Recovery of Hydrothermal Wustite-Magnetite Spherules from the Central Indian Ridge, Indian Ocean.

Not many studies have reported the hydrothermal-related origin of the magnetite-bearing spherules, and hardly any literature discusses the hydrothermal-related origin of wustite-magnetite-bearing spherules. A sediment sample with high abundance (19 spherules in ~85 g) of spherules is recovered from Central Indian Ridge (CIR) segment S2 (70°54′E, 25°14′S to 70°50′E, 24°41′S), ~85 km north of Rodrigues triple junction (RTJ). On the external surface of the spherules, magnetite appears as crystals, whereas wustite mostly appears as a homogenous glass phase. These spherules are composed of wustite and magnetite hosting Mn, unlike micrometeorites which essentially hosts Ni. Mn is more heterogeneously distributed with a relatively higher concentration in the wustite phase than the magnetite, suggesting hydrothermal origin. Furthermore, the presence of sulfide nano-particles in the wustite phase and a minor quantity of Pb and S in the ferrihydrite matrix points to the fact that CIR spherules are of hydrothermal origin. We propose that the CIR spherules originated by the interaction of the reduced hydrothermal fluids with the ultramafic/basaltic rocks or silica-undersaturated magmatic melts. The finding of Mn hosting wustite-magnetite assemblage suggests an active hydrothermal system in the near vicinity and can be considered as an additional proxy for locating hydrothermal vents.

Megafauna of the German exploration licence area for seafloor massive sulphides along the Central and South East Indian Ridge (Indian Ocean)

The growing interest in mineral resources of the deep sea, such as seafloor massive sulphide deposits, has led to an increasing number of exploration licences issued by the International Seabed Authority. In the Indian Ocean, four licence areas exist, resulting in an increasing number of new hydrothermal vent fields and the discovery of new species. Most studies focus on active venting areas including their ecology, but the non-vent megafauna of the Central Indian Ridge and South East Indian Ridge remains poorly known. In the framework of the Indian Ocean Exploration project in the German license area for seafloor massive sulphides, baseline imagery and sampling surveys were conducted yearly during research expeditions from 2013 to 2018, using video sledges and Remotely Operated Vehicles. This is the first report of an imagery collection of megafauna from the southern Central Indian- and South East Indian Ridge, reporting the taxonomic richness and their distribution. A total of 218 taxa were recorded and identified, based on imagery, with additional morphological and molecular confirmed identifications of 20 taxa from 89 sampled specimens. The compiled fauna catalogue is a synthesis of megafauna occurrences aiming at a consistent morphological identification of taxa and showing their regional distribution. The imagery data were collected during multiple research cruises in different exploration clusters of the German licence area, located 500 km north of the Rodriguez Triple Junction along the Central Indian Ridge and 500 km southeast of it along the Southeast Indian Ridge.

Refertilization of Mantle Peridotites from the Central Indian Ridge: Response to a Geodynamic Transition

The phenomena of reactive percolation of enriched asthenospheric melts and pervasive melt-rock interactions at mid oceanic ridge-rift systems are the principal proponents for mantle refertilization and compositional heterogeneity. This study presents new mineralogical and geochemical data for the abyssal peridotites exposed along the Vema and Vityaz fracture zones of the Central Indian Ridge (CIR) to address factors contributing to the chemical heterogeneity of CIR mantle. Cr-spinel (Cr#: 0.37-0.59) chemistry classifies these rocks as alpine-type peridotites and corroborates a transitional depleted MORB type to enriched, SSZ-related arc-type magma composition. HFSE and REE geochemistry further attests to an enriched intraoceanic forearc mantle affinity. The distinct boninitic signature of these rocks reflected by LREE>MREE<HREE and PGE compositions substantiates refertilization of the CIR mantle harzburgites by boninitic melt percolation concomitant to initiation of oceanic subduction. The mineral chemistry, trace, and PGE signatures of the CIR peridotites envisage (i) replenishment of depleted sub-ridge upper mantle by impregnation of subduction-derived boninitic melts, (ii) tectonic transition from mid oceanic ridge-rift to an embryonic suprasubduction zone, and (iii) initiation of spontaneous intraoceanic subduction along submarine transform faults and fracture zones of slow-spreading CIR owing to the weakness and mechanical instability of older, denser, and negatively buoyant Indian Ocean lithosphere.

A New Branchipolynoe (Aphroditiformia: Polynoidae) Scale worm from Deep-Sea Hydrothermal Vents in The Onnuri Vent Field on The Northern Central Indian Ridge

Background: Deep-sea hydrothermal vents are dynamic environments with exotic faunas. In this study, we found a new species of Branchipolynoe (Aphroditiformia: Polynoidae) polynoid scale worm living in the recently discovered mussel Gigantidas vrijenhoeki in deep-sea hydrothermal vents and methane seeps at depths of 2,014 - 2,023 m. Associations between scale worms and giant mussels are common in hydrothermal ecosystems.Results: We analyzed the morphology of Branchipolynoe from the Onnuri vent field (OVF) on the northern Central Indian Ridge and sequenced the full mitochondrial genome. Based on its morphological traits and mitochondrial genes, we designated the specimens as Branchipolynoe onnuriensis n. sp., described herein. This species resembles B. longqiensis and B. tjiasmantoi, but is distinguished by its notopodial acicular lobe form and the tips of the subacicular neurochaetae. The identity of the new species was well supported by genetic distance and phylogenetic analyses of the mitochondrial c oxidase subunit I (COI) gene. Genetically, the new species is closest to the Western Pacific species B. tjiasmantoi; phylogenetic analyses support the correlation between Indian Ocean and Western Pacific hydrothermal polychaetes. This study provides a foundation for exploring the evolutionary relationship between scale worms and giant mussels.