Geological Magazine
- Geological Magazine / Volume 149 / Issue 05 / September 2012, pp 783-797
- Copyright © Cambridge University Press 2011
- DOI: http://dx.doi.org/10.1017/S0016756811000975 (About DOI), Published online: 16 December 2011
Original Articles
U–Pb zircon dating and Sr–Nd–Hf isotopic evidence to support a juvenile origin of the ~ 634 Ma El Shalul granitic gneiss dome, Arabian–Nubian Shield
K. ALIa1a5, A. ANDRESENa2 c1, W. I. MANTONa1, R. J. STERNa1, S. A. OMARa3 and A. E. MAURICEa4
a1 Geosciences Department, University of Texas at Dallas, 800 West Campbell Rd, Richardson, TX 75080 USA
a2 Department of Geosciences, P. O. Box 1047, University of Oslo, Blindern, O316 Oslo, Norway
a3 Nuclear Materials Authority, P. O. Box 530, El Maadi, Kattamyia, Egypt
a4 Geology Department, Faculty of Earth Science, Beni Suef University, 62517 Beni Suef, Egypt
a5 Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Abstract
The calc-alkaline, gneissic El Shalul granite is the westernmost gneiss dome or core complex within the Arabian–Nubian Shield. Previous studies have indicated that it represents either a window into the underlying pre-Neoproterozoic Sahara metacraton or a melt derived from the metacraton. U–Pb LA-ICP-MS dating of magmatic zircons from two samples of the variably foliated El Shalul pluton gives ages of 637 ± 5 Ma and 630 ± 6 Ma, excluding it from representing exhumed cratonic rocks. The ages are, however, indistinguishable from the age of the Um Ba'anib pluton, constituting the core of the Meatiq Gneiss Dome, as well as several other plutons in the Eastern Desert, indicating an important magmatic pulse in the Arabian–Nubian Shield in Late Cryogenian time. Major and trace element data indicate a within-plate setting. Bulk rock Nd-isotope and Hf-isotope data on zircons from the El Shalul pluton indicate derivation of the primary melt from a relatively juvenile source, either the lower crust of a mid-Neoproterozoic volcanic arc or as a result of fractionation of a mantle-derived mafic melt. Sm–Nd bulk rock isotopic data indicate a model age of c. 720 Ma for the protolith from which the melt was derived. Time-corrected Hf-isotope data obtained on the magmatic zircons indicate that the bulk of the source rock was extracted from the mantle around 810 Ma.
(Received February 16 2011)
(Accepted October 07 2011)
(Online publication December 16 2011)
Keywords:
- Eastern Desert;
- gneiss dome;
- geochronology;
- geochemistry
Correspondence:
c1 Author for correspondence: arild.andresen@geo.uio.no
