RESUMO
This dataset article contains petrographic and mineral-glass chemical data of igneous rock clasts from Early Oligocene Aveto-Petrignacola Formation (APF; Northern Italy). Methods for obtaining the dataset include optical microscopy, scanning electron microscopy and electron probe microanalysis. The APF volcanic rocks are basalts, basaltic andesites, andesites, dacites and rhyolites. Rare gabbroic cumulate nodules complete the dataset. Basalts are porphyritic, with calcic plagioclase (An72-92Ab7-27Or0-1), ferroan enstatite (En59-68Fs29-37Wo3-4) and augite (En38-39Fs18-20Wo41-44) phenocrysts, in a hypocrystalline groundmass made up of bytownite (An71-85Ab14-28Or1), augite (En37-38Fs19Wo43-44), ferroan enstatite (En62-68Fs30-35Wo1-4) and rare pigeonite (En46-50Fs37-42Wo7-17). The basaltic andesites are porphyritic to glomeroporphyritic with phenocrysts of zoned plagioclase (An44-67Ab32-55Or1), orthopyroxene, Mg-rich augite (En38-42Fs15-17Wo43-45), rare pargasite to edenite amphibole (Mg# 69-59) and very rare biotite in a hypocrystalline to holohyaline groundmass. Andesites are highly porphyritic with phenocrysts of plagioclase (An47-79Ab20-52Or0-1), pargasite to magnesio-hornblende (Mg# 72-67), Mg-rich augite (En43-46Fs12-17Wo41-43), subordinate ferroan enstatite (En68-74Fs23-29Wo3-4), biotite (Mg# 53) and Ti-magnetite (Usp29-41). Dacites (massive lavas and ignimbrites) are porphyritic, with phenocrysts and phenoclasts of plagioclase (An33-79Ab20-62Or0-4), calcic amphibole (Ti-pargasite, Mg-hornblende and edenite; Mg# 81-46), biotite (Mg# 67-56), very rare Mg-rich augite (En41-42Fs16-18Wo40-43) and resorbed quartz in hypohyaline to holohyaline groundmass with a dense mat of anhedral quartz, labradorite-andesine (An36-66Ab33-61Or1-4) and rare anorthoclase (An22Ab66Or12). Rhyolitic compositions have been found both as volcanic clasts (massive lava and ignimbrites) with andesine to oligoclase phenoclasts (An25-38Ab61-71Or1-4), quartz, biotite (Mg# 55-53) and Ti-magnetite (Usp18-77), and as interstitial glasses (residual melt drops) in other APF volcanic rocks. The cumulate nodules are olivine-gabbro and amphibole-gabbro/gabbronorite with a mineral paragenesis dominated by plagioclase (An41-73Ab26-57Or1-3), olivine (Fo68-72), Mg-rich augite to ferroan diopside (En41-45Fs12-15Wo42-45; Mg# 79-74), ferroan enstatite (En65-74Fs24-33Wo2-3; Mg# 76-68), magnetite (Usp15-28) and titanian pargasite (Mg# 67-65). The main cumulus phases are plagioclase, olivine and pyroxene, while intercumulus/postcumulus phases are titanian pargasite and magnetite. The dataset can be used to compare petrographic features and chemical compositions of calc-alkaline rocks emplaced in other subduction-related settings. Above all, it can represent a useful contribution in solving the problem linked to the identification of a hidden Early-Oligocene source of the thick volcaniclastic APF succession in the Alpine-Apennine belt geodynamic evolution.
RESUMO
Emissivity and reflectance spectra have been investigated on two series of silicate glasses, having compositions belonging to alkaline and subalkaline series, covering the most common terrestrial igneous rocks. Glasses were synthesized starting from natural end-members outcropping at Vulcano Island (Aeolian Islands, Italy) and on Snake River Plain (USA). Results show that the shift of the spectra, by taking Christiansen feature (CF) as a reference point, is correlated with SiO2 content, the SCFM factor and/or the degree of polymerization state via the NBO/T and temperature. The more evolved is the composition, the more polymerized the structure, the shorter the wavelength at which CF is observable. CF shift is also dependent on temperature. The shape of the spectra discriminates alkaline character, and it is related to the evolution of Qn structural units. Vulcano alkaline series show larger amount of Q4 and Q3 species even for mafic samples compared to the subalkaline Snake River Plain series. Our results provide new and robust insights for the geochemical characterization of volcanic rocks by remote sensing, with the outlook to infer origin of magmas both on Earth as well as on terrestrial planets or rocky bodies, from emissivity and reflectance spectra.
RESUMO
The small upper Pleistocene diatreme of Polino (central Italy) is known in literature as one of the few monticellite alvikites (volcanic Ca-carbonatite) worldwide. This outcrop belongs to the Umbria-Latium Ultra-alkaline District (ULUD), an area characterized by scattered and small-volume strongly SiO2-undersaturated ultrabasic igneous rocks located in the axial sector of the Apennine Mts. in central Italy. Petrographic and mineralogical evidences indicate that Polino olivine and phlogopite are liquidus phases rather than mantle xenocrysts as instead reported in literature. The presence of monticellite as rim of olivine phenocrysts and as groundmass phase indicates its late appearance in magma chambers at shallow depths, as demonstrated by experimental studies too. The absence of plagioclase and clinopyroxene along with the extremely MgO-rich composition of olivine (Fo92-94) and phlogopite (average Mg# ~93) suggest for Polino magmas an origin from a carbonated H2O-bearing mantle source at depths at least of 90-100 km, in the magnesite stability field. In contrast with what reported in literature, the ultimate strongly ultrabasic Ca-rich whole-rock composition (~15-25 wt% SiO2, ~31-40 wt% CaO) and the abundant modal groundmass calcite are not pristine features of Polino magma. We propose that the observed mineral assemblage and whole-rock compositions result mostly from the assimilation of limestones by an ultrabasic melt at a depth of ~5 km. A reaction involving liquidus olivine + limestone producing monticellite + CO2 vapour + calcite is at the base of the origin of the Polino pseudocarbonatitic igneous rocks.
