Date of Award

6-2011

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Geology

First Advisor

Holli Frey

Language

English

Keywords

petrology, Panama, Pleistocene, cores, collapse, rock

Abstract

The purpose of this study is to gain a better understanding of the petrologic conditions of the magma chamber beneath Volcán Barú in western Panama. Volcán Barú is an andesite stratovolcano that experienced a large sector collapse during the Late Pleistocene, which destabilized the southwestern flank of its edifice. Samples were taken from the cores of hummocks and megaclasts deposited as a result of this sector collapse, which are inferred to have been intact wall rock from the pre-collapse edifice. These samples range in composition from 51.8 to 61.7 wt. % SiO2 and have a geochemical signature that is consistent with adakites. Adakite lavas at Barú are thought to have formed by the combination of melting the subducted slab, the opening of a slab window, and the upwelling of primitive mantle melt. Numerous disequilibrium mineral textures were observed in samples taken from hummocks and megaclasts. Reaction rims on hornblende phenocrysts in conjunction with mafic glomerocrysts and dusty sieve-textured plagioclase suggest disequilibrium possibly due to the injection of a hotter mafic batch of magma into Volcán Barú’s andesite storage chamber. Opacitization of hornblende phenocrysts further suggests that hornblende was raised out of its stability field by decompression during ascent. The combination of an increase in temperature, a decrease in pressure, and a reduction in dissolved water content of the pre-existing andesite magma may have possibly triggered eruptive activity at Barú. Processes associated with mafic recharge, such as volatilization and pressurization, may have further implications for the origin of the sector collapse at Volcán Barú during the Late Pleistocene.

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