Gabon Regional Structural Framework, Derived from Gravity

Michael Alexander and Karim Aimadeddine
Integrated Geophysical Corporation, Houston, TX

This regional interpretation of western Gabon is based on satellite-derived gravity data offshore, a bathymetry/topographic grid, and a compilation of published data offshore and onshore. Local features of primary exploration interest include a series of basins and high blocks trending subparallel to and subnormal to the coastline. Fault/fracture zones extend northeast from oceanic crust of the South Atlantic onto the offshore shelf and the onshore coastal areas of Gabon.

Gabon’s coastal plain is flanked to the east by basement outcrop from the Gabon-Congo border to the Gabon-Equatorial Guinea border. It widens northward and is subdivided north-south into two main structural provinces by the N’Komi fault/fracture zone. It contains five basins, two of which extend into the offshore, and five high blocks, one of which extends into the offshore. Gabon’s offshore shelf contains five significant basins and five major high blocks.

An interpreted oceanic-continental crust boundary lies offshore, trending northwest parallel the shoreline and along an alignment of residual gravity maxima. It is locally offset by northeast-southwest shears, has a major dextral offset at the N’Komi, and then trends north along another alignment of residual maxima as far as the Gabon-Equatorial Guinea border.

The Atlantic Hinge Zone, or shelf-slope break, south of N’Komi Fault Zone can be correlated with the seaward edge of a northwest-southeast residual gravity maximum trend. Similar gravity anomalies suggest that a hinge zone continues north of the N’Komi before either turning northeast between Loiret and Fang Fault Zone or trending north to the Equatorial Guinea border.

While interpretation of satellite-derived gravity can provide a regional geologic framework, integration with other data sets is necessary to produce a map with more immediate exploration value.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery