2 research outputs found
Post-collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield: time constraints from ion-probe U–Pb dating of zircon
<p>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 <em>c</em>. 635–590 Ma and <em>c</em>. 608–580 Ma, respectively. The earliest dated CA2 rocks are slightly deformed to undeformed, indicating that penetrative
deformation ceased by <em>c</em>. 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 <em>c</em>. 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.
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Early Carboniferous anorogenic magmatism in the Levant: implications for rifting in northern Gondwana
<p>The Variscan orogenesis in Europe peaked during the Late Devonian–Early Carboniferous times when Gondwanan terranes collided with Laurasia. Hitherto it has been thought that Carboniferous tectonics in northern Arabia and the adjacent parts of NE Africa were broad swells (‘arches’) and depressions (‘basins’) that formed as a far-field contractional effect of the Variscan compression. The discovery of a 351 ± 3 Ma (U–Pb in zircon) within-plate felsic volcanism in the Helez borehole, southern coastal Israel, suggests that the Levant Arch is, instead, extensional in origin. Felsic volcanism was associated with gabbro underplating of the crust, an extreme (~50°C/km) crustal thermal gradient, major uplift, and truncation of the ≥2.5 km section. Taken together with the recent discovery of the ~340 Ma oceanic crust in the Eastern Mediterranean, the Levant Arch is interpreted as an uplifted shoulder of a rift, preceding ocean spreading.</p