Scienze Naturali, Scienze dei Sistemi Naturali,
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The occurrence of coesite, a Ultrahigh Pressure (UHP) index mineral, in tectono-metamorphic belts is of paramount importance to pinpoint the depths attained during subduction. Such mineral is generally found as inclusions within garnets and is often the sole remnants of an UHP mineralogy in largely re-equilibrated rocks. UHP tectonometamorphic units in subducted oceanic lithosphere are of particular interest because they are natural laboratories to study element-exchange and fluid rock interactions occurring in a subducting slab at depths > 80 km. In this context, the meta-ophiolites of the Western Alps are a perfect case study, as they offer a continuous outcrop along the entire belt. Here, we focus on the UHP meta-ophiolites of the Internal Piedmont Zone (IPZ) in the Western Alps, where coesite inclusions in garnet have recently been found in two localities: i) Lago Superiore Unit (Monviso Massif) and ii) Susa Valley. These localities lay on the same structural position of the Lago di Cignana Unit, wherein coesite was discovered in the early 90’s. Coesite was identified via µ-Raman spectroscopy, showing the typical vibrational modes of the phase (521, 427, 271 and 180 cm-1), slightly shifted due to elastic residual strain. A targeted sampling campaign along the entire Western Alpine meta-ophiolitic belt allowed to better understand the distribution of coesite-bearing rocks. In this talk we will present the results that highlight a large occurrence of coesite along the whole Western Alpine belt among the meta-ophiolites, suggesting that a large volume of oceanic lithosphere was subducted at ca. 100 km depth and then returned to the surface.

The Speaker: Stefano Ghignone (Università degli Studi di Torino)

Stefano Ghignone is a post-doc research fellow at the Earth Sciences Department of the University of Torino. He defended his PhD in Torino with a thesis on a first-order shear zone of primary importance for the Western Alps (Susa Shear Zone), combining structural geology, petrology, and geochronology. After the PhD, he focused on mineralogy and different aspects of crystal growth, studying inclusion-host mineral systems, applying different analytical techniques (µ-Raman, SEM-EDS). In the last few years, he concentrated his research on characterizing index mineral inclusions within metamorphic rocks, aiming to assess the extent of Ultra-High-Pressure domains.

Onsite: h. 16:00 Aula Ruffini DST

Website at this link.

Contacts: geoseminar.dst@unito.it