Orogenic float of the Venezuelan Andes

Abstract

The Venezuelan (or Mérida) Andes are a NE-trending intracontinental orogen that started to rise from the Middle Miocene due to the E–W far field convergence between the Maracaibo block to the northwest and the Guyana shield to the southeast. Oblique convergence is responsible for strain partitioning with thrusting along both foreland basins and right-lateral strike–slip faulting along the NE–SW Boconó fault cutting the Venezuelan Andes along-strike. The central part of the belt is also cut by the N–S left-lateral strike–slip Valera fault that connects the Boconó fault, both faults bounding the Trujillo block that escapes towards the NNE. Even though the regional geology of belt is well known, its structure at depth remains a matter of debate. Our work, based on the integration of geological and geophysical data aims to better constrain the deep geometry of faults and the tectonic evolution of the mountain belt. We used the orogenic float model to construct two NW–SE trans-Andean crustal scale balanced sections. The Late Neogene–Quaternary shortening varies from 40 km in the south to 30 km in the north across the Trujillo block, indicating that a quarter of the deformation seems to be absorbed by the tectonic escape process. More importantly, a major reorganization in the crust took place in the Early Pliocene. It is characterized by the imbrication of the Maracaibo crust into the Guyana crust. This resulted in the subduction of the Guyana lower crust and the formation of a NW-vergent basement thrust propagating upwards and surfacing along the Las Virtudes thrust. Rapid uplift of the northern flank of the belt subsequently occurred together with massive deposition of the Plio–Quaternary coarse grained Betijoque formation in the northwestern foreland basin.