Xiaomei Zhang (Utrecht University), Jeannot Trampert (Utrecht University),
Robert Clayton (California Institute of Technology)
Active extension in the Gulf of California is characterized
by the transition from continental rifting to seafloor spreading.
Puzzling variations in the patterns of both tectonics and magmatism
are observed along the length of the gulf and are likely
to be related to mantle heterogeneity. Regional-scale mantle
structure, however, has been difficult to constrain due to the
lack of broadband seismic stations in the region. In this study
we utilized data from the deployment of the NARS-Baja array
and other networks, and computed a three-dimensional shearspeed
model of the upper mantle beneath the region. Applying
a combination of cross-correlation analysis and multimode
waveform inversion, we measured interstation Rayleigh wave
dispersion for 450 pairs of stations in a broad period range of
9–250 s. We computed phase velocity maps and then inverted
the phase-velocity data for shear-speed structure. Our results
suggest that the location of the transition from seafloor
spreading (South) to continental rifting (North) in the Gulf
of California, as well as differences in volcanism across Baja
California and the gulf, can be explained by heterogeneity in
the upper mantle, in particular by the presence of a slab remnant
beneath the south-central part and an absence of such a
slab remnant beneath the northern part of the gulf.
References
Trampert J., H. Paulssen H, A. van Wettum, J. Ritsema, R. Clayton, R.
Castro, C. Rebollar, and A. Perez-Vertti (2003) New array monitors
seismic activity near Gulf of California, Mexico, Eos, 84, 4,
pp 29,32.
Zhang X., H. Paulssen, S. Lebedev, and T. Meier (2007) Surface wave
tomography of the Gulf of California, Geophys. Res. Lett., 34,
L15305, doi:10.1029/2007GL030631.
Zhang X., H. Paulssen, S. Lebedev, and T. Meier (2009) 3D shear
velocity structure beneath the Gulf of California from Rayleigh
wave dispersion, Earth Planet. Sci. Lett., 279, 255-262.
Acknowledgements: Funding for this project was provided by the U.S.
National Science Foundation (Grant number EAR-0111650 of the
MARGINS program) and the Dutch National Science Foundation
(Grant number NWO-GOA-750.396.01).
Crustal thickness
60 km
120 km
140 km
160 km
180 km
200 km
300 km
45
Crustal thickness, km
40
35
30
25
20
15
10
−7 −6 −5 −4 −3 −2 −1 0 1
Shear velocity anomaly, %
5
Maps of the crustal thickness (upper panel), and the shear velocity anomalies
relative to the global reference model AK135 (Kennett et al., 1995) at depths of
60, 100, 120, 160, 200, and 300 km. The slab remnant is imaged as the relatively
high velocity anomaly beneath the south-central part of the Gulf of California at
depths between roughly 120 and 160 km.
2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics | II-177