Intracontinental deformation in southern Africa during the Late Cretaceous

Roderick Brown,Michael Summerfield,Andrew Gleadow,Kerry Gallagher,Andrew Carter,Romain Beucher,Mark Wildman

doi:10.1016/j.jafrearsci.2014.05.014

Abstract

Intracontinental deformation accommodated along major lithospheric scale shear zone systems and within associated extensional basins has been well documented within West, Central and East Africa during the Late Cretaceous. The nature of this deformation has been established by studies of the tectonic architecture of sedimentary basins preserved in this part of Africa. In southern Africa, where the post break-up history has been dominated by major erosion, little evidence for post-break-up tectonics has been preserved in the onshore geology. Here we present the results of 38 new apatite fission track analyses from the Damara region of northern Namibia and integrate these new data with our previous results that were focused on specific regions or sections only to comprehensively document the thermo-tectonic history of this region since continental break-up in the Early Cretaceous. The apatite fission track ages range from 449±20Ma to 59±3Ma, with mean confined track lengths between 14.61±0.1μm (SD 0.95μm) to 10.83±0.33μm (SD 2.84μm). The youngest ages (c. 80–60Ma) yield the longest mean track lengths, and combined with their spatial distribution, indicate major cooling during the latest Cretaceous. A simple numerical thermal model is used to demonstrate that this cooling is consistent with the combined effects of heating caused by magmatic underplating, related to the Paraná-Etendeka continental flood volcanism associated with rifting and the opening of the South Atlantic, and enhanced erosion caused by major reactivation of major lithospheric structures within southern Africa during a key period of plate kinematic change that occurred in the South Atlantic and SW Indian ocean basins between 87 and 56Ma. This phase of intraplate tectonism in northern Namibia, focused in discrete structurally defined zones, is coeval with similar phases elsewhere in Africa and suggests some form of trans-continental linkage between these lithospheric zones.

Highlights

The influence of pre-existing lithospheric structure on the geometry and location of intra-continental rifting, associated with the development of the Atlantic Ocean, has been well documented by studies in northeastern Brazil and in West, Central and East Africa
1 Current address: Department of Earth Science, Faculty of Mathematics and Natural Sciences, University of Bergen, 5020 Bergen, Norway. 1991; Fairhead and Binks, 1991; Binks and Fairhead, 1992; McHargue et al, 1992; Maurin and Guiraud, 1993; Winn et al, 1993; Loule and Pospisil, 2012). These studies have highlighted the genetic relationship between the tectonic development of intracontinental rift basins, within Africa and South America, and changes in the nature and geometry of the surrounding plate boundaries, in particular those associated with the development of the North and Central Atlantic Ocean basins, from their initiation during the Late Triassic (e.g. Manspeizer, 1988; Torsvik et al, 2009) through to the present (Blundell, 1976)
The fission track data presented in this paper place some important new constraints on the post-Damara thermal history of the shallow crust in northern Namibia

Summary

Introduction

The influence of pre-existing lithospheric structure on the geometry and location of intra-continental rifting, associated with the development of the Atlantic Ocean, has been well documented by studies in northeastern Brazil and in West, Central and East Africa 1991; Fairhead and Binks, 1991; Binks and Fairhead, 1992; McHargue et al, 1992; Maurin and Guiraud, 1993; Winn et al, 1993; Loule and Pospisil, 2012) These studies have highlighted the genetic relationship between the tectonic development of intracontinental rift basins, within Africa and South America, and changes in the nature and geometry of the surrounding plate boundaries, in particular those associated with the development of the North and Central Atlantic Ocean basins, from their initiation during the Late Triassic

Objectives

Discussion

Conclusion