Detailed in-depth mapping of the world largest anorthositic complex: Magnetic anomalies, 2.5-3D modelling and emplacement constraints of the Kunene Complex (KC), SW Angola

Abstract

The Kunene Complex (KC) represents a very large Mesoproterozoic igneous body, mainly composed of anorthosites and gabbroic rocks that extends from SW Angola to NW Namibia (outcropping 18,000 km2 , NE-SW trend, and ca. 350 km long and up to 50 km wide). Little is known about its structure at depth. Here, we use recently acquired aerogeophysical data to accurately determine its hidden extent and to unravel its morphology at depth. These data have been interpreted and modelled to investigate the unexposed KC boundaries, reconstructing the upper crustal structure (between 0 and 15 km depth) over-lain by the thin sedimentary cover of the Kalahari Basin. The modelling reveals that the KC was emplaced in the upper crust and extends in depth up to ca. 5 km, showing a lobular geometry and following a large NE-SW to NNE-SSW linear trend, presumably inherited from older Paleoproterozoic structures. The lat-eral continuation of the KC to the east (between 50 and 125 km) beneath the Kalahari Cenozoic sediments suggests an overall size three times the outcropping dimension (about 53,500 km²). This affirmation clearly reinforces the economic potential of this massif, related to the prospecting of raw materials and certain types of economic mineralization (Fe-Ti oxides, metallic sulphides or platinum group miner-als). Up to 11 lobes have been isolated with dimensions ranging from 135.5 to 37.3 km in length and 81.9 to 20.7 km in width according to remanent bodies revealed by TMI mapping. A total volume of 65,184 km³ was calculated only for the magnetically remanent bodies of the KC. A long-lasting complex contractional regime, where large strike-slip fault systems were involved, occurred in three kinematic pulses potentially related to a change of velocity or convergence angle acting on previous Paleoproterozoic inherited sutures. The coalescent magmatic pulses can be recognized by means of mag-netic anomalies, age of the bodies as well as the lineations inferred in this work: (i) Emplacement of the eastern mafic bodies and granites in a stage of significant lateral extension in a transtensional context between 1500 Ma and 1420 Ma; (ii) Migration of the mantle derived magmas westwards with deforma-tion in a complex contractional setting with shearing structures involving western KC bodies and base-ment from 1415 Ma to 1340 Ma; (iii) NNW-SSE extensional structures are relocated westwards, involving mantle magmas, negative flower structures and depression that led to the formation of late Mesoproterozoic basins from 1325 Ma to 1170 Ma. Additionally, we detect several first and second order structures to place the structuring of the KC in a craton-scale context in relation to the crustal structures detected in NW Namibia.

Keywords

Angola / Kunene Complex (KC) / Magnetic prospecting / 2.5 modelling / 3D inversion

CrediT authorship contribution statement

T. Mochales: Writing - review & editing, Writing - original draft, Visualization, Software, Methodology, Formal analysis, Data curation, Conceptualization. E. Merino-Martínez: Writing - review & editing, Writing - original draft, Project administration, Methodology, Data curation, Conceptualization. C. Rey-Moral: Writing - review & editing, Writing - original draft, Software, Methodology, Conceptualization. A. Machadinho: Writing - review & editing, Writing - original draft, Visualization, Validation, Software. J. Carvalho: Writing - review & editing, Project adminis-tration, Methodology. P. Represas: Writing - review & editing, Visualization, Methodology. J.L. García-Lobón: Writing - review & editing, Supervision, Project administration, Funding acquisition, Conceptualization. M.C. Feria: Visualization. R. Martín-Banda: Writing - review & editing, Conceptualization. M.T. López-Bahut: Visualization. D. Alves: Visualization. E. Ramalho: Visualization. J. Manuel: Visualization, Project administration. D. Cordeiro: Visualization.

Declaration of competing interest

The authors declare that they have no known competing finan-cial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work is a result of the National Geological Plan of Angola (PLANAGEO) and Investigación de procesos geológicos y recursos mineros críticos para la transición energética en Angola y en España (PIE-PLANAGEO). This project was supported by the Government of the Republic of Angola and implemented by the Geological Survey of Angola (IGEO), under the oversight of the Angolan Ministry of Mineral Resources, Oil and Gas (MIREMPET). Further analytical data and isotopic results were also supported by the subsidiary programme ‘‘Ayudas Extraordinarias Menciones Excelencia Severo Ochoa” of the CN IGME-CSIC (project AECEX2021, grant 15903). We would like to express our gratitude for the assistance provided by the local staff during our fieldwork. We also highly appreciate the contribution of the staff of Impulso Industrial Alternativo to this project. The Geotransfer group (University of Zaragoza) and the staff of the Paleomagnetism laboratory (University Polytechnic of Burgos) kindly helped us with the laboratory analyses. Isabel Fanlo, Nacho Subias (Univer-sity of Zaragoza), Mario Iglesias kindly provided samples of areas with complex access that were used in this work. Part of this work was performed by T. Mochales as a Visiting Fellow at the Institute for Rock Magnetism (IRM) by funding from the University of Min-nesota and National Science Foundation (award NSF-EAR 2153786). A. Machadinho thanks the Portuguese Foundation for Science and Technology (FCT) support, Geosciences Center project UIDB/ 00073/2020 (doi:10.54499/UIDB/00073/2020), University of Coimbra and and GeoBioTec project UIDB/04035/2020 (doi:10.54 499/UIDB/04035/2020), Nova School of Science and Technology. The authors are very grateful to Dr. Geissler and an anonymous reviewers for their suggestions to improve this paper.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.gsf.2025.102030.23

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