Tectónica y morfologia de la margen continental en el sur de Guerrero-Oaxaca, México, a partir de datos geofísicos

http://dx.doi.org/10.18268/BSGM1988v49n1a3

José Héctor Sandoval Ochoa*

*Instituto de Ciencias del Mar y Limnología, UNAM.

Abstract

Extrapolation of the typical model for the active continental margin suggests a dislocation of a continental portion located in the south of Guerrero-Oaxaca Masiff. The phenomenon was a truncation that offset crustal piece of the margln toward the east, due lo tectonic erosion. The break up was favorable to vertical movements in the massif. A subsequent sequential emplacement of wedges made up of turbidites and hemipelagic sediments, has tended to define an accretionary prism at the toe of the so created sharp inner slope.

The geophysical modellng under this area attempts, to explain the ocurrence of the trench-trough due to tensional effects along the subducting oceanic crust when the upper slab bands and plunges. The evolution of accretion starts when there is no space for material input to a compressional ambit, or consequent to existence of a sharp toe the continental wall (truncation boundary) against the subducting oceanic crust. Then, as ocean crust passes the trench axis, normal faulting evolves with the majority of fault planes diping toward the trench. When it reaches the toe of slope, the normal faulting appears to convert in inverse faulting below the inner slope. This is the mechanisms for growth of accretionary prism made up widely of: hemipelagic, turbiditic, slump sediments and occasionally pieces of basalt from the oceanic crust in some wedges. Among these structures in an overall view, a few kilometers in front of the inner slope the contrast is quite apparent since the trench trough itself is made up of down faulting and tensional gaps. This trench in some places is full of sediments and other portions are completely empty. The resulting tectonical setting can be determinated for this narrow butl long regional feature.