The eastern boundary of the Pacific basin from northern Mexico to Panama is the Middle America Trench, a morphological expression of convergence between the oceanic Cocos Plate and the North American and Caribbean Plates (Fig. 1). A transect of seismic and drill core data across the northern part of the trench off southern Mexico where the Cocos and North American Plates converge is described by Watkins (this volume). In this chapter, I describe a corridor of seismic and drill core data across the Guatemalan convergent margin. The tectonic structure off Guatemala differs from other examples along the Middle America Trench in the lack of accreted rock younger than Eocene. The unique character of the trench between Mexico and Costa Rica is seen in its morphology. North of the Gulf of Tehuantepec (Fig. 1 and Plate 1C), the continental shelf is narrow and much of the continental margin is a steep continental slope. South of the Gulf of Tehuantepec, the continental shelf is underlain by a wide fore-arc basin. At the Santa Elena Peninsula of Costa Rica, the shelf becomes narrow again, and locally the slope of the trench begins at the shore. Thus, the segment of the Middle America Trench between the Gulf of Tehuantepec and the Santa Elena Peninsula is the only one associated with a broad offshore fore-arc basin.
Figures & Tables
This new synthesis includes a section on plate kinematics, documenting the basis for a new interpretation of the magnetic anomaly patterns. It also includes: six chapters on various aspects of tectonics, petrologic characteristics, and hydrothermal processes of active ridges from the Galapagos Rift to the Juan de Fuca Ridge; a section on mid-plate volcanism, including the Hawaii-Emperor chain; five chapters on various aspects of northeastern Pacific sedimentary regimes; and nine chapters on the geology of the Pacific continental margin from the Aleutians to Guatemala, seen from the perspective of marine geology. Three separate oversize plates illustrate the bathymetry of the northeast Pacific; two more on the same base show distribution of sediment samples and types and magnetic anomaly data and tectonic interpretations; and others include a synthesis of the geology and bathymetry of the Hawaiian Islands, details of bathymetry along parts of the East Pacific Rise, and a major seismic profile across the Pacific margin of Guatemala.