South Kwanza Basin (Offshore Angola) as a Major Cornerstone of West African Margin

Abstract

The south Kwanza basin is a major structural feature for west African segmentation, separating a narrow upper plate margin to the south (Namibe basin), and a wide lower plate one to the north (North Kwanza to Gabon). Here, the extension is highly oblique and dissects the margin in narrow stripes, offsetting structural domains apart from transverse structures, superimposing two structural fabrics. Significantly affected by volcanism, the area marks the transition from a margin with high magmatic budget to a magma-poor margin. Three main magmatic stages are recognized: the first one in Neocomian-Barremian, recording the Large Igneous Province volcanism of Parana-Etendeka trapp, most likely consists of small-scale SDR's with intercalated lava flows-intrusives and volcanoclastic sediments. This tholeiitic magmatism is well developed onshore down to the necking zone of the margin. The second phase occurred in Late Aptian, close to salt deposition. Intrusives are found affecting Barremian to Aptian series, or trapped at the base of salt, even intruding the salt itself. This transitional tholeiitic magmatism is well developed offshore from the hyper-extended to exhumation domains of the margin. The third event is an alkaline magmatism, it occurred in Albian to Turonian, synchronously to oceanic crust accretion, attest of the magmatic shift through the evolution of a margin, accompanying the proximal to distal migration of the main magmatic activity centers. Both transverse structures and structural domain transitions appear crucial for hydrothermal carbonates commonly found in South Kwanza. Timing between mantle-coupling processes, volcanism and salt deposition is considered as a main driver controlling fluid circulations and diagenesis (see abstracts by Girard et al. & San Miguel et al. herein). Combining observations and measurements at various scale, this integrated interdisciplinary study provides comprehensive proxies for the petroleum system of a basin in such a structural setting.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017