Tectonic of the offshore Manzanillo and Tecpan basins, Mexican Pacific, from heat flow, bathymetric and seismic data

Abstract

Separation of the Jalisco Block has been proposed to be the main results of oblique differential subduction of the Rivera and Cocos plates beneath North America and of the interaction between the four plates. Vector analysis of the subduction process of the Rivera and Cocos plates relative to North America results in a N11°E trending strike-slip fault boundary between the oceanic plates (at 4.2 cm/yr). most of the onshore structures are in the range of N30°-40°E and N60°-70°E, as in the Tecpan area (between Zihuatanejo and Acapulco). These results agree with the interoperation of detailed marine geophysical data collected by the R/V "Akademik Nikolai Strakhov" during February-March 1989 off Manzanillo and Tecpan. The data include seismic reflection profiles, swath bathymetric data, and 122 new direct heat flow data. Also 39 indirect heat flow values were estimated based on location of gas-hydratelayers in the Manzanillo continental slope from seismic records. In the Manzanillo Basin seismic profiling and swath bathymetric data indicate a recent uplift associated with strike-slip faulting. Heat flow ranges between 20-35 mW/m². (average of 28±6 mW/m²) in the western Manzanillo Basin and 51±7 mW/m² in the eastern basin. Both areas are bound by strike-slip faulting with a vertical component. The low heat flow is attributed to a portion of the coastal batholith that may have moved seaward along left-lateral faults in the Jalisco Block. The average heat flow value in the eastern portion is typical of the continental slope of the Middle American Trench; as measure off Tecpan, Guerrero, at an average of 55±8 mW/m². High heat flow (>100 mW/m²) was found on the oceanic slope of the Middle American Trench. It is attributed to the younger age of the oceanic crust and/or to surface hydrothermal and local magmatic sources in the area of the El Gordo Graben.