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Authors: Billi, A.* 
Tiberti, M. M.* 
Title: Possible causes of arc development in the Apennines, central Italy
Other Titles: Arc development in the Apennines
Issue Date: 2008
Keywords: oroclines
fold and thrust belts
gravity anomalies
seismic reflection profiles
Subject Classification04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes 
04. Solid Earth::04.03. Geodesy::04.03.04. Gravity anomalies 
04. Solid Earth::04.04. Geology::04.04.09. Structural geology 
04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics 
Abstract: In central Italy, geometry, kinematics, and tectonic evolution of the late Neogene Umbrian Arc, which is one of the main thrusts of the northern Apennines, have long been studied. Documented evidence for orogenic curvature includes vertical-axis rotations along both limbs of the arc and a positive orocline test along the entire arc. The curvature’s cause is, however, still unexplained. In this work, we focused our attention on the southern portion of the Umbrian Arc, the so-called Olevano-Antrodoco thrust. We analyze, in particular, gravity and seismic reflection data and consider available paleomagnetic, stratigraphic, structural, and topographic evidence from the central Apennines to infer spatial extent, attitude, and surface effects of a mid-crustal anticlinorium imaged in the CROP-11 deep seismic profile. The anticlinorium has horizontal dimensions of about 50 by 30 km and is located right beneath the Olevano-Antrodoco thrust. Stratigraphic, structural, and topographic evidence suggests that the anticlinorium produced a surface uplift during its growth in early Pliocene times. We propose an evolutionary model in which, during late Neogene time, the Olevano-Antrodoco thrust developed in an out-of-sequence fashion and underwent about 16° of clockwise rotation when the thrust ran into and was then raised and folded by the growing anticlinorium (late Messinian-early Pliocene time). This new model suggests a causal link between mid-crustal folding and surficial orogenic curvature that is consistent with several available data sets from the northern-central Apennines; more evidence is, however, needed to fully test hypothesis. Additionally, due to the occurrence of mid-crustal basement-involved thrusts in other orogens, this model may be a viable mechanism for arc formation elsewhere.
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