Browsing by Author "Villarroel, Matías"

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    Reconciling mechanical models of caldera ring-fault nucleation within the transcrustal magmatic system paradigm
    (Elsevier B.V., 2024) Villarroel, Matías; Browning, John; Marquardt Roman, Carlos Jorge; Clunes Squella, Matias; Zañartu Torres, Gabriela Antonia; Giordano, Guido
    © 2024 Elsevier B.V.The formation of a collapse caldera requires the nucleation of circumferential ring-faults that connect an underlying magma chamber with the Earth's surface. The roof of the magma chamber collapses as a consequence of magma withdrawal due to either over- or under-pressure within the chamber. Recent inferences have suggested that calderas may form atop complex transcrustal magma systems with several individual or interconnected magma chambers residing at depth throughout the crust. Whilst there have been several attempts to define the mechanical conditions leading to caldera fault nucleation, the assumptions for these models often rely on a single shallow magma chamber or the combination of a single shallow magma chamber with doming of a deep-seated magma reservoir. There have, so far, been no attempts to reconcile the mechanical conditions leading to ring-fault nucleation and potential collapse caldera formation with inferred geometries and arrangements of complex transcrustal magmatic systems. Here we address this issue using Finite Element Method (FEM) to reconcile mechanical conditions for caldera ring-fault nucleation within the transcrustal magma system paradigm by modeling multiple magma pocket arrangements. Out of the 150 distinct combinations of shallow magma chambers and pressure conditions that were tested, only 15% yielded the necessary conditions for the successful formation of a caldera ring-fault, supporting the need for special or very specific conditions for the occurrence of calderas in nature. Results show that relatively small lateral distances in the position between magma chambers inhibit the stress conditions required for caldera fault nucleation and propagation. Changes in the vertical spacing between stacked magma chambers do not significantly alter the distribution of either tensile or shear stress. This implies that the specified criteria for initiating ring-faults are consistently met, regardless of the number or arrangement of magma chambers. However, vertical offsets between laterally distributed magma compartments lead to an uneven distribution of shear stress, potentially triggering a trapdoor-type collapse. Consistent with the results presented here, the concept of vertically stacked magma compartments has been proposed as an explanation for both contemporary and ancient volcanic systems.
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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