U-Pb zircon ages and geochemical data for the Monumental Granite and other granitoid rocks from Aswan, Egypt:: implications for the geological evolution of the western margin of the Arabian Nubian Shield

U-Pb zircon ages and geochemical data are presented for Pan-African granitoid rocks sampled in the area of Aswan, Egypt, close to the inferred boundary between the Saharan Metacraton and the Arabian Nubian Shield. The sample set includes tonalitic gneisses as well as undeformed, post-tectonic tonalites to granites (Aswan Tonalite, Monumental Granite, High-Dam Granite, Saluja-Sehel Granite). A tonalitic gneiss with a volcanic-arc type geochemical signature gave a zircon age of 622 +/- 11 Ma, while the Aswan Tonalite and the Monumental Granite intruded at 606 +/- 1 and 606 +/- 2 Ma, respectively. The age of the High-Dam Granite was constrained at 595 +/- 11 Ma. These data imply that the western parts of the Arabian Nubian Shield were accreted to the Saharan Metacraton prior to 606 Ma in the area of Aswan, most probably between 630 and 615 Ma. The Aswan Tonalite, the Monumental Granite and the High-Dam Granite have high Zr, Y and LREE contents and can be classified as A-type granitoids. Furthermore they are rich in K, Ba, Sr, Ti and P, thus displaying affinities to shoshonitic magma series. The shoshonitic A-type plutonism at Aswan constitutes an exceptional feature within the Late Neoproterozoic granite terrain of the Arabian Nubian Shield. It may contain components from an enriched, subduction-modified mantle wedge, that had developed beneath the western margin of the Arabian Nubian Shield in response to the eastward subduction of the Mozambique ocean. It is suggested that slab break-off provided the tectonothermal conditions for a post-collisional melting of this subduction-modified mantle wedge.