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

Abstract

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 Soufrière 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 Soufrière 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 Soufrière Hills were active during at least ∼2.17–1.03 Ma, ∼1.14–0.38 Ma, and ∼0.45 Ma to present, respectively. Combined with timings of volcanism on Basse‐Terre, Guadeloupe, these ages suggest that ∼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 Soufrière Hills activity ∼450–290 ka characterized by the eruption of hornblende‐orthopyroxene‐phyric lavas, demonstrating that the petrology of the Soufrière Hills eruptive products has changed at least twice throughout the volcano's development.

Carbonate crusts around volcanic islands: Composition, origin and their significance in slope stability

“…Montserrat is a predominantly andesitic volcanic island in the eastern Caribbean that is elevated to a height of almost 2 km above the surrounding seafloor from water depths of 800 to 1000 m. The island comprises four volcanic centres (Fig. 1) which become younger from north to south (Rea, 1974;Harford et al, 2002;Coussens et al, 2017;Hatter et al, 2018).…”

The polygenetic Kahouanne Seamounts in the northern Lesser Antilles island arc: Evidence for large-scale volcanic island subsidence

“…Sediment thicknesses have previously been mapped throughout the Kahouanne valley using a grid of 2D seismic reflection profiles collected on the JC45/46 research cruise (see Watt et al, 2012, for acquisition details and complete descriptions of interpreted horizons). Watt et al (2012) identified a fan of volcaniclastic debris east of the Centre Hills volcano, and correlated the base of this fan with the earliest known age of Centre Hills volcanism (current estimates range from 950 ka (Harford et al, 2002) to 1.14 Ma (Hatter et al, 2018)). This horizon can be traced throughout the graben ( Fig.…”

“…1). Montserrat consists of four volcanic centers that decrease in age from the Silver Hills (~2.1-1.04 Ma) in the north through the Centre Hills (~1.14-0.38 Ma), Soufrière Hills (~0.45 Ma to present) and South Soufrière Hills (0.13-0.12 Ma) in the south (Hatter et al, 2018;Harford et al, 2002). Eruptive products consist of andesitic lava domes, volcaniclastic debris aprons produced by pyroclastic flows and lahars, debris avalanches and lithic-and pumice-rich tephra fall Feuillet et al (2010) and on interpretation of seismic reflection data in Watt et al (2012).…”

“…(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) deposits (Hatter et al, 2018;Coussens et al, 2017;Harford et al, 2002). Basaltic and basaltic-andesite lava flows, domes and scoria fall characterize the South Soufrière Hills center (Cassidy et al, 2015a(Cassidy et al, , 2015bHarford et al, 2002).…”

“…If a higher seismic velocity value were assumed, the thicknesses estimated above would be higher, but the age estimates would not change. If a slightly older age is used for the onset of Centre Hills volcanism (the 1.14 Ma age from Hatter et al, 2018), the estimated base-Unit 2 age becomes 2.1-2.6 Ma. Independent support for the ages derived from the above approach is provided by the age of the Deposit 2 landslide from Montserrat (Fig.…”