Role of crustal contribution in the early stage of the Damara Orogen, Namibia: New constraints from combined U–Pb and Lu–Hf isotopes from the Goas Magmatic Complex

• The age of the first Pan-African magmatic event in the Damara Belt is constrained.
• A possible origin for the crustal components of this early magmatism is inferred.
• The Damara orogeny might have not represented a major crustal forming episode.

The tholeiitic to calc-alkaline Goas Complex represents the earliest magmatic activity of the inland branch of the Damara Orogen, and reflects the Pan-African convergence between the Congo and Kalahari Cratons. New results from laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb geochronology coupled with single-zircon Lu–Hf isotopic data constrain the age of emplacement and allow the identification of a crustal contribution to the magma sources. No temporal gap is registered between the first tholeiitic intrusion at ca. 575 Ma and the main diorite to granite episodes. Invariably sub-chondritic εHft values (− 3.8 to − 34.4) attest to a significant crustal residence time with long-term reworking of multiple and mixed crustal components. No significant juvenile magma was involved in the magmatogenesis. Hf model ages coupled with an exhaustive dataset of U–Pb geochronological data suggest that the crustal components which fed the Goas sources might have formed during specific orogenic events with a major contribution of material derived from the central-western African Paleoproterozoic Eburnean Orogen. Geochemistry, U–Pb geochronology and Hf isotope systematics however, do not unequivocally clarify the long debate regarding whether or not the Pan-African orogenic cycle included ocean closure and subduction, as the involvement of crustal melting processes during the early stage of the Damaran event seems to have played a major role.

Figure optionsDownload as PowerPoint slide