Silica-metal spherules in ignimbrites of southern Primorye, Russia

Abstract

A comprehensive mineralogical-geochemical and petrological study of ignimbrites from the Yakut-Gora volcanic depression (Primorye, Far Eastern Russia) revealed a wide distribution of silica-metal spherules ("globules") that are typical liquid immiscibility resultant. The metallic portion of a spherule (composition varies from low-carbon iron to cohenite) borders gas pores and is rimmed by symplectite that consists of quartz, magnetite, and silica-potassic glass. This allows us to consider that the whole formation formed through reduction of the enclosing silicate melt. Abundant evidence of high reduction states of ignimbrite melts and the presence of iron carbides suggest an H 2 -CH 4 composition of the fluidal phase in ignimbrite magmas.

Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (new mexico, usa)

“…For example, volcanic magnetic microspherules (real microspherules, not rounded crystals) are always titaniferous, (usually >10% of Ti) and, as important, are never hollow (Cornen et al . ; Grebennikov ; Voldman et al . and references therein).…”

“…Szöőr et al 2001;Grachev et al 2008;Voldman et al 2012 and references therein), the element is useful to distinguish between terrestrial and extraterrestrial magnetic particles. For example, volcanic magnetic microspherules (real microspherules, not rounded crystals) are always titaniferous, (usually >10% of Ti) and, as important, are never hollow (Cornen et al 1992;Grebennikov 2011;Voldman et al 2012 and references therein). However, while low concentration of Ti is possible in detrital magnetite crystals of metamorphic and igneous origins (not so low though as in cosmic microspherules), they never occur as real spherules, are never hollow, and never display dendritic surfaces.…”

Silicate, Iron Oxide and Copper-Gold-Silver Microspherules in Ores and Pyroclastics of the Kostenginskoye Iron Ore Deposit (Russian Far East)

“…Силикатные микросферулы зафиксированы в лавовых фонтанах вулкана Килауэа, Гавайи [69], в мелилитовых шлаках вулкана Кабесо Сегура в Испании [29], а также в пепловом столбе вулкана Этна [65]. Большое количество металло-силикатных сферул различного состава, напоминающих Костеньгинские, обнаружены в игнимбритах Сихотэ-Алиня [43].…”

Discovery of a meteoritic ejecta layer containing unmelted impactor fragments at the base of Paleocene lavas, Isle of Skye, Scotland

“…Native iron is not unique to meteorite impact and occurs rarely on Earth. The shape, texture, and chemistry of Skye spherules strongly suggest that crystallization was rapid, in conditions of very low oxygen fugacity (Grebennikov, 2011).…”