Browsing by Author "Gomila R."

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    Quantitative anisotropies of palaeopermeability in a strike-slip fault damage zone: Insights from micro-CT analysis and numerical simulations
    (Elsevier B.V., 2021) Gomila R.; Arancibia G.; Cembrano J.; Gomila R.; Arancibia G.; Morata D.; Cembrano J.; Gomila R.; Nehler M.; Bracke R.; Morata D.
    © 2021 Elsevier B.V.Fracturing and damage around faults related to seismogenesis can enhance hydrothermal fluid percolation, causing mineral precipitation. This study uses hydrothermally sealed microfractures across an ancient exhumed fault to unravel the 3D-spatial distribution of fault damage and related anisotropy in permeability. We studied the fault damage zone of the Jorgillo Fault, a left-lateral strike-slip fault, exposed by ca. 20 km in the Atacama Fault System, northern Chile. The study was conducted by addressing the 3D-spatial distribution of the microfracture network through X-ray micro-computed tomography and palaeopermeability modeling using a computational fluid dynamic approach, thus assessing mm-scale fault-related permeability tensors. 3D modeled fault-directed permeability ellipsoids on both sides of the fault core are transverse anisotropic, where palaeopermeability (matrix permeability) in the fault-parallel plane is higher than across-strike of the Jorgillo Fault (2.4 and 1.9 times in the eastern and western block of the fault, respectively). Modeled 3D permeability values (ca. 10−11 to 10−15 m2) show a mean overestimation factor of 8.4 of the estimated 2D permeability (ca. 10−9 to 10−12 m2). Permeability anisotropy distribution in the damage zone is related to off-fault damage generation, and could be explained by tip propagation fault growth and dynamic rupture due to earthquakes under the fault-valve mechanism. Whereas the fault would act as an impermeable seal except for post-failure, when it became highly permeable for fluids.
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    Sinistral shear during Middle Jurassic emplacement of the Matancilla Plutonic Complex in northern Chile (25.4° S) as evidence of oblique plate convergence during the early Andean orogeny
    (Elsevier Ltd, 2022) Mavor S.P.; Singleton J.S.; Heuser G.; Arancibia G.; Gomila R.; Seymour N.M.; Williams S.
    © 2022Arc magmatism in a continental subduction zone facilitates rheological weakening of the rigid upper plate, and can accommodate the partitioned trench-parallel component of oblique subduction into an intra-arc shear zone. We document a shear zone at latitude 25.4° S near Taltal, Chile that was associated with intrusion of the Matancilla Plutonic Complex at ∼169 Ma to evaluate intra-arc deformation and possible tectonic plate configurations during this time period. Polyphase folding of Paleozoic metasedimentary rocks is overprinted by mylonitic fabrics that are most extensive in a zone up to 1.4 km wide in the thermal aureole of the granodioritic Matancilla pluton, where contact metamorphic andalusite porphyroblasts are synkinematic with fabric development. Mylonite in metasedimentary rocks is overprinted by a ∼130 Ma granodiorite (zircon U–Pb) and by ∼133 Ma postkinematic monazite (U–Pb). Within the Jurassic Matancilla granodiorite, pervasive ductile shear occurs along the intrusive contact while centimeter-scale discrete high-strain zones throughout the pluton are associated with focused hydrothermal alteration and reaction weakening. Mylonitic foliation in the metasedimentary rocks and within the pluton strikes N- to NE and dips steeply, while stretching lineations are subhorizontal on average. Kinematic indicators record dominantly sinistral shear, though some dextral or symmetric indicators and S > L fabrics suggest a component of coaxial strain and flattening. Sinistral strike-slip kinematics in the Matancilla shear zone may indicate that Middle Jurassic convergence had sinistral obliquity that was locally partitioned into the contemporaneous magmatic arc. Sinistral-oblique convergence would require the Phoenix-Farallon spreading center to be north of ∼25° S in the Middle Jurassic, providing a constraint to plate reconstructions during the early Andean orogeny.