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Pre-rift and synrift exhumation, post-rift subsidence and exhumation of the onshore Namibe Margin of Angola revealed from apatite fission track analysis

2015; Geological Society of London; Volume: 438; Issue: 1 Linguagem: Inglês

10.1144/sp438.2

2041-4927

Paul F. Green, Vladimir Machado,

Geological and Geochemical Analysis

Abstract A series of cooling events in the development of the Namibe margin of Angola is defined by apatite fission track analysis data from samples of outcropping Cretaceous sandstones and crystalline Precambrian basement. Regional exhumation in the Late Carboniferous–Early Permian and Jurassic preceded Early Cretaceous rifting. Further episodes of uplift and erosion affected the margin in the Early and Late Cretaceous before it was buried by up to 2 km of post-break-up section, which was subsequently removed during Cenozoic uplift and erosion beginning between 35 and 20 Ma. This timing is consistent with published analyses of river profiles suggesting that uplift of the margin began at c. 30 Ma. Estimates of between 1.5 and 2 km of section removed during Cenozoic exhumation are consistent with burial depths estimated from the diagenesis of former evaporite horizons now at outcrop. These results add further support to a growing body of evidence showing that the evolution of ‘passive’ margins is anything but passive. The key episodes of exhumation defined in this study are broadly synchronous with events identified in many areas of the West Africa margin from Namibia to Equatorial Guinea and are regarded as representing a continent-scale response to stresses related to tectonic plate movements.