Petrographic and mineral-glass chemical dataset of igneous rock clasts from Early Oligocene Aveto-Petrignacola Formation (Northern Italy)

摘要

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.