Abstract
U-Pb ion-microprobe zircon dating of the Moneiga quartz-diorites, located within the Katherine ring-complex of the Sinai, reveals a crystallization age of 844 ± 4 Ma and the presence of 1045 Ma pre-magmatic zircon cores. These rocks are much older than previously believed, and represent the oldest magmatic rocks so far dated in the Sinai. Their chemical composition corresponds to mildly silicic, low- to medium-K, metaluminous, calcic to calc-alkaline rocks with somewhat elevated FeO total/MgO, low Ba/La and high Cs/Sc and Zr/Yb. The initial Sr and Nd isotope composition ( 86Sr/ 87Sr 844Ma = 0.703187 ± 0.000034 and ɛNd 844Ma 3.5 ± 0.5) is slightly less primitive than expected from similar rocks of Arabian-Nubian Shield with the same age. Trace-element and isotope ratios reveal the presence of a non-juvenile crustal component that caused a T DM = 1.06 ± 0.06 Ga identical to the age of the oldest pre-magmatic cores of zircons. These data support the idea that the Moneiga quartz-diorites formed by re-melting of a ∼200 Ma old island-arc crust during the early stages of the prolonged break-up process of Rodinia.
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