Mafic and ultramafic xenoliths in San Bartolo lava field: New insights on the ascent and storage of Stromboli magmas

Abstract

Mafic and ultramafic xenoliths are well represented within a large basaltic lava field of Stromboli. These basalts, known as San Bartolo lavas, show a high-K calc-alkaline (HKCA) affinity and were erupted <5 ka BP. Xenoliths consist of olivin-gabbro, gabbronorite, anorthosite, dunite, wehrlite and clinopyroxenite. Thermobarometric estimates for the crystallization of gabbroic materials show minima equilibration pressures of 0.17-0.24 GPa, at temperatures ranging from 940 to 1,030 • C. These materials interacted with hydrous ascending HKCA basaltic magmas (with temperatures of 1,050-1,100 • C) at pressures of about 0.2-0.4 GPa. These pressure regimes are nearly identical to those found for the crystallization of phenocrystic phases within HKCA basaltic lavas. Gabbroic inclusions are regarded as cumulates and represent crystallized portions of earlier HKCA Strombolian basalts.Dunite and wehrlite show porphyroclasticheterogranular textures, whereas the clinopyroxenite exhibit a mosaic-equigranular texture typical of mantle peridotites. These ultramafic materials are in equilibrium with more primitive basaltic magmas (under moderately hydrous and anhydrous conditions) at pressures of 0.8-1.2 GPa, which is below the crust-mantle transition, located at about 20 km depth under Stromboli.Major and trace element distributions indicate comagmatism between the host basaltic lava and the mafic and ultramafic inclusions. REE patterns for mafic nodules are relatively regular and overlap the field of basaltic lavas (HKCA). They show moderate to high LREE enrichments and moderate enrichments in HREE relative to chonrites. Spider diagrams also show significant similarities between the lavas and the mafic-ultramafic xenoliths as well.Editorial responsibility: R. Cioni M. Laiolo ( ) · C. Cigolini

Numerical simulations of convection in crystal‐bearing magmas: A case study of the magmatic system at Erebus, Antarctica

“…Motivated by the fact that they provide a window into the underlying magmatic system, many field studies have been devoted to lava lakes. The nature of convection can be best understood in long‐lived systems where low viscosity magmas (e.g., phonolitic, nephelinitic, basaltic andesitic, basaltic) are permanently exposed, such as Erebus volcano in Antarctica [ Oppenheimer and Kyle , 2008, and references therein], Nyiragongo in the Democratic Republic of Congo [ Demant et al , 1994], Villarrica in Chile [ Witter et al , 2004], Erta'Ale in Ethiopia [ Bizouard et al , 1980], Pu' u O' in Hawaii [ Garcia et al , 2000], and Stromboli in Italy [e.g., Giberti et al , 1992; Laiolo and Cigolini , 2006]. Several aspects of Erebus volcano motivated us to choose it as a subject for a numerical study of convective processes.…”

Mechanical erosion of xenoliths by magmatic shear flow

“…Xenoliths occur in many lava flows, pyroclastics, diatremes and intrusive bodies [ Gribble and O'Hara , 1967; Dawson , 1977; Laiolo and Cigolini , 2006; Chadwick et al , 2007]. They represent fragments eroded from the wall‐rock of magma chambers and/or conduits, or from the Earth surface during lava flow emplacement.…”

Cognate xenoliths in Mt. Etna lavas: witnesses of the high-velocity body beneath the volcano

“…Some cognate xenoliths have a mantle or high-pressure origin, while others form in a shallower context (Holness et al 2007 and references therein). Magmatic xenoliths have also been studied in products of active Italian volcanoes, namely Stromboli (Renzulli and Santi 1997;Mattioli et al 2003;Laiolo and Cigolini 2006;Corazzato et al 2008;Tibaldi et al 2009) and, to a lesser extent, Mt. Etna (Lo Giudice and Ritmann 1975;Aurisicchio and Scribano 1987;Andronico et al 2005;Corsaro et al 2007).…”