The central Falcon igneous suite, Venezuela: alkaline basaltic intrusions of oligocene-Miocene age

Abstract

Basaltic igneous rocks crop out in a 50 km belt within Oligocene sedimentary rocks in the central Falcon Basin of northwestern Venezuela. Outcrop patterns, structural orientations, chilled margins, baked contacts, sedimentary inclusions, igneous breccias and uniformly alkaline compositions suggest these bodies are shallow intrusives and extrusives. Potassium-Argon determinations on a sill yield a 22.9 ± 0.9 Ma age which is 5 Ma younger than paleontologic ages of surrounding sedimentary rocks. A span of igneous activity from 28 to 23 Ma is inferred from stratigraphic constraints. Locally, normal NNW-SSE growth faults are present in Oligocene units. Features of similar regional trend and evidence of growth faulting offshore imply a tensional tectonic regime during Oligocene-Miocene time. The tensional regime, silica undersaturated, alkaline nature of the igneous rocks, and rapid basin subsidence rates suggest a pull-apart basin model for the Falcon Basin – Bonaire Trough area. This resulted from commencement of Caribbean - South American transform motion over a wide zone of offset transform faults.