Post-collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield: time constraints from ion-probe U–Pb dating of zircon

Abstract

Ion-probe U–Pb dating of plutonic rocks from the northern Arabian–Nubian Shield in Sinai and southern Israel constrains the timing of late East African batholithic post-collisional calc-alkaline (CA2) magmatism and within-plate alkaline to peralkaline (AL) magmatism to c . 635–590 Ma and c . 608–580 Ma, respectively. The earliest dated CA2 rocks are slightly deformed to undeformed, indicating that penetrative deformation ceased by c . 630 Ma. Within the CA2 suite a change from mafic to felsic magmatism is manifested in most of the region, peaking in a voluminous pulse of granodiorite to granite intrusion at 610–600 Ma. The AL magmatism started contemporaneously with the peak in CA2 felsic activity at c . 608 Ma and lasted until 580 Ma. It includes mostly alkaline and peralkaline granites, probably representing variable degrees of differentiation of similar parental magmas. Thus CA2 and AL granites do not represent different tectonic settings, but coeval derivation from variable sources during crustal extension. The majority of rocks dated in this study show minor to non-existent zircon inheritance and thus indicate very minor interaction with previously formed felsic crust. The rare zircon xenocrysts span a typical East African age range (900–607 Ma) and confirm the absence of older crustal components in the juvenile Arabian–Nubian Shield. Supplementary material: Geochemical and geochronological methods, sample descriptions and data are available at http://www.geolsoc.org.uk/SUP18327 .

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

“…Such features do not fit well with AFC or magma-mixing processes as a mechanism for enrichment of the radiogenic isotope compositions. The results of ion-microprobe In addition to the isotope data discussed earlier, it is important to mention that the vast majority of CA2 and AL rocks of the study area carry no xenocrystic zircons, and in the rare cases where such xenocrysts have been detected they are minor components within the zircon population (Ali et al 2009;Be'eri-Shlevin et al 2009a). This feature typifies all lithologies and all regions discussed earlier and thus clearly provides no support for any AFC or magmamixing processes associated with the petrogenesis of the CA2 and AL magmas.…”

“…A meta-pelitic schist (Kid schist) from the Umm-Zarik formation (Shimron 1984) represents the Kid-MC. Although Rb-Sr ages of *610 Ma were reported for the Kid-MC (Bielski 1982;Halpern and Tristan 1981), it has been shown recently that formation and metamorphism of this complex predated *630 Ma and is more plausibly associated with the *820-740 Ma tectonomagmatic phase (Be'eri-Shlevin et al 2009a).…”

“…Calc-alkaline plutonic magmatism lasted up to 590 Ma (Ali et al 2009;Be'eri-Shlevin et al 2009a), but from *635 to 625 Ma onwards plutons record little to no ductile deformation and are considered to represent a transition to post-collisional setting (CA2 suite; Be 'eri-Shlevin et al 2009a). Regarding the timing of deformation we note the important difference between the northernmost ANS and more southern ANS segments.…”

“…2). However, such deviations mostly stem from the overrepresentation in the ion-microprobe analysis of xenocrystic zircons, which form minor components in these populations (Ali et al 2009;Be'eri-Shlevin et al 2009a), and from targeting high-U zircon domains, which were probably affected by post-crystallization oxygen exchange with late fluids. A clear case demonstrating the latter effect is the Iqna pluton, where CL-dark, high-U, metamict zircons are characterized by variable and high d 18 O(Zrn) values of 6.1 to 14.2% whereas CL-bright, low-U zircon domains define a much more restricted d 18 O(Zrn) range from 6.2 to 7.7% comparable with the multi-grain value (Fig.…”

“…However, while CA2 magmatism commenced at *635 Ma with the intrusion of complex quartz-diorite to granodiorite plutons and minor gabbros and peraluminous monzogranites the main phase of this event occurred during *610-590 Ma with a shift in the composition of the intrusions to dominantly granodiorites and monzogranites. More important is the fact that this stage overlapped the main phase of AL silicic (and mafic) magma formation (Be'eri-Shlevin et al 2009a). Thus, possible derivation from different levels of geochemically heterogeneous crust is possible.…”