William E. Bonini, 1984. "Magnetic provinces in western Venezuela", The Caribbean-South American Plate Boundary and Regional Tectonics, William E. Bonini, Robert B. Hargraves, Reginald Shagam
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Magnetic provinces, recognized by trend geometry and anomaly character, are delineated in western Venezuela utilizing aeromagnetic data from the 1950s oil company surveys. In northwestern Venezuela, the Guajira-Paraguaná province (east-west anomalies) lies north of a proposed east-west fault zone extending from the southern Para-guaná Peninsula across the Gulf of Venezuela and south of the pre-Tertiary outcrops on the Guajira Peninsula. South of this fault zone and on the west is the Perijá province (northeasterly trends) and on the east the Coro province (northwesterly trends). The Oca zone province (east-west trends) separates the northern and southern parts of the Perijá province. Geologic features which can result in these magnetic anomalies are fault blocks, east-west faults, some in sets, faults oblique to east-west shear, and probably intrusions into the crust parallel to these features. These have been produced by differential motion between the major zones of dislocation resulting from right-lateral offsets on east-west transcurrent faults during extension in the Tertiary. Thus, the magnetic anomalies locate a complex zone of Cenozoic interaction on this margin of the Caribbean-South American plate boundary.
South of the Oca fault, the Perijá province trends are related to the geologic trends of the Sierra de Perijá, and the Jurassic La Quinta graben complex and the Central Lake Graben. There are only modest, trendless anomalies in the eastern Maracaibo Basin, the Falcón Basin, and the area to the south. Magnetic basement rocks here are probably igneous and metamorphic Paleozoic units, similar to those exposed in the Venezuelan Andes. Southeast of the Andes, a major lineation between the Barinas and Río Meta provinces is correlated with the projection of the Altamira fault. Unmetamorphosed lower Paleozoic sedimentary rocks are preserved in a block dropped down to the north. This is possibly an extension of the Espino Graben complex, which is 300 km to the northeast and in which Jurassic basalt is preserved. Strong magnetic anomalies west and south of the El Baúl Uplift are probably associated with Jurassic volcanics, similar to those exposed in the uplift, perhaps preserved in the same graben complex. These appear as major features of the interior plains (llanos) north of the Guayana Shield.
The primary subdivision of the magnetic provinces is two-fold. North of and including the Oca fault-Coro area, magnetic anomalies document the complex zone of interaction related to east-west shear in Cenozoic time. South of this, magnetic anomalies are related to the distribution of pre-Cretaceous rocks, some of which were involved in the plate boundary interactions, but others to the south are related to the development of the pre-Cretaceous terrane north of the Guayana Shield.