Zn-Al-rich chlorite in interleaved phyllosilicate grains from the low-temperature metamorphic Ordovician terrane of Iglesiente, south-west Sardinia, Italy

Zn-Al chlorite with a ZnO content of 2–3 wt% has been found in the Monte Argentu Formation that belongs to the external zone of the Variscan Sardinian Belt in SW Sardinia. This chlorite occurs in metasiltite rocks characterized by the alternation of dark-coloured layers rich in Fe- and Tioxides and light-coloured layers rich in quartz and phyllosilicates. The Zn-Al chlorite is associated with Kwhite mica, pyrophyllite, and quartz. The most common interleavings consist of K-white mica+Zn-Al chlorite, K-white mica+pyrophyllite, K-white mica+Zn-Al chlorite+pyrophyllite, and Zn-Al chlorite+pyrophyllite. The X-ray patterns of the <2 μm fraction of the investigated samples are characterized by peaks for illite, pyrophyllite, chlorite and quartz. Metamorphic temperatures of 300°–400°C have been estimated on the basis of the pyrophyllite occurrence. Pressure estimated on the basis of K-white mica composition is in the 0.3–0.6 GPa range.