Metamorphic evolution of the Sa'al-Zaghra Complex in Sinai: Evidence for Mesoproterozoic Rodinia break-upα

Recently published age data indicate that the Sa'al-Zaghra metamorphic complex in Sinai, Egypt contains the oldest rocks found in the northernmost Arabian-Nubian Shield, preserving evidence for a 1110-1030. Ma rift-related volcanic system formed during Rodinia break-up (Be'eri-Shlevin et al., 2012). As such, its metamorphic evolution provides evidence for an important part of the geological history of the shield. Here we use petrographic, mineral chemistry and thermodynamic modeling, in combination with structural data from the field, to derive a P T D t path for the complex. It is shown that the metamorphic rock of the complex equilibrated during an early deformation event that involves a flat lying fabric and is interpreted as an extensional event. P T conditions attained during this event are between 370-420. °C and around 3. kbar. These conditions correspond to a geothermal gradient of 38-41. °C/km which is much higher than that documented elsewhere in the metamorphic complexes of Sinai (i.e. 25-27. °C/km). We suggest that this is because metamorphism in the Sa'al-Zaghra complex records an earlier stage of metamorphism and deformation during breakup of Rodinia, whereas the lower gradients documented elsewhere is related to the Gondwana collision. During the subsequent East-West-Gondwana collision, the Sa'al-Zaghra complex remained at shallow crustal levels (<9. km), and therefore it escaped the deep crustal metamorphism of the Pan-African event.