Ophiolites derive from different tectonic settings, including mid-ocean ridges (MOR), supra-subduction zones (SSZ), and ocean–continent transitions (OCT). However, discriminating among these settings and relocating ophiolitic fragments nowadays in orogens to their original paleo-position in space and time remains challenging.
This study aims at constraining the original tectonic setting and paleo-position of three isolated and fragmented ophiolite slivers belonging to the North Calabria Unit (Basilicata region, southern Italy). The North Calabria Unit represents a strongly dismembered association of mantle, mafic, and continental crustal rocks incorporated into the southern Apennine orogenic system. These units are interpreted as remnants of the Jurassic Alpine Tethys, later affected by Alpine–Apennine convergence and tectonic reworking.
We investigate three ophiolite slivers using a multiscale approach integrating detailed field observations, petrological and geochemical analyses, zircon geochronology, and plate-kinematic reconstructions. Particular emphasis is placed on the characteristics of key lithologies and, critically, on the nature of their contacts, which provide first-order constraints on the original tectonic setting of these slivers.
Key observations include: (i) Mid-Jurassic cherts stratigraphically overlying MOR-type basalts, sealing tectonic contacts between depleted mantle and gabbros affected by crustal contamination; (ii) amphibolite and gneiss tectonically juxtaposed with gabbros, with zircon age and composition compatible with a pre-rift lower continental crustal origin; and (iii) the possible circulation of Cr-rich, mantle-derived fluids along low-angle faults at the top of continental crustal rocks.
When integrated with kinematic reconstructions, these observations indicate that the studied ophiolite slivers originated in an OCT setting developed during Jurassic rifting of the European side of the Alpine Tethys, possibly near Sardinia, rather than in a fully oceanic MOR or SSZ environment.
Our workflow provides a framework to locate fragmented ophiolites in rifted margins and can be applied to interpret dismembered ophiolites in orogenic belts worldwide.
How to cite: Frasca, G., Manatschal, G., Prosser, G., Rubatto, D., Ulrich, M., Barale, L., Curetti, N., and Compagnoni, R.: Decoding ophiolite settings through primary lithological contacts: the case-study of the North Calabria Unit (Southern Apennines, Italy), 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-57, https://doi.org/10.5194/egusphere-alpshop2026-57, 2026.
The Balkan terrains form a complex tectonic mosaic within the Vardar Tethys mega-suture zone. Constraining their pre-Alpine paleogeographic affinities remains puzzling due to intense Alpine structural overprinting. In this contribution, we present a regional dataset comprising U-Pb geochronology and Lu-Hf isotopes of >2,000 zircons from 20 localities across Adria-affiliated (Dinarides, Pelagonides) and Europe-affiliated (Serbo-Macedonian Massif, Tisza, Carpatho-Balkanides) domains.
Ubiquitous late Neoproterozoic (750-540 Ma) zircon populations in all investigated zircon grains confirm a shared provenance along the northern active margin of Gondwana. However, Paleozoic to Mesozoic trajectories reveal a considerable lithospheric asymmetry between the two blocks.
In the Europe-affiliated northern Serbo-Macedonian Massif (Juhor Mountains), schists and peraluminous leucogranites yield overlapping Middle Ordovician (~460 Ma) core ages. Coupled with Ordovician-Silurian metamorphic rims, this records a long-lived volcano-sedimentary arc linked to the Cenerian orogeny, making the SMM the most pristine Cenerian remnant. A subsequent late Early Carboniferous (~330 Ma) tectonomagmatic signal marks Variscan collision, a signature that also dominates the Carpatho-Balkanides aswell. Importantly, Triassic magmatism is entirely absent across the Serbo-Macedonian Massif north of Bujanovac and Carpatho-Balkanides.
On the other hand, the Adria-affiliated Dinaric basement (Drina-Ivanjica and Jadar-Kopaonik units) shows a distinct evolution. In the Kopaonik block, the lower Studenička Series displays a unique spectrum dominated (>60%) by a narrow Devonian population (360-400 Ma; peak ca. 370 Ma) with highly variable εHf values, recording early Paleotethyan rifting. Furthermore, the Dinaric units record a prominent Variscan signal (320-290 Ma) and a sharp, dominant Mid-Triassic (~240 Ma) magmatic pulse with within-plate Hf signatures. This Permo-Triassic signature records advanced continental rifting preceding the Neotethyan Vardar Ocean opening, which is absent in the European margin. Finally, Pelagonian S-type magmatism yields Lower Cretaceous ages (~130-105 Ma), revealing syn-collisional melting and postcollisional rifting during final Tethyan closure.
Overall, our dataset demonstrates a fundamental lithospheric asymmetry between the margins, constraining the diachronous evolution of the Paleo- and Neotethyan Oceans.
How to cite: Prelević, D., Sokol, K., Xie, J.-C., Mladenović, A., and Cvetković, V.: Zircon provenance and Hf isotope constraints on the Pre-Alpine evolution of the Balkan terrains: from Peri-Gondwanan accretion to Tethyan rifting, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-55, https://doi.org/10.5194/egusphere-alpshop2026-55, 2026.
The call for an “energy transition” undeniably requires finding low-emission energies, among which serpentinization-sourced natural hydrogen (H2) is one potential candidate. However, the knowledge needed to successfully explore for this new energy source, i.e., to understand when and where natural H2 forms during the Wilson cycle, is yet incomplete. Answering these questions is challenging and requires not only a much-improved understanding of serpentinization processes, but also a deep understanding of the geological systems in which serpentinization occurs.
The aim of this contribution is not only to focus on how natural H2 forms, migrates and is trapped, but also to investigate the characteristics and evolution of the geological systems that hosted, or host, serpentinization and potential natural H2 production. More specifically, we examine the evolution of mantle rocks during their emplacement in ocean continent transitions (OCTs) and their later reactivation and emplacement in rift-inversion orogens. To do so, we review the evolution of OCT-derived ophiolites located in the Alpine system. We focus on two settings: the Western Pyrenean fossil OCT exposed in SW-France and the Grischun-Malenco fossil OCTs exposed in SE-Switzerland and northern Italy. Their choice is linked to the fact that they are not only the best documented and exposed examples of OCT-derived ophiolites worldwide, but also to the fact that they bear active H2 systems. Compared with ophiolites derived from Mid Ocean Ridges (MOR) or Supra-Subduction Zones (SSZ), OCT-derived ophiolites are substantially different in terms of mantle rock composition, emplacement mechanisms during collision, and potential for natural H2 production.
In this study, we review the characteristics of OCTs based on the well calibrated distal Iberian margin and the Grischun-Malenco fossil OCT. We then synthesize the state-of-the art knowledge on these well described OCTs and OCT-derived ophiolites and their potential for natural H2 systems. Finally, we discuss how far this knowledge can be used to explore for native H2 along the Tethyan suture zones in Eastern Europe, and in collisional orogens in general.
How to cite: Manatschal, G., Dimasi, F., Gasser, Q., Blin, C., Chenin, P., Ulrich, M., Frasca, G., Kusznir, N., Zwaan, F., Zhang, C., Gaucher, E. C., Alt-Epping, P., Pierre, S., Ducoux, M., and Masini, E.: The fate of the subcontinental mantle in Alpine-type rift inversion orogens and its significance for natural H2 exploration, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-41, https://doi.org/10.5194/egusphere-alpshop2026-41, 2026.
The onset of the Toarcian Oceanic Anoxic Event (TOAE) in the NW Europe affected by extensive anoxia is characterized by a unique peak in abundance of the epibenthic bivalve Bositra radiata in the uppermost part of the Semicelatum Subzone of the Tenuicostatum Zone (in southern Germany or in the Cleveland Basin), typically occurring in laminated organic-rich beds just at the onset of the extinction interval (coinciding with the onset of the main negative carbon isotopic anomaly). New work on Toarcian successions in the Tethys Ocean (Eastern Alps) or in successions not affected by anoxia in the Beni Snassen Mountains (Ain Reggada) shows that this bivalve occurs in a distinct ~20-50 cm-thick (non-laminated) shell-rich interval that is also associated with the initial fast depletion in d13C at these sections. These bivalves are preserved as fragments formed by an outer prismatic layer in marls (with the initially aragonitic inner layer being dissolved) or are still formed by bi-layered remains in limestones, forming a distinct filament microfacies (stratigraphically preceding the onset of the classic filament microfacies formed by Bositra buchi since the bifrons Zone). Their valves tend to be oriented concordantly but are also frequently fragmented, vary in size and do not form any discrete pavements, indicating they represent within-habitat time averaged assemblages. These assemblages are either almost monospecific or B. radiata still co-occurs with micromorphic brachiopods (that went extinct during the the TOAE), and indicate that the unique seafloor colonization phase by this bivalve occurred over a relatively broad geographic extent of the western Tethys (both on its northern and southern margins) just at the onset of the main extinction phase. This research was supported by the Slovak Agency for Research and Development (APVV 22-0523).
How to cite: Tomašových, A., Boudchiche, L., Müller, T., Sadki, D., and Schlögl, J.: Filament microfacies at the onset of the Toarcian Oceanic Anoxic Event, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-31, https://doi.org/10.5194/egusphere-alpshop2026-31, 2026.
