Re‐evaluation of the Roseau Tuff eruptive sequence and other ignimbrites in Dominica, Lesser Antilles

Abstract

The island of Dominica hosts several ignimbrites, including the Roseau Tuff, thought to represent the largest eruption in the Caribbean in the past 200 000 years. The volcanic stratigraphy of the island is poorly understood due to limited outcrops and a paucity of geochemical and geochronological data. The discovery of a new fully accessible exposure of three ignimbrites intercalated with paleosols provides an opportunity to re‐evaluate the current stratigraphic framework of ignimbrite‐forming eruptions on the island. Whole‐rock analyses of pumice clasts from Dominica ignimbrites are andesitic (61–66% SiO2) and in most cases are geochemically indistinguishable. Ignimbrites in the north of the island have less evolved glass compositions (73–75% SiO2) and more mafic orthopyroxene compositions (En > 56) than their southern counterparts (75–78% SiO2; En < 56). Pumice clasts from ignimbrites in southern Dominica have indistinguishable groundmass glass and mineral chemistry, making correlation of these deposits difficult. New (U–Th)/He eruption ages for the southern ignimbrites indicate that at least six separate explosive eruptions occurred between 24 and 61 ka. The non‐unique geochemistry of these deposits, together with the new (U−Th)/He ages, suggests that the large volume inferred for the Roseau Tuff eruption may actually be a composite of six smaller, geochemically homogeneous eruptions.

Evolution of young andesitic–dacitic magmatic systems beneath Dominica, Lesser Antilles

“…Sourced from south-central Dominica, the Roseau Sequence is a series of six to seven ignimbriteforming eruptions that occurred between ca. 20 and 70 ka (Table 1; Howe et al, 2014). Deposits from these eruptions outcrop throughout the Roseau Valley and along the southern coast of Dominica outside the Soufrière Depression (Table 1; Fig.…”

“…No enclaves were found in any of the pumices. See Howe et al (2014) for full petrographic information of the pumices.…”

“…A minimum of two pumices per outcrop were coarse crushed for mineral picking. Geochemical data from the pumices is presented in detail in Howe et al (2014).…”

Integrating Volcanic Hazard Data in a Systematic Approach to Develop Volcanic Hazard Maps in the Lesser Antilles

“…Although the dominant type of past volcanic activity in the Lesser Antilles has taken the form of effusive andesitic dome growth and associated pyroclastic activity associated with moderate-sized explosive eruptions, between about 20,000 to 40,000 years ago the islands of Dominica and Saint Lucia were the sites of several violent Plinian eruptions that resulted in the deposition of thick pumiceous pyroclastic flow deposits (e.g., the eruptions that make up the Roseau Tuff in Dominica; Howe et al, 2014, and the Belfond unit in Saint Lucia; Lindsay et al, 2013). Should such large explosive eruptions occur today, they would not only affect the island in question but would probably have an impact on the entire region.…”

“…Numerous recent studies carried out on the various volcanoes of the Lesser Antilles, especially those in Dominica and Saint Lucia (e.g., Lindsay et al, 2013;Howe et al, 2014Howe et al, , 2015aBoudon et al, 2017), together with recent monitoring data and recent developments in methods for probabilistic volcanic hazard assessment (e.g., Connor et al, 2015;Bear-Crozier et al, 2016 and references therein), means that this is an approach that can be trialled in future studies.…”