Browsing by Author "Cornthwaite, John Paul"

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    Tectonic Evolution of the South Caribbean-Northwest South America Subduction Zone
    (2022-12-02) Cornthwaite, John Paul; Levander, Alan
    In this work I image the northwest South American-southern Caribbean subduction zone beneath the Maracaibo Block from the crust to the mantle transition zone. I tie together the different structures I model to propose the tectonic evolution that explains the physiography observed at the surface. Finite-frequency teleseismic P-wave tomography illuminated the large structures of the subducting Caribbean plate and provided the first-order explanation of how a flat-subducting Caribbean plate contributed to the uplift of three mountain ranges far from the trench. P- and S-wave local earthquake tomography showed the finer structure of the upper mantle and crust and supported the idea that the Caribbean plate interacted with the South American plate deep into the interiors of Colombia and Venezuela. Ps receiver functions revealed critical boundaries in the upper mantle and crust and corroborated substantial crustal deformation in the crust in response to subduction. My first project focused on the large-scale structures of the Caribbean-northwest South American subduction zone. I modeled the subduction structures using finite frequency teleseismic P-wave tomography and connected those structures to the Laramide-style deformation on the overriding South American plate. I identified three segments of subducting Caribbean plate with one segment completely detached from the surface. The timing of the detachment aligns with other regional events, including the uplift of the Mérida Andes, about 10 Ma. Slab buoyancy post-detachment likely resulted in recoupling with the overriding plate, reactivation of Jurassic-aged rift structures and subsequent uplift of the Mérida Andes. Mantle counterflow over the broken segment induced by rollback of the attached slab likely contributed to the uplift of the Mérida Andes. I concluded that the northern limit of subduction lies south of the Oca-Ancón fault, though the fault itself may be the surface expression of the boundary. In my second study I use P- and S- wave local earthquake tomography to model shallow structures within the subduction zone that connect subduction processes to deformation in the overriding plate. I identified several large fast anomalies (dlnVp ~ +4%) extending from the base of the Maracaibo block to near the top of the currently subducting plate under the whole length of the Maracaibo block. I hypothesized this anomaly is buoyant Caribbean lithosphere that has remained attached to the base of the Maracaibo block lithosphere during slab fragmentation. Upwelling mantle that replaced the descending slab is observed beneath the Serrania de Perijá and the Mérida Andes and possibly contributes to dynamic uplift of those mountains. A fast anomaly observed beneath the Moho under Lake Maracaibo is likely similarly negatively buoyant eclogitized slab crust that has not yet detached and contributes to subsidence in the overriding plate. My third study provides a regional view of crustal and upper mantle structure using Ps receiver functions. I revealed variable crustal thickness that thickens due continental underthrusting under the Serrania de Perijá and the Mérida Andes. South American crust appears to underthrust Maracaibo block crust under the Mérida Andes. I found that the crust within the Maracaibo Block is highly heterogeneous and blocky. Poisson ratios within the Maracaibo block appear to trend higher than outside of the block. In the mantle I identified the transition from subduction to underthrusting of the Caribbean plate south of the Oca-Ancón fault, in agreement with my first study. Finally, I speculated that mantle upwelling could be occurring throughout the Maracaibo Block.