Anomalous crust in the Eastern Venezuela Basin and the Bouguer gravity anomaly field of northern Venezuela and the Caribbean borderland.

Abstract

A new Bouguer gravity anomaly map is presented for the southern Caribbean borderland and northern South America. Major features are; the Lake Maracaibo-Venezuela Andes minimum (-160 mgal); gravity maxima in the Venezuelan offshore area and on the Netherland Antilles; a steep gradient (- 4.7 mgal/km) south across the Western Caribbean Mountains; the termination on Margarita ultra-mafic rocks of the minimum trend of the Lesser Antilles; and the broad gravity minimum (-200 mgal) to the east and anomalous maxima (+10 mgal) to the west associated with the Eastern Venezuela Basin. Gravity models have been calculated for two sections over this basin. The broad gravity minimum in the east can be explained by up to 15 km of sediment and crustal downwarping to a depth of 47 km. The maxima suggest an anomalous crust, possibly caused by a higher-density basement, a crustal upwarp, or both. The trend of the gravity maxima parallels those of the Eastern Venezuela Basin minimum and the Antillean trends as they enter Venezuela. In addition they are parallel to the ENE structural trends of the Precambrian south of the Orinoco River. Thus, the anomalous sub-sediment rocks could be related to Mesozoic tectonics, or Precambrian basement features.