No abstract

No abstract

The Kid plutonic suite in southeast Sinai, Egypt is composed of: (1) a gabbro–diorite complex; (2) quartz monzodiorite; (3) granodiorite–monzogranite association; (4) syenogranite. Major- and traceelement analyses and radiogenic isotope data (Rb/Sr, Sm/Nd and Pb/Pb) are presented for these rocks. Rb–Sr isochrons indicate ages of 581±11 Ma, 576±11 Ma and 570±4 Ma for the quartz monzodiorite–granodiorite–monzogranite association and syenogranite, respectively. The gabbro–diorite complex is a layered intrusion varying in SiO2 from 42 to 59 wt%. It shows a calc-alkaline trend, and the trace element characteristics of arc lavas. Subsequently, this magma fractionated to give quartz monzodiorite andsyenogranite magmas. The quartz monzodiorite has low initial 87 Sr/ 86 Sr ratios (0.703) and high ɛ Nd values (+4.4±0.3), with trace element characteristics of volcanic-arc granites. The granodiorite–monzograniteassociation has higher initial Sr ratio (0.7044), lower ɛ Nd (+1.5–+2.7) and relatively high 207 Pb/ 204 Pb and 208 Pb/ 204 Pb, significantly different from those of the older rocks. Isotopic data and REE modelling suggestthat it formed by partial melting of an early Pan-African amphibolitic lower crust. The syenogranite isa typical highly fractionated post-orogenic granite, with a deep negative Eu anomaly, HFSE and REEenrichment, a 87 Sr/ 86 Sr initial ratio of 0.7033, ɛ Nd of 4.5 & 0.5 and distinct variations in the 206 Pb/ 204 Pbratio. The isotopic compositions of Sr, Nd and Pb indicate that the syenogranite and the quartzmonzodiorite are comagmatic. Increasing fluorine concentration from the quartz monzodiorite to thesyenogranite suggests that fluid fractionation involving fluorine complexing played an important role inthe genesis of the syenogranite. This process led to the enrichment of HFSE and HREE, to extensivefractional crystallization, to changes in the U/Pb ratios and a distinct variation in 206 Pb/ 204 Pb.

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. *

No abstract