Monte Duria peridotite (south), Peglio, Como Province, Lombardy, Italyi

Regional Level Types
Monte Duria peridotite (south)	Group of Outcrops
Peglio	Commune
Como Province	Province
Lombardy	Region
Italy	Country

Outcrops of peridotite lenses along the south slope of Monte Duria.

The Monte Duria peridotite consists of tens of 1–100 m size peridotite lenses embedded in biotite-plagioclase gneisses that are tightly folded. Both poikiloblastic and porphyroblastic garnet peridotites occur in close distance to each other. Along the south slope of Monte Duria the peridotite lenses crop out in a NW-SW direction, then they turn eastwards in the Val Piana extension - see Monte Duria peridotite (east).

Peridotites are often garnet bearing, although pyrope garnet (millimetre- to centimetre-sized) is invariably surrounded by kelyphites and often fully replaced by pseudomorphic assemblages. Orthopyroxene (enstatite) and emerald-green clinopyroxene (diopside) occur often as millimetre- to centimetre-sized porphyroclasts in an oriented dark fine-grained olivine (forsterite) matrix. Garnet-bearing clinopyroxenite veins locally cut these peridotite bodies. The peridotite lenses commonly display a strongly foliated rim, with a chlorite foliation parallel to the main foliation of hosting gneisses and a core where compositional layering with garnet-rich and garnet-poor horizons occurs.

Tiny crystals (∼1 μm) of srilankite in double coronas formed at the contact between olivine and garnet have been observed. Srilankite occurs both in the orthopyroxene coronae replacing former olivine and in orthopyroxene + clinopyroxene + spinel kelyphites replacing garnet. In this latter intergrowth, also a few crystals of zircon and baddeleyite have been found. In some samples, symplectites developed along garnet fractures contain sapphirine in textural equilibrium with spinel, orthopyroxene and amphibole (Tumiati et al., 2018).

Coordinates are indicative.

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References