Two contrasting pressure-temperature-time paths in the Villa de Cura blueschist belt, Venezuela: Possible evidence for Late Cretaceous initiation of subduction in the Caribbean

Abstract

The Villa de Cura blueschist belt is one of several east-west–trending allochthonous belts comprising the Caribbean Mountain system of northern Venezuela. This blueschist belt consists of four structurally coherent subbelts that also trend east-west; from north to south these are characterized by: (1) pumpellyite-actinolite, (2) glaucophane-lawsonite, (3) glaucophane-epidote, and (4) barroisite. The retrograde pressure-temperature ( P-T ) path of the northern three subbelts generally parallels their prograde path. Such P-T paths are typical for Franciscan-style subduction settings and are characterized by relatively low geothermal gradients indicative of refrigeration during subduction-zone-parallel ascent and exhumation of these rocks. The barroisite subbelt formed at high pressures similar to those of the glaucophane-epidote subbelt, but at substantially higher temperatures, and followed a counterclockwise P-T path. New 40 Ar/ 39 Ar ages record peak metamorphism at 96.3 ± 0.4 Ma for the barroisite subbelt and 79.8 ± 0.4 Ma for the northern three subbelts. The Caribbean plate is thought to have been a fragment of the Farallon plate, which together with the “Great Arc of the Caribbean” (Greater Antilles–Aves Ridge–Lesser Antilles–Leeward Antilles) migrated northeastward after a subduction polarity reversal and overrode the young Proto-Caribbean lithosphere that had formed by spreading between North America and South America. The more silicic barroisite subbelt may have been part of the arc that was subducted immediately after polarity reversal, whereas the other three belts formed much later when the geothermal gradient had decreased substantially. The Villa de Cura belt was exhumed in two stages, first by Late Cretaceous arc-parallel extension, and second by Miocene southward thrusting onto the South American continent.