Cutting of the European continental lithosphere: Plasticity theory applied to the present Alpine collision

Abstract

Abstract. Presently active European Alpine collision has a history of more than 100 Myr convergence. We investigate the collisional contact problem of an apparently rigid African promontory (currently the Italy/Adria block (IAB)) steadily penetrating at 1 cm/yr, over at least the past 45 Myr, into the deformable European plate. We assume that neither continental subduction nor delamination occurs presently in the 300-km-wide contact zone enabling use of the indenter-indentee approach. A key parameter is the aspect ratio h/a, defined by the width of the deformable foreland over the width of the indenter itself. This parameter controls the activation of two fundamentally different modes of deformation: (1) classical indentation mode for h/a > 4.4, described by previous authors, and having effect only in a portion of the deformable plate in the vicinity of the indenter and (2) cutting mode for h/a _< 4.4 giving plane strain longitudinal splitting of the entire deformable plate and plastic separation of the two halves. We use a matrix operator method to solve for slip lines in the mixed boundary value problem (obliquity, velocity, friction, stress) of the European Alpine case. Implications are as follows: (1) plane stress, vertical lithospheric thickening is the first indentation mode of continental collision; and (2) for the present ratio of h/a • 3 deformation is in the cutting mode and slow plane strain intraplate extension (rifting) is predicted. This mode explains the intraplate stress field obtained from borehole and earthquake data. Considering that the paleoindenter probably has been larger than the IAB it is inferred that h/a has been below 4.4 since at least the end of the Eocene and that consequently the intraplate graben system (Lower Rhine, Rhine, Bresse, Limagne) is due to the cutting of the European plate by Alpine collision.

Geodetic and hydrological aspects of the Merano earthquake of 17 July 2001

“…The pre-Alpine earthquakes in NE Italy are mostly associated with a rough N-S compression, implying a sinistral strike slip kinematics along the Giudicarie system. This structural setting is consistent with the concept of an active northwards indentation of the Adria plate towards Europe (Bressan et al, 1998;Regenauer-Lieb and Petit, 1997;Renner and Slejko, 1994), as also confirmed by independent geodetic data (Caporali et al, 2003a) (Fig. 2b).…”

“…The North Giudicarie system is an important segment of the Periadriatic lineament, the tectonic divide between the Alpine north-vergent collisional wedge and the South Alpine south-vergent thrust and fold belt. A sinistral kinematics along the North Giudicarie inferred from the focal mechanisms of this event would completely agree with a northwards indentation of the Adria microplate or promontory into the Eurasian plate (Bressan et al, 1998;Regenauer-Lieb and Petit, 1997;Renner and Slejko, 1994). Hence the importance to understand as exactly as possible the geometry of the fault plane of this earthquake.…”

Analysis of central western Europe deformation using GPS and seismic data

“…The regional change in the tectonic style observed in central western Europe has been discussed by many authors and can be linked to: (a) variation in the force along the southern European boundary, due to irregular shape of the colliding continental margins (Illies, 1975;Regenauer-Lieb and Petit, 1997), (b) variation in the lithosphere strength of thermal origin (Grünthal and Stromeyer, 1992;Müller et al, 1997), (c) mechanical decoupling between crust and lithospheric mantle, allowing crustal fragments to move independently of each other Garcia-Castellanos et al, 2000). On the other hand, tomography studies (Granet et al, 1995a;Marquering and Sneider, 1996;Bijwaard et al, 1998) showed significant velocity variations under central western Europe.…”

Pressure conditions for shear and tensile failure around a circular magma chamber; insight from elasto-plastic modelling

“…For instance Lake Baikal results from the indentation of Asia by India (e.g. Tapponnier & Molnar, 1976), and the Eifel volcanic zone would result from the Alpine-European indentation (Regenauer & Petit, 1997 R approximately) may be invoked to a first order to assess whether a magmatic chamber is deep enough to generate a secondary magmatic reservoir very close to the surface. This speculative process requires a systematic investigation of double sources below volcanoes worldwide (e.g.…”