Precambrian Research 216–219 (2012) 1–22 Contents lists available at SciVerse ScienceDirect Precambrian Research journa l h omepa g e: www.elsevier.com/locate/precamres The late Ediacaran (580–590 Ma) onset of anorogenic alkaline magmatism in the Arabian–Nubian Shield: Katherina A-type rhyolites of Gabal Ma’ain, Sinai, Egypt Mohammed Z. El-Bialy a,∗ , Imbarak S. Hassen b a Geology Department, Faculty of Science, Port Said University, Port Said 42521, Egypt b Geology Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt a r t i c l e i n f o Article history: Received 26 September 2011 Received in revised form 25 April 2012 Accepted 3 June 2012 Available online xxx Keywords: A-type rhyolite Anorogenic Arabian–Nubian Shield Volcanics Geochemistry Sinai a b s t r a c t The Katherina Volcanics of Gabal Ma’ain in the Sinai comprise an Ediacaran (580–590 Ma) approximately 450 m thick succession dominated by porphyritic rhyolite lava flows with subordinate related pyro- clastics. These volcanics unconformably overlie the calc-alkaline Younger Granites (≥590 Ma) and are intruded by alkaline granitoids (578 ± 8 Ma). The rhyolites have a potassic alkaline affinity and peralu- minous to slightly metaluminous character. They exhibit many of the classic features of A-type magmas, including enrichment of incompatible elements, such as Zr, Nb, Y, Ga, Zn and Ce and total REE, as well as high FeO*/(FeO* + MgO) and 10,000*Ga/Al 2 O 3 ratios. The A-type rhyolites have LREE-enriched patterns with pronounced negative Eu anomalies that are comparable with typical REE profiles for “hot-dry- reduced rhyolites”. Saturation thermometry has yielded zircon and apatite crystallization temperatures ranging between 913 and 925 ◦ C and 669 and 931 ◦ C, respectively. The investigated trace element patterns indicate that the Katherina A-type rhyolites were very likely to have evolved through simple fractional crystallization of a parental magma derived from an enriched (most probably asthenospheric) mantle source, supplemented by a crustal component inherited from pre-collision subduction events, or a ‘recy- cled component’ in the source. Katherina A-type rhyolites were likely erupted in a within-plate setting. The eruption of these rhyolites marks the onset of the anorogenic period during which the rigid massif (Arabian–Nubian Shield) was subjected to post-collisional tensional stresses and intra-plate rifting. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The Arabian Nubian Shield (ANS) extends over most of NE Africa and the western part of the Arabian Peninsula, represent- ing an area of about 3 million km 2 . It is considered by some to be the best-preserved and most widely exposed Neoproterozoic juvenile continental crust on Earth (Dixon and Golombek, 1988; Vervoort and Blichert-Toft, 1999; Patchett and Chase, 2002; Stern, 2002; Gradstein et al., 2004). The ANS evolved during the Neo- proterozoic East African Orogeny (900–550 Ma), by accretion of juvenile volcanic arc terranes and associated ophiolite remnants plus microcontinental plates that were assembled to form east- ern Gondwana (Kröner et al., 1992; Stern, 1994, 2002; Beyth et al., 1994; Stein and Goldstein, 1996; Jarrar et al., 2003; Johnson and Woldehaimanot, 2003; Meert, 2003; Hargrove et al., 2006; Stoeser and Frost, 2006; Stern et al., 2010; Farahat et al., 2011; Johnson et al., 2011). The latest tectonomagmatic stages of the Arabian–Nubian Shield (610–550 Ma) record the growth and maturation of the continental crust from orogen to craton. Throughout this phase ∗ Corresponding author. E-mail address: mzbialy@yahoo.com (M.Z. El-Bialy). magmatism changed from calc-alkaline to alkaline, and the tec- tonic regime in which these magmas were generated changed from collision to post-collision to within-plate extension, and ultimately to a stable cratonic setting (Bentor, 1985; Stern and Hedge, 1985; Beyth et al., 1994; Garfunkel, 1999; Jarrar et al., 2003; Johnson and Woldehaimanot, 2003; Moussa et al., 2008; Ali et al., 2009; Be’eri-Shlevin et al., 2009a,b, 2011; El-Bialy, 2010; Morag et al., 2011; Johnson et al., 2011). The final chapter in the Precambrian history of the ANS commenced with intense alkaline volcanism (590–550 Ma) marking the transition to intra-plate setting that was to prevail throughout the Phanerozoic. These late Precambrian alkaline volcanics are represented by minor exposures that are nev- ertheless widespread across the Arabian–Nubian Shield (Harris, 1982). The Precambrian basement exposures of Sinai (Fig. 1), along with those of the Eastern Desert of Egypt, southern Israel and Jor- dan constitute the northern portion of the ANS and share some common features in their post-collision geological history (Stern, 1994; Garfunkel, 1999; Jarrar et al., 2003; Meert, 2003; Katzir et al., 2007; Samuel et al., 2011). In Sinai, the latest Neoproterozoic alka- line volcanism was mainly represented by alkaline rhyolitic flows and pyroclastics, known as the “Katherina Volcanics” (Eyal and Hezkiyahu, 1980; Agron and Bentor, 1981). 0301-9268/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.precamres.2012.06.004