Vlad Constantin Manea

The pore structure of volcanic rocks such as andesites typically shows a rather heterogeneous structure due to the origin of such rocks. The porosity exhibits a random distribution and fluctuates as the size of the sample increases, complicating its estimation at scales of interest. In this work, we examined the behavior of porosity fluctuations for five andesitic rock samples as a function of scale, and for the first time, two differential equations with initial conditions were formulated and solved analytically. With these equations we derive the mathematical expressions of the upper and lower bounds that describe the maximum and minimum limits within porosity fluctuations as a function of the scale. The equations only require a few input parameters, such as the maximum pore size, maximum solid phase size, and porosity of the characterized sample, along with two porosity measures (maximum and minimum) at a specific scale. The scope of this investigation is focused to the scales accessible throughout micro-CT imaging while providing potential implications for broader-scale applications. It is noteworthy that no previous works have provided mathematical expressions for these bounds. We performed a detailed porosity analysis by dividing binary multi-resolution and multi-scale micro-CT images into smaller images in order to extract an extensive dataset comprising hundreds of thousands of porosity data points. Modeling results show that rock heterogeneities directly affect the behavior of the porosity with the scale, showing more disperse fluctuations in the more heterogeneous samples but stabilizing and approaching a constant value assumed as the representative elementary volume (REV). Although it is not always reached within the investigated scales, all porosity fluctuations can be enveloped by two upscaling porosity bounds (upper and lower). This trend continues until a scale is reached at which either a REV may be identified, or the porosity progressively converges toward a stable value, at least for a range of scales where porosity variations become negligible.

Tectonic plates bend and deform when approaching a subduction zone, creating intense faulting and highly variable stress and strain fields across short distances inside the slab. In September 2017, a large M_w8.2 intraplate normal fault occurred in southern Mexico, with an epicentral area located within a seismic gap where no megathrust had struck in more than a century. Despite the relatively young and hot Cocos plate, this seismic episode ruptured almost the entire slab below the brittle–ductile transition zone that normally limits the depth extent of such events. Here, we present a high-resolution thermomechanical model of spontaneous subduction for this area, where bending-induced brittle and ductile deformation and grain plate damage are considered. Modeling results show that the 2017 M_w8.2 Tehuantepec normal fault earthquake occurred due to the reactivation of one of the outer-rise-formed abyssal faults. In addition, the hypocenter was located in a stable, hydrated region of the lithospheric mantle at the transition limit between the elastic and ductile regimes. We found that earthquake rupture orientation is consistent with a region where a clear localized shear band of reduced effective viscosity is predicted. We propose that the rupture of this large intraslab event propagated in the ductile portion of the slab initially by a transformational faulting process, followed by a thermal runaway mechanism at greater depths and higher temperature.

An outstanding question in the geological evolution of the Chilean Andes is the cause of the westward shift and relocation of magmatism from the High Andes (HA) to the Coastal Cordillera (CC) during the Late Triassic, Pre–Andean stage. The spatiotemporal distribution of Permian–Triassic–Jurassic igneous rocks in northern‐central Chile (20°S–32°S) reveals a significant westward magmatic shift of ∼120 km during the Norian time. Despite diverse proposed models, the precise geodynamic mechanism behind this shift remains unclear. To address this, we used 2D numerical modeling to investigate two contrasting scenarios: (a) subduction rollback and (b) subduction transference/jump and reinitiation by terrane accretion. Our modeling results strongly support Scenario B, where mantle density and the size of the oceanic plateau are crucial for triggering subduction jump and reinitiation. This model aligns with geological and geophysical evidence and offers new insights into unraveling the Pre– and Early–Andean evolution.

The rapid development of computer technology in the last decades provided scientists with new opportunities to expand their research fields and in the same time to compress the necessary time to obtain research based scientific conclusions. This fast tendency also significantly affected the scientific discovery trend, and in many research fields we observe a transition from standard laboratory experiments to numerical experiments. In the particular research field of Earth Sciences, computational modeling constitutes a powerful predictive tool that fills a geological and geophysical data gap. The geological record covers well the Earth’s surface but is quite limited in depth, whereas geophysical information can provide depth-based information but it is limited in time to present day. Therefore, there is a large data gap in time and space that cannot be covered unless some indirect and intuitive prediction method is used. In this picture, numerical simulations come as an essential research tool. In this work, we provide a review about the research progress obtained in the last 15 years using high-performance computing at the Computational Geodynamics Laboratory at the Centro de Geociencias, Universidad Nacional Autónoma de México.

Compared to normal arc-related volcanic eruptions, the formation of a volcanic caldera is a relatively atypical event. During caldera formation a series of large volumes of magma are erupted, reducing the structural support for the rock above the magma chamber and creating a large depression at the surface called caldera. Los Humeros volcanic field (LHVF) represents one of the largest volcanic calderas in Mexico. It is located some 400 km from the trench at the eastern edge of the Trans Mexican Volcanic Belt where the depth to the Cocos slab is more than 300 km. In this study we employ high-resolution two-dimensional thermomechanical numerical simulations of magma intrusions and a horizontal tectonic strain rate to better understand the influence of crustal deformation for the formation of Los Humeros caldera. A minimum number of three thermal anomaly pulses of hydrated mantle material (with diameter of 15 km or more) and a regional strain rate of 7.927 × 10^–16 s⁻¹ are required for magma to reach the surface. Modeling results show that regional extension coupled with deep thermal anomalies (with a temperature excess of ΔT ≥ 100 °C) that come in a specific chain-type sequence produce surface deformation patterns similar to LHVF. We propose an asthenospheric sub-slab deep source (> 300 km depth) for the thermal anomalies where previous studies showed the existence of a gap or tear in the Cocos slab.

The subduction of the Philippine Sea (PHS) plate along the Nankai Trough in in southwest Japan is a relatively recent process compared with subduction along the Japan Trench in northeast Japan. However, the tectonic evolution of the PHS plate along the Nankai Trough is still controversial and not fully understood. There are several competing hypotheses based on different estimates for the time variations of convergence rate and plate age. Our study employs numerical modelling of subduction in order to evaluate the slab evolution for the last 15 Myr and aims to evaluate each tectonic scenario against the present-day slab geometry along a profile passing through the Shikoku and Chugoku regions. The modelling strategy involves a parameter study where subduction initiation and various subduction parameters are analyzed in terms of subduction geometry evolution. Two-dimensional visco-elasto-plastic numerical simulations of spontaneous bending subduction predict that convergence rate and plate age variations play an important role in the evolution of subduction geometry. Modeling results after 15 Myr of evolution reveal that the tectonic model based on a high convergence rate between ~ 15 Ma and ~ 3 Ma produces a slab geometry that agrees well with the observed present-day slab shape specific for the Shikoku and Chugoku regions.

Oceanic plates are far from homogeneous, and a large number of bathymetric discontinuities such as seamounts of different sizes are transported along by plate motion towards the mid ocean trenches and beyond. Seamounts currently colliding with plate margins show a major role in shaping the forearc morphology, and several studies even suggest that they might be related with seismicity. However, it is not clear what happens after seamounts are subducted, they can be accreted to the forearc, carried down into the subduction zone and recycled into the deep mantle, or a mix of the two scenarios. Using high-resolution two-dimensional thermomechanical numerical simulations, we investigate subduction processes of oceanic plates with a heterogeneous structure marked by a series of basaltic seamounts arranged in a chain like structure. We solve the 2D momentum, continuity and energy equations with the finite differences coupled with PIC (particle-in-cell) method. Our models also incorporate a depth-dependent, realistic non-Newtonian visco-elasto-plastic rheology, and plasticity is implemented using a yield criterion which limits the creep viscosity. Preliminary results show that initially seamounts preserve they structure when impacting with the trench. Their integrity is partially conserved until they subduct to a depth of about 25-30 km when they finally start to succumb to the great deformations and stresses along the slab interface. We observed that the lower part of the seamount continuously deforms and amalgamates along the slab interface. The upper part is detached and incorporated into the forearc structure. The subsequent seamounts that trail the first seamount, follow the same deformation pattern, and the top of them are maintained in the highly deformed forearc region. Our preliminary modeling results confirm that seamount subduction represent a key tectonic process that influences on a long-term time scale the structure and evolution of subduction zones.

Variation of subduction parameters (i.e., plate age and velocity) along trenches show in general a smooth spatial variation. However, despite these gradual changes heat flow measurements show large variations. For example, previous studies show that heat flow direct observations along the Middle America Trench (MAT) range from 14 to 261 mW/m2, without a clear pattern. One of the common hypotheses that can explain such variations is the presence of hydrothermal circulation within the oceanic crust that enters subduction. Here we present modeling results of hydrothermal circulation using finite elements to calculate the flow, temperature and pressure distribution in oceanic crust. We employ PDE2D (www.pde2d.com), a general-purpose finite element program for solving multidimensional partial differential equations, to solve the coupled equations of continuity, Darcy equation, and energy conservation equation in two dimensions. Our model setup incorporates a low permeability sedimentary layer, a high permeability oceanic crust layer and a basal heat source. Modeling results show that hydrothermal circulation is sensitive to the basal source and multiple convection cells are formed within the permeable oceanic basaltic crust. The sedimentary layer located on top of the permeable layer acts as an insulator. Therefore, smooth temperature fluctuations are observed at the surface. We adapted this model setup and incorporate a series of permeable paths in the sedimentary layer that connect the oceanic crust with the ocean bottom. Modeling results show significant changes in the convection patterns for the oceanic crust, and depending on the width of the permeable conduits and basal heat source, high temperature water plume can infiltrate all the way to the ocean bottom. Some models show that these high temperature plumes have a transitory character and they are followed by infiltration of cold seawater into the oceanic aquifer. Our modeling results show that the observed large heat flow variations along oceanic trenches can be attributed to hydrothermal circulation only when permeable pathways connect the permeable upper crust with the ocean.