Paleogeography of the Gondwana passive margin fragments involved in the Variscan and Alpine collisions: Perspectives from metavolcanic-sedimentary basement of the Western Carpathians

Abstract

The general configuration of the main continental blocks in the Gondwana supercontinent and the Ediacaran–early Paleozoic tectonic evolution of its northern margin are widely accepted. However, reconstruction of the original positions and the question of potential separation of the Gondwana-derived crustal segments that are now included in the Variscan and Alpine orogenic belts remain controversial. The Western Carpathians, part of the Alpine–Carpathian belt, represents an important crustal segment broken-off from northern Gondwana and later incorporated into both the Variscan and Alpine collisional orogens. The earliest tectonic evolution and paleogeography of the pre-Variscan basement of the Western Carpathians remains poorly known, due to insufficient age data and intense polyphase tectonometamorphic overprints, both Variscan and Alpine. This paper provides new results of U–Pb dating and Hf isotopic analysis of detrital zircons as well as a whole-rock geochemical study from metavolcanic-sedimentary basement units of the Western Carpathians. The obtained age spectra suggest that the sedimentary succession was supplied dominantly by Ediacaran (c. 600 Ma) zircons, with a relatively minor role for Stenian–Tonian (c. 1.2–0.9 Ga) and Paleoproterozoic cratonic (c. 2.2–1.8 Ga) zircons. The mixed Hf isotopic signature (ε_Hf(t) values ranging from −20 to +12) of the Ediacaran zircons indicates substantial mixing of mantle-derived magmas with mature crustal material, typical of continental magmatic arcs. In contrast, the mostly negative ε_Hf(t) values (−15 to +4) of the cratonic zircons suggest recycling of an older continental crust. The presumably youngest part of the sequence is also characterised by high proportion of early Paleozoic zircons with generally negative ε_Hf(t) values (−10 to −2). The zircon U–Pb age spectra, Hf isotopic patterns and whole-rock geochemical signatures of the studied Western Carpathians sequences are interpreted as reflecting deposition at a progressively developing Cambrian–Silurian passive margin setting. The West Carpathian data have been correlated with a comprehensive detrital zircon U–Pb age and Hf isotope data set compiled from possible source areas and other Gondwana-derived units to test the possibility of their primary linkages. These correlations indicate strong similarity in both zircon U–Pb age spectra and Hf isotopic compositions to other parts of the Ediacaran (Cadomian) continental magmatic arc. Older, cratonic sources are linked to the Saharan or East African parts of northern Gondwana, whereas the early Paleozoic detritus must represent a local volcanic source. Taken together, our new data from the Western Carpathians provide constraints for a new paleogeographic model of the northern African part of the Gondwana passive margin.