Damara Orogen and Gondwana Assembly
Significance of the Damara Orogen in Gondwana Assembly
Supercontinent cycles remain one of the most significant and poorly understood aspects of the evolution of the global geodynamic system. The Rodinia-Gondwana supercontinent cycle, in particular, defines a unique and challenging period in Earth history that remains enigmatic in spite of impressive improvements in geological and geophysical data sets and the cycle’s significance for the evolution of life and global dispersion of life forms. We are testing two very different hypotheses for the relationship between the Congo and Kalahari cratons during this supercontinent cycle. At present, Congo and Kalahari reside within the African continent and are juxtaposed across the Neoproterozoic-Cambrian Damara-Lufilian-Zambezi orogenic system. The primary controversy surrounding the role/roles of these two cratons in the Rodinia-Gondwana cycle centers on the extent to which Congo and Kalahari remained associated geographically throughout the cycle, i.e., were the two cratons directly adjacent to one another in Rodinia, and, did they remain so until amalgamated in Gondwana, or was one (or both) not in Rodinia at all and were not joined until Gondwana formed? The answers to these questions have implications for the origin of the Damara-Lufilian-Zambezi orogenic system (e.g., ensialic or ensimatic), defining whether final Gondwana suturing was along an east-west or north-south axis, and constraining the degree to which Rodinia was fragmented during break-up.
We are addressing these questions by performing detailed U-Pb geochronologic and Hf-isotopic studies of the detrital zircon populations in Neoproterozoic clastic sediments within the Pan-African Damara Orogen and on selected basement samples from the two cratons. We will also measure the Nd-isotopic compositions of metasedimentary rocks to further fingerprint the origin of this detritus. We will use these data to test hypotheses for the relative locations and interactions of the Congo and Kalahari cratons in Neoproterozoic time. In particular, these data will allow us to address whether the oft-discussed model for the formation of Gondwana as the result of a final collision of East and West Gondwana upon closing of the Mozambique Ocean is correct. This remains an open question because the youngest intracontinental mobile belts in Africa, India, Antarctica, and Australia seem most compatible with the final suturing occurring between “North” and “South” Gondwanan fragments at about 530 Ma along the proposed Kuunga suture, which includes the Damara-Lufilian-Zambezi orogenic system. The details of Gondwana amalgamation in turn have implications for the setting and time of initiation of Paleozoic tectonic cycles like the Delamerian-Ross Orogeny and the Iapetus-Taconic cycle in the northern and southern hemispheres.
Map of the supercontinent of Gondwana showing the location of the Damara Orogen (from Foster et al. 2009).