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

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.

Lu–Hf and O isotopic compositions on single zircons from the North Eastern Desert of Egypt, Arabian–Nubian Shield: Implications for crustal evolution

“…The older granitoids comprise calc-alkaline diorite, tonalite, trondhjemite and granodiorite intrusions (~850-635 Ma), whereas the younger granites (~630-540 Ma) range from quartz-monzonite to alkali granite (e.g., El-Ramly, 1972;Fleck et al, 1980;Greenberg, 1981;Jackson et al, 1984;Bentor, 1985;Harris, 1985;Stern and Hedge, 1985;Stern and Gottfried, 1986;El-Gaby et al, 1988;Ali et al, 2012a). The older granitoids are I-type, calc-alkaline intrusions, most likely originated by fractionation of mafic melts generated by partial melting of mantle wedge with little or no crustal contamination (e.g., Hussein et al, 1982) or by anatexis of granulitic lower crust in subduction zones (e.g., Furnes et al, 1996;Moghazi, 1999).…”

“…Oxygen isotopes in igneous zircon are sensitive to whether a rock underwent magma contamination or not (Valley, 2003;Zheng et al, 2004Zheng et al, , 2006Be'eri-Shlevin et al, 2009a,c;Hiess et al, 2009;Be'eri-Shlevin et al, 2010 Stern and Hedge, 1985;Ali et al, 2012a). the mineral (Valley, 2003;Valley et al, 2005).…”

An Expanding Arabian-Nubian Shield Geochronologic and Isotopic Dataset: Defining Limits and Confirming the Tectonic Setting of a Neoproterozoic Accretionary Orogen

“…However, the protoliths of the Eastern Desert gneiss domes consistently yield Neoproterozoic U-Pb zircon ages and the rocks have neodymium, strontium, and hafnium isotope characteristics of a juvenile origin. The data strongly indicate that they derived from the lower crust of a mid-Neoproterozoic volcanic arc or a mantle-derived mafic melt [41], not from older crust, and the gneisses are most reasonably interpreted as syn-tectonic intrusions [43,50]. An analogous debate occurred in the Arabian Shield, where gneisses in the Khamis Mushayt area of the southern Arabian Shield were mapped in the 1970s as basement of possible Mesoproterozoic age, stratigraphically beneath younger arc assemblages [123].…”

“…2), there is no significant extent, if any, of pre-Neoproterozoic crust beneath the shield. Critical reviews of geochronological and isotopic data from both the northern ANS (Saudi Arabia, Egypt, Sudan: [2,5,23,31,[41][42][43][44][45][46][47][48][49][50]) and the southern ANS (Eritrea, Ethiopia, Kenya: [40,[51][52][53][54]) show that the internal portions of the ANS are dominantly composed of juvenile Neoproterozoic crust. Another important conclusion, despite the caveat mentioned above, is the growing ability to assign time ranges to volcanic, magmatic, and deformation events.…”

“…Additional sample locations exist for parts of the Eastern Desert, Sinai, and the Midyan terrane (e.g. [38][39][40][41][42][43][44][45], but are omitted here because of crowding of data points.…”