Tomography and thermal state of the Cocos plate subduction beneath Mexico City

[1] The geometry and thermal state of the subducting Cocos plate beneath Mexico City has been enigmatic because of the absence of a deep Wadati-Benioff zone. We present a tomographic image of the slab based on inversion of 8869 teleseismic P wave travel times measured on a portable broadband seismic network. The images combined with receiver function analysis show that the slab runs flat from the coast to near Mexico City, where it dives into the mantle just before the Trans-Mexican Volcanic Belt with a dip of ∼75°. It continues down to a depth of ∼500 km at a distance of 400 km from the trench, where the tomography reveals that the dipping portion ends. As well as standard block tomography, we invert the travel time residuals for the parameters of a thermal slab model and find a slab thickness of 40 km that is consistent with the (15 Ma) age of the Cocos plate. The combination of a young hot plate and truncation at depth can explain the lack of deep seismicity due to high temperatures and lower negative buoyancy compared with an older, thicker, nontruncated plate.

[1]  P. R. Bevington,et al.  Data Reduction and Error Analysis for the Physical Sciences , 1969 .

[2]  R. Clayton,et al.  Lateral velocity variations in southern California. I. Results for the upper crust from Pg waves , 1986 .

[3]  Cinna Lomnitz,et al.  Crustal structure of Oaxaca, Mexico, from seismic refraction measurements , 1986 .

[4]  B. Kennett,et al.  Traveltimes for global earthquake location and phase identification , 1991 .

[5]  S. Stein,et al.  A model for the global variation in oceanic depth and heat flow with lithospheric age , 1992, Nature.

[6]  D. Stevenson,et al.  Physical model of source region of subduction zone volcanics , 1992 .

[7]  P. Patriat,et al.  Thermal diffusivity of the lithosphere derived from altimetry and bathymetry profiles across the Southwest Indian Ridge , 1992 .

[8]  A. John Mallinckrodt,et al.  Data Reduction and Error Analysis for the Physical Sciences , 1993 .

[9]  M. Pardo,et al.  Shape of the subducted Rivera and Cocos plates in southern Mexico: Seismic and tectonic implications , 1995 .

[10]  T. Lay,et al.  Modern Global Seismology , 1995 .

[11]  G. Nolet,et al.  Seismic image of the subducted trailing fragments of the Farallon plate , 1997, Nature.

[12]  G. Nolet,et al.  Slab temperature and thickness from seismic tomography: 2. Izu‐Bonin, Japan, and Kuril subduction zones , 1999 .

[13]  Guust Nolet,et al.  Slab temperature and thickness from seismic tomography: 1. Method and application to Tonga , 1999 .

[14]  L. Ferrari Slab detachment control on mafic volcanic pulse and mantle heterogeneity in central Mexico , 2004 .

[15]  V. Manea,et al.  Thermo-mechanical model of the mantle wedge in Central Mexican subduction zone and a blob tracing approach for the magma transport , 2005 .

[16]  Y. Fukao,et al.  Tomographic search for missing link between the ancient Farallon subduction and the present Cocos subduction , 2005 .

[17]  Ellen M. Syracuse,et al.  Global compilation of variations in slab depth beneath arc volcanoes and implications , 2006 .

[18]  V. Manea,et al.  Intraslab seismicity and thermal stress in the subducted Cocos plate beneath central Mexico , 2006 .

[19]  J. Arzate,et al.  Fluid release from the subducted Cocos plate and partial melting of the crust deduced from magnetotelluric studies in southern Mexico: implications for the generation of volcanism and subduction dynamics , 2006 .

[20]  R. Clayton,et al.  Horizontal subduction and truncation of the Cocos Plate beneath central Mexico , 2008 .

[21]  K. Priestley,et al.  New views on the structure and rheology of the lithosphere , 2008, Journal of the Geological Society.