Formation of juvenile continental crust in the Arabian–Nubian shield: evidence from granitic rocks of the Nakasib suture, NE Sudan

Abstract

Major and trace element data, U-Pb zircon ages, and initial isotopic compositions of Sr, Nd, and Pb are reported for ten granitic and one rhyolitic rock sample from the neo-Proterozoic Nakasib suture in NE Sudan. Chemical data indicate that the samples are medium-to high-K, "I-type" granitic rocks that mostly plot as "volcanic arc granites" on discriminant diagrams. Geochronologic data indicate that rifting occurred 790±2 Ma and constrain the time of deformation associated with suturing of the Gebeit and Haya terranes to have ended by approximately 740 Ma. Isotopic data show a limited range, with initial 87 Sr/ 86 Sr=0.7021 to 0.7032 (mean=0.7025), εNd(t) =+5.5 to +7.0 (mean=+6.4), and 206 Pb/ 204 Pb = 17.50-17.62. Neodymium model ages (T DM ; 0.69-0.85 Ga; mean = 0.76 Ga) are indistinguishable from crystallization ages (0.79-0.71 Ga; mean=0.76 Ga), and the isotopic data considered together indicate derivation from homogeneously depleted mantle. The geochronologic data indicate that the terrane accretion to form the Arabian-Nubian shield began just prior to 750 Ma. The isotopic data reinforces models for the generation of large volumes of juvenile continental crust during neo-Proterozoic time, probably at intra-oceanic convergent margins. The data also indicate that crust formation was associated with two cycles of incompatible element enrichment in granitic rocks, with an earlier cycle beginning approximately 870 Ma and culminating approximately 740 Ma, and the second cycle beginning after pervasive high-degree melts -possibly hot-spot relatedwere emplaced approximately 690-720 Ma.

Significance of the Tambien Group (Tigrai, N. Ethiopia) for Snowball Earth events in the Arabian–Nubian Shield

“…Non-radiogenic Sr igneous rock compositions are typical of especially metavolcanic sequences like the Tsaliet elsewhere in the ANS (e.g. Stern and Abdelsalam, 1998), and remobilization of such non-radiogenic Sr and exchange with Tambien carbonates could be responsible for the unusual effect of more altered carbonates having less radiogenic Sr than carbonates that are better preserved.…”

Nd, Pb, and Sr isotope composition of Late Mesozoic to Quaternary intra-plate magmatism in NE-Africa (Sudan, Egypt): high-μ signatures from the mantle lithosphere

“…Pb isotope compositions of the juvenile Pan-African basement including ophiolites are substantially less radiogenic than those of the reworked craton ( Fig. 6c; Pallister et al 1988;Brueckner et al 1995;Zimmer et al 1995;Stern and Abdelsalam 1998;Bailo et al 2003). The widespread juvenile Pan-African magmatic crust of the Arabian Plate shows a similar isotope composition (Stacey and Stoeser 1984; new data and compilation in Stoeser and Frost 2006).…”

“…Data sources: Davidson and Wilson (1989), Harms et al (1990), Zimmer et al (1995), Küster and Liégois (1998), Stern and Abdelsalam (1998), Teklay et al (2001), Bailo et al (2003), Küster et al (2008) and our unpublished data (2006). Mesozoic to Cenozoic intra-plate magmatic rocks of the studied area include crust-contaminated samples.…”

“…The 207 Pb/ 204 Pb ratios of most samples from the reworked craton are substantially higher than in average continental crust (S&K; Stacey and Kramers 1975). The Pan-African juvenile basement is represented by the measured and initial composition of ophiolite (Zimmer et al 1995) and igneous rocks (Stern and Abdelsalam 1998;Bailo et al 2003). Late Mesozoic to Cenozoic intra-plate magmatic rocks of the studied area include crust contaminated samples.…”

“…The latter is characterized by juvenile material from Pan-African magmatic arcs and accretion of island-arcs (e.g. Küster and Liégois 1998;Stern and Abdelsalam 1998;Teklay et al 2001;Bailo et al 2003;Stoeser and Frost 2006). Beyond this large scale subdivision, local occurrences of juvenile basement are known west of the Pan-African suture (e.g.…”