Date of Graduation
Master of Science in Geospatial Sciences
Geography, Geology, and Planning
Lazufre, geochemistry, geothermobarometry, magma plumbing system, andesite, Andes Mountains, Cordon del Azufre, Lastarria
Geochemistry | Geology | Volcanology
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).
© Brooke Erin Benz
Benz, Brooke Erin, "Geochemistry of the Lazufre Volcanic Complex: Determining the Geometries and Processes of the Magmatic Sources in the Central Andean Volcanic Zone" (2020). MSU Graduate Theses. 3501.