Work

Garnet-Free Mineral Assemblage at Eclogite-Facies Conditions in the Riffelberg–Garten Unit, Italian Western Alps

Year: 2026

Type: article

Abstract: The peculiar high-pressure mineral assemblage omphacite, epidote, quartz, calcite, titanite, and opaque minerals, ±phengite, has been observed in the Riffelberg–Garten Unit (RGU), a heterogeneous metasedimentary rock assemblage of the Zermatt–Saas Zone. Microstructural analysis, mineral chemistry, and petrologic modelling allowed to refine the syn-D2 P-T peak conditions for the Alpine tectono-metamorphic evolution. In the upper Valtournenche, S2 foliation is the dominant fabric at the regional scale of the Zermatt–Saas Zone. Petrologic modelling of the syn-D2 mineral assemblage indicates climax conditions of P = 1.85–2.0 GPa and T = 500–525 °C. These estimates are in good agreement with those inferred in the RGU metasedimentary matrix and enclosed eclogite and metagabbro elements. During exhumation, RGU rocks re-equilibrated texturally and mineralogically under blueschist–/epidote–amphibolite (P = 0.4–1.3 GPa and T = 350–500 °C during D3) and greenschist (P ≤ 0.25 GPa and T ≤ 400 °C during) facies conditions. This study highlights the potential of petrologic modelling for constraining the environmental conditions of metamorphism even in anomalous mineral assemblages where conventional thermobarometry is not applicable.

Source: Minerals

DOI: 10.3390/min16010079

Authors: Gisella Rebay, Thomas Gusmeo, Maria Iole Spalla, Davide Zanoni

Institutions: University of Pavia, University of Milan, University of Bologna

Language: English

Topic: Geological and Geochemical Analysis

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,896

Funders: Università degli Studi di Milano, Papua New Guinea University of Technology