Pacific offshore record of plinian arc volcanism in Central America: 2. Tephra volumes and erupted masses

Abstract

Sediment gravity cores collected from the Pacific seafloor offshore Central America contain numerous distal ash layers from plinian‐type eruptions at the Central American Volcanic Arc dating back to more than 200 ka. In part 1 of this contribution we have correlated many of those ash layers between cores and with 26 tephras on land. The marine ash layers cover areas of up to 10 6 km 2 in the Pacific Ocean and represent a major fraction (60–90%) of the erupted tephra volumes because the Pacific coast lies within a few tens of kilometers downwind from the volcanic arc. Combining our own mapping efforts on land and published mapping results with our marine data yields erupted volumes of all major tephras along the arc that range from ∼1 to 420 km 3 . Recalculated to erupted magma mass, the widespread tephras account for 65% of the total magma output at the arc. Complementing our tephra data with published volumes of the arc volcanic edifices and volcano ages, we calculate the long‐term average magma eruption rates for each volcano. Moreover, we use incompatible element variations to calculate the cumulate masses that were fractionated during variable degrees of differentiation. This yields a minimum estimate of long‐term average magma production rate at each volcano, because intrusives without surface expression and losses by erosion are not accounted for. Peak magma production rates increase from Costa Rica to Guatemala, but there is considerable scatter within each region and large differences even between neighboring volcanoes.