Collage of tectonic slivers abutting the eastern Romeral Fault System in central Colombia

Abstract

We investigated the U–Pb zircon geochronology of the metamorphic basement that abuts the east Romeral Fault System in north-central Colombia between the San Jerónimo Fault and the western border of the Antioquia Batholith. Our results indicate that this basement is more heterogeneous than previously realized, bearing crustal components with Cambro-Ordovician, Triassic, Late Jurassic–earliest Cretaceous, and middle Cretaceous ages. Metamorphic rocks with Ordovician and older protoliths are the La Aguadita Amphibolites and the La Miel Gneiss and associated amphibolites; the age of their metamorphism is poorly constrained. High-grade, Triassic metamorphic units also occur near the Romeral Fault System, and they are analogous to the bulk of the basement of the Central Cordillera (Tahamí terrane). In contrast, Late Jurassic–Early Cretaceous metamorphic units and middle Cretaceous amphibolite-facies rocks seem restricted to the studied area. The contacts among metamorphic units of disparate age is invariably tectonic. Whereas the older metamorphic units show no evidence of recrystallizations produced by the events that metamorphosed the younger units, the latter do not contain inherited zircon populations that would undoubtedly indicate recycling of the former. We conclude that the studied area is characterized by relatively small but distinct tectonic slivers (mostly <103 km2) and that the length scale of geologic heterogeneity is comparable to that of blocks within the Romeral Fault System. We propose that strike slip displacement along early strands of the long-lived fault system produced anastomosed slivers of diverse origin in the area between the San Jerónimo Fault and the western Antioquia Batholith. As the Romeral Fault System evolved, these strands were mostly abandoned as evidenced by their near absent morphotectonic expression.