STRATIGRAPHY, GEOCHEMISTRY AND GEOCHRONOLOGY OF A QUATERNARY PYROCLASTIC SEQUENCE OF THE CHICHONTEPEC VOLCANO, EL SALVADOR

Abstract

In this paper we present sedimentological, chemical and geochronological data on a pyroclasticsequence deposited at Chichontepeque Volcano (El Salvador) during a caldera-forming Plinian phase.Granulometric analyses and width distribution patterns of airfall pyroclastics showed that these are the result ofat least two eruptions, the oldest being the more complete. The Basal Fall, which marks the beginning of thePlinian eruption, shows the typical features of Plinian air-fall deposits.Chemical trends mirror roughly a downward tapping from a zoned magma chamber; inside each fall unit crys-tal fractionation trends can be recognized. 39Ar/40Ar dating of lavas underlying and overlying the pyroclasticsequence show that the Plinian phase occurred between 0.59 ±0.09 and 0.55±0.04 Ma before present.