Middle America Neogene explosive volcanism and ash layers: evidence from the Middle America Trench Transect, Deep Sea Drilling Project Leg 67 ( Guatemala, Pacific Ocean).

Abstract

The ash-layers deposited off Guatemala in this E Pacific subduction zone are related to three magmatic groups differentiated by their relative content in aluminas and alkaline elements (calc-alkaline character). A first weakly calc-alkaline, potassic, differentiated magma emerged during the early and middle Miocene. Its last rhyodacitic occurrences were in the late Miocene. The moderately potassic magma emerged in the middle Miocene, with rhyolites. Rhyo-dacites appeared in the Pliocene to Pleistocene, then either basaltic andesites or rhyolites in the late Pleistocene. This moderately potassic magma is responsible for the bulk of the Quaternary ash deposits, which are essentially rhyolitic. Its magmatic bimodality corresponds to the products from diverse volcanoes now found at Fuego and Pacaya, Atitlan and Izalco (basic lavas), and Santa Maria and Santiaguito (acid lavas). The highly calc-alkaline and potassic magma was marked by rhyolites towards the end of the middle Miocene. It showed again in the early Pliocene with dacites turning to rhyo-dacites, then rhyolites in the late Pliocene and early Pleistocene. -from Authors