Volcanic activity and its link to glaciation cycles: Single-grain age and geochemistry of Early to Middle Miocene volcanic glass from ANDRILL AND-2A core, Antarctica

摘要: Abstract In the frame of ANtarctic DRILLing Program, volcanic glass fragments were collected from AND-2A core between ~ 354 and 765 m below sea floor (mbsf) as accumulations (5–70 vol.%) within sediments. Here, we present physical characteristics, age geochemistry glass, which enable us to reconstruct Early Middle Miocene activity in southern McMurdo Sound and, for first time, document response volcanism climate change Antarctica. Glass-rich sediments include muddy-to-fine sandstone stratified diamictite. Glass varies color, size, vesicularity, crystal content, angularity, degree alteration. The mostly fresh exhibits delicate cuspate forms indicating deposition primary ash fall. 40Ar–39Ar determinations on individual grains are good agreement with depositional model (ca. 15.6 18.6 Ma), supporting most them a origin, however, some samples do contain older that indicate recycling during times enhanced glacial erosion. Most glasses mafic (MgO = 3 9 wt.%) vary hypersthene nepheline normative restricted range SiO2 (45.2 ± 0.8 wt.%, 1σ) trace element concentrations typical rift-related alkaline rocks Erebus Volcanic Province. extends known composition early phase Mount Morning 11–19 Ma), only source, more end, revealing previously unknown explosive, strongly alkaline, basaltic primitive both (basanite phonolite) moderately (alkali basalt trachyte) magma associations. glass-rich occur glacimarine sequences record 56 cycles advance retreat. cyclicity is observed physically geochemically glass. Higher volumes correlate ice minimum conditions 300 800 mbsf. Ratios Ba Hf, Nb, La Zr (≥ 5 wt.% MgO) show systematic increase mean values intervals retreat decreasing expansion, suggesting tapping magmas variable incompatible compatible ratios. This may be related changes stress state crust rapid volume fluctuations over volcano, influence chemistry by varying duration depth storage.