Date of Graduation

Spring 2020

Degree

Master of Science in Geospatial Sciences

Department

Geography, Geology, and Planning

Committee Chair

Gary Michelfelder

Keywords

Lazufre, geochemistry, geothermobarometry, magma plumbing system, andesite, Andes Mountains, Cordon del Azufre, Lastarria

Subject Categories

Geochemistry | Geology | Volcanology

Abstract

The Central Andes in South America contain many active volcanoes and volcano complexes due to constant subduction producing extrusive rocks varying in composition. The Lazufre Complex, Chile-Argentina border, consists of two Pleistocene volcanic centers, Lastarria and Cordon del Azufre andesite and dacite lava flows and domes. Whole-rock K-Ar dates of lavas from Cordon del Azufre place the most recent eruptions at 0.6-0.3 Ma ±0.3 Ma. Major-element data of plagioclase and pyroxene show homogeneous compositions between the centers, which is consistent with whole rock major- and trace-element compositions. The primary composition of the pyroxenes are augite and diopsides for cpx and hypersphene for opx and the primary composition of the plagioclases are An35-78. The Fe-Ti oxide thermo-oxybarometric, feldspar-liquid thermobarometirc, and cpx and cpx-liquid thermobarometric models were used. Temperatures and pressure calculations of both centers range from 970-1070°C and 60-700 MPa, respectively. Detailed investigation of plagioclase textures provide evidence for magma mixing and fractional crystallization as major pre-eruptive processes. Distinct magma storage zones are suggested, with a deeper zone at mid crustal levels (>20 km depth), a second zone at shallow-crustal levels (10-15 km depth).

Copyright

© Brooke Erin Benz

Available for download on Monday, May 31, 2021

Open Access

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