ALPINE PALAEOSTRESS OF THE CENTRAL ITALY

BELOUSOV T.P.

Institute of Physics of the Earth, RAS, Moscow E-mail: belousov@ifz.ru

During 2004, we accomplished several tectonophysical routes on the left side of the Arno River valley to the southeast of Florence City. Primary goal of field researches was the reconnaissance data gathered on interstratum fracturing sedimentary rocks of this area with the purpose of checking an opportunity of their use for reconstruction of alpine palaeostress in Italy.

The area of Florence settles down within the limits of North Apennines consisting of Umbria and Tuscan integumentary plates, displaced from the south northwards. Integumentary plates are combined with carbonate by the adjournment submitted by Jurassic limestones and marls, Cretaceous-Oligocene argillites and Early-Middle Miocene flysch. The main Tuscanian phase of formation of covers occurred in Miocene.

In carbonate to thickness of the Tuscan cover in adjournment of Sillano formation (Late Cretaceous - Early Eocene) were incorporated four points of supervision, in each of them it is made 100 gauging elements of attitude planes joints superficial adjournment. Basing on experience of studying in various regions of the Earth of systems of easing in young sedimentary adjournment, we accept, that directions of the future initial fracturing are pawned at initial stages of lithogenesis horizontally deposited sediments owing to their internal instability. The instability connected to influence of an existing field of palaeostress, results to localization shift plastic deformations in the narrow regularly located connected microzones, normal in a plane of a sedimentary layer. Microzones of localization shift deformations with increase of a degree of lithification deposits pass a skeleton of the future in initial joints.

On the basis of the analysis of pattern initial interstratum fracturing sedimentary breeds of Sillano formation the direction of compression was reconstructed within the limits of researched area of Italy. In all four points of supervision of the axis of maximal compression of the palaeostress field at the end of Mesozoic - beginning of Cenozoic was focused on line NNW-SSE, 325-350° (Table 1).

Table 1. Points of supervision of the maximal compression axis of the palaeostress field at the end of Mesozoic - beginning of Cenozoic.

Other area of Italy within the limits of which supervision in two points it was investigated fracturing sedimentary breeds Quarternary of age the island Ischia which is settled down approximately in 30 km west from Naples. The island is combined with volcanic lavas and Pleistocene-Holocene layered pyroclastic rocks. Reconstruction of the intense condition has shown, that in the northwest part of island on the Quarternary stage of his formation compression had latitudinal direction. Thus, in area of Ischia island the axis of the maximal compression in post-Eocene time has changed the orientation, having undergone turn in approximately 60-80° counter-clockwise.

Results of field tectonophysical researches in area of Florence City have shown that the data on pattern interstratum fracturing sedimentary rocks are easily interpreted and can be used for reconstruction of the alpine palaeostress of the earth's crust of Italy.