Geochronology, Petrogenesis and Tectonic Implication of A-Type Granite from Zaranda (North-Central Nigeria)

A-type granites were emplaced in Zaranda at 203 ± 1 Ma corresponding to Late Triassic. Petrologically, the A-type granite association includes syenite, quartz syenite and alkali granite of ferroan-alkalic composition. In Yb/Ta versus Y/Nb binary plots, they display certain characteristics typical of OIB derived A-type granites. The depletion in Ba, Sr, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and augite. The isotopic analysis of Zaranda, as drawn from a previously conducted study yielded lower 87Rb/86Sr values of 0.7048 and positive ɛNd(t) + 0.9. Overall, the above data proved to reveal that the Zaranda A-type granites were formed from assimilation fractional crystallization of OIB-like magmas, as derived from lithospheric mantle. Late Triassic crustal extension, preceding the opening of the Atlantic Ocean in Early Jurassic, was most probably the main trigger for the emplacement of such A-type granite suites, which ranks them within plate A-type granite sensu stricto.