Origin of sediments during Cretaceous continent—continent collision in the Romanian Southern Carpathians: preliminary constraints from 40Ar/39Ar single-grain dating of detrital white mica

Abstract

Single grains of detrital white mica from the lowermost Upper Cretaceous Sinaia Flysch have been dated using the 40 Ar/ 39 Ar technique. The Sinaia Flysch was deposited in a trench between the Danubian and Getic microcontinental pieces after the closure of the Severin oceanic tract. The Danubian basement is largely composed of a Panafrican/Cadomian basement in contrast to the Getic/Supragetic units with a Variscan-aged basement, allowing the distinction between these two blocks. Dating of detrital mica from the Sinaia Flysch resulted in predominantly Variscan ages (329 ± 3 and 288 ± 4 Ma), which prove the Getic/Supragetic source of the infill of the Sinaia Trench. Subordinate Late Permian (263 ± 8 and 255 ±10 Ma), Early Jurassic (185 ±4 and 183 ± 3 Ma) and Late Jurassic/Early Cretaceous (149 ± 3 and 140 ± 3 Ma) ages as well as a single Cretaceous age (98 ± 4 Ma) are interpreted as representing the exposure of likely retrogressive low-grade metamorphic ductile shear zones of various ages. Ductile shear zones with similar 40 Ar/ 39 Ar white mica ages are known in the Getic/Supragetic units. The Cretaceous ages also show that Cretaceous metamorphic units were already subject to erosion during the deposition of the Sinaia Flysch.

Strain partitioning during formation of oroclines and indentation

“…Chapter 2 demonstrates that the orocline was structured during three major tectonic events: the Cretaceous orogen-building shortening, the Paleogene to middle Miocene oroclinal bending, and the late-stage thin-skinned thrusting during the final Carpathians docking against the Moesian Platform in the late Miocene. The Cretaceous thrusting was an orogen-building event associated with the closure of the Ceahlău-Severin branch of the Alpine Tethys Ocean, resulting in the Supragetic-Getic nappes emplacement, which was well documented in other segments of the orocline (e.g., Săndulescu, 1984Săndulescu, , 1988Dallmeyer et al, 1996;Bojar et al, 1998;Willingshofer et al, 1999;Fügenschuh and Schmid, 2005;Iancu et al, 2005a;Neubauer and Bojar, 2013) and further supported by the structural data of this thesis. This initially relatively straight to slightly curved orogen was subsequently bent around the rigid Moesian Platform in post-Cretaceous times by gradually changing the amount of rotation from >90° in the South Carpathians to 30-40° in the Serbian Carpathians and 0° in the Balkanides (Chapter 1, van Hinsbergen et al, 2008;Panaiotu and Panaiotu, 2010;Lesić et al, 2019).…”

“…The initial late Early Cretaceous thrusting (~100-110 Ma, 'Austrian' event in local literature, see Schmid et al, 2008 and references therein) of the Supragetic unit was followed by the latest Cretaceous thrusting (late Campanian-early Maastrichtian, ~75-67 Ma, 'Laramian' event in local literature, see Schmid et al, 2008 and references therein) of the Getic unit and the formation of a Danubian nappe stack derived from the margin of the Moesian Platform (e.g., Csontos and Vörös, 2004;Iancu et al, 2005a;Neubauer, 2015;Săndulescu, 1988;Seghedi et al, 2005). These events were coeval with significant exhumation of the entire nappe stack, well quantified by thermochronological studies in the South Carpathians (e.g., Bojar et al, 1998;Fügenschuh and Schmid, 2005;Neubauer and Bojar, 2013;Willingshofer et al, 1999).…”

“…Many previous studies have focused on the structure, kinematics and timing of deformations and rotations observed in the South Carpathians and Balkanides (e.g., Ratschbacher et al, 1993;Pătraşcu et al, 1994;Bojar et al, 1998;Schmid et al, 1998;Matenco and Schmid 1999;Willingshofer et al, 1999;Matenco et al, 2003;Dupont-Nivet et al, 2005;van Hinsbergen et al, 2008;Kounov et al, 2010Kounov et al, , 2011Kounov et al, , 2018Panaiotu and Panaiotu, 2010;de Leeuw et al, 2013;Krézsek et al, 2013, Neubauer andBojar, 2013;Vangelov et al, 2013;Burchfiel and Nakov, 2015, among others). A number of large-scale tectonic reconstructions have inferred the general large-scale Topography is based on SRTM data (Farr et al, 2007) rotations and translations of large continental units (e.g., Csontos and Vörös, 2004;Fügenschuh and Schmid, 2005;Ustaszewski et al, 2008;van Hinsbergen et al, 2020).…”

“…Renewed shortening took place during the latest Cretaceous (~75-67 Ma), postdating the extension and magmatism in the ABTS belt (Iancu et al, 2005a;Neubauer and Bojar, 2013;Schmid et al, 2008), which created the Supragetic-Getic-Danubian nappe stack (Figs. 4.2 and 4.3, Ciulavu et al, 2008;Csontos and Vörös, 2004;Berza et al, 1983;Maţenco, 2017;Săndulescu, 1984).…”