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 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. 575Ma and the main diorite to granite episodes. Invariably sub-chondritic εHf_t 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.