Geochemical and Sr–Nd–Pb isotopic data bearing on the origin of Pan-Africangranitoids in the Kid area, southeast Sinai, Egypt

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.

Nd–Sr–Hf–O isotope provinciality in the northernmost Arabian–Nubian Shield: implications for crustal evolution

“…Sr i and eNd(T) calculated for the Kid schist over the age range of 800-640 Ma vary from 0.6981 to 0.7028 and ?3.8 to ?2.6, respectively. eNd(T) values calculated for all rocks for the Figure 4 shows an eNd(T) versus age diagram, where results of the present study are plotted along with data from the literature (Azer et al 2009;Beyth et al 1994;Katzir et al 2007a, b;Moghazi et al 1998;Mushkin et al 2003;Stein and Goldstein 1996). The 820-740 Ma rocks of the northernmost ANS define a restricted eNd(T) field, which falls slightly below the DM evolution curve of DePaolo (1981).…”

“…A Sr i locality map including data from this study and the literature (Azer et al 2009;Beyth et al 1994;Katzir et al 2007a, b;Moghazi et al 1998;Mushkin et al 2003;Stein and Goldstein 1996;Stern and Manton 1987) is shown in Fig. 3c.…”

“…6b. Data points include single zircon eHf(T) and WR eNd(T) from this study and from the literature (Beyth et al 1994;Katzir et al 2007a;Moghazi et al 1998;Stein and Goldstein 1996) for the same rocks. Also shown are WR eNd(T)-eHf(T) fields for the *630 Ma Elat schistose dikes from southern Israel (Katz et al 2004) located in the NWregion and for rocks from southern Sudan (Vervoort and Blichert-Toft 1999) representing more southerly segments of the ANS.…”

“…Nevertheless, older granites of this phase intruded prior to the formation of such basins at *608 Ma (Be 'eri-Shlevin et al 2009a;Beyth et al 1994) and magmatic activity lasted up to 580-570 Ma. Rocks of the AL suite include alkaline to peralkaline felsic (A-type granites) and rare mafic and intermediate plutons, as well as bimodal (mafic-felsic) alkaline and peralkaline volcanic rocks, and dike swarms (Bentor 1985;Beyth et al 1994;Garfunkel 1999;Katzir et al 2006Katzir et al , 2007aMoghazi et al 1998).…”

“…This interpretation is in accordance with high-d 18 O(Zrn) for some of the oldest rocks in this region interpreted by Be'eri- Shlevin et al (2009b) to show that part of the 820-740 Ma magmas have assimilated variable amounts of supracrustal material. Data points include single zircon eHf(T) from this study and WR eNd(T) from this study and the literature (Beyth et al 1994;Katzir et al 2007a;Moghazi et al 1998;Stein and Goldstein 1996) for the same rocks. Also shown are WR eNd(T)-eHf(T) fields for the *630 Ma Elat schistose dikes from southern Israel (Katz et al 2004) located in the NW-region and for rocks from southern Sudan (Vervoort and Blichert-Toft 1999) Isotope constraints on 635-570 Ma crustal evolution The late stages in the evolution of the ANS (post *650 Ma) were characterized by vast intrusion of mostly granitic batholiths and their associated volcanics (Bentor 1985).…”