PELLEGRINI G. B.
Aspetti morfologici ed evidenze neotettoniche della linea Schio-Vicenza – Morphological and neotectonic evidences along the Schio- Vicenza Line
Pages 69-81
Abstract
This study considers the morphological and neole<:tonic evidence of Ihe Schio-Vicenza Line al the point where il cuts the Marana-l'iovene Line and along part of Ihe teetonie scarp boundcd to the East by the relicf of the Lessini Moumains. In this area, the l'ermo-Triassic, Jurassic, Cretaceous and Tertiary sedimentary formations lie over the outcropping South-Alpine crystalline basement. Eruptive products from two magmatic cycles cross or are intercalatcd with the varioLls rocks of the stratigraphic serics: the Middle Tl'iassic cycle is characterized by acid materials, the l'aleogene cycle by basaltic ones. In Ihe plain sector, deep drillings have shown that Quaternary marine deposits are lacking; in the uppermost pan, fluvial deposits aboul 100 m are found. The mosl imporlam structures of the area are the Marana-Piovene and Schio·Vicenza Lincs. The former, running ENE-\VIS\VI, corresponds to a fold-fauh overthrusting towards the East. The latter runs straight N\VI-SE and cuts the Marana-Piovene Line perpendicularly near Poleo. According to the bibliography. the Schio-Vicenza Line has the fol1owings features: Strike: NWI-SE. generaUy subvertical or, in the plain, dipping NE sharply. Lengtb: between Besenello in Val Lagarina and near Conselve, to SE of the Euganean I-Iills. DiJplacements al1d types o/movemenl: both throws and stl'ike-slips. Age o//ol'l1/Oliol1: probably Triassic; it dcfinitc1y existed in the Paleogene. Pbases o/activiJy: variolls, from Triassic to Quaternary. In particular, lhe activity of the !inc dllring the Quaternary is proven only for some parts buried under lhe piain. These bibliographical data (ormed the basis of a detailed morphological examination carricd aut in three areas believed to be of importance in verifying the hypothesis of uplift in the sector \'(fest of the Schio-Vicenza Line. maximum movement occurring near to the piedmont beh a10ng tlle Marana-Piovene Line and. for a short stretch North of Schio. along the Schio-Vicenza Line itself. A simiIar detailed morphotectonjc survey, carried out near S. Vito di Leguzzano, revealed that the eastern margin of the Lessini Mountains is uplifted with respcct to the centre of the Venetian l'art of the Po Plain, which is lowered, as stated by FINE'lvl'I (1972). In parlicuiar, in the Val Gogna, terraces \Vere identified cut both on rocks and on landslide dcposits, deepiy dissected but closely linked a1timetrically untiI they reach the plain, where their links with the l'resent valley bottom suddenly seem to be interrupted. A comparison of the trends of the present and the ancient (pre-quaternary) longitudinal profiIes c1carly shows a divergence attributed to a Pleistocene (?) uplih of this sector of the pre-Alpine margin, at the intersection between the Schio-Vicenza fault and the Marana-l'iovene Line. In this area of interference of the two large structurcs, other evidence may confirm the differential uplift of the western sector of the Schio-Vicenza Line, e.g., eastwarcl clispiacement of the Gogna seasonal stream, which now runs alollg a gorge excavalecl in the rock at the [oot of M. GuizzaFaedo, and the clear SE deviation of the stream descending from the Val Mara. Near S. Vito di Leguzzano, paleosurfaces and a palco-riverbed were also identified, both interrupted at the Schio-Vicenza Line. Here tao, the longitudinal profiles diverge with respect to the presem vuLley bottom, supporting the hypothesis that the western sector of the Schio tectonie system was upliftoo, with consequent lowering of the eastern sector. The trend of the Leogra seasonal stream, which in the past ran at the foot of the eastern scarp of the Lessini Mountains. as shown by a paleo-riverbed near Magré Vicentino, underwent the uplih cffects of Ihe western sector and runs initially eastwards as far as the hiUs NE of Schio. h then returns (as MOLON hud reported as far back as 1883) towards the eastern f1ank of the Lessini Mountains, along the fault angle depression caused by the Schio-Vicenza Line.