Browsing by Author "Clunes, Matías"

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    Crustal folds alter local stress fields as demonstrated by magma sheet - Fold interactions in the Central Andes
    (2021) Clunes, Matías; Browning, John; Cembrano, José; Marquardt, Carlos; Gudmundsson, Agust
    For magma chambers to form or volcanic eruptions to occur magma must propagate through the crust as dikes, inclined sheets and sills. Most models that investigate magma paths assume the crust to be either homogeneous or horizontally layered, often composed of rocks of contrasting mechanical properties. In regions that have experienced orogenesis, like the Andes, the crust has been deformed over several million years, resulting in rock layers that are commonly folded and steeply dipping. The assumption of homogeneous properties or horizontal layering then does not capture all of the potential magma path-crustal interactions. Here we tackle this problem by determining the effect of a crust made of steeply inclined layers in which sills and inclined sheets are emplaced. We combine field observations from a sill emplaced in the core of an anticlinal fold at El Juncal in the Chilean Central Andes, including lithologies, sill and fold limbs attitude, length and thickness with a suite of finite element method models to explore the mechanical interactions between inclined layers and magma paths. Our results demonstrate that the properties of the host rock layers as well as the contacts between the layers and the geometry of crustal structures all play an important role in magma propagation and emplacement at shallow levels. Sill propagation and emplacement in heterogeneous and anisotropic crustal segments change the crustal stress field promoting sill arrest, deflection or further propagation. Specifically, sills are more likely to be deflected when encountering shallow dipping layers rather than steeply dipping layers of a fold. Mechanically weak contacts encourage sill deflection due to the related rotation of the stress field and this effect is attenuated when the folded layers are steeper. These processes may change the amount and style of recorded surface deformation, with implications for monitoring of active volcanoes. (C) 2021 Elsevier B.V. All rights reserved.
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    Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile
    (2021) Clunes, Matías; Browning, John; Marquardt, Carlos; Cembrano, José; Villarroel, Matías; Rivera, Orlando; Mpodozis, Constantino
    In the Atacama Desert, at the Precordillera of northern Chile, a series of Paleocene-Eocene caldera deposits and ring-faults are exceptionally well-preserved1. Here we aim to build on previous mapping efforts to consider the location, timing and style of pre, syn and post caldera volcanism in the region. We focus on the partially nested caldera complexes of Lomas Bayas and El Durazno2,3 where deposits record several stages of caldera evolution (pre-collapse, collapse/intra-caldera and extra-caldera, resurgence and post-collapse eruptive deposits). The pre-caldera basement is a thick sequence of early Paleocene mafic lavas4, 5. The caldera complex formed between around 63 and 54 Ma4, 5. Both calderas constitute subcircular structures approximately 13 km in diameter and are cut by several NNW to NNE-trending felsic dikes which are spatially related to felsic domes interpreted as resulting from post caldera formation unrest1,4. These calderas have been interpreted as part of the Carrizalillo megacaldera complex2 . We combine field observations, such as the attitude of dikes, as well as information on their dimension and composition, the size, location and composition of domes and lava flows, as well as the evidence of the regional stress field operating during the caldera evolution from measurements of fault kinematics. This data will be used as the input to finite element method models to investigate the effect of nested caldera geometry, ring-faults and crustal heterogeneities on the location of domes and eruptive centers generated during caldera unrest. The results will be potentially useful for constraining models of eruption forecasting during periods of unrest in calderas and ore deposition models which have been shown to be linked to caldera structure and magma emplacement
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    Variable elastic anisotropy controls stress in shallow crown pillars
    (2025) Cortez, Jorge; Browning, John; Marquardt, Carlos; Clunes, Matías; Carmona, Nicolás; Benson, Philip; Koor, Nick
    As easily accessible natural resources become depleted, it is necessary to extract material from deeper levels and so mines may opt to develop a process of transition from open-pit to underground mining methods. In some cases, however, the process develops in the opposite direction where shallower resources from historic underground districts are mined by surface extraction methods. In both cases, it is necessary to maintain a crown pillar to ensure the stability of the pit and underground infrastructure. The dimensions of these crown pillars are typically designed using a combination of empirical methods and numerical modelling. In both methodologies, rocks are often treated as elastic and isotropic materials, even when they exhibit a clear direction of anisotropy caused by bedding planes, foliation, or closely spaced joints. To explore the role of this anisotropy in the stress state surrounding and within crown pillars, a series of two-dimensional finite element models were built using the code FEniCS. The results of this study show that tectonic loading leads to significantly higher compressive stresses, 2 to 4 times greater than gravitational loads alone. Tensile stress also increases notably, with values reaching almost -11 MPa compared to −1 MPa under gravitational loads. Therefore, the degrees of anisotropy and its orientation is likely to play a significant role in stress distribution. Our findings highlight the importance of constraining the in-situ stress, the geology of the host rock and the degree of anisotropy at laboratory scale for adequately addressing the risk of crown pillar failure and mining subsidence.