Document Type

Thesis

Degree

Master of Science (MS)

Department

Geosciences

First Advisor's Name

Rosemary Hickey-Vargas

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Guatam Sen

Third Advisor's Name

Andrew McFarlane

Fourth Advisor's Name

Grenville Draper

Fifth Advisor's Name

Fidel Costa Rodriguez

Date of Defense

2-16-2007

Abstract

Calbuco Volcano, in Southern Chile, has eruptive products of predominantly andesitic hornblende-bearing lava. A purpose of this work is to understand magmatic processes and how Calbuco magma chemistry is related to the explosive volcanic character. Calbuco lava has a mineral assemblage of plagioclase, hornblende, orthopyroxene, clinopyroxene, olivine, and magnetite and entrained gabbroic xenoliths with the same mineral assemblage. The presence of hornblende is evidence for dissolved water in the magma. Detailed petrographic/textural analysis has been done using petrographic microscopy and back-scattered electron imaging (BSE); geochemical analysis by electron microprobe (EPMA). Major findings include 1) that hornblende and hornblende-bearing gabbroic cumulates crystallize from Calbuco magma, 2) that plagioclase grains are compositionally zoned, recording evidence of temperature, chemical, and water content fluctuations in the magma, and 3) that hornblende is unstable under upper magma chamber conditions at Calbuco, and is breaking down into plagioclase, olivine, orthopyroxene, clinopyroxene, and magnetite in the magma.

Identifier

FI15071602

Comments

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Geology Commons

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