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
- 1 February 2018
- journal article
- research article
- Published by Schweizerbart in European Journal of Mineralogy
- Vol. 30 (1), 45-59
- https://doi.org/10.1127/ejm/2017/0029-2682
Abstract
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 δ18O values, supported by δ13OC and δ34OS 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 2mm 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.Keywords
This publication has 7 references indexed in Scilit:
- Sulfur isotope signatures in the lower crust: A SIMS study on S-rich scapolite of granulitesChemical Geology, 2017
- Carbon elemental and isotopic composition in mantle xenoliths from Spain: Insights on sources and petrogenetic processesLithos, 2017
- Space–time evolution of monogenetic volcanism in the mafic Garrotxa Volcanic Field (NE Iberian Peninsula)Bulletin of Volcanology, 2013
- Complex interaction between Strombolian and phreatomagmatic eruptions in the Quaternary monogenetic volcanism of the Catalan Volcanic Zone (NE of Spain)Journal of Volcanology and Geothermal Research, 2011
- Eruptive mechanisms of the Puig De La Garrinada volcano (Olot, Garrotxa volcanic field, Northeastern Spain): A methodological study based on proximal pyroclastic depositsJournal of Volcanology and Geothermal Research, 2009
- THE CRYSTAL CHEMISTRY OF THE SCAPOLITE-GROUP MINERALS. I. CRYSTAL STRUCTURE AND LONG-RANGE ORDERThe Canadian Mineralogist, 2008
- Evidence of diverse depletion and metasomatic events in harzburgite–lherzolite mantle xenoliths from the Iberian plate (Olot, NE Spain): Implications for lithosphere accretionary processesLithos, 2007