Rheological, petrophysical and geometrical constraints of a subduction channel from a numerical model perspective: Insights from La Cabaña Paleozoic peridotites, Coastal Cordillera of south-central Chile. (March 2022)

• Record Type: Journal Article
• Authors: Sanhueza, Jorge; Yáñez, Gonzalo; Barra, Fernando; Maringue, José; Figueroa, Ronny; Sáez, Esteban
• Is Part Of: Journal of South American earth sciences. Volume 114(2022)
• Publication Date: 2022-03
• Subjects: Subduction zones -- Subduction channel numerical model -- Accretionary prism -- Exploration geophysics; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2021.103706
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: The emplacement of ultramafic blocks in accretionary complexes poses a geodynamic problem due to their negative buoyancy. In this study, we explore plausible emplacement scenarios for peridotite bodies in the Coastal Cordillera of south-central Chile by combining geophysical observations, numerical modeling and available petrological data for ultramafic blocks exhumed along the subduction channel. The La Cabaña massif is the largest serpentinized peridotite complex yet recognized in the Coastal Cordillera, however, its size and petrophysical characteristics remain unknown. The geophysical measurements were performed to determine the size of this body, involving magnetic airborne surveys and electrical resistivity tomography. Inversion data show that the largest ultramafic block in La Cabaña is 3 km long, 1.5 km wide and at least 1.2 km deep. This result constrains the characteristics of the block transported by the subduction channel. In the second step, we developed a numerical model for the subduction channel assuming a viscous rheology. In this modeling effort we search for tectonic scenarios that provide adequate conditions for the exhumation of the ultramafic body in La Cabaña. These scenarios included a combination of key parameters, subduction angle dip and velocity, subduction channel geometry, rheology and density contrast. Scenarios compatible with the exhumation of La Cabaña body type includes channel viscosity range of 10 19−20 Pa s, fast exhumation rates at mantle depths (10–20 mm/yr; >30–40 km), steep subduction angles (30°–60°), subduction channel widths of 3–5 km, density contrast between −200 and −400 kg/m 3 and a body diameter of 1.5 km which is consistent with our geophysical inversions. On the contrary, slow exhumation rates (∼1 mm/yr), low subduction angles (15°), high-density contrasts (−400 to −600 kg/m 3 ) and bodies larger than 1.5 km wide, are not viable exhumation scenarios. The methodology developed provided insights to infer ancient subduction channel geometries and rheologies that include peridotite. Highlights: We test the concept that the subduction channel drives the exhumation of ultramafic blocks within accretionary prisms. We perform a parametric study of the rheology, geometry and density for ultramafic blocks exhumed in accretionary prisms. Critical conditions regarding the serpentinization degree and subduction channel rheology are also explored.