The long-term evolution of Montserrat volcanism
Studying the long-term behaviour of volcanism at individual volcanic centres, and throughout the history of a given arc island, may reveal insights into the processes controlling eruption styles and geochemical evolution of volcanic deposits, and how they change with time. In this talk I will present a revised geochronology of volcanism on Montserrat, and investigate the long-term geochemical trends of volcanism on Montserrat and Guadeloupe, through both their terrestrial and marine (from IODP core U1396C) records, to examine the processes driving geochemical evolution in the Lesser Antilles.
New 40Ar/39Ar ages from terrestrial samples, combined with new palaeomagnetic and biostratigraphic ages of tephra layers from marine sediment core U1396C, provide a revised geochronology of volcanism on Montserrat. They show that the centres of Silver, Centre and Soufrière Hills were active during at least ~2.17–1.03 Ma, ~1.14–0.38 Ma, and ~0.45 Ma–present, respectively, revealing the previously unrecognised overlap in activity between the different volcanic centres.
Pb and Nd isotope and trace element data are presented for lava samples from Montserrat and tephra layers from core U1396C, providing a record of the geochemical evolution of volcanism on Montserrat and Guadeloupe over the past ~4.5 Myr. For Montserrat, the observed temporal geochemical trends are the result of changes in the melt source components (variable slab sediment input and mantle wedge heterogeneity), whereas on Guadeloupe temporal geochemical variation has been driven by assimilation and fractional crystallisation, most likely with a mid-ocean ridge basalt assimilant in the lower crust.