Dacite formation at Ilopango Caldera, El Salvador: U-series disequilibrium and implications for petrogenetic processes and magma storage time
Article first published online: 30 JUN 2012
©2012. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Volume 13, Issue 6, June 2012
How to Cite
2012), Dacite formation at Ilopango Caldera, El Salvador: U-series disequilibrium and implications for petrogenetic processes and magma storage time, Geochem. Geophys. Geosyst., 13, Q06018, doi:10.1029/2012GC004107., , and (
- Issue published online: 30 JUN 2012
- Article first published online: 30 JUN 2012
- Manuscript Accepted: 18 MAY 2012
- Manuscript Revised: 16 MAY 2012
- Manuscript Received: 20 FEB 2012
- National Science Foundation; MARGINS. Grant Number: OCE 0405262
- El Salvador;
 Ilopango Caldera was formed ∼1810 years ago by eruption of the Tierra Blanca Joven (TBJ) dacite (70 km3) in central El Salvador. A subsequent eruption in 1880 produced a cluster of dacite domes in the center of Lago Ilopango that contain olive-bearing enclaves of basaltic andesite. The purpose of this study is to use trace element, isotope, and U-series data from the TBJ and 1880 eruptions to assess petrogenesis and the timescale of magma storage. We find that although the range of trace element data in the TBJ dacite can be reproduced by simple crystal fractionation of a plagioclase- and amphibole-rich mineral assemblage, the87Sr/86Sr and 207Pb/204Pb data suggest that the 1880 basaltic andesite enclave has a different source than the dacites. This is consistent with U-series data that show the TBJ dacites have lower (230Th/232Th) than the 1880 basaltic andesite enclave (1.5 versus 1.6, respectively). All Ilopango rocks have 230Th excesses, and the range in (238U/232Th) of the TBJ dacites can be modeled by crystal fractionation of a mineral assemblage including accessory zircon and allanite from a magma that is similar in composition to the enclave. Mineral isochrons yield crystallization ages of <10,000 years, and disequilibrium (226Ra/230Th) values suggest a similarly short residence time. Our data suggest that the large volumes of erupted dacite at Ilopango Caldera are generated very rapidly.