Preprints
https://doi.org/10.5194/se-2021-97
https://doi.org/10.5194/se-2021-97

  06 Aug 2021

06 Aug 2021

Review status: this preprint is currently under review for the journal SE.

Onset of Aegean-style extensional deformation in the contractional southern Dinarides documented by incipient normal fault scarps in Montenegro

Peter Biermanns1, Benjamin Schmitz2, Silke Mechernich3, Christopher Weismüller1, Kujtim Onuzi4, Kamil Ustaszewski4, and Klaus Reicherter1 Peter Biermanns et al.
  • 1Institute of Neotectonics and Natural Hazards, RWTH Aachen University, 52064 Aachen, Germany
  • 2Institute of Geosciences, University Jena, 07749 Jena, Germany
  • 3Institute of Geology and Mineralogy, University Cologne, 50937 Köln, Germany
  • 4Institute of Geosciences, Energy, Water and Environment, Polytechnic University of Tirana, 1016 Tirana, Albania

Abstract. We describe two previously unreported, 5–7 km long normal fault scarps (NFS) occurring atop fault-related anticlines in the coastal ranges of the Dinarides fold-and-thrust belt in southern Montenegro, a region under predominant contraction. Both NFS show well-exposed, 6–9 m high, striated and locally polished fault surfaces in limestones, documenting active faulting during the Holocene. Sharply delimited ribbons on free rock faces show different color, varying karstification and lichen growth and suggest stepwise footwall exhumation, typical of repeated normal faulting earthquake events. Displacements, surface rupture lengths and geometries of the outcropping fault planes imply paleoearthquakes with Mw ≈ 6 ± 0.5 and slip rates of c. 0.3–0.5 mm/yr since the Last Glacial Maximum. Slip rates based on cosmogenic 36Cl data from the scarps are significantly higher: modeling suggests 1.5 ± 0.1 mm/yr and 6–15 cm slip every c. 35–100 yrs, commencing c. 6 kyr ago. The total throw on both NFS – although poorly constrained – is estimated to max. 200 m, and offsets the basal thrust of a regionally important tectonic unit. Both NFS are incipient extensional structures that postdate growth of the fault-related anticlines on top of which they occur. Interestingly, the position of the extensional features agrees with recent geodetic data, suggesting that our study area is located exactly at the transition from NE-SW-directed shortening in the northwest to NE-SW-directed extension to the southeast. While the contraction reflects ongoing Adria-Europe convergence taken up along the frontal portions of the Dinarides, the incipient extensional structures might be induced by rollback of the Hellenic slab in the SE, whose effects on the upper plate appear to be migrating along-strike the Hellenides towards the northwest. The newly found NFS provide evidence for a kinematic change of a thrust belt segment over time. Alternatively, the NFS might be regarded as second-order features accommodating changes in dip of the underlying first-order thrust faults to which they are tied genetically.

Peter Biermanns et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-97', Gerald P. Roberts, 11 Aug 2021 reply
  • AC1: 'Comment on se-2021-97', Peter Biermanns, 24 Aug 2021 reply

Peter Biermanns et al.

Peter Biermanns et al.

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Short summary
We introduce two spectacular, up to 7 km long normal fault scarps near the city of Bar (Montenegro). The fact that these widely visible earthquake-related structures have never been described before is even less surprising than the circumstance that they apparently do not fit the tectonic setting that they are located in. By quantifying the age and movement of the newly discovered fault scarps and by partly re-interpreting local tectonics, we introduce approaches how this is still compatible.