Vulcano-tettonica e morfologie vulcaniche

The main tectonic elements affecting the Monte Amiata area are a series of faults oriented NE-SW that are the prosecution of the Bágnore and Bagni San Filippo shear zones, located to the south-west and northeast of the volcano, respectively. In addition to these transtensional faults, other three family of lineaments has been recognized on the volcanic area and surrounding sedimentary rocks. They are the older NNESSW trend, and the ESE-WNW and SSE-NNW trends that accommodate the stress produced by the NESW prevailing trend. All these tectonic regional trends were repeatedly active during the volcano eruptive history. The interaction of these structural elements with stratigraphy and volcanic morphologies, such as domes, "coulées" and lava flows that compose the Monte Amiata edifice, hallowed to assess the presence of a number of volcano-tectonic graben-like structures that formed at different moments of the volcanic history. The first of these grabens, correspond to a depressed area inside the sedimentary substratum under the south-western portion of the volcanic edifice. This first collapse occurred in relationship with the emplacement of the thick succession of domes and lava flows cored by the David Lazzaretti drilling. During the subsequent volcanic history, other grabens formed, interdigitated with Monte Amiata main episodes of volcanic activity. These volcano-tectonic structures repeatedly interested trachidacitic lava flows and domes, generating narrow structural strip nested on the summit portion of the volcanic edifice. From a couple of these fractures, the less evolved lavas were emitted during, and not at the end, of the volcanic history of Monte Amiata. The last emitted volcanics are the exogenous domes of La Montagnola and Poggio Trauzzolo formations, unaffected by graben structures. The presence of these volcano-tectonic collapses give reason of all the structural elements still visible on the volcano and depict a new picture of the Monte Amiata volcano grown, that is in agreement with morpho-sructural and stratigraphic findings.