Source of CO2 in large Talc-Carbonate veins in serpentinites of the Zermatt-Saas Fee unit

Abstract

The Zermatt-Saas Fee zone represents an ophiolitic sequence within the Western Alps derived from the paleo ocean Liguro-Piemontaise. The melting of the Unterer Theodulgletcher glacier newly uncovered some Tc-Mgs and Atg-Dol veins within serpentinite host rock. Both the serpentinite and veins are fresh as they have been protected from weathering by the glacier, which makes this area ideal for investigation.

The SW-NE orientation of the veins indicates that the veins were formed in context with the backfolding event of the Alpine orogeny. Temperature estimations indicate that the veins formed at 350-450C at middle- to lower greenschist facies conditions during or shortly after the backfolding event. The veins are metasomatic and formed due to infiltration of a CO2 and Ca rich fluid which reacted with the serpentinite to form carbonate veins. Stable isotope d13C analysis implies that the fluids might be derived from the overlying metasediments – the Bündnerschiefer.