The Meliata suture in the Carpathians: regional significance and implications for the evolution of high-pressure wedges within collisional orogens

Abstract

The Meliata nappe of the Western Carpathian orogen is comprised of Triassic deep-sea metasedimentary rocks and fragments of blueschist-bearing ophiolite. These were structurally emplaced onto Permian/Triassic shelf sequences and its Variscan basement. The nappe records a succession of deformational events which formed under decreasing pressure conditions. Subduction-related burial and resulting blueschist metamorphism is dated by 40 Ar/ 39 Ar plateau ages recorded by four phengitic muscovite concentrates (160-150 Ma). These crystallized during ductile deformation characterized by predominantly coaxial NW-SE stretching. The structures were overprinted by semiductile, nonpenetrative fabric elements which formed under greenschist facies conditions and contemporaneously with fabrics which developed in footwall tectonic units. Kinematic indicators record top north to NW shear during Middle Cretaceous loading of the Meliata unit onto the Inner Carpathian nappe complex recorded by a 40 Ar/ 39 Ar whole rock phyllite age of 105.8 + 1.5 Ma. A subsequent southeastern sense of shear is interpreted to have resulted from extension during Late Cretaceous uplift along hinterland margins of the tectonic wedge. The Meliata unit is part of a major Late Jurassic/Early Cretaceous suture which initially extended from the Alps to the Hellenides. It has been subsequently disrupted as a result of later strike-slip faulting following Tertiary collision of the Cretaceous orogen, and was transported onto extra-Alpine European units.

40 Ar/ 39 Ar ages of crystallization and recrystallization of rock-forming polyhalite in Alpine rocksalt deposits

“…Dallmeyer et al 2008). Coevally, the sea floor reached maximum water depths with the formation of radiolarites in the footwall plate of the Northern Calcareous Alps by means of thrust loading.…”

Structural evolution of the Turňa Unit constrained by fold and cleavage analyses and its consequences for the regional tectonic models of the Western Carpathians

“…of northern Hungary provided similar metamorphic temperatures of approximately 300-350 °C at pressures of 300-450 MPa (Árkai & Kovács 1986;Kövér et al 2009). This prograde metamorphic event was coeval with partial retrogression of the Meliata HP/LT rocks in the greenschist-facies conditions (e.g., Faryad 1995Faryad , 1999Dallmeyer et al 2008) and likely reflects the maximum thickening of the wedge due to thrust stacking, including exhumed blueschist Meliata slices at the wedge sole (Fig. 6A).…”

“…Relying on the supposed palaeogeographical position of the Turňa Unit on the flanks of the Meliata Ocean, its origin was most probably caused by a tectonic burial related to formation of the accretionary wedge during subduction processes and closure of the Meliata Ocean in the Late Jurassic to earliest Cretaceous times (e.g., Faryad 1995Faryad , 1999Mello et al 1998;Mock et al 1998;Árkai et al 2003;Dallmeyer et al 2008). As a result, all rocks of the Turňa Unit were buried within the nappe pile of the accretionary wedge and were affected by a very low-grade metamorphism.…”

“…For instance, assuming the general northward progradation of the Western Carpathian orogen, the structural superposition of Silica over Turňa over Meliata units and some north-vergent thrust-sense criteria would indicate the original palinspastic position of the Turňa and Silica nappes south of the Meliata Ocean (Grill et al 1984;Hók et al 1995;Rakús 1996;Mello et al 1997;Lexa et al 2003;Csontos & Vörös 2004;Dallmeyer et al 2008). On the contrary, facies relationships of especially the Middle-Late Triassic complexes apparently point to the "northern" shelfslope settings of these units (e.g., Mandl 2000;Gaál 2008; Schmid et al 2008;Gawlick et al 2012).…”

A geological snapshot from the front of the Northern Calcareous Alps: Well Obermoos TH-1, Salzburg, Austria

“…The ridges were suggested to relate to Triassic salt diapirism (Mandl, 1982(Mandl, , 2000Plöchinger, 1984 (Lein, 1987;Mandl, 2000). The Hallstatt-Meliata Ocean was considered as being subducted (e.g., Dallmeyer et al, 2008) and / or finally closed during the Late Jurassic (Missoni and Gawlick, 2011a, b;Gawlick and Missoni, 2015 and references therein). Coevally, the sea floor of the NCA subsided and reached considerable water depths with the formation of radiolarites.…”