Cryogenian crustal evolution in western Nigeria shield: whole-rock geochemistry, Sr-Nd and zircon U-Pb-Hf isotopic evidence from Bakoshi-Gadanya granites

ABSTRACT

The Bakoshi-Gadanya area, with widespread Neoproterozoic granites, is located within the Pan-African Trans-Sahara Belt, sandwiched between the West African and the Sahara metacraton. The whole-rock geochemistry, Sr-Nd isotope systematics and LA-(MC)-ICP-MS U-Pb-Hf isotopes of zircon were analysed to shed light on the age and genesis of the Bakoshi-Gadanya granites in the Precambrian basement of the northern western Nigeria shield. The granites are silicic (SiO₂: 72.8–77.2 wt.%), ferroan, high-K, calc-alkalic to alkali-calcic in composition, with A-type granite affinities. The ferroan calc-alkalic types range in age from 706.6 ± 1 Ma to 638.4 ± 1 Ma, and the alkali-calcic type is dated at 710 ± 1 Ma. Whole-rock Sr-Nd and zircon Hf isotope systematics have constrained the ferroan calc-alkalic granites to an enriched mantle lithospheric magma source, contaminated by Archaean-Palaeoproterozoic crustal components. On the other hand, the magma that crystallized the alkali-calcic Gadanya granite originated from an enriched mantle source, triggered by reactivation of the lithosphere-scale Kalangai fault during the post 750 Ma major collision between West African Craton and the Saharan metacraton. Both alkali-calcic and calc-alkalic ferroan granites were formed contemporaneously with the last major Pan-African syn-metamorphic deformation in northern western Nigerian shield; thus, they are syn-kinematic granites. Neoproterozoic magmatism at Bakoshi-Gadanya area is related to easterly dipping subduction at the margin of microcontinental blocks in northern western Nigeria shield. Zircon U-Pb-Hf data envisaged both early Neoproterozoic and Cryogenian juvenile magmatic additions in this part of western Nigeria shield.

Graphical abstract

KEYWORDS:

• Bakoshi-Gadanya area
• juvenile magma source
• Neoproterozoic granites
• Pan-African orogeny
• high-K granite
• zircon U-Pb-Hf isotopes

Highlights

1. Zircon U-Pb dating constrained the Bakoshi-Gadanya granites at ca. 710-638 Ma.

2. Melt from mantle lithosphere produced the calc-alkalic Bakoshi-Gadanya granites.

3. Reactivation of Kalangai fault responsible for alkali-calcic Gadanya granite magmatism.

4. The investigated granites are ferroan calc-alkalic to alkali-calcic A-type granites.

Acknowledgments

This research benefited from the financial support provided by the National Natural Science Foundation of China (Grant No. 41502067). We are indebted to Jean-Paul Liégeois and one anonymous reviewer whose comments and criticism benefits the manuscript greatly. To the editorial team, we say thank you for the editorial handling.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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Funding

This work was supported by the National Natural Science Foundation of China [41502067].