Protracted emplacement and multi-stage evolution of the Kunene Complex (Angola and Namibia) revealed by multi-mineral U-Pb geochronology
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Elsevier
Abstract
The Mesoproterozoic Kunene Complex of Angola and Namibia is the world’s largest massif-type anorthosite complex, and represents an exceptional area for studying the large-scale magmatic and thermal record of long-lived Proterozoic anorthosites. We examined evolved pegmatoidal enclaves and their host anorthosites from the central part of the complex to clarify their crystallisation sequence and investigate the magma emplacement dynamics and post-crystallisation thermal and metasomatic history. In combination with detailed petrography and mineral mapping, zircon, apatite and titanite were analysed for U-Pb isotope and trace element concentrations. Zircon dates for both the enclaves and the host anorthosites are ca. 1500 Ma, indicating contemporaneous crystallisation, but some zircon grains underwent coupled dissolution-reprecipitation, likely driven by high-temperature fluids related to protracted regional Kunene magmatism. The oldest age for one Kunene anorthosite, at 1510 ± 4 Ma, attests to a total duration for the magmatism reaching 150 Myr. Apatite also crystallised at ca. 1500 Ma as it mostly preserves magmatic textures and igneous trace element compositions, but records resetting ages of ca. 1400 Ma, corresponding with a subset of zircon dates and the crystallisation ages of secondary titanite, which may reflect a major Kunene magmatic pulse at this time. Overall, zircon age variability in single samples, combined with trace element decoupling, suggest localised post-crystallisation disturbance of the magmatic system. This study shows the contribution that multiple geochronological datasets from large igneous bodies can provide to explain prolonged histories of magma recharge, thermal rejuvenation and fluid-rock interaction.
HIGHLIGHTS
• Combined multi-mineral geochronology testifies to prolonged magmatic activity in the Kunene Complex, extending up to 150 Myr.
• Anorthosite and pegmatoidal enclaves crystallised simultaneously, at ca. 1.5 Ga.
• Protracted magmatism produced age decoupling and heterogeneous trace elements in zircon and apatite.
Description
DATA AVAILABILITY : No data was used for the research described in the article.
APPENDIX A. Supplementary data
SUPPLEMENTARY DATA 1.
TABLE SM1. Zircon U-Th-Pb data measured by LA-MC-ICP-MS (University of Johannesburg).
TABLE SM2. Zircon trace element content (ppm) measured by iCAP RQ ICP-MS (University of Johannesburg).
TABLE SM3. Zircon U-Th-Pb data measured by LA-SF-ICP-MS (University of the Witwatersrand).
TABLE SM4. Apatite U-Th-Pb data measured by LA-SF-ICP-MS (University of the Witwatersrand).
TABLE SM5. Apatite trace element content (ppm) measured by LA-SF-ICP-MS (University of the Witwatersrand).
TABLE SM6. Titanite U-Th-Pb data measured by LA-SF-ICP-MS (University of the Witwatersrand).
TABLE SM7. Titanite trace element content (ppm) measured by LA-SF-ICP-MS (University of the Witwatersrand).
TABLE SM8. Ti-in-zircon estimated temperature obtained with the algorithm in TZT (Dardier et al., 2021).
FIGURE SM1. U-Pb zircon dates for the Graniserra and Chibemba samples, expressed as weighted means calculated on concordant U-Pb data. Weighted means are not reported in the first two diagrams as the data are widely spread and define two populations.
FIGURE SM2. Kernel density estimation (KDE) measuring density probability for U-Pb in zircons from two anorthosite samples from Graniserra
FIGURE SM3. Temperature variation (as Celsius degrees) with Th/U obtained from Ti content in zircon for the two populations of the Graniserra anorthosite KSAT279-2A and KSAT279-4A after Dardier et al. (2021).
FIGURE SM4. BSE detail of Graniserra enclave KSAT279-94C. Zircon (light blue) rimming ilmenite (and magnetite) is elongated in thin chains but also as more discrete, larger, subhedral grains. Abbreviations: Ilm = ilmenite, Mag = magnetite, Zrc = zircon.
FIGURE SM5. U vs. Th for apatite grains.
FIGURE SM6. Log Sr/Y vs. log LREE (La+Ce+Pr+Nd) apatite discriminant fields by O'Sullivan et al. (2020). Square = anorthosite; circle = enclaves. Acronyms: ALK = alkali-rich igneous; HM = high-grade metamorphic; IM = mafic granitoids and mafic igneous rocks; LM = low- to medium-grade metamorphic and metasomatic; S = felsic granitoids; UM = ultramafic igneous.
FIGURE SM7. Details of TIMA-mapped thin sections from Graniserra with titanite crystallisation (orange). A: Thin section detail from KSAT279-2A (anorthosite) with titanite developed together with metasomatic chlorite and calcite. B: Detail of thin section KSAT279-1F (enclave) with titanite mostly developed in association with pyrite; other minerals are chlorite, pyroxene, magnetite. C: Detail of thin section KSAT279-1G (enclave) with titanite developed mostly in association with pyrite, calcite, and magnetite. Other phases are plagioclase and chlorite. Tit = titanite.
FIGURE SM8. REE patterns and calculated Tera-Wasserburg dates for the 2 secondary titanite types in anorthosite KSAT279-2A. A gap of at least 30 Myr between 2 metasomatic events is suggested, with youngest titanite characterised by REE-depletion and positive Eu anomaly.
Keywords
Geochronology, Mesoproterozoic Kunene Complex, Angola, Namibia, Proterozoic anorthosites, Zircon, Apatite
Sustainable Development Goals
SDG-15: Life on land
Citation
Milani, L., Ngomane, G., Lekoetje, T. et al. 2026, 'Protracted emplacement and multi-stage evolution of the Kunene Complex (Angola and Namibia) revealed by multi-mineral U-Pb geochronology', Precambrian Research, vol. 444, art. 108201, pp. 1-22, doi : 10.1016/j.precamres.2026.108201.