3D geological modeling of the Trujillo block: Insights for crustal escape models of the Venezuelan Andes

摘要

The Venezuelan Andes form a N50°E-trending mountain belt extending from the Colombian border in the SW to the Caribbean Sea in the NE. The belt began to rise since the Middle Miocene in response to the E-W collision between the Maracaibo block to the NW and the Guyana shield belonging to South America to the SE. This oblique collision led to strain partitioning with (1) shortening along opposite-vergent thrust fronts, (2) right-lateral slip along the Bocond fault crossing the belt more or less along-strike and (3) crustal escape of the Trujillo block moving towards the NE in between the Bocono fault and the N-S-striking left-lateral Valera fault. The geology of the Venezuelan Andes is well described at the surface, but its structure at depth remains hypothetic. We investigated the deep geometry of the Merida Andes by a 3D model newly developed from geological and geophysical data. The 3D fault model is restricted to the crust and is mainly based on the surface data of outcropping fault traces. The final model reveals the orogenic float concept where the mountain belt is decoupled from its underlying lithosphere over a horizontal decollement located either at the upper/lower crust boundary. The reconstruction of the Bocono and Valera faults results in a 3D shape of the Trujillo block, which floats over a mid-crustal decollement horizon emerging at the Bocono-Valera triple junction. Motion of the Trujillo block is accompanied by a widespread extension towards the NE accommodated by normal faults with listric geometries such as for the Motatan, Momboy and Tufiame faults. Extension is explained by the gravitational spreading of the upper crust during the escape process.