Structural setting of the Cicolano - M. Calvo area (Central Apennines, Italy)

The studied area, belonging to the Central Apennines, is comprises between the M. Filone-M. Navegna ridge in the west, and the M. Calvo-Colle dei Montanari ridge in the east. Four tectonic units, characterized by different sedimentary successions and by different structural setting can be recognized in the area. They form a complex embricate fan thrust system and are, from the higher to the lower one: Reatini unit, Navegna unit, Salto-Nuria-Calvo unit, La Torretta unit. The Reatini unit is made of the Umbria-Marchean sedimentary succession, and is tectonically placed on the Navegna and the Salto- Nuria-Calvo units, by a thrust plane developed along the Ancona- Anzio Auct. tectonic line. Its internal structural setting is characterized by a minor thrust plane that placed a syncline involving the Jurassic deposits on the overturned Cretaceous-Paleogene succession. A Mesozoic slope-to-basin and a Cenozoic carbonate ramp succession, developed along the northwestern margin of the Lazio- Abruzzi carbonate platform paleodomain constitutes the Navegna unit, located in the south of the Reatini unit. It is overthrust onto the Salto-Nuria-Calvo unit by a thrust plane which corresponds to the Olevano-Antrodoco line. Several minor thrust planes associated to narrow hangingwall anticlines verging eastward in the Navegna unit have been recognized. The Salto-Nuria-Calvo unit can be divided in three sector belonging to the Lazio-Abruzzi carbonate platform paleodomain: the sedimentary succession of the Salto sector is made up of Cretaceous carbonate platform deposits, covered unconformably by a Miocene succession of carbonate ramp environment, and by a thick Early Messinian siliciclastic turbidites succession. The internal structural setting comprises minor folds and thrust planes that constitute carbonate ridges surrounded by siliciclastic deposits. On the eastern side of Salto lake, small carbonate ridges sometimes associated to back thrust planes occur. The M. Nuria sector is made of a Mesocenozoic sedimentary succession deposited in a carbonate platform environment, that passes southeastward to carbonate margin deposits. The stratigraphic organization shows a progressive sinking of this sector during Cretaceous- Paleogene time. Miocene carbonate ramp and Early Messinian siliciclastic turbiditic deposits cover unconformably the previous ones. This unit is organized in anticlines associated to thrust plane trending NW-SE. Minor back thrust planes and splays with thin levels of turbiditic sandstone cropping out in their footwall, can be observed in the eastern sector of the area. M. Calvo sector, constituted by a Mesozoic carbonate platform margin sedimentary succession, is the more external part of the the Lazio-Abruzzi carbonate platform paleodomain, and it overthrusts with a low angle thrust plane onto the more external unit of La Torretta unit, that is, on its turn, made of the Meso-Cenozoic pelagic succession. The M. Calvo area is organized in several minor tectonic slides, while its footwall (La Torretta unit) shows narrow synclines and anticlines with an inclined to overturned setting. Tear faults associated to the compressive structures, trending SW-NE and E-W, are also recognized. From the Late Pliocene on, an extensional tectonic phase occurs in the studied area with the development of main normal faults and the reactivation of some ancient structures.