The Cinotepeque Range of central El Salvador: Geology, magma origin, and volcanism


Authors: Rapprich V, Hradecký P

Published in: Bulletin of Geosciences, volume 80, issue 4; pages: 277 - 286; Received 24 January 2004; Accepted in revised form 30 August 2005;

Keywords: El Salvador, Cinotepeque Range, volcanostratigraphy, back-arc volcanism, Rana ignimbrite,

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The Cinotepeque Range is a geological block in NW El Salvador with a complicated volcanic history. Due to the absence of data concerning the geological basement, it remains unclear when volcanic activity started in this zone. The oldest rocks found in the Cinotepeque Range are rhyolitic basal ignimbrites produced from unknown sources. Volcanic activity then proceeded with the silicic pyroclastic products of calderas, the activity of which can be traced up to the Holocene. It is difficult to identify the exact sources of individual pumiceous deposits. Their potential candidates are the three calderas Ilopango Antiguo, Old Coatepeque, and Chilamatal. Later, extrusions of lava sheets of 'inferior' and 'superior' andesites, interrupted by the deposition of agglomeratic pyroclastic flows, called 'Rana', covered the majority of the landscape. The Rana pyroclastic flows were most probably produced from Texistepeque Caldera located between the towns of Santa Ana and Metapán. The youngest volcanism is represented in this area by monogenic volcanic cones. Source vents of these youngest volcanic products are situated mostly on faults that cut and displace all older volcanic rocks. Two different processes of magma origin occurred during the volcanic history of this part of El Salvador: a) during the first stage magma originated by flux melting at a subduction zone; b) during the next stage the decompressional melting in a back-arc environment occurred.