P11- Basalto

Porphyritic rock with millimetric crystals, milky white or dark green in colour, set in a grey, fine-grained matrix. The rock sample comes from the thick sequence of basaltic lava flows developed during the Middle Triassic in the Dolomites (Southern Alps, North Italy); the lava flows are associated to hyaloclastite deposits (e.g., P9 volcanoclastite) and are coeval to mafic-intermediate magmatic intrusions (e.g., Mt Monzoni intrusion; see the P3 monzonite). See Storck et al., 2018 (https://doi.org/10.1144/jgs2018-123) for geological details.

Thin section description 

The images show phenocrysts of clinopyroxene (Cpx) and plagioclase (Pl) set in a groundmass (gm) that is rich in microlites of Pl (widespread) and Cpx, and that also contains opaque minerals (Opq), that exhibit a black colour. A green-coloured component occupies the interstices between microlites; it was in origin interstitial glass, now replaced by chlorite. The three phenocrysts of Cpx in the left of the field exhibit (in the XPL view) a wide range in the interference colours and appear zoned. The plagioclase (Pl) crystals exhibit a dusty aspect in the PPL view, due to sericite alteration; these crystals are easily recognizable in the XPL view because they often display multiple twinning.

thin section PPL	thin section XPL