Time scales of intra‐oceanic arc magmatism from combined U‐Th and (U‐Th)/He zircon geochronology of Dominica, Lesser Antilles

Abstract

AbstractThe island of Dominica, located in the intra‐oceanic Lesser Antilles arc, has produced a series of intermediate (mostly andesitic) lava domes and ignimbrites since the early Pleistocene. (U‐Th)/He eruption ages from centers across the island range from ∼3 to ∼770 ka, with at least 10 eruptions occurring in the last 80 ka. Three eruptions occurred near the southern tip of Dominica (Plat Pays Volcanic Complex) in the past 15 ka alone. Zircon U‐Th ages from individual centers range from near‐eruption to secular equilibrium implicating protracted storage and recycling of zircons within the crust. Overlapping zircon crystallization peaks within deposits from geographically separated vents (up to 40 km apart) indicate that magma associated with separate volcanic edifices crystallized zircon contemporaneously. Two lava domes from the southern sector of the island display exclusively young zircon rim ages (<50 ka) with narrow crystallization peaks consistent with the construction of a new magma reservoir. The younging of eruption and crystallization ages implies that the magmatic foci leading to the construction of this reservoir have migrated southward, arc‐parallel over time. Overall, our data support geochemical models for the ongoing construction of a silicic intrusive complex, consisting of varying amounts of crystal mush, beneath the island. U‐Pb zircon ages <1–2 Ma indicate that accumulation of this complex is entirely Quaternary in age. Together zircon U‐Th and U‐Pb ages for Dominica suggest that the magmatic processes and time scales operating in intra‐oceanic arcs are similar to those documented for continental arcs.