Late Cambrian–Ordovician northeastern Gondwanan terranes in the basement of the Apuseni Mountains, Romania

Abstract: The pre-Alpine basement of the Apuseni Mountains (Romanian Carpathians) comprises three terranes: Somes, Baia de Aries and Biharia. Metaigneous rocks within these terranes record Late Cambrian–Ordovician U–Pb zircon crystallization ages. Two samples from an orthogneiss layer in the Somes terrane yielded an age of 459.8 ± 2.7 Ma. In the Baia de Aries 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 Aries 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 Somes, Baia de Aries and Biharia terranes, adjacent to the Arabian–Nubian Shield. Lead loss in some zircons is interpreted to have taken place during the Variscan orogeny. Supplementary material: Coordinates for samples from the Apuseni Mountains, Palaeozoic palaeogeographical models of Gondwana, Laurentia and Baltica to the formation of Pangaea, sample preparation and analytical procedures, sample description, and age measurements of zircon grains are available at http://www.geolsoc.org.uk/SUP18425.