The volcanic geology and petrology of Montserrat, West Indies

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Abstract
The island of Montserrat is made of the products of five major and three parasitic volcanoes of Pliocene to Recent age. Apart from South Soufrière Hill where some basalt lava flows and pyroclast falls occur, the volcanoes have erupted only andesites, mostly dome lavas and pyroclast flows. The Montserrat lavas belong to the calc-alkaline series. Major and trace element analyses of rocks and minerals are presented and used in a computer test which shows that fractionation of a basaltic parent could account for the composition of all the Montserrat lavas. Other considerations, notably of field relationships and relative volumes of rock types, suggest that andesites are produced in this way only at South Soufrière Hill. Alternative origins for the Montserrat lavas are considered briefly.