4th Swiss Geoscience Meeting, Bern 2006 Sector zoning in garnets as growth mechanisms indicator.

Garnets from graphite rich meta marls of the Nufenen Pass area in the Swiss Alps display textural and chemical sector zoning, and irregular birefringent lamellae normal to the sector growth. The metamarls were collected in the Kalkschiefer from the Termen zone (Liskay; 1965) and underwent lower amphibolites pressure-temperature conditions (Kamber; 1993). The metamarls contain up to 1.6 wt % and have an assemblage consisting of garnet, biotite, white mica, clinozoisite, carbonates (calcite and ankerite), ilmenite, pyrite and accessories minerals such as zircon, tourmaline and apatite. Garnets are dodecahedral porphyroblasts with a size of 0.6 mm to 4.8 mm. Their diameter is larger in S1 schistosity plane. All garnets display two distinct zones. The outer zone is graphite rich and has clinozoisite, carbonates, and quartz inclusions. The width of the graphite rich rim decrease with an increase of garnet diameter. The central zone shows 6 sectors without graphite inclusions and radiating from the centre of the crystal. The sectors contain a few quartz rods oriented normal to the garnet growth face. Irregular birefringent lamellae oriented also normal to the face o