Geomorfologia e neotettonica dell’area di Colfiorito (Umbria)

Geomorphology and neotectonics of Colfìorito area (Umbria, Italy)

Abstract

The studied area extends from the Colfiorito plain to the Percanestro R. (Eastern Umbria) and is particularly interesting with regard to morphoneotectonics, which takes place because of faults concentrated along three belts: the northernmost with a SW-NE direction, in the zone from Colfiorito plains to the Chienti valley; the intermediate (nearly W-E) between Rasiglia and M. Tolagna. The southernmost (the Carpineto Fault) directed nearly W-E too. These faults control the hydrographical evolution and the landscape in the whole studied area. Besides, also other faults, parallel to the apenninics structures activated during the tensional stage of Apennine tectonics (such as the M.Tolagna fault and the faults between those of Percanestro and Carpineto). These faults divided the area in polygonal blocks of horst and graben type. These tectonic events drove the paleogeographic evolution of the zone, which can be outlined as follows: 1. In the Upper Pliocene-Lower Pleistocene (?) a W-E watershed existed, which separated the basin of the paleo-Rio, flowing northward (Colliorito plains) from the basins of the streams Fauvella and Piè di Cammoro, flowing southward. 2 – In the Middle Pleistocene (?) the anti-Apennine faults intersected by normal Apennine faults, determined the fragmentation of the Colfiorito area in blocks, whose relative movement led to the formation of the depression of Ricciano, Arvello, Colle Croce, Annifo, la Palude, the Colfiorito plain and Borgo. The Percanestro and M. Tolagna faults determined the formation of the S. Martino basin, while further N the Popola depression was forming. The Percanestro fault beheaded the paleo-Rio, bringing northward the watershed between the streams directed into the Rio-Chienti hydrographic system and those which would gather along the fracture, flowing together southward into the Percanestro- Vigi. In the western part of the block between the Percanestro and Carpineto faults the activity of the new normal faults downthrow the Rasiglia area, where a centripetal drainage occurred (in this area flowed together the streams which previously had a southward direction). In this period the Verchiano basin was probably fortmed. 3 – The last movements of the tensional tectonics determine the extinction of lake basins: they were emptied by the paleo-Rio and drained into the Chienti valley. The regressive erosion of the Menotre river cutoff the W-E watershed, taking in the waters of the Verchiano basin through the cutoff M. Molino structure.