Genesis of alkaline-peralkaline A-type granite from El Dair complex, SW Arabian-Nubian Shield, Sudan: geochronology, geochemistry and isotopic constraints

Abstract

The formation time and origin of the Neoproterozoic alkaline-peralkaline rocks from the SW Arabian-Nubian Shield (ANS) are poorly constrained. An assessment of petrography, whole-rock geochemistry, incorporated with zircon U–Pb dating, trace element, and Hf isotope, has been done on the El Dair granitic complex, NE Nuba Mountains, Sudan. LA-ICPMS U–Pb zircon ages from two granite samples yield a weighted mean of 567.3 ± 2.5 Ma and 598.3 ± 21 Ma, respectively, signifying that the El Dair complex was formed at ca. 560–600 Ma. The El Dair granite samples exhibit alkaline-peralkaline affinity (A.I. = 1.04–1.17) and are classified as high-K calc-alkaline series. The samples display similar composition with typical A-type granite: e.g., elevated Na2O + K2O contents, Ga/Al, FeOT/MgO, TiO2/MgO, ratios, and HFSEs (i.e., Zr, Ta, Nb, and Y) with negative Ba, Sr, and Ti anomalies and depleted contents of CaO, MgO, and P2O5. The El Dair granite samples illustrate high Zr (563–1163 ppm) contents, yielding high magma temperatures of 884–966 °C. The zircon trace elements investigations show HREE enrichment and positive Ce but negative Eu anomaly, characteristic of igneous zircons. The initial eHf(t) of + 4.2 − +5.8 and eNd isotopic values of + 1.83 − +1.92 from El Dair A-type granite samples are rather enriched than the values of depleted mantle (eHf ~ + 14 and eNd ~ + 6.5). Whole-rock elemental and isotopic data from the El Dair complex apparently denote that the magmas were produced via low degrees partial melting of juvenile crust through the assemblage of ANS during Neoproterozoic time.