STRUCTURAL AND GEOPHYSICAL ANALYSIS ON ROATAN ISLAND, HONDURAS, WESTERN CARIBBEAN

Roatan Island is is the largest island of the Bay Islands of Honduras trending SW to NE along the Honduran Caribbean shoreline. The Bay Islands of Honduras have been referred to historically as the Bonacca Ridge, an emergent crest found just south of the Bartlett Trough. The Bartlett Trough and subsequent Bonacca Ridge were likely formed due to the transform fault system of the Motagua and Swan Islands Faults. This fault system forms the tectonic plate boundary between the North American and Caribbean plates. Although the timing and kinematics are poorly constrained, the Bay Islands and the Bonacca Ridge were uplifted due to transpression along this left-lateral strike-slip system.

Roatan Island consists of an exposed metamorphic basement composed of two schist members (biotite schist and chlorite schist), intruded by quartz pegmatite. Large bodies of amphibolite and serpentinite are present in the basement where the age and structural relationship is unclear. Irregular deposits of carbonates (dolomite) are found on the island showing variable degree of distribution and metamorphism (low grade marble). A conglomerate overlays all rock units outcroped in the eastern area of the island, not well observed during the field study from access restraints.

To better constrain the kinematics of uplift and exhumation of Roatan Island, we conducted a structural, gravity, and magnetic survey. Principal attention was directed to the structural relationship between the geologic units and the relationship of each unit through deformation. The metamorphic basement exposed on the island displays a normal stratigraphic order of biotite schist overlain by the subsequent chlorite schist, carbonate, and conglomerate units. Each of these units appear to have relatively concordant strike and dip measurements, consistent with the readings presented from the magnetic survey. The amphibolite and serpentinite intrusive bodies appear to have been emplaced as mafic and ultra-mafic dikes and sills along Early Paleogene transform system fault planes before metamorphic alteration. Additionally, the current structural outcrop patterns of these stratigraphic units and intrusive amphibolite and serpentinite bodies have been interpreted locally to be emplaced by transpressive tectonics (flower structure) along the Flowers Bay Fault.