Work

Magma storage conditions of Lascar andesites, central volcanic zone, Chile

Year: 2024

Type: article

Abstract: Lascar volcano, located in northern Chile, is among the most active volcanoes of the Andean Central Volcanic Zone (CVZ). Its activity culminated in the last major explosive eruption in April 1993. Lascar andesites which erupted in April 1993 have a phase assemblage composed of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxides, and rhyolitic glass. To better constrain storage conditions and mechanisms of magmatic differentiation for andesitic magmas in a thick continental crust, crystallization experiments were performed in internally heated pressure vessels at 300 and 500 MPa, in the temperature ( T ) range of 900–1050 °C, at various water activities ( a H 2 O) and oxygen fugacities (log f O 2 between QFM+1.5 and QFM+3.3 at a H 2 O =1; QFM is quartz–fayalite–magnetite oxygen buffer). The comparison of experimental products with natural phase assemblages, phase compositions, and whole-rock compositions was used to estimate magma storage conditions and to reconstruct the magma plumbing system. We estimate that Lascar two-pyroxene andesitic magmas were stored at 975±25 °C, 300±50 MPa, and log f O 2 of QFM+1.5±0.5, under H 2 O-undersaturated conditions with 2.5 wt % to 4.5 wt % H 2 O in the melt. The geochemical characteristics of the entire suite of Lascar volcanics indicates that a fractionating magmatic system located at a depth of 10–13 km is periodically replenished with less evolved magma. Some eruptive stages were dominated by volcanic products resulting most probably from the mixing of a mafic andesitic magma with a felsic component, whereas compositional variations in other eruptive stages are better explained by crystal fractionation processes. The relative importance of these two mechanisms (mixing vs. crystal fractionation) may be related to the amount and frequency of magma recharge in the reservoir.

Source: European Journal of Mineralogy

DOI: 10.5194/ejm-36-721-2024

Authors: André Stechern, Magdalena Blum-Oeste, Roman E. Botcharnikov, François Holtz, Gerhard Wörner

Institutions: Leibniz University Hannover, Federal Institute for Geosciences and Natural Resources, University of Göttingen, Johannes Gutenberg University Mainz

Language: English

Topic: Geological and Geochemical Analysis

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,024

Funder: Deutsche Forschungsgemeinschaft