Fluid‐driven Hydrovolcanic Activity along Fracture Zones and near Seamounts: Evidence from Deep‐sea Fe‐rich Spherules, Central Indian Ocean Basin

Abstract

An insight on occurrence of Fe-rich spherules from the Central Indian Ocean Basin (CIOB) provides an understanding of their distribution at a water depth of >5,000 m. In the present study, Fe-rich spherules are identified to occur in two different sediment types (i.e., siliceous and pelagic) and tectonic settings (i.e. near seamounts and fracture zones). These are single spheres or aggregates, of different sizes (63 to 390 µm) and show textural variability (smooth/ quenched, brickwork, corkscrew, interlocking and dendritic). A comparative study based on physical morphology and chemical composition suggests a common mechanism of formation. The association of spherules with fracture zones (FZ) and seamounts signifies that morpho-tectonic features play an important role in fluid-driven hydrovolcanism. Based on the evidence and geologic conditions existing in the basin, we conclude that molten fuel-coolant interaction (MFCI) coupled with submarine hydrothermal exhalations could be an ideal mechanism for the formation of spherules and Fe-particles. The accretion of the spherules on the surface sediments could be a result of recent volcanic phenomena, while those occurring at different depths (280-355, and 460-475 cm-bsf) within the sediment core indicate two different episodes. The study provides a global implication in understanding fluid-driven magmatism in a deep-sea intraplate environment.

Fluid-Assisted Aggregation and Assembly of Magnetite Microparticles in the Giant El Laco Iron Oxide Deposit, Central Andes

“…Notably, magnetite spherules have been documented in hydrothermal vents associated with sea-floor volcanism. These records include magnetite-hematite granules in the Earth’s oldest hydrothermal vent precipitates in the Nuvvuagittuq belt in Quebec, Canada, and magnetite spherules in sediments from the Central Indian Ocean Basin (CIOB). − It has been suggested that the magnetite spherules reported at CIOB formed as a result of hydrovolcanic processes involving Fe-rich hydrothermal emanations. These spherules vary from smooth-surfaced low-crystallinity structures to crystalline particles showing well-developed magnetite crystals and dendritic patterns. , The low-crystallinity spherules are interpreted as having formed by rapid quenching processes, whereas well-crystallized spherules would have experienced slower cooling, leading to the development of euhedral magnetite crystals .…”

“…These records include magnetite-hematite granules in the Earth’s oldest hydrothermal vent precipitates in the Nuvvuagittuq belt in Quebec, Canada, and magnetite spherules in sediments from the Central Indian Ocean Basin (CIOB). − It has been suggested that the magnetite spherules reported at CIOB formed as a result of hydrovolcanic processes involving Fe-rich hydrothermal emanations. These spherules vary from smooth-surfaced low-crystallinity structures to crystalline particles showing well-developed magnetite crystals and dendritic patterns. , The low-crystallinity spherules are interpreted as having formed by rapid quenching processes, whereas well-crystallized spherules would have experienced slower cooling, leading to the development of euhedral magnetite crystals . However, in addition to these temperature-mediated processes, it is likely that pressure drops related to the activity of these hydrovolcanic systems have also played a key role triggering magnetite precipitation, as demonstrated in magnetite solubility experiments under hydrothermal conditions …”

“…These spherules vary from smoothsurfaced low-crystallinity structures to crystalline particles showing well-developed magnetite crystals and dendritic patterns. 31,32 The low-crystallinity spherules are interpreted as having formed by rapid quenching processes, whereas wellcrystallized spherules would have experienced slower cooling, leading to the development of euhedral magnetite crystals. 32 However, in addition to these temperature-mediated processes, it is likely that pressure drops related to the activity of these hydrovolcanic systems have also played a key role triggering magnetite precipitation, as demonstrated in magnetite solubility experiments under hydrothermal conditions.…”

“…31,32 The low-crystallinity spherules are interpreted as having formed by rapid quenching processes, whereas wellcrystallized spherules would have experienced slower cooling, leading to the development of euhedral magnetite crystals. 32 However, in addition to these temperature-mediated processes, it is likely that pressure drops related to the activity of these hydrovolcanic systems have also played a key role triggering magnetite precipitation, as demonstrated in magnetite solubility experiments under hydrothermal conditions. 33 Magnetite microspheres and dendrites have been synthetized experimentally for technological applications in the fields of material science and biomedicine.…”