Formation of a Composite Albian–Eocene Orogenic Wedge in the Inner Western Carpathians: P–T Estimates and 40Ar/39Ar Geochronology from Structural Units

Marián Putiš,Peter Ružička,Fred Jourdan,Ján Soták,Ondrej Nemec,Martin Danišík,Alexandra Molnárová,Čestmír Tomek

doi:10.3390/min11090988

Abstract

The composite Albian–Eocene orogenic wedge of the northern part of the Inner Western Carpathians (IWC) comprises the European Variscan basement with the Upper Carboniferous–Triassic cover and the Jurassic to Upper Cretaceous sedimentary successions of a large oceanic–continental Atlantic (Alpine) Tethys basin system. This paper presents an updated evolutionary model for principal structural units of the orogenic wedge (i.e., Fatricum, Tatricum and Infratatricum) based on new and published white mica 40Ar/39Ar geochronology and P–T estimates by Perple_X modeling and geothermobarometry. The north-directed Cretaceous collision led to closure of the Jurassic–Early Cretaceous basins, and incorporation of their sedimentary infill and a thinned basement into the Albian–Cenomanian/Turonian accretionary wedge. During this compressional D1 stage, the subautochthonous Fatric structural units, including the present-day higher Infratatric nappes, achieved the metamorphic conditions of ca. 250–400 °C and 400–700 MPa. The collapse of the Albian–Cenomanian/Turonian wedge and contemporary southward Penninic oceanic subduction enhanced the extensional exhumation of the low-grade metamorphosed structural complexes (D2 stage) and the opening of a fore-arc basin. This basin hemipelagic Coniacian–Campanian Couches-Rouges type marls (C.R.) spread from the northern Tatric edge, throughout the Infratatric Belice Basin, up to the peri-Pieniny Klippen Belt Kysuca Basin, thus tracing the south-Penninic subduction. The ceasing subduction switched to the compressional regime recorded in the trench-like Belice “flysch” trough formation and the lower anchi-metamorphism of the C.R. at ca. 75–65 Ma (D3 stage). The Belice trough closure was followed by the thrusting of the exhumed low-grade metamorphosed higher Infratatric complexes and the anchi-metamorphosed C.R. over the frontal unmetamorphosed to lowest anchi-metamorphosed Upper Campanian–Maastrichtian “flysch” sediments at ca. 65–50 Ma (D4 stage). Phengite from the Infratatric marble sample SRB-1 and meta-marl sample HC-12 produced apparent 40Ar/39Ar step ages clustered around 90 Ma. A mixture interpretation of this age is consistent with the presence of an older metamorphic Ph1 related to the burial (D1) within the Albian–Cenomanian/Turonian accretionary wedge. On the contrary, a younger Ph2 is closely related to the late- to post-Campanian (D3) thrust fault formation over the C.R. Celadonite-enriched muscovite from the subautochthonous Fatric Zobor Nappe meta-quartzite sample ZI-3 yielded a mini-plateau age of 62.21 ± 0.31 Ma which coincides with the closing of the Infratatric foreland Belice “flysch” trough, the accretion of the Infratatricum to the Tatricum, and the formation of the rear subautochthonous Fatricum bivergent structure in the Eocene orogenic wedge.

Highlights

Subduction–collision processes and the formation of accretionary wedges [1] are usually related to the closure of oceanic basins
Some authors argued that metamorphosed olistolithic to clastogenic material, including the Lower Cretaceous slates found in the Upper Cretaceous “flysch” of the Infratatricum, provide evidence for a tectono-metamorphic event prior to the Late Cretaceous [3,6,7]. This tectono-thermal event was constrained to ca. 100 Ma based on white mica 40Ar/39Ar geochronology applied to the Infratatricum [3,7]
We focus on the subautochthonous Fatricum and the Infratatric basement–cover structural complexes which show much more distinct tectono-thermal overprint than the central Tatric sliver

Summary

Introduction

Subduction–collision processes and the formation of accretionary wedges [1] are usually related to the closure of oceanic basins. Some authors argued that in the pre-collision stage, a continuous cover succession without any tectono-metamorphic events was formed within the Infratatric Unit (Infratatricum) of the FTI wedge during Triassic to Late Cretaceous times ([5] and references therein). Some authors argued that metamorphosed olistolithic to clastogenic material, including the Lower Cretaceous slates found in the Upper Cretaceous “flysch” of the Infratatricum, provide evidence for a tectono-metamorphic event prior to the Late Cretaceous [3,6,7]. This tectono-thermal event was constrained to ca. This tectono-thermal event was constrained to ca. 100 Ma based on white mica 40Ar/39Ar geochronology applied to the Infratatricum [3,7]

Methods

Results

Conclusion