Neotectonic evolution of Northeastern Venezuela . Geomorphological and seismic analysis in the Monagas Fold and Thrust Belt

Abstract

In Northeastern Venezuela, since 10 Ma, the tectonic setting is dominated by the eastward translation of the Caribbean Plate accommodated mainly by the E-W El Pilar strike-slip fault. However, to the south, in the Monagas Fold and Thrust Belt (MFTB), evidence of active compression has been identified in the southern limit of the Urica dextral fault. The objective of this study is to integrate geomorphological, dating terraces and 2D-3D seismic data in four zones of the MFTB: Tarragona, Punta de Mata, Jusepín, and Amarilis to understand the tectonics relationship between surficial and deep deformation in the area. These zones show surface deformations such as topographic uplifts, tilted, folded and faulted terraces, and drainage anomalies.The age of the river terraces obtained through 10Be and 26Al methods indicates that these terraces were formed in the late Pleistocene. The oldest terrace, located in the Tarragona zone, has a maximum exposure age of 90 ± 5 ka and the youngest, located in the Punta de Mata zone of 15 ± 5 ka. Additionally, we calculated an uplift rate of 0.3–0.4 mm/y for Plio-Pleistocene units using the deformation of the Late Miocene Unconformity (LMU). This rate coincides with the vertical deformation rate average calculated from terraces dating, which suggests that the deformation rate in the MFTB has not changed significantly for the last 5.3 Ma.The ridges observed at the surface and the structural highs interpreted from seismic sections indicate that the uplifting has been active up to the present through the activation of deep thrusts. We propose that the deformation on the surface is linked to the Tarragona, Pirital, Furrial thrusts, and the Amarilis backthrust activity and the youngest thrusts developed in the Carapita Formation. However, this surface deformation decreases towards the SSE away from the Urica fault; therefore, the neotectonic deformation is believed to be caused by the horsetail termination activity at the southern limit of the Urica fault.