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

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