Abstract
Processing and analysis of new multichannel seismic records, coincident with wide-angle seismic profiles, acquired in the framework of the TsuJal project allow us to investigate in detail the complex structure of the oceanic domain in the collision zone between Rivera Plate and Block Jalisco at its northern termination. The subducting Rivera Plate, which is overridden by the North American Plate–Jalisco Block, is clearly identified up to 21.5°N (just south of Maria Magdalena Island) as a two clear reflections that we interpret as the interplate and Moho discontinuities. North of the Tres Marias Islands the seismic images display a different tectonic scenario with structures that are consistent with large faulting and rifted margin. A two-dimensional velocity approach for the crustal geometry is achieved using joint refraction/reflection travel time tomography, the uncertainty of the results is assessed by means of Monte Carlo analysis. Our results show an average oceanic crustal thickness of 6–7 km with a moderate increase towards the Jalisco Block, an anomalous thick layers (~3.0 km) displaying a relatively low velocity (~5.5 km/s) underneath Maria Magdalena Rise, and an estimated Moho depth deeper than 15 km in the collision zone between Rivera Plate and Jalisco Block. We have also determined an anomalous crust on the western flank of the Tres Marias Islands, which may be related to the initial phases of continental breakup of the Baja California Peninsula and Mexico mainland. High-resolution bathymetry provides remarkable images of intensive slope instabilities marked by relatively large slides scars of more than 40 km2 extent, and mass-wasting deposits probably triggered by the intense seismicity in the area.
Highlights
The crustal architecture of the western boundary of Mexico is strongly controlled by the Middle America Trench (MAT) which is the morphological expression of an active subduction zone involving the North American Plate overriding the relatively young Rivera and Cocos plates, and it is the location of significant tectonics, widespread seismicity and magmatism (Fig. 1)
Acquired seismic data illuminate the complex interactions between Rivera and North American plates, giving insights of the geodynamics at the northern edge of these plates
We have identified in the multichannel seismic (MCS) sections the collision zone between the Rivera and North American plates in the region of the Tres Marias Islands, which shows noteworthy differences from north to south
Summary
The crustal architecture of the western boundary of Mexico is strongly controlled by the Middle America Trench (MAT) which is the morphological expression of an active subduction zone involving the North American Plate overriding the relatively young Rivera and Cocos plates, and it is the location of significant tectonics, widespread seismicity and magmatism (Fig. 1). The main objective was to define the crustal architecture of this active margin and recognize potential structural sources that can trigger earthquakes and tsunamis at the Rivera– North America convergence zone To achieve these goals a wide range of geophysical data were acquired aboard the RRS James Cook. We describe the spatial distribution of the incoming plates (sediment, crust and uppermost mantle lithosphere) and identify some of the geodynamic processes occurring in this area
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