Abstract
Abstract. Some 20 Myr after the Late Jurassic to Early Cretaceous obduction and collision at the eastern margin of Adria, the eroded Pelagonia (Adria)–Axios/Vardar (oceanic complex) contact collapsed, forming the Kallipetra Basin, described around the Aliakmon River near Veroia (northern Greece). Clastic and carbonate marine sediments deposited from the early Cenomanian to the end of the Turonian, with abundant olistoliths and slope failures at the base due to active normal faults. The middle part of the series is characterized by red and green pelagic limestones, with a minimal contribution of terrigenous debris. Rudist mounds in the upper part of the basin started forming on the southwestern slope, and their growth competed with a flux of ophiolitic debris, documenting the new fault scarps affecting the Vardar oceanic complex (VOC). Eventually, the basin was closed by overthrusting of the VOC towards the northeast and was buried and heated up to ∼ 180 ∘C. A strong reverse geothermal gradient with temperatures increasing up-section to near 300 ∘C is recorded beneath the VOC by illite crystallinity and by the crystallization of chlorite during deformation. This syntectonic heat partially reset the zircon fission track ages bracketing the timing of closure just after the deposition of the ophiolitic debris in the Turonian. This study documents the reworking of the Pelagonian–Axios/Vardar contact, with Cenomanian extension and basin widening followed by Turonian compression and basin inversion. Thrusting occurred earlier than previously reported in the literature for the eastern Adria and shows a vergence toward the northeast, at odds with the regional southwest vergence of the whole margin but in accordance to some reports about 50 km north.
Highlights
The Hellenides are an integral segment of the main Alpine– Himalayan orogenic belt (Fig. 1)
To elucidate part of these controversies, this study investigates the small Upper Cretaceous Kallipetra Basin that formed on both oceanic and continental units along the eastern Pelagonian margin (Fig. 1) and was overthrusted by serpentines of a Jurassic oceanic floor
Based on illite and petrographic data, we find an inverted, high, non-linear geothermal gradient related to a heating event, which likely occurred during the overriding of the Vardar oceanic complex (VOC) in the Late Cretaceous
Summary
The Hellenides are an integral segment of the main Alpine– Himalayan orogenic belt (Fig. 1) They have recorded polyphase Alpine deformation since the Middle Jurassic, when they were involved in the obduction of imbricate oceanic units over the eastern Apulian margin (e.g., Bernoulli and Laubscher, 1972; Zimmerman and Ross, 1976; Schmid et al, 2020). In the Internal Hellenides (Fig. 1), continuous convergence led to the collision of continental promontories with Eurasia in the Late Jurassic–Early Cretaceous that built a metamorphic crustal-scale orogenic wedge involving the Pelagonian zone and Rhodope (Ricou et al, 1986; Burg et al, 1996; Schenker et al, 2014). The buried Pelagonian basement experienced regional amphibolitic-facies metamorphism to the north (U–Pb zircon ages from the leucosomes of migmatites at 130–117 Ma; Schenker et al, 2015, 2018) and an upper greenschist- to blueschist-facies metamorphism to the south
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