Hydrovolcanic activity in the central Indian ocean basin. Does nature mimic laboratory experiments?

Classical works in the 1960ʹs on spherules (volcanic, extraterrestrial, cosmic etc.) were carried out in order to distinguish these morphologically and compositionally so as to understand their genesis yet, in some cases their origin has remained enigmatic and indeterminate. We present here the finding of volcanic magnetite spherules up to 475 μm in diameter which were recovered from the base of a seamount (basement age ~ 50 Ma) in the Central Indian Ocean Basin (CIOB). The spherules have quenched and crystalline textures, analogous to cosmic ones but compositionally are Fe-enriched (avg. 74%) together with other magmaphile elements. A distinctive lack of a Ni core is noted vis-a-vis Si-enriched areas. The spherules are very similar to those experimentally produced by simulated hydrovolcanic activity involving interaction of a thermite melt with water-saturated quartzo-feldspathic sand. Our finding seems to indicate such a process to have occurred in nature at abyssal depth. The plausible mechanism we conceive is the reaction of Fe-rich lavas or hydrothermal emanations with the abundant surrounding siliceous ooze which is the dominant sediment type in the basin. We regard this is as the first report of an authentic proof for hydrovolcanism at oceanic depth of 5200 m, which probably occurred ~ 10 ka ago as suggested by the associated radiolarian species.