Román-Colón, Yomayra A.

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    Apatite and zircon (U-Th)/He constraints on the exhumation history of Puerto Rico
    (2014) Román-Colón, Yomayra A.; Cavosie, Aaron J.; College of Arts and Sciences - Sciences; Stockli, Daniel; Santos, Hernán; Department of Geology; Cruzado, Ivette
    The island of Puerto Rico preserves a complex volcanic arc history. Paleogeographic reconstructions of Puerto Rico during the evolution of island arc magmatism have been illustrated in diverse models as a combination of complex multistage volcanism, eustatic fluctuations and tectonic changes across the three main igneous provinces; southwest, central and northeast. However, the timing of their accretion, the temporal and thermal interaction of the three igneous provinces, and the upper crustal response to paleo-stress fields produced by subduction and collision during the Late Eocene to Early Miocene are not well constrained. In order to better understand and constrain these fundamental processes this research employs an (U-Th)/He low temperature thermochronometric approach using accessory minerals like zircon and apatite from different plutonic bodies strategically located along the three igneous provinces of Puerto Rico and also from neighboring islands. (U-Th)/He zircon data suggest that the earliest major exhumation phase started during the Early Eocene in southwestern Puerto Rico at ~55 Ma and at ~49 Ma in the northern and central section of Puerto Rico. This exhumation phase may be recording the collision of the Caribbean plate with the Bahamas Bank. A smaller thermal signature is recorded by zircon at ~41 Ma during the Middle Eocene and was identified on both the east and the west sides of the island where exhumation reached maximum rates. During the Middle Eocene exhumation, cooling ages are progressively younger to the south. This suggests that the paleo-north section of the island experienced faster cooling and similar exhumation rates due to the proximity to the northern collisional arc boundary. Calculated exhumation rates vary by location and time. Assuming a typical geothermal gradient (20°C/km) calculated exhumation rates range from 0.34-0.15 km/Myr. Islands east of Puerto Rico (Culebra, Vieques and the British Virgin Islands) record apatite cooling ages of ~20 Ma (Early Miocene), younger than most apatite He ages in Puerto Rico. These younger cooling ages may be explained by either the final stages of arc magmatism in the eastern Greater Antilles, or alternatively, an early episode of rifting by right-lateral transtension in the Virgin Islands platform. These findings provide new insights on post volcanic tectono-thermal events marked by the Eocene collision of the Caribbean plate with the Bahamas Bank, the eastward migration of volcanism, later island structural arrangements and the onset of the Muertos Trough southern subduction zone.