Progressive Growth of the Cerro Bayo Cryptodome, Chachahuén Volcano, Argentina—Implications for Viscous Magma Emplacement

Abstract

Cryptodome and dome collapse is associated with volcanic hazards, such as explosive eruptions, pyroclastic density currents, and volcanic edifice collapse. The study of the growth and evolution of volcanic domes provides vital information on the link between dome growth and the development of weakness zones that may cause collapse. The Cerro Bayo cryptodome is superbly exposed in the eroded Miocene Chachahuén volcano in the Neuquén basin, Argentina. Cerro Bayo is a >0.3‐km3 trachyandesitic cryptodome that intruded within the uppermost kilometer of the Chachahuén volcano. Here we investigate the emplacement of the Cerro Bayo cryptodome using structural mapping, photogrammetry and measurement of magma flow indicators, brittle deformation features, and magnetic fabrics with anisotropy of magnetic susceptibility. Magma flow fabrics near the margin are concentric and indicate contact‐parallel flow and internal inflation of the body. Magmatic and magnetic fabrics and fracture patterns in the interior of the cryptodome are more complex and outline several structural domains. These domains are separated by magmatic shear zones that accommodated intrusion growth. The shear zones locally overprint the earlier formed concentric fabric. The nature of the structural domains shows that the emplacement of Cerro Bayo occurred in three stages that resemble the endogenous to exogenous growth of volcanic domes. The formation of magmatic shear zones during cryptodome formation may have a profound effect on cryptodome stability by creating weakness zones that increase the risk of collapse.

Segment tip geometry of sheet intrusions, II: Field observations of tip geometries and a model for evolving emplacement mechanisms

“…However, in these cases an evolving pathway also occurs [e.g. Currier and Marsh, 2015;Mattson et al, 2018;Burchardt et al, 2019], which is consistent with our findings here.…”

“…Haug et al, 2017, 2018]. Other factors affecting emplacement mechanism include the magma viscosity [Mattsson et al, 2018;Burchardt et al, 2019;Wilson et al, 2019], magma driving pressure relative to the tectonic stress [Gill and Walker, 2020], the depth of emplacement (Gill and Walker, 2020), and the remote stress state [e.g. Pollard 1973;Pollard et al, 1975;Rubin, 1993;Chanceaux and Menand, 2016;Walker and Gill, 2020].…”

“…Modifications to the conditions of emplacement during magma propagation, such as increasing magma viscosity during cooling, have been shown to result in modifications to the intrusion geometry and the associated style of host rock deformation for cryptodomes and laccoliths [e.g. Currier and Marsh, 2015;Mattson et al, 2018;Burchardt et al, 2019]. Such modifications are also likely to occur in segmented sheet intrusions, and since late stage processes have the potential to overprint early structures, segment geometries as observed in the field, may be representative only of the final stage of emplacement, rather than the emplacement process as a whole [Walker et al, in prep].…”

Comparative field study of shallow rhyolite intrusions in Iceland: Emplacement mechanisms and impact on country rocks

“…Holness, 2018;Healy et al, 2018). Magma emplacement style depends on physical properties and structure of surrounding rocks, regional tectonics and magma rheology (Pollard, 1973;Spence and Turcotte, 1985;Hutton, 1988;Clemens and Petford, 1999;Galland et al, 2006;Matsson et al 2018;Stephens et al, 2018;Burchardt et al 2019). As examples, transition from a dyke to a sill is associated to a variation of strength in layered country rocks (Kavanagh et al 2006;Maccaferri et al, 2011) and/or to the occurrence of a strong compressive tectonic stress (Gudmundsson., 1990;Maccaferri et al, 2011), and the intrusion width is affected by the country rock lithology and magma viscosity (e.g.…”

Decrypting Magnetic Fabrics (AMS, AARM, AIRM) Through the Analysis of Mineral Shape Fabrics and Distribution Anisotropy

“…% TiO 2 and the amphibole phenocrysts have been classified as pargasite and hastingsite (Sun, 2018). Interpretations of magma flow in the Cerro Bayo cryptodome utilizing the AMS data in this study are presented in Burchardt et al (2019).…”