We attempt to reconstruct the kinematics (deformation and motion) of the Western Alpine Arc between the Mercantour and Aar Massifs. First, we compile a map showing principal extension (X) direction within three major structural units. In the external zone, X directions are broadly radial to the Alpine Arc; in the internal zone, they are uniform or smoothly varying in some domains; whereas in the intermediate zone they often show much scatter. Next, we use geochronological data and P‐T conditions, estimated from metamorphic mineral reactions, to time the deformation. On each of a series of interval maps, we show X‐directions for strain accumulated during a chosen time interval. We argue that these incremental X‐directions are approximately equivalent to segments of particle paths, showing displacements relative to stable Europe. For 120–100 Ma, the displacement direction was about N150 and coeval with eclogite facies metamorphism; it is interpreted as a direction of overthrusting by the African Plate. Around 40 Ma, the displacement in the south part of the arc became westerly. Finally, between 25 and 15 Ma, displacement directions were generally radial to the arc.

A detailed study of garnet-chloritoid micaschists fom the Sesia zone (Western Alps) is used to constrain phase relations in high pressure (HP) metapelitic rocks. In addition to quartz, phengite, paragonite and rutile, the micaschists display two distinct parageneses, namely garnet + chloritoid + chlorite and garnet + chloritoid + kyanite. Talc has never been observed. Garnet and chloritoid are more magnesian when chlorite is present instead of kyanite. The distinction of the two equilibria results from different bulk rock chemistries, not from P-T conditions or redox state. Estimated P-T conditions for the eclogitic metamorphism are 55(Moo°C, 15-18 kbar.The presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible AFM topologies for the Sesia metapelites. The paper describes a W A S H multisystem for HP pelitic rocks, which extends the grid of Harte & Hudson (1979) towards higher pressures and adds the phase talc. Observed parageneses in HP metapelites are consistent with predicted phase relations. Critical associations are Gt-Ctd-Chl and Gt-Ctd-Ky at relatively low temperatures and G1-Chl-Ky and Gt-Tc-Ky at relatively high temperatures.

This paper concentrates on the petrology of eclogite-facies metapelites and, particularly, the significance of staurolite in these rocks.A natural example of staurolite-bearing eclogitic micaschists from the Champtoceaux nappe (Brittany, France) is first described. The Champtoceaux metapelites present, in addition to quartz, phengite, and rutile, two successive parageneses: (1) chloritoid + staurolite -I-garnet cores, and (2) garnet rims -hkyanite± chloritoid.Detailed microprobe analyses show that garnet and chloritoid evolve towards more magnesian compositions and that staurolite is more Fe-rich than coexisting garnet. A comparison of the studied rocks with other known occurrences of eclogitic metapelites shows that whereas staurolite is always more Fe-rich than garnet in high-pressure eclogites, the reverse is true in low-to medium-pressure micaschists.Phase relations between garnet, staurolite, chloritoid, biotite, and chlorite are analysed in the KFMASH system (with excess quartz, phengite, rutile, and H20). The topology of univariant reactions is depicted for a normal and a reverse Fe-M g partitioning between garnet and staurolite. Mineral compositional changes are also predicted for varying bulk-rock chemistries.In the studied micaschists, the zonal arrangement of garnet inclusions and the progressive compositional changes of ferromagnesian phases record part of the prograde P-T path, before the attainment o f 'peak' metamorphic conditions (at about 650-700 °C, 18-20 kb). The retrograde path, which records the uplift of the Champtoceaux nappe, occurs under decreasing temperatures.