Table 2 Summary of deformation phases in the Western Alps
Age [Ma] | Domain | Characteristics | Phase | Monazite age [Ma] | Remarks | Ref |
|---|---|---|---|---|---|---|
Large-scale deformation history: | ||||||
Cretaceous to Eocene | Western Alps | Subduction of the Thetys Ocean | Related to subduction prism formation, composed of internal Penninic units | K, P, V | ||
Middle to Late Eocene | Western Alps | Subduction of the European continental margin | E, K, Q | |||
Late Eocene to Early Oligocene | Western Alps | European margin—Apulia collision | Related to the exhumation of the internal units and the onset of the external Alps shortening | B, U | ||
Eocene to earliest Oligocene | Western Alps | Oblique collision associated to top-NNW thrusting in sinistral transpression; PF activation | 1st episode of B / Stage 1 of R | Related to N-S-directed convergence and frontal collision in the Central Alps; ECM underthusted below internal units | B, G, K, S | |
~ 35 | Western Alps | End of oblique collision | End of 1st episode of B | Related to the end of N-S-directed head-on collision in the Central Alps | B, T | |
35–25 | Western Alps | Top-WNW-directed thrusting along the PF, associated to backfolding and backthrusting | 2nd episode of B / Stage 2 of R | Related to WNW-directed indentation of the Ivrea mantle wedge. Overprint of Eocene sinistral transpression | B, C, R, S | |
Miocene | Western Alps | Shortening phase and exhumation of the ECM | Contemporaneous westwards migration of the deformation front | D, T | ||
Miocene—Pliocene | Western Alps | Orogen-parallel deformation | SW-directed normal faulting (Simplon Fault), NE-striking dextral strike-slip (around and through the ECM), SW-directed trusting (Digne) | F, L | ||
25–0 | Southern part of the Western Alps | Top-SW thrusting, oroclinal bending and anticlockwise rotation of the Corsica-Sardinia block (20.5–15 Ma) | Stage 3 of R | Related to orogeny in the Apennines and opening of the Liguro-Provençal Basin | J, N, S | |
After 5 | Western Alps | Late brittle normal faulting, orogen-perpendicular extension | 3rd episode of B | Related to reactivation of the Houiller Front in the N and the Penninic Front in the S | B, G, W | |
Deformation in the high-pressure units (internal domains): | ||||||
Late Eocene to Oligocene | Briançonnais Zone | Alpine collision. PF activation, Briançonnais thrusting and westward propagation of deformation | D1 to D2 phase of C | ~ 32 | Mnz age coincides with the exhumation along the PF | C, K |
Late Oligocene | Briançonnais Zone | Back-thrusting (main folding phase) | D3 phase of C | ~ 23 | Mnz age is difficult to attribute to a given deformation episode | C, K |
Miocene—Actual | Briançonnais Zone | Normal/strike-slip faults (late Alpine tilting) | D4 phase of C | |||
Deformation in the ECM (external domains): | ||||||
~ 22.5 | Argentera Massif | First major shortening phase related to shear zone formation (horizontal veins) | ~ 20.6 | Mnz age likely related to NW-striking dextral strike slip | D, K | |
~ 20–15 | Pelvoux Massif | Exhumation and cooling related to thrusting (horizontal veins) | ~ 17.6 | Mnz from a horizontal vein records the major uplift of the Pelvoux Massif (horizontal vein) | D, H, I | |
~ 11–10 and 7–5 | Belledonne Massif | Polyphased transpressive regime and "En echelon" arrangement of vertical veins | ~ 12—5.5 | Mnz ages are related to dextral movements along the Ornon-Roselend fault and the Rhone-Simplon fault (vertical veins) | I, K | |
~ 23–22 and ~ 16 | Mont Blanc Massif | First and second shortening related to shear zone formation (horizontal veins) | ~ 11.5—6.5 | Mnz ages related to NE striking dextral strike slip (vertical vein) | A, K, M, O | |
Aiguilles Rouges Massif | ~ 9—8 | Mnz ages related to NE striking dextral strike slip (vertical veins) | ||||