The Evolution of the Silver Hills Volcanic Center, and Revised 40Ar/39Ar Geochronology of Montserrat, Lesser Antilles, With Implications for Island Arc Volcanism

Studying the older volcanic centers on Montserrat, Centre Hills and Silver Hills, may reveal how volcanic activity can change over long time periods (1 Myr), and whether the recent activity at the Soufriere Hills is typical of volcanism throughout Montserrat's history. Here we present the first detailed mapping of the Silver Hills, the oldest and arguably least studied volcanic center on Montserrat. Volcanism at the Silver Hills was dominated by episodic andesite lava dome growth and collapse, produced Vulcanian style eruptions, and experienced periodic sector collapse events, similar to the style of volcanic activity that has been documented for the Centre Hills and Soufriere Hills. We also present an updated geochronology of volcanism on Montserrat, by revising existing ages and obtaining new 40Ar/39Ar dates and paleomagnetic ages from marine tephra layers. We show that the centers of the Silver, Centre, and Soufriere Hills were active during at least approximate to 2.17-1.03 Ma, approximate to 1.14-0.38 Ma, and approximate to 0.45 Ma to present, respectively. Combined with timings of volcanism on Basse-Terre, Guadeloupe, these ages suggest that approximate to 0.5-1 Ma is a common lifespan for volcanic centers in the Lesser Antilles. These new dates identify a previously unrecognized overlap in activity between the different volcanic centers, which appears to be a common phenomenon in island arcs. We also identify an older stage of Soufriere Hills activity approximate to 450-290 ka characterized by the eruption of hornblende-orthopyroxene-phyric lavas, demonstrating that the petrology of the Soufriere Hills eruptive products has changed at least twice throughout the volcano's development.