Pre-Cretaceous Rocks of Northwestern Honduras: Basement Terrane in Sierra de Omoa

Abstract

A basement ridge of metamorphic and plutonic rocks trends easterly along the northern border and coast of Honduras. It is bounded on the south by the Chamelecon and Aguan faults, which juxtapose Mesozoic strata against the basement terrane. Comprehensive regional studies have revealed the following chronology of events in the evolution of the basement complex of northwestern Honduras. (1) An undifferentiated sequence of Paleozoic, and possibly Precambrian, sedimentary and volcanic strata was metamorphosed to the almandine-amphibolite facies in the pre-Pennsylvanian. (2) This sequence was intruded by plutons of intermediate composition that are deformed penetratively and metamorphosed regionally; one of the plutons bears a Rb-Sr whole-rock isochron age of 305 ± 12 m.y (3) This complex is overlain unconformably by a thick sequence of pelitic strata that was metamorphosed weakly in the pre-Jurassic. (4) The latter sequence was intruded by other plutons of intermediate composition that are not metamorphosed; one such pluton bears a Rb-Sr whole-rock isochron age of 150 ± 13 m.y. (5) The entire basement complex probably was blanketed unconformably in the Early Cretaceous by sublittoral carbonate deposits which were removed subsequently by erosion and deposited to the south as conglomerates in the Late Cretaceous. (6) Late Cretaceous-early Tertiary granitic plutonism was widespread across northern Honduras and probably resulted in pronounced isostatic uplift of the basement ridge along the Chamelecon and Aguan faults. (7) Late Tertiary faulting along northerly trend dislocated the ridge and the Chamelecon-Aguan faults, and resulted in development of the Ulua Valley.