Three-phase tectonic evolution of the northern margin of Puerto Rico as inferred from an integration of seismic reflection, well, and outcrop data

Abstract

Integration of seismic reflection, well, and outcrop data from the Oligocene–Pliocene Puerto Rico–Virgin Islands platform (PRVI platform), north of Puerto Rico, indicates that three major tectonic phases characterize this seismically-active region within the North America–Caribbean plate boundary zone. Tectonic phase 1: Cretaceous to Eocene formation and sedimentary infilling from a southern source area into a forearc basin, formed between down-to-the-north normal faults near the present-day coast of Puerto Rico and an outer-arc ridge near the present-day shelf break. Tectonic phase 1 concluded the last volcanic arc activity in Puerto Rico produced by the subduction of oceanic crust of the North America plate beneath the Caribbean arc system. Formation of the outer arc high defining the northern limit of this elongate basin may have been related to the accretion of off-scraped sedimentary rocks beneath the northern margin of Puerto Rico in a manner similar to that observed in active arcs. The end of tectonic phase 1 is related to initial collision between the Caribbean arc and the Bahama carbonate platform. Tectonic phase 2: Oligocene to Pliocene formation of a ∼1600 m thick, northward-thickening PRVI platform, predominately formed by carbonate rocks. This phase started with a period of non-deposition and erosion, resulting in an Latest Eocene–Oligocene unconformity. The base of the PRVI platform is formed by a ∼400 m thick middle to late Oligocene, basal siliciclastic sequence that prograded northward across the forearc basin. Depositional thicknesses of sedimentary layers deposited during phase 2 are controlled by two large arches: the NNW-trending Guajataca arch appears to have formed as the result of tectonic activity in the Mona Passage area; the northeast-trending San Juan arch cannot be related to any adjacent structure or plate boundary feature. Onlap relations between carbonate rocks of the platform and both arches suggest that the arches were most active in the period from middle Oligocene to early Miocene. Rocks deposited during Tectonic phase 2 are surprisingly devoid of faults and folds given their central position within the North America–Caribbean strike–slip plate boundary zone that is known from regional studies to have been active throughout the deposition of the platform rocks. Tectonic phase 3: Pliocene to Holocene northward tilting of the PRVI platform, submerged the northern edge of the platform to a depth of 4 km and elevated the southern edge of the platform to several hundred meters above sea level on Puerto Rico. Northward tilting of this area occurred on the northern limb of a large arch or anticline formed parallel to the long axis of the island of Puerto Rico and its shelf areas. The arch formed in response to a post-Pliocene convergence between the North America and Caribbean plates.