Tectonic Fabric of the Cocos Plate and Conjugate Pacific Plate Crust Near Mexico

Abstract:

Existing satellite gravity data, along with publicly available single beam bathymetry, multibeam bathymetry, and shipboard and satellite magnetic anomalies were compiled to make an updated map of tectonic features of the Cocos Plate offshore Mexico and the conjugate crust on the Pacific Plate. The area includes the northern Cocos plate as far south as the Tehuantepec Ridge, and Pacific plate crust on both sides of the Mathematician Rise. This thus includes the modern East Pacific Rise (EPR), the submarine rift margins that bound it – Moctezuma and Manzanillo Troughs - and features previously identified such as the Orozco and O’Gorman Fracture Zones near the Middle America Trench (MAT). The goal was to use existing data to evaluate the likely features that may have existed on the now subducted Cocos Plate crust north of the Clarion Fracture Zone-Tehuantepec Ridge. This can then be compared to seismic imaging of the downgoing slab and geochemical variations along the Mexican Volcanic Arc.

Bathymetric slopes were computed automatically from multibeam data gridded at 200 m, 300 m, and 400 m pixel size, and processed to remove signals of circular features such as seamounts, and regions of low slope, while emphasizing higher slopes controlled by linear abyssal hill fabric and fracture zones. Tectonic fabrics at all 3 scales are generally similar. In the resulting tectonic fabric map, the domain of modern East Pacific Rise spreading is clearly visible, truncating older fabrics at the Manzanillo Trough on the east and the Moctezuma Trough on the west. The Orozco Fracture Zone lies entirely within the young part of this crustal province and does not reach the Manzanillo Trough or the MAT. Hence, it is not a feature of the downgoing Cocos Plate and should not be used to explain variations in geochemistry of the arc or geometric variations in the subducted plate. A zone of E-W to ENE-WSW oriented abyssal hills and lineated magnetic anomalies in a bathymetric low between the Moctezuma Trough and the Mathematician Rise forms a separate crustal province, truncated by the Moctezuma Trough. There is a possible conjugate fragment of this older province preserved east of the Manzanillo Trough, next to the MAT. Thus, features of the downgoing Cocos Plate appear to be more complicated than has been envisioned in most previous interpretations.