Nd-Sr-Hf-O isotope provinciality in the northernmost Arabian-Nubian Shield: implications for crustal evolution
Abstract
Multi-isotope study including whole-rock Nd-Sr, single zircon Hf, and SIMS delta(18)O analyses of zircons sheds light on magma sources in the northernmost Arabian-Nubian Shield (ANS) during similar to 820-570 Ma. Reconnaissance initial Nd and Sr isotope data for the older rocks (similar to 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 similar to 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 epsilon Nd(T)-epsilon Hf(T) and higher Sr(i) and delta(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 delta(18)O values. Comparison with southern segments of the ANS shows that the source for most similar to 635-570 Ma rocks can be modeled as the isotopically aged lower-intermediate 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 NW-region 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 similar to 0.9 Ga.