March 3, 2026Open Access

Columbia supercontinent remnants in the Tuareg Shield (Iforas, Mali)

Key Points

Granulites in the Iforas unit demonstrate two key Paleoproterozoic events occurring at around 2.0 Ga and 1.89 Ga.
U-Pb and Hf isotopic analyses show intricate histories of metamorphic conditions, with temperatures reaching 920°C.
The tectonic setting indicates a micro-continental block positioned between two larger cratons, defining its evolutionary context.
Findings may reshape our understanding of the Columbia supercontinent and its geological evolution over 1.8 Ga.

Abstract

• Rocks from Western Hoggar recorded two Paleoproterozoic granulitic events. • These granulites form a micro-continental block sandwiched between two cratons. • Iforas granulites are witnesses of the assembly of the Columbia supercontinent. • Iforas granulites are connected to coeval granulitic belts of the North China Craton. • LASS-ICP-MS (U-Pb age and Hf isotopes) has been achieved during this study. The Iforas Granulitic Unit (Tuareg Shield), east of the West African Craton, is a key place to help reconstructing the Columbia supercontinent evolution. In this area, the emplacement of magmatic protoliths is constrained at c. 2.05–2.06 Ga and the production of the magmas involved recycling of a Paleoproterozoic to Archean crustal component (up to 3.0 Ga). For the first time, this study emphasizes two distinct Paleoproterozoic granulitic events. The first one occurs at ca. 2.0 Ga and was followed by a second event of very-high temperature (up to 920°C) at ca. 1.89 Ga. Rocks from the Iforas Granulitic Unit subsequently remained at high temperature (≥500°C) for a protracted period of c. 150 Myrs and record multiple phases of accessory mineral growth, dissolution and recrystallisation. This is illustrated by U-Pb monazite ages, peaking at 1780–1760 Ma, reflecting fluid driven replacement reactions as documented by apatite / allanite coronas around monazite. Cooling of the granulites, down to c. 500°C, occurred in the range 1720–1700 Ma (apatite and rutile ages). The chronology of the magmatic/metamorphic events is consistent with a collisional setting involving a micro-continental block consisting of the Iforas / In Ouzzal granulitic units sandwiched between the West African Craton and an eastern landmass which may be the Saharan metacraton. This study has major consequences for global reconstructions of the Columbia supercontinent as it demonstrates that, at c. 1.8 Ga, this microcontinent fits as a continuation of the Khondalite Belt or Trans North China Belt of the North China Craton.

Columbia supercontinent remnants in the Tuareg Shield (Iforas, Mali)

Key Points

Abstract

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