Late Cretaceous S-verging thrusting in the central Southern Alps (N Italy) proved by U-Pb syn-tectonic calcite geochronology
- 1Dipartimento di Scienze dell'Ambiente e della Terra, Università degli Studi di Milano-Bicocca, I
- 2Dipartimento di Scienze della Terra, Università degli Studi di Firenze, I
- 3Dipartimento di Scienze della Terra, Sapienza, Università degli Studi di Roma
- 4Earth Sciences, UC Santa Barbara, USA
The central Southern Alps (cSA) form a complex S-verging polyphase fold-and-thrust belt formed in response to the Alpine convergence to the S of the Periadriatic Fault System. Despite the onset of the final continent-continent collision in the Alps is constrained in the Late Eocene, evidence of Late Cretaceous deformation occur in the northern part of the belt, along the Orobic Thrust stacking the Variscan basement onto the Permo-Triassic cover. Here, pseudotachylytes associated to faulting close to the brittle-ductile transition display radiometric ages that trace back to 80 Ma.
No radiometric ages on structures in the central and southern part of the belt are until now available, with only indirect constrains (andesitic dikes and stocks cross-cutting tectonic structures) providing a pre-Late Eocene age of deformation related to the Alpine crustal shortening.
We present here new U-Pb radiometric ages of calcite tectonites located along the main structures of the central and southern sectors of the cSA that consist here of a thick pile of thrust sheets deforming the Lower to Middle Triassic carbonate successions. Our new U-Pb calcite ages obtained on growth fibers along fault planes, veins and calc-mylonites sampled along some of the most important regional thrust planes mainly result in Late Cretaceous ages, suggesting that N-S to NW-SE directed compression already affected the central part of the cSA at those times. Similar ages also occur within the southern portion of the belt, where the Norian “Dolomia Principale” thrust sheets, override the Rhaetian Riva di Solto Shale immediately to the north of the frontal portion of the belt. Younger ages resulted from the Paleogene units which are involved in the exposed frontal part of the belt, which is mostly buried under the recent infilling of the Po Plain forming the Milan Belt.
These data confirm that S- to SE-directed thrusting and folding affected the central Southern Alps since the Late Cretaceous, well before the onset of the Alpine collision.
How to cite: Zanchetta, S., Rocca, M., Montemagni, C., Fiorini, A., Carminati, E., Aldega, L., Kylander-Clark, A., and Zanchi, A.: Late Cretaceous S-verging thrusting in the central Southern Alps (N Italy) proved by U-Pb syn-tectonic calcite geochronology, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-56, https://doi.org/10.5194/egusphere-alpshop2024-56, 2024.
