DETRITAL ZIRCON GEOCHRONOLOGY OF METAMORPHIC AND SEDIMENTARY UNITS OF THE BAY ISLANDS, HONDURAS: IMPLICATIONS FOR SEDIMENT UNDERPLATING BY SUBDUCTION

The geology of the western Caribbean reflects a complex tectonic history of convergent and divergent kinematics between the North American and Caribbean plates. The Bay Islands archipelago resides on the stable, continental Chortis block of the Caribbean plate, along the right-lateral Motagua-Swan islands fault zone. Of the three islands that comprise the archipelago, the islands of Roatan and Guanaja are lithologically diverse with an assemblage of metamorphic, sedimentary and igneous rocks. The absence of discrete contacts and variable structural boundaries (transform faults, normal faults and shear zones) between these units reflects characteristics of mélange zones in subduction complexes. Metamorphic rocks of the Bay Islands are divided into medium-grade and low-grade metamorphic facies. Medium-grade rocks comprise biotite gneiss and schist and are the most widely dispersed unit on the Bay Islands. Low-grade metamorphic rocks are mapped as chlorite schist. Sedimentary units are primarily olistostromes, conglomerates and alluvium. We present the first detailed U-Pb zircon geochronology conducted on metamorphic and sedimentary rocks of the Bay Islands. Detrital zircons from biotite, amphibole gneiss yielded a maximum depositional age of 121 Ma (±1.76). The minimum stratigraphic age of Guanajan biotite gneiss is ~78 Ma, which is the U-Pb zircon age of a crosscutting granitic pluton. Detrital zircons from chlorite schist yield a maximum depositional age of 51.75 Ma (±0.27). Zircon from olistostrome units yielded a maximum depositional age of 54.71 Ma (±0.23). Zircons from all metamorphic and sedimentary rocks share populations of Grenvillian and early Triassic ages. The metasedimentary rocks are younger than the Chortis block crust and were most likely transported via subduction under the Caribbean plate and then exposed via extension due to oblique motion on the Motagua-Swan island transform.