CRUSTAL STRUCTURE AND GEOLOGIC HISTORY OF THE ESPINO RIFT, VENEZUELA, BASED ON INTEGRATION OF POTENTIAL FIELDS, SEISMIC REFLECTION, AND WELL DATA
Rodriguez Milano, Lourdes Gabriela Del Carmen 1989-
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The Espino rift of north-central Venezuela is a 60-100-km-wide, 250-km-long symmetrical, subsurface rift that formed in Cambrian-Ordovician time and experienced a second phase of rifting during the late Jurassic breakup of Pangea. During Oligocene and Miocene, normal faults bounding the Espino rift were reactivated especially at its northern end by transpression between the eastward-moving Caribbean plate and the northern margin of South America. During this period, the Espino rift became deeply buried beneath the Eastern Venezuela foreland basin. I apply filters to gravity and magnetic from the region of the Espino rift in central Venezuela to delineate the crustal setting of the Espino rift. I use three 2D gravity transects combined with five seismic reflection transects tied to twelve wells to reconstruct the multi-stage geologic and structural evolution of the Espino rift from its initial rift phase in Cambrian-Ordovician time through its subsequent period of rifting during the latest Jurassic, and a final period of Oligocene-Miocene tectonic transpression related to the oblique collision of the Great Arc of the Caribbean with northern South America. Because there is no direct well evidence for the type and age of basement underlying the Espino rift, my gravity and magnetic transects provide new observations on crustal thickness variations across and along the rift which ranges from 13 to 30 km. Gravity modeling also reveals a variation in Moho depths from ~30 km on its rift flanks to 24-29 km beneath the rift axis. These data constrain the subsurface extent of the rift that can be traced for 200 km along-strike from a shallow rift in the south (basement 1.8 km beneath the rift axis) to a central rift area (basement 12 km beneath the rift axis) to a zone of Cenozoic tectonic transpression in the northern rift area (basement 10 km beneath the rift axis). Based on wells and seismic reflection data, I infer that the Cambro-Ordovician rift phase was accompanied by a greater degree of crustal thinning and transpression than the late Jurassic rift phase.