Field observations and numerical models of a Pleistocene-Holocene feeder dyke swarm associated with a fissure complex to the east of the Tatara-San Pedro-Pellado complex, Southern Volcanic Zone, Chile

Abstract

Magma is transported through the lithosphere as dykes which, during periods of unrest, may feed eruptions at the surface. The propagation path of dykes is influenced by the crustal stress field and can be disturbed by crustal heterogeneities such as contrasting rock units orfaults. Moreover, as dykes propagate, they themselves influence the surrounding stress field through processes of stress transfer, crustal deformation and seismic failure. The re suit is the formation of arrested dykes, as well as contrasting strike and dip angles and dyke segmentation. Here, we study the mechanisms of dyke injection and the role played in modifying the stress field and potential prop agation paths of laterdyke injections. To do this we combine field data from an eroded and well exposed shallow feeder dyke swarm with a suite of two dirnensional FEM numerical models. We mapped 35 dyke segments over a-1 km long dyke swarm exposed-5 km to the East of Pellado Volcano. in the Tatara San Pedro Pellado (TSPP) volcanic complex , Southem Volcanic ° Zone of the Andes. Detailed mapping of the swarm eluddates two preferen tial strike orientations, one -N80 E and the other -N60"E. Our numerical models simulate bath the TSPP volcanic complex and the studied dyke swarm as zones of either magmatic excess pressure or as a rigid inclusion. The crustal segment hosting the volcanic complex and dykes is mode lied using an elastic domain subjected to re gional compression in select mode( cases. Mode( outputs provide the stress and strain fields resulting from the different geometries and applied boundary loads. The mode( results indicate that individual dyke injections can locally rotate the principal stresses such as to influence the range of orientations over which later dykes will form. The orientation of a 1 at the dyke tip ranges over 60° ( ±30° either side of the dyke tip) indicating that the strike orientation of later dykes will fall within this range. The elfect of adding a bulk regional compres sion is to locally increase the magnitude of favorably oriented tensile stresses in the bedrock but to reduce the range of a 1 orientati ons to 40° (±20°). This implies that under a far field transpressive stress regime, as is corn mon in Andean settings, regional dyke swarms will tend to maintain their strike orientation parallel to the re gional bulk stress. These results should be accounted for when studying periods of volcanic unrest in order to discern the location and orientation of potential fissure eruptions in active volcanic are as such as the Southern Volcanic Zone of the Andes.

Geothermal potential of small sub-volcanic intrusions in a typical Icelandic caldera setting

“…This contrasts with the more uniform orientation and dimensions of fractures and dykes associated with Krafla and other fissure swarms [e.g. Paquet et al 2007;Hjartardóttir et al 2012;Ruz et al 2020]. Nonetheless, the predominant fissure-parallel N to NNE orientation of fractures opening within the Krafla caldera in the 1975-1984 rifting episode indicates that the local caldera-related stress field does not always strongly influence dyke orientations [Hjartardóttir et al 2012], and so temporal changes in caldera-related stress fields must also be an important factor.…”

“…The fluctuations in temperature for models 8D-SHI and 8S-SHI between 25 and 30 years is due to the downwelling of cold plumes in the geothermal system. Walker 1999;Khoei et al 2015;Karaoğlu et al 2016;Burchardt et al 2018;Mordensky et al 2018;Bazargan and Gudmundsson 2019;Ruz et al 2020;Satow et al 2021].…”

“…Further systematic analysis of the spacing of fossil dissected intrusions [e.g. Paquet et al 2007;Ruz et al 2020] and the timing of intrusion events during instrumentally observed rifting episodes [e.g. Björnsson et al 1979;Ágústsdóttir et al 2016] will provide useful new constraints.…”

The interplay of a fault zone and a volcanic reservoir from 3D elasto-plastic models: Rheological conditions for mutual trigger based on a field case from the Andean Southern Volcanic Zone

“…The volcanic products include lava flows and pyroclastic deposits with compositions ranging from basalts to rhyolites (Singer et al, 1997). ENE-striking sub-vertical dykes have been mapped on the northern, eastern, and southern sides of the volcanic complex and are interpreted as coeval with Late Pleistocene-recent oblique-slip tectonics (Singer et al, 1997;Sielfeld et al, 2019b;Ruz et al, 2020).…”

Geología de diques emplazados en tefra, SE Sierra de Pachuca

“…Los diques son estructuras que se forman al solidificarse el magma presurizado que asciende desde el reservorio hacia la superficie, ya sea a través de fracturas preexistentes o mediante la propagación de grietas formadas por fracturamiento hidráulico (Daniels et al, 2012;Pansino et al, 2019;Ruz et al, 2020).…”