Page 137 - Caldera Volcanism Analysis, Modelling and Response

112 A. Pittari et al.

Table 2 Description and classification of mafic/intermediate and felsic crystalline to glassy
volcanic clasts.
Classi¢cation: clast type Description
MV1: Aphyric basalt (may Aphyric, grey micro-to finely crystalline groundmass;
include intermediate rocks) intergranular to trachytic groundmass
(Pl+Cpx+FeOx7rare Ne); rare phenocrysts,
Ol+Cpx+FeOx
MV2: Porphyritic basalt and Porphyritic (mostly Cpx, up to 8 mm and/or Ol, up to
ankaramite 5 mm); grey micro- to medium crystalline groundmass;
TiAugWOlWWFeOx7rare Pl phenocrysts;
intergranular to trachytic groundmass
(Pl+Cpx+FeOx)
MV3: Porphyritic dark grey Porphyritic (mostly Pl, up to 1 mm and/or Cpx); dark grey,
intermediate rock crypto- to medium crystalline groundmass;
Pl+Cpx+Mag7Am7Ne7Sdl/Hyn phenocrysts,
may also contain An and Tte; Pl may be resorbed or
glomerophyric; intergranular to trachytic
groundmass (Pl+Cpx/Am+FeOx); Fsp laths
commonly curved, branching; some flow banding
MV4: Finely porphyritic pale Finely porphyritic; light grey, micro- to finely crystalline
grey intermediate rock groundmass; Pl+Krs+Cpx+Mag+Tte7Bi7Foids
(Sdl/Hyn and/or Ne) phenocrysts; intergranular to
trachytic groundmass (Fsp+Am/Cpx+Mag7Ap);
some flow banding
MV5: Vesicular basalt and Mafic to intermediate compositions; vesicularity, 20 to
intermediate rocks W40% of the whole rock
FV1: Highly Afs-phyric green Porphyritic (B30%, up to 8 mm, randomly oriented Afs
phonolite laths); green, very finely crystalline groundmass;
Afs WW (Agt+Mag+Ne7Bi7Sdl/Hyn)
phenocrysts; intergranular groundmass with acicular,
fibrous and spherulitic textures
FV2: Mottled green phonolite Mottled appearance defined by fine-grained, anastomosing
white felsic and green mafic domains; minor Afs7rare
Cpx phenocrysts; felsic domains are Afs-rich, and
form a trachytic texture which wraps around
phenocrysts and less common equigranular mosaic-
textured subdomains; mafic domains have abundant
sodic Am and minor Aeg/agt intergrown with Afs,
dendritic textures
FV3: Foliated green phonolite Foliated (‘‘slaty cleavage’’); felsic-mafic domains as in FV2,
but stronger mineral alignment; very fine to coarsely
crystalline groundmass; Afs+Ne+Sdl/Hyn+Mag
phenocrysts; trachytic groundmass; curved and
branching Fsp microlites and spherulites;
equigranular Fsp mosaic domains.