Mantle source characteristics of the late Neoproterozoic post-collisional gabbroic intrusion of Wadi Abu Hadieda, north Arabian-Nubian Shield, Egypt

This article presents geochemical and mineralogical data for the Neoproterozoic Abu Hadieda mafic intrusion (AHMI), which exposed at the boundary between the northern and central domains of the Eastern Desert of Egypt, to study its magma source and petrogenesis. Field relations indicate that the AHMI is younger than the syn-tectonic tonalite-granodiorite, but older than post-collisional monzogranite and alkali feldspar granite. The AHMI is neither deformed nor metamorphosed and keep the primary texture and mineralogy indicating a post-collisional setting. It consists mainly of medium to high-K calk-alkaline pyroxene-hornblende gabbro with minor diorite. The low Mg# (32-41) values of the gabbro are typical of young post-collisional mafic intrusion in the Arabian-Nubian Shield (ANS). Geothermobarometric calculations suggest that the pyroxene-hornblende gabbro was crystallized at relatively high pressure (0.6 GPa) and temperature (800-915 C). The samples show a general enrichment in LREEs and LILEs (e.g., Sr, Ba, K) relative to HREEs and HFSEs (e.g., Nb, Ta, Hf, Ti, Zr). The chemical and mineralogical signatures are consistent with evolution of the AHMI from emplacement of a primitive partial melt derived from a lithospheric mantle source that had previously been metasomatized, in an early stage of ANS evolution, by subduction-related melts. Remobilization and melting of this lithospheric source occurred in a post orogenic setting, likely driven by crustal thinning and extension.