The small island of Dominica (750 km2) is located in the center of the Lesser Antilles arc, formed by the subduction of the North American Plate beneath the Caribbean plate. Remnants of previous lava flows cover the island, and have been dated through K-Ar dating to be approximately 7 Ma. However, in these lava flows older, detrital zircons have been found. Zircons can be used for provenance studies through U-Pb geochronology and Hf isotope analysis.
Approximately 300 zircon grains were analyzed by U-Pb using LA ICP-MS at the University of Arizona Laserchron Center. Approximately 5% (16 grains) yielded concordant, old ages, >1Ma. These grains appeared round, small, and yellow in CL, but displayed no zoning in BSE images obtained using a scanning electron microscope at Union College. The data collected was then combined with previous data from Kittross et al., 2016 and subdivided in to 5 categories based on age: 53-123Ma (18 grains), 160-230Ma (5 grains), 342-600Ma (5 grains), 1057-1094Ma (2 grains) and 1200-1726Ma (6 grains). Potential sources for these grain populations include the Great Arc of the Caribbean (youngest grains), the Western Andean arc, and the Guyana Shield (oldest grains).
LA ICP-MS can also be used for Hf isotope analysis, that when combined with U-Pb ages can correlate the time of crystallization with mantle extraction time. Epsilon Hf values ranged from -26 to 15. In general, grains that yielded a younger crystallization age correlated to a higher epsilon value, and older ages correlated to smaller epsilon values. The negative epsilon Hf values confirm that some of the zircons are Proterozoic. These detrital zircons have survived 1000s of kilometers in transport from South America and have been entrained in relatively modern erupting magmas, suggesting a contribution from a crustal component.