The anorogenic late Ediacaran granite-rhyolite porphyries of Gabal Abu Durba, Sinai: termination of magmatism in the Neoproterozoic Arabian-Nubian Shield crust

Anorogenic magmatism in the northern Arabian-Nubian Shield occurred during a long-lasting crustal extension event (2O/MgO >16, total alkalis >8.5 wt.%, (K2O + Na2O)/CaO >10, agpaitic index (NK/A) >0.85 and Zr (>250 ppm), Nb (>20 ppm), Y (>80 ppm), Zn (>100 ppm) and Ce (>100 ppm), and 10,000 × Ga/Al >2.6 and [Zr + Nb + Y + Ce] >350 ppm are suggestive of an A-type granite genesis. Zircon U-Pb dating of two representative samples returned crystallization ages of 569 ± 2.6 Ma and 561.7 ± 3.2 Ma for granite and rhyolite porphyries, respectively. The melting temperatures estimated at 997–1020°C are consistent with high-temperature liquidus conditions. Fractional crystallization, coupled with less significant crustal assimilation, was likely the main mechanism of formation of these rocks from a common primitive asthenospheric mantle-derived trachytic magma in an anorogenic intra-plate setting. The A-type alkali granite and rhyolite porphyries of Gabal Abu Durba are manifestations of mantle upwelling and lower crust underplating in the late Ediacaran anorogenic stage. These felsic subvolcanic intrusions (≈ 569–562 Ma) along with their volcanic counterparts constitute a new unmatched rock unit that most probably represent the last chapter of the anorogenic magmatism in the Neoproterozoic Arabian-Nubian Shield crust before the beginning of Phanerozoic era.