Central America.

Abstract

The Central American volcanic chain is divided into eight segments, separated by transverse fault zones and differing in the dip of the underlying subduction zone. The relationship between seismicity and volcanism is close. Major earthquakes are preceded by lulls in volcanic activity and followed by intense volcanism. The relationship between volcanism and seismicity suggests that magma is produced near the top of a descending slab. The Quaternary lavas are typically calc-alkaline in geochemistry and mineralogy. Most volcanoes show fractionation trends from abundant high-alumina basalt and basaltic andesite to subordinate dacite. Very large amounts of rhyolitic pumice erupted in Guatemala may have had a different origin. -A.H.