Geomorphic and exhumational response of the Central American Volcanic Arc to Cocos Ridge subduction

Abstract

The timing of collision of the Cocos Ridge at the Middle America Trench remains one of the outstanding questions in the tectonic evolution of the Central American convergent margin. New analyses of the tectonic geomorphology of the Cordillera de Talamanca, the extinct volcanic arc inboard of the Cocos Ridge, coupled with low temperature thermochronometry data, provide insight into the cooling and erosional history of the arc from late Miocene to present. We identify a low‐relief surface at high elevation along the northeastern flanks of the range, which represents a relict erosional landscape cut across shallow plutonic rocks of the arc edifice. Longitudinal profiles of rivers on this surface are isolated from steep downstream sections by prominent knickzones that are interpreted to reflect a migrating wave of transient incision generated during differential rock uplift of the range. Reconstruction of pre‐incision profiles suggests that rock uplift during the growth of the Cordillera de Talamanca is no greater than ∼2 km. This inference is corroborated by results from our apatite (U‐Th)/He and apatite fission track analyses along an elevation transect on Mt. Chirripó, the highest mountain in the Cordillera de Talamanca. Low‐temperature cooling ages overlap significantly with published high‐temperature40Ar/39Ar ages; the combined results imply that rapid cooling in the late Miocene was related to secular cooling of a shallow pluton, rather than exhumation. Our results imply that rapid incision along downstream channel segments, differential rock uplift, and growth of the Talamanca as a bivergent orogenic wedge associated with the onset of Cocos Ridge subduction are relatively young characteristics of the range. A review of previously published radiometric ages and revised plate reconstructions for the late Miocene further suggest that the cessation of arc volcanism in both the Cordillera de Talamanca and the Cordillera Central of western Panama was coeval with the initiation of oblique subduction of the Nazca plate during the late Miocene. Thus, we conclude that the cessation of arc volcanism in the late Miocene (>5–8 Ma) and the onset of Cocos Ridge collision (<3 Ma) are separate events that reflect recent changes in the configuration of the plate boundary system.