TY - JOUR
T1 - The incipient flash melting of scapolite and plagioclase megacrysts in alkali basalts of the Olot suite, Catalunya, Spain, and at Chuquet Genestoux, Puy-de-Dôme, France
AU - Torró, Lisard
AU - Martin, Robert F.
AU - Schumann, Dirk
AU - Cox, Julia
AU - Medina, Salvador Galí
AU - Draper, Joan Carles Melgarejo
N1 - Publisher Copyright:
© 2018 E.Schweizerbart'sche Verlagsbuchhandlung.
PY - 2018
Y1 - 2018
N2 - Megacryst-bearing alkaline basic rocks of Cenozoic age occur in scattered centers in western Europe, from the Rhine graben to southern Spain. We focus on two volcanic fields, La Garrotxa in northeastern Spain, and in particular the Pomareda and Roca Negra monogenetic cones in the Olot suite, and the Chuquet Genestoux occurrence, Puy-de-Dôme, France. The explosive emplacement of the basanitic magma favored the entrainment of xenoliths of clearly crustal and mantle origin in both suites. We seek to characterize the megacrysts of scapolite and andesine. The sulfate-bearing scapolite crystallized in space group I4/m rather than the expected P42/n, likely because of disorder in the sulfate groups. The megacrysts in both suites are part of an igneous mantle-derived assemblage, to judge from d18O values, supported by d13C and d34S values of the sulfate-bearing scapolite. We document signs of flash melting in both scapolite and plagioclase megacrysts from Pomareda. A white rim of up to 2 mm on the scapolite megacrysts consists of skeletal individuals of calcic plagioclase; these crystals contain wollastonite, silvialite, diopside, and myriads of vacuoles. The andesine megacryst also underwent melting at its margin, to a sieve-textured assemblage of neoformed labradorite, glass, and free silica. The flash melting of individual megacrysts encapsulated in basanitic melt, documented here for the first time, has produced metastable products. Progress of the melting reactions was arrested by a thermal quench upon eruption.
AB - Megacryst-bearing alkaline basic rocks of Cenozoic age occur in scattered centers in western Europe, from the Rhine graben to southern Spain. We focus on two volcanic fields, La Garrotxa in northeastern Spain, and in particular the Pomareda and Roca Negra monogenetic cones in the Olot suite, and the Chuquet Genestoux occurrence, Puy-de-Dôme, France. The explosive emplacement of the basanitic magma favored the entrainment of xenoliths of clearly crustal and mantle origin in both suites. We seek to characterize the megacrysts of scapolite and andesine. The sulfate-bearing scapolite crystallized in space group I4/m rather than the expected P42/n, likely because of disorder in the sulfate groups. The megacrysts in both suites are part of an igneous mantle-derived assemblage, to judge from d18O values, supported by d13C and d34S values of the sulfate-bearing scapolite. We document signs of flash melting in both scapolite and plagioclase megacrysts from Pomareda. A white rim of up to 2 mm on the scapolite megacrysts consists of skeletal individuals of calcic plagioclase; these crystals contain wollastonite, silvialite, diopside, and myriads of vacuoles. The andesine megacryst also underwent melting at its margin, to a sieve-textured assemblage of neoformed labradorite, glass, and free silica. The flash melting of individual megacrysts encapsulated in basanitic melt, documented here for the first time, has produced metastable products. Progress of the melting reactions was arrested by a thermal quench upon eruption.
KW - Andesine
KW - Basanite
KW - Chuquet Genestoux
KW - Explosive emplacement
KW - Flash melting
KW - France
KW - Megacryst
KW - Olot volcanic suite
KW - Scapolite
KW - Spain
UR - http://www.scopus.com/inward/record.url?scp=85047095531&partnerID=8YFLogxK
U2 - 10.1127/ejm/2017/0029-2682
DO - 10.1127/ejm/2017/0029-2682
M3 - Article
AN - SCOPUS:85047095531
SN - 0935-1221
VL - 30
SP - 45
EP - 59
JO - European Journal of Mineralogy
JF - European Journal of Mineralogy
IS - 1
ER -