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The right-lateral El Pilar fault system extends from the Gulf of Cariaco in northeastern Venezuela to the east coast of Trinidad. The fault is seismically active, deforms Quaternary strata, and is the boundary between two very different geological provinces. North of the fault is the eastern Cordillera de la Costa, which is composed of Lower Cretaceous metasediments and igneous rocks that accumulated in a tectonically and volcanically active environment, probably a fore-arc setting. These rocks were metamorphosed to greenschist facies during the Late Cretaceous, and deformed by imbricate fold and thrust faults during the Cretaceous and Tertiary. South of the fault is the Serrania del Interior, a fold and thrust belt composed of Cretaceous and Paleogene sediments that were deposited, at least during the Early Cretaceous, in a comparatively stable tectonic environment, probably a passive continental margin, and deformed during post-Middle Eocene time.

In northeastern Venezuela the El Pilar fault consists of two major branches, one of which was not recognized in previous studies. Geologic mapping demonstrates a cumulative dextral displacement that must exceed 20 km. A steep gravity gradient across the fault system suggests that the fault plane is a nearly vertical density discontinuity to a depth of at least 5 to 10 km. Gravity models imply that a relatively dense mafic crust is present north of the fault, and regional geology demonstrates that a similar crust does not exist south of the fault anywhere east of the Gulf of Cariaco. It follows that a total right-lateral displacement of 150 to 300 km may be necessary to account for the steep gravity gradient at the fault.

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