Western Alps-Northern Apennine junction area: the role of the Corsica-Sardinia block rotation
The major role of the Corsica-Sardinia block-rotation in shaping the Western Alps-Northern Apennine junction area and in the fragmentation of the former prolongation of the Alpine chain in the western Mediterranean has been suggested for more than 40 years (Boccaletti and Guazzone, 1971; Debelmas, 1972; Elter and Pertusati, 1973; Alvarez et al., 1974; Vanossi et al., 1980; Laubscher, 1988; Vanossi et al., 1994). Recently acquired paleomagnetic data (Maffione et al., 2008) completing those of Bormioli and Lanza, 1995; Muttoni et al., 1998, 2000; Collombet et al., 2002; Carrapa et al. 2003, help better defining timing and magnitude in rotation between the TPB, the underlying Ligurian Alps and the Corsica-Sardinia block (Speranza et al., 2002; Gattacceca et al., 2007).
Fig. 7 reports the documented amounts of block rotations and their timing in the different domains and units (see also Ciffelli and Mattei this volume). Although paleomagnetic studies from different working groups and sites have different reference frame (Africa or Europe), they can be considered comparable (see Maffione et al., 2008) thanks to the documented negligible rotation relative to the geographic north of the two major plates during Tertiary times (e.g. Besse and Courillot, 2002; Maffione et al., 2008).
For the Brianconnais units of the LA, rotations (with respect to stable Europe) along vertical axis between 47°- 117° were dated as post-late Oligocene by Collombet et al. (2002), although some rock samples refer to highly strained domains that have suffered important rotational deformations. For the TPB basin Bormioli and Lanza (1995), Carrapa et al. (2003) and more recently Maffione et al. (2008) documented in lower Oligocene-Middle Miocene sediments, counterclockwise rotation (up to c.50°) (with respect to Africa) during Aquitanian-Serravalian time. Although a detailed structural and paleomagnetic integrated study was not performed by Maffione et al. (2008), the result of their statistic oroclinal tests allowed them to exclude that differential rotations occured in the different studied sites of TPB, thus supporting the idea that the basin rotated as a whole. Following these conclusions (but see below) a major concern is relative to the pole of rotation of the system which has been located differently as illustrated in Fig.6 (Debelmas, 1972; Elter and Pertusati, 1973; Laubscher, 1988; Vanossi et al., 1994; Hoogerdujin Strating et al. 1994; Ghelardoni, 1994). The AXF basal thrust (Mosca et al., 2009) whose kinematics possibly changed through time could be indicated as the major structure which accomodated the roto-translational displacement of the LA sector. The possible lateral (?) surface splays of the AXF fault can be identified along a VVL and eastward in the OLL.