Abstract

The Espino rift of north-central Venezuela is a 60–100 km (35–60 mi) wide, 250 km (155 mi) long, symmetrical, subsurface rift that formed in the Cambrian–Ordovician and underwent a second phase of rifting during the Late Jurassic breakup of Pangea. During the Oligocene and Miocene, normal faults bounding the Espino rift were more strongly inverted at its northern end by right-lateral transpression between the eastward-moving Great Arc of the Caribbean (GAC) and the northern margin of South America. During the Oligocene to Holocene, the Espino rift became deeply buried beneath clastic sedimentary rocks of the Eastern Venezuela foreland basin. We apply filters to gravity and magnetic data from the region of the Espino rift in central Venezuela to delineate the crustal setting of the rift. We use three 2-D gravity transects combined with five seismic reflection transects tied to 12 wells to reconstruct the multistage geologic and structural evolution of the Espino rift from its initial rift phase in the Cambrian–Ordovician, through its subsequent latest Jurassic period of rifting, and its final period of Oligocene–Miocene transpression related to the oblique collision of the GAC with northern South America. Because there is no direct well evidence for the type and age of basement underlying the Espino rift, our gravity and magnetic transects provide new observations on crustal thickness variations across and along the rift, which ranges from 13 to 30 km (8–19 mi). Gravity modeling also reveals a variation in Moho depths from approximately 30 km (19 mi) on its rift flanks to 24–29 km (15–18 mi) beneath the rift axis. These data constrain the subsurface extent of the rift that can be traced for 200 km (125 mi) along-strike with three main segments: (1) a shallower rift in the south (top basement buried 1.8 km [5905 ft] beneath the rift axis), (2) the deepest, central rift area (top basement buried 12 km [39,370 ft] beneath the rift axis), and (3) a zone of Cenozoic tectonic transpression in the northern rift area (top basement buried 10 km [32,800 ft] beneath the rift axis). Based on wells and seismic reflection data, we conclude that the Cambrian–Ordovician rift phase was accompanied by a greater degree of crustal thinning than the Late Jurassic rift phase. The northwest–south extension direction remained the same for both rifting events.