Late cambrian-ordovician northeastern gondwanan terranes in the basement of the Apuseni Mountains, Romania

The pre-Alpine basement of the Apuseni Mountains (Romanian Carpathians) comprises three terranes: Someş, Baia de Arieş and Biharia. Metaigneous rocks within these terranes record Late Cambrian Ordovician U-Pb zircon crystallization ages. Two samples from an orthogneiss layer in the Someş terrane yielded an age of 459.8 ± 2.7 Ma. In the Baia de Arieş terrane, an augen gneiss yielded an age of 470.8 ± 3.8 Ma, a porphyroid yielded an age of 467.8 ± 3.8 Ma and two metagranites yielded ages of 467.8 ± 4.7 Ma and 467.1 ± 3.9 Ma, respectively. Three samples from a metagranitoid outcrop located in the lower part of the Biharia terrane yielded an age of 495.0 ± 2.1 Ma. Three other samples from a metabasite layer situated lithostratigraphically several hundred metres above the metagranitoid yielded an age of 477.8 ± 3.2 Ma. Detrital U/Pb zircon ages from a paragneiss interlayered within the Baia de Arieş terrane scatter between 548 and 3518 Ma. Detrital zircon ages together with the inherited ages recorded by magmatic zircon populations suggest a northeastern Gondwanan provenance for the Someş, Baia de Arieş and Biharia terranes, adjacent to the Arabian-Nubian Shield. Lead loss in some zircons is interpreted to have taken place during the Variscan orogeny.