Modes of Oblique Inversion: A Case Study From the Cretaceous Fold and Thrust Belt of the Western Transdanubian Range (TR), West Hungary

Abstract

Inversion of pre‐existing normal faults is a frequent phenomenon in orogenic belts. However, their impact on the evolution of the Cretaceous Eoalpine orogeny is poorly studied, despite the widespread presence of Triassic and Jurassic normal faults. Our study area is the SW part of the Transdanubian Range (TR), which represents the uppermost thick‐skinned nappe of the Eoalpine orogeny in the Alpine realm. The variable trend of Cretaceous contractional structures within the Transdanubian Range has been traditionally explained by poly‐phase shortening. However, based on the combined analyses of field observations and 3D seismic data, we found that the complex geometry of Cretaceous contractional structures can be explained rather by the oblique inversion of segmented Late Triassic grabens. In general, the SW part of the TR can be characterized by N‐S trending contractional structures. NW‐SE striking oblique ramps are nucleated above Late Triassic normal faults, whereas NE‐SW trending folds and thrust with limited strike‐parallel length evolved due to the inversion of pre‐existing breached relay ramps, which connected the segments of Late Triassic normal faults. We determined different types of oblique ramps, incuding normal faults, which suffered transpressional reactivation, oblique hanging wall breakthrough thrusts, oblique footwall short‐cut and hanging wall by‐pass thrusts. Only very steep normal faults, or those that strike at low angle to the regional E‐W shortening direction, were not reactivated.

Complex deformation history of the Keszthely Hills, Transdanubian Range, Hungary

“…1b), which is traditionally explained by two or even three phases of folding and thrusting in the TR, well separated in time and in tectonic context (Tari, 1994;Csontos and Vörös, 2004;Csontos et al, 2005;Pocsai and Csontos, 2006;Palotai et al, 2006;Sasvári, 2008Sasvári, , 2009Tari and Horváth, 2010;Fodor et al, 2018;Szives et al, 2018). In contrast, our early results suggested that deviations of fold trends can be explained rather by inheritance of Triassic and Jurassic pre-orogenic normal faults than by multiphase folding (Héja et al, 2016(Héja et al, , 2017(Héja et al, , 2022. In this work, we document outcrop-scale structures and faults-slip analysis which serve as the basis of this alternative explanation for the number and character of folding phases.…”

“…In a recent paper, Héja et al (2022) give an alternative interpretation for the three generation of folds in the KH. This concept (third scenario, Fig.…”

“…It is also possible that such oblique inversion of a segmented graben system resulted in the development of a heterogeneous stress field, whose stress trajectory can show important variations (Fodor, 2019). The NW-SW shortening could have occurred on these inverted relay ramps (Héja et al, 2022). Deviation of the shortening directions along oblique and lateral ramps have been documented in many fold and thrust belts based on faultslip data (e.g., Ustaszewsky and Schmid, 2006).…”

“…The third and fourth columns (first and second scenarios) are the correlation of our results with the models of Tari (1994) and Fodor (2010), respectively. In the last column (third scenario) we considered the various trending folds of the KH as the result of one single deformation, which was a consequence of oblique inversion of pre-existing faults, causing a heterogeneous stress field (Héja et al, 2022). In this third scenario we also supposed that the compressional/transpressional stress fields with E-W (D3), NW-SE (D4) and NE-SW (D5) directed σ 1 might have been repeatedly recurrent during the Late Cretaceous and Cenozoic.…”

Inversion of extensional basins parallel and oblique to their boundaries: Inferences from analogue models and field observations from the Dolomites Indenter, eastern Southern Alps

“…Shortening of passive continental margins is typically associated with the reactivation of inherited normal faults, inversion of sedimentary basins, and their incorporation in fold-and thrust belts (e.g., Turner and Williams, 2004;Cooper and Warren, 2020). Inverted sedimentary basins are known from numerous orogenic settings worldwide, from, e.g., the European Alps (Boutoux et al, 2014;Gillcrist et al, 2015;Granado et al, 2016;Oswald et al, 2018;Héja et al, 2022), the Apennines (Scisciani et al, 2001;Pace et al, 2014), the Pyrenees (Tavani et al, 2011;Mencos et al, 2015), Iberia (Ramos et al, 2017), the Atlas Mountains of Morocco (Beauchamp et al, 1999) and Algeria (Bracène and Froizon De Lamotte, 2002), and from the South American Andes (Kley and Monaldi, 2002;Giambiagi et al, 2003;Kley et al, 2005;Carrera et al, 2006). For understanding complex and large-scale 3D tectonic patterns resulting from superposed extension and compression phases, tectonic inversion was already long studied through analogue (e.g., Buchanan and Mcclay, 1991;Sassi et al, 1993;Brun and Nalpas, 1996;Amiliba et al, 2005;Panien et al, 2005;Mattioni et al, 2007;Yagupsky et al, 2008;Cerca et al, 2010;Yamada and Mcclay, 2010;Bonini et al, 2012;Di Domenica et al, 2014;Granado et al, 2017;Deng et al, 2020;Zwaan et al, 2022) and numerical (Buiter et al, 2006;Panien et al, 2006;Buiter et al, 2009;Granado and ...…”