Paleomagnetic evidence of large fault displacement around the po-basin

Abstract

New paleomagnetic data are presented from Tuscany and the Southern Alps (Italy). A paleomagnetic study of the autochthonous Verrucano near Siena revealed two characteristic paleomaghetic directions, one of the Ladinian to Carnian Verrucano (D = 301.1”) I = +60.2”, aa5 = 6.0”) and the other of the Late Carboniferous to Early Permian Farma formation (D = 318.8”, I = +20.8”, “95 = 12.8”). A paleomagnetic study on a limestone sequence in the Vicentinian Alps revealed characteristic directions for Late Jurassic (D = 328.5”, I = +45.3”, eg5= 3.0”), for Turonian-Coniacian (D = 345.5”, Z = +38.2”, ass= 3.3”), for Early Santonian (D = 344.2”. I = +43.3”, (ugs = 5.3’) and for Late Santonian to Early Campanian rocks (D = 342.7”, Z = +50.9”, a95 = 5.3”). Comparison of these new data with published data of Permian and younger age from the Southern Alps and from Umbria respectively, leads to conclusions about movements of crustal blocks North and South of the PO-basin. Further comparison of the data from the Northern Apennines with published Sardinian data seems to support that Sardinia belonged to the central Italian Peninsula until present times. It is argued that the Northern Apennines and the Vicentinian Alps belonged to the African plate and that their movements were defined by the opening history of the Atlantic. It was found, however, that during Late Cretaceous and again in Early Tertiary the two Italian crustal blocks must have been uncoupled to some degree. This supports the hypothesis of a major fault zone in the area of the Po-basin, which is now buried under a thick Late Tertiary to Quaternary sedimentary cover.