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The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex. [ABSTRACT FROM AUTHOR]

Combined whole-rock geochemistry, zircon U–Pb dating, and Sr–Nd–Pb isotopic analyses were carried out to constrain the petrogenesis and tectonic implications of the "Zaranda Older Granites" (ZOG) and "Younger Granites" (ZYG) in north-central Nigeria. Zircon U–Pb dating yielded 633 ± 3 Ma for the ZOG and 203 ± 1 Ma for the ZYG, corresponding to Late Neoproterozoic and Late Triassic, respectively. The ZOG consists dominantly of biotite granite, which displays a whole-rock ɛNd(t) values of − 3.48 to − 5.00 and Nd model ages of 1620–1720 Ma. Most ZOG samples exhibit elevated Sr/Y (107–128) and La/Yb ratios (36–40), with a positive Eu anomaly (Eu/Eu* = 2.2–2.58), interpreted to reflect magma derivation through partial melting of a thickened lower crust. The ZOG is geochemically and geochronologically similar to the Pan-African granites from Togo–Benin (West Africa) and Northeast Borborema, Sao Paulo (Brazil), suggesting that their emplacement probably marked the initial phase of the Pan-African orogeny during which the Gondwana was amalgamated. The ZYG consists of compositionally diverse alkaline granitoids including aegirine syenites, quartz syenite, and fayalite granite porphyry. These rocks are strongly ferroan, alkalic and show petrographic and geochemical features of classical A-type granites. Substantial depletion in Ba, Sr, P, Ti, and Eu signifies fractionation of felsic and mafic minerals such as feldspar, biotite, amphibole, and Ti-rich augite. The low Y/Nb and Yb/Ta ratios (≤ 2) indicate that the ZYG samples display geochemical features typical of OIB-derived A-type granites. The ɛNd(t) values in the ZYG range from + 4.16 to − 2.76 and the Nd model ages range from 0.6 to 1.2 Ga. Based on these results, we propose that the ZYG samples and by extension, other alkaline granitoids from the Nigerian Younger Granite (NYG) province with similar geochemical compositions were likely generated through extensive differentiation of OIB-type mantle-derived magma. The concentrations of Nb and other HFSEs are much higher in ZYG than ZOG, indicating that the former has higher rare metal mineralization potential. [ABSTRACT FROM AUTHOR]

The Nigerian alkaline ring complexes have long been regarded as typical anorogenic A-type granite. However, uncertainty still surrounds many aspects of their petrogenesis and tectonic implication. In this paper, a combined study of whole rock geochemistry, Nd-Pb isotope and zircon U-Pb dating was carried out on the Kudaru ring complex from north-central Nigeria. The complex consists of mildly alkaline fayalite granite porphyry, peralkaline arfvedsonite granite and metaluminous biotite granite, which were emplaced between 176.9 ± 2.5 and 180.55 ± 0.6 Ma. These rocks are characterized by variably high alkalis, HFSEs, Ga/Al ratios, and zircon saturation temperature, typically of A-type granites. Notably, the popular subdivision scheme of A-type granite permits the discrimination of the alkaline-peralkaline granites as typical "A1-type" granites and the metaluminous granite as "A2-type". These co-existing A1 and A2 granites show distinct isotopic compositions with less negative εNd (t) values and higher 206Pb/204Pb ratios for the former, indicating that the magma which gave rise to the A1 and A2 suites was derived from an enriched mantle source but modified to different extent during ascent. Notably, the coexistence of A1-A2 granites do not indicate discrete tectonic regimes (intraplate setting for A1 and post-orogenic setting for A2), but rather point to a significant role of crustal contamination, as seen also from the differences in Y/Nb ratios. [ABSTRACT FROM AUTHOR]

The Younger Granite province of Niger and Nigeria exemplifies a classical anorogenic alkaline ring granite belt with southward age migration from ca. 470 Ma to 140 Ma. However, the precise age transition from the older Nigerien Younger Granite (NrYG) to the younger Nigerian Younger Granite (NaYG) is poorly constrained. The Daura and Dutse complexes, located at the northernmost tip of the NaYG province, represent a temporal and spatial link between the NrYG and NaYG provinces. The Daura complex is composed of amphibole syenite and biotite granite, while the Dutse complex consists of fayalite syenite and arfvedsonite aegirine granite. Similar to other alkaline rocks of the NrYG and NaYG provinces, the Daura and Dutse samples all chemically show typical A 1 -type granite features, such as high alkalis (K 2 O + N 2 O = 8.33–11.27 wt%.), Ga/Al ratios, Zr + Nb + Ce + Y contents (527–2345 ppm) and FeOt/(FeOt+MgO) ratios (0.03–0.70) as well as elevated HFSEs. The Nd Hf and Pb isotopic systematics show that all the syenite-granites yield εNd (t) = −2.9 to +1.5, ɛHf (t) = −3.8 to +16.7, and 206Pb/204Pb = 17.818 to 19.555, suggestive of magmas derived from a slightly depleted mantle source with OIB imprints. A reduced to slightly oxidized redox state is invoked for the parental melt based on estimations from mineral chemistry. The Daura amphibole syenite is composed of >60% alkali feldspar, show high Eu/Eu* (>1), Ba/Zr (>3.5) values and cumulate textures, resembling an alkali feldspar cumulate rock. The other alkaline granitic rocks were likely generated from variable fractional crystallization of the residual melt with distinct crustal contaminations. Zircon U Pb dating reveal that the Daura amphibole syenite and biotite granite were emplaced at 324 ± 1 Ma and 321 ± 3 Ma, respectively, whereas the Dutse granitoids showed episodic intrusive periods of ca. 264 Ma and 232 Ma. All these results predate other anorogenic alkaline complexes of the NaYG and update the oldest age (ca. 214 Ma in previous references) recorded in the alkaline granite province. To the north, it connects well with ages from the Zinder complex (~330 Ma) in the southernmost NrYG province, reflecting a significant link between the NrYG and NaYG provinces. From a broad view, a linear age migration from north to south in the Niger-Nigeria Younger Granite province remains well preserved, although temporal and spatial intervals exist in local region. This emplacement pattern can be traced to the periodic and repeated reactivation of lithospheric shear zones and transcurrent faults. • The Daura syenite records onset of the alkaline magmatism in the NaYG province. • AFC process plays a key role in the diversity of the studied alkaline granitoids. • Reactivation of transcurrent faults accounts for age migration in the NaYG province. [ABSTRACT FROM AUTHOR]