Magma source and evolution of Late Neoproterozoic granitoids in the Gabal El-Urf area, Eastern Desert, Egypt: geochemical and Sr–Nd isotopic constraints

Abstract

Granitoids in the Gabal El-Urf area in Eastern Egypt consist of a monzogranite pluton, belonging to the Younger Granite province, emplaced in granodioritic rocks. Whole rock Rb-Sr dating indicate ages of 650 ± 95 Ma and 600 ± 11 Ma for the granodiorites and monzogranites, respectively. The granodiorites (65-70% SiO 2 ) are calc-alkaline and metaluminous with low Rb/Sr, Th and Nb contents, moderate enrichment in the LILE (K 2 O, Rb, and Ba) and display most of the chemical and field characteristics of syn-to late-tectonic I-type granitoids described elsewhere in the ArabianNubian Shield. The monzogranites (72-77 % SiO 2 ) are metaluminous to mildly peraluminous, highly fractionated and depleted in Al 2 O 3 , MgO, CaO, TiO 2 , Sr and Ba with corresponding enrichment in Rb, Nb, Zr, and Y. They can be correlated with the undeformed post-orogenic granites in the Arabian-Nubian Shield that chemically resemble A-type granites emplaced in extensional settings. The mineralogical and chemical variations within the granodiorites and monzogranites are consistent with their evolution by fractional crystallization. The granodiorites have a low initial 87 Sr/ 86 Sr ratio (0.7024) and high ∈ Nd values (+ 6.9 -+ 7.3) and are significantly different from those (initial 87 Sr/ 86 Sr ratio = 0.7029, ∈ Nd values = + 5.2 -+ 5.8) of the monzogranites. These data suggest a predominant mantle derivation for both granite types and demonstrate that they originated from different source materials.The granodiorite melt was most probably generated through vapour-saturated partial melting of an early Neoproterozoic depleted mafic lower-crust reservoir due to crustal thickening associated with orogenic compression and/or arc magma underplating. The mineralogical and geochemical data of the A-type monzogranites are consistent with their derivation as a residual granitic liquid from a LILE-enriched mafic magma through crystal-liquid fractionation of plagioclase, amphibole, Fe-Ti oxides and apatite. The parental mafic magma was originated in the upper mantle due to crustal thinning associated with extension in the late stage of the Neoproterozoic crustal evolution of northeastern Egypt. *

Origin and hydrothermal alteration of rare-metal granites in the Al-Hamra area, northeastern Arabian Shield, Saudi Arabia

“…Central European Geology 50, 2007 Table 2 Rb-Sr and Sm-Nd data for Al Hamra granites Similar models were suggested for other A-type granites of the Arabian-Nubian Shield (Beyth et al 1994;Moghazi 1999;Katzir et al 2006). The high initial Sr ratio (0.7068) may be attributed to addition of Sr from hydrothermal fluids.…”

Late Neoproterozoic alkaline magmatism in the Arabian–Nubian Shield: the postcollisional A-type granite of Sahara–Umm Adawi pluton, Sinai, Egypt

“…1), and covering more than 1,000 km 2 (Bentor 1985). Granitoid rocks in the Arabian-Nubian Shield include (1) syn-to lateorogenic granitoid assemblages (880-610 Ma) and (2) postorogenic to anorogenic granitoid assemblages emplaced between 600 and 475 Ma (Hashad 1980;Bentor 1985;Stern and Hedge 1985;Hassan and Hashad 1990;Beyth et al 1994;Stern 1994;Kröner et al 1994;Moghazi 1999;Moussa et al 2008). They were previously identified as older granitoids and younger granitoids, respectively (Akaad and Noweir 1980).…”

“…The older granitoids are calc-alkaline I-type granitoids (syn-orogenic), varying in composition from quartz diorite to monzogranite, and were emplaced during active subduction processes between 800 and 614 Ma (Hussein et al 1982;Stern and Hedge 1985;Hassan and Hashad 1990;Stern 1994;Kröner et al 1994;Moghazi 1999Moghazi , 2002El-Bialy 2004;Moussa et al 2008). Younger granitoids are highly fractionated calc-alkaline I-type granites and rarely gran- Naqab (modified after Mushkin et al 2003) odiorites and were emplaced during the termination of compressive orogeny by suturing at plate boundaries between 610 and 550 Ma (Hashad 1980;Hussein et al 1982;Stern and Hedge 1985;Beyth et al 1994;El-Bialy 1999;Moghazi 1999Moghazi , 2002.…”

“…Younger granitoids are highly fractionated calc-alkaline I-type granites and rarely gran- Naqab (modified after Mushkin et al 2003) odiorites and were emplaced during the termination of compressive orogeny by suturing at plate boundaries between 610 and 550 Ma (Hashad 1980;Hussein et al 1982;Stern and Hedge 1985;Beyth et al 1994;El-Bialy 1999;Moghazi 1999Moghazi , 2002.…”

Synoblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt

“…The Barud batholith exhibit distinct intrusive features to the Fatira sheared metavolcanics and also to metavolcanics and amphibolites around Qena-Safaga road (Abd ElWahed and Abdeldayem 2002;Fowler et al 2006), and not an autochthonous igneous body separated from a remobilized granitized pre-Pan-African basement (Fowler et al 2006), as proposed by Akaad et al (1973), El-Gaby and Habib (1982), Habib (1987), El-Gaby et al (1990), El-Gaby (1994), andEl-Shazley andEl-Sayed (2000). Petrochemical studies of the Barud tonalite-granodiorite considered it as subduction-related volcanic arc melts of probable mantle origin (Hussein et al 1982; Abdel- g biotite schist after banded tuffs still preserve the original banding with S 1 parallel to S 0 , the light band is rich in chlorite retrogressed after biotite; h migmatitic amphibolite from the eastern domain exhibiting weak foliation; and i migmatitic amphibolite showing granoblastic texture Rahman 1995; Moghazi 1999;El-Shazley and El-Sayed 2000;El-Sayed et al 2003). The intrusion age of the gneissic syntectonic granitoids is 680-620 Ma (Stern and Hedge 1985).…”