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

Abstract

Multi-isotope study including whole-rock NdSr, single zircon Hf, and SIMS d 18 O analyses of zircons sheds light on magma sources in the northernmost Arabian-Nubian Shield (ANS) during *820-570 Ma. Reconnaissance initial Nd and Sr isotope data for the older rocks (*820-740 Ma) reaffirms previous estimates that early crustal evolution in this part of the shield involved some crustal contamination by pre-ANS material. Prominent isotope provinciality is displayed by post-collisional calc-alkaline and alkaline igneous rocks of *635-570 Ma across a NW-SE transect across basement of the Sinai Peninsula (Egypt) and southern Israel. Silicic rocks of the NW-region are characterized by lower eNd(T)-eHf(T) and higher Sr i and d 18 O compared with rocks of the SE-region, and the transition between the regions is gradual. Within each region isotope ratios are independent of the extent of magma fractionation, and zircon cores and rims yield similar d 18 O values. Comparison with southern segments of the ANS shows that the source for most *635-570 Ma rocks can be modeled as the isotopically aged lowerintermediate crust in the ANS core (SE-region) and its northern, more contaminated ANS margins (NW-region). Nevertheless, Nd-Sr isotope enrichment of the lithospheric mantle is indicated by some basic magmas of the NWregion displaying the most enriched Nd-Sr isotope compositions. Comparison of Nd and Hf depleted mantle model ages for rocks of the SE-region may indicate that crustal formation events in the ANS geographical core took place at 1.1-1.2 Ga and were followed by crustal differentiation starting at *0.9 Ga.

Zircon Geochemical and Geochronological Constraints on Contaminated and Enriched Mantle Sources beneath the Arabian Shield, Saudi Arabia

“…The systematic change in ANS tectonic processes provides the ideal opportunity to use zircon geochemistry to further constrain existing whole-rockbased models. Prior studies have argued that systematic changes in granite chemistry in part reflect changes in a mantle component of the granite magmas from depleted mid-ocean ridge basalt (MORB)-like to enriched (Stein and Goldstein 1996;Stoeser and Frost 2006;Be'eri-Shlevin et al 2010). Focusing on A-type granites (Frost et al 2011), which are commonly associated with fractional crystallization of magmas produced during crustal extension (Turner et al 1992), recent ANS studies in Sinai suggest that two distinct mantle sources are involved in the tran-sition from postcollisional/calcalkaline to anorogenic alkaline granitoids (Eyal et al 2010;Azer and Farahat 2011).…”

An Expanding Arabian-Nubian Shield Geochronologic and Isotopic Dataset: Defining Limits and Confirming the Tectonic Setting of a Neoproterozoic Accretionary Orogen

“…The values plot above the typical mantle range for zircon and suggest that supracrustal recycling was involved in the formation of the Kibaran-age crust that was the source of the detrital grains [58]. A ε Nd (t=1.0 Ga) value of +2 for the Sa'al schist is significantly lower than typical neodymium values for metamorphic rocks elsewhere in the region and suggests that the complex was derived from different sources than most of the northern ANS crust [73].…”

“…The Paleoproterozoic and Archean grains were possibly sourced from the Saharan Metacraton or crust similar to the Khida terrane [67]. Late Mesoproterozoic-early Neoproterozoic crust is known in the Bayuda Desert [71,72] and, as mentioned, suspected in Sinai [58,73].…”

“…In addition, agecorrected epsilon values (εHf) are calculated using 176 Hf/ 177 Hf and 176 Lu/ 177 Hf measured on zircon and the apparent U-Pb age of the same zircon or on a zircon population [49]. A study [73] Neodymium initial ratios and model ages for the northern part of the ANS are plotted in Fig. (9).…”

“…On a larger scale, [81] compiled Pb isotope data for the northern part of the EAO and [23] presented a review of Nd data for the same region. [73] is an important example of the use of δ 18 O values to track the process of supracrustal recycling in the formation of 1.0-1.1 Ga crust in northern Sinai. [63] uses negative ε Hf(t) values together with U-Pb dating of single detrital zircon grains to suggest that arc magmas in the same area were contaminated by older crustal components [63].…”