To satisfy experimental data of phase equilibria and rock strength, current plate-tectonic models suggest that blueschist parageneses in Mesozoicophiolites in mountain belts may have formed in subduction-zone environments. However, structural geometry and estimates of overburden thickness in the region of the Mischabel backfold in the western Alps suggest that mesoscopic linear fabrics of glaucophane and other minerals formed at a relatively shallow depth during backfolding. They either grew syntectonically or were rotated as pre-existing minerals into a preferred linear orientation. It is proposed that the glaucophane lineation formed during the Barrovian Lepontine phase of Alpine metamorphism late in, or after, the northward transport of the Monte Rosa nappe, which in turn moved after obduction of its Mesozoic envelope of oceanic ophiolites (with its blueschist parageneses formed in a Tethyan subduction zone) onto European sialic crust that now forms the core of this nappe.
- Geological Society of America