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The Hardawu granites in the eastern segment of the ultrahigh-pressure metamorphic belt, the northern Qaidam Basin, were studied by whole-rock major and trace elements and in-situ zircon U-Pb geochronology and Hf isotopes to discuss the petrogenesis and tectonic evolution. Geochronological results show that the granites have a crystallization age of 401 ± 3 Ma, suggesting that they were formed in the Early Devonian. The granites have SiO2 contents of 75.32 wt.%–76.05 wt.%, total alkali contents of 8.23 wt.%–8.36 wt.%, and K2O/Na2O ratios of 1.62–1.91. They were rich in K2O, poor in TiO2, MnO, MgO, and P2O5, and have A/CNK values of 1.05–1.07, Rittmann index δ values of 2.05–2.14, and differentiation index (DI) values of 92.85–94.18. They are high potassium calc-alkaline, weak-peraluminum, and highly differentiated I-type granites. The granites also show enrichment of large ion lithophile elements (LILE) such as Rb, Ba, and Th, and depletion of high field strength elements (HFSE) such as Nb, Ta, and Ti. The total REE concentrations range from 169 ppm to 232 ppm, with enrichments of light rare earth elements and negative Eu anomalies (δEu = 0.39–0.55). The zircon εHf(t) values range from −0.65 to −2.29, and the two-stage model ages (tDM2) changed within a small range of 1.44 to 1.54 Ga, indicating that the magma of the Hardawu granites was originated from the partial melting of Mesoproterozoic lower crustal materials. Combined with previous studies, we suggest that the Hardawu granites were formed in the extensional tectonic setting after the collision between the Qaidam Block and the central and southern Qilian Block in the Early Devonian. [ABSTRACT FROM AUTHOR]

Zircon holds crucial information for deciphering the origin of granitic rocks, enabling robust scrutiny of their magmatic evolution. Herein, we report an integrated whole‐rock and zircon U–Pb and Lu–Hf isotope chemistry of Ropp alkaline granites in north‐central Nigeria. The rock units include riebeckite‐biotite granite porphyries (161.1 ± 1.7 Ma), aegirine‐biotite granites (162.4 ± 1.6 Ma), biotite granites (162.3 ± 5.1 Ma), and albite riebeckite granites. They show diagnostic characteristics of ferroan alkaline granites such as high FeOt/(FeOt + MgO), low Y/Nb (<1.2), and high Nb/Y (>1.0). Their zircon Hf isotopic compositions (εHf(t) = −8.08 to −4.38; 176Hf/177Hf = 0.282492–0.282543), major and trace element compositions such as high SiO2 >70% and incompatible trace elements (e.g., Rb, Ba, and La), low ratios of whole rock Th/U, Hf/Ta. Ni/Co and Th/Ta = 2.82, and zircon U/Yb, Gd/Yb, and Th/Yb ratios as well as oxygen fugacity (logfO2 = −26.09 to −12.32) reflect protracted fractional crystallization of a highly reduced mantle‐derived oceanic island basalt (OIB) magma from EM2 with considerable crustal involvement. Magma evolution was fuelled by fractionation of calcic‐pyroxene, calcic‐amphibole, Mg‐olivines, feldspars, titanite, and apatite, as corroborated by the marked depletions of CaO, MgO, TiO2, and P2O5. Intense crustal assimilation, particularly in the biotite granite masked their enriched mantle (EM) ancestry. This is attested by the presence of inherited Pan‐African (ca. 582 Ma) zircon, elevated crustal‐like zircon U/Yb, low zircon Gd/Yb, and Th/Yb ratios as well as high whole‐rock Rb/Nb ratios and relatively low estimated temperatures, which mimic crustal‐derived granites. Reactivation of pre‐existing megashear zones of weaknesses and opening of related transcurrent faults following periodic plate movements generated intense stress field which invoked the release of pressure and hot metasomatic fluids that partially melted the lower EM, giving rise to the Ropp OIB magmas. [ABSTRACT FROM AUTHOR]