Jurassic ophiolites within the Valais domain of the Western and Central Alps: geochronological evidence for re-rifting of oceanic crust

摘要: Metabasic rocks from different parts of the Antrona ophiolites, Western Alps, as well Misox zone, Central were dated using ion microprobe (SHRIMP) U-Pb analyses zircon, in association with cathodoluminescence (CL) imaging. HP metamorphism must have affected at least major part although relics are rarely preserved, probably due to Lepontine metamorphic overprint. has also area zone. The origin ophiolites is arguable. They interpreted both Piemont–Ligurian (PL) and Valais ocean, two main oceans Alps before Alpine convergence. SHRIMP-analyses co-magmatic zircon domains (Guggilihorn, Passo del Mottone Quarata areas) yielded identical (within uncertainty) weighted mean 206 Pb/238U ages 155.2±1.6 Ma, 158±17 Ma (or 163.1±2.4 Ma: one analysis; 1σ error) 155.6±2.1 respectively, time crystallization magmatic protoliths. These Late Jurassic fit span considered for formation oceanic crust. metagabbro zone (Hinterrhein area), which a Valaisan generally accepted, gave Jurassic, PL protolith age 161.0±3.9 Ma. amphibolitized eclogite an 38.5±0.7 metamorphism. This good agreement reported previous SHRIMP-data eclogites amphibolites other domain. In order bring line ages, we suggest scenario involving emplacement crust north newly formed Brianconnais peninsula, inside geotectonic paleotectonic configuration was established when younger by spreading re-rifting, partly within