Tectonic Background of Four Hydrothermal Fields Along the Central Indian Ridge

Abstract

Since the discovery of the Kairei hydrothermal field at the southernmost end of the Central Indian Ridge (CIR) in 2000, only four active hydrothermal vent fields have subsequently been discovered. These four hydrothermal fields show remarkable diversity in the chemical compositions of fluids and associated ecosystems. Focused geophysical mapping and rock sampling indicate that different tectonic setting constrains the different hydrothermal activity for each field. Two hydrothermal fields in the southern CIR are located on the axial rift-valley wall. The hydrogen-rich Kairei hydrothermal field at 25 19 0 S is constrained by both basaltic magmatism and detachment faulting that exhume ultramafic rocks on a shallow subsurface, whereas no evidence of ultramafic exposure is recognized in the typical mid-ocean ridge type Edmond hydrothermal field at 23 52 0 S. Two other hydrothermal fields have been newly discovered in the central CIR. The Solitaire field at 19 33 0 S is located about 2.6 km away from the neo-volcanic zone and is likely influenced by intra-plate volcanism. The Dodo field at 18 20 0 S is located at the center of the axial valley floor, where a basaltic sheet-lava flow buries the seafloor. The lava morphology and the existence of an adjacent large off-axis seamount support the idea that excess melt is supplied in this segment. The anomalous magmatism is likely influenced by mantle plume components or by a large-offset transform fault just north of the segment. The large diversity found in the four hydrothermal fields along the CIR provides important insights on the tectonic control of global hydrothermal systems.

Variation in magnetic properties of serpentinized peridotites exposed on the Yokoniwa Rise, Central Indian Ridge: Insights into the role of magnetite in serpentinization

“…and CIR-S2, the Yokoniwa Rise occurs with a height of 1700 m from the rift valley floor as shallow dome-like NTO massif Fujii et al, 2016]. Sea-surface magnetic anomalies were identified along the Brunhes/Matuyama boundary in the eastern off-axis area of CIR-S1 and S2 far from the Yokoniwa Rise [Honsho et al, 1996;Sato et al, 2009;Okino et al, 2015]. These results suggest that the Yokoniwa Rise formed during the Brunhes normal chron (<0.78 Ma).…”

“…Ridge‐parallel abyssal hill patterns are distributed along the trace of this NTO, where several domed highs composed of ultramafic rocks are present, such as the 25°S OCC, Uraniwa Hills, and Phoenix knoll [ Kumagai et al ., ; Morishita et al ., ; Nakamura et al ., ; Sato et al ., ; Okino et al ., ] Between two nodal basins of CIR‐S1 and CIR‐S2, the Yokoniwa Rise occurs with a height of 1700 m from the rift valley floor as shallow dome‐like NTO massif [ Okino et al ., ; Fujii et al ., ]. Sea‐surface magnetic anomalies were identified along the Brunhes/Matuyama boundary in the eastern off‐axis area of CIR‐S1 and S2 far from the Yokoniwa Rise [ Honsho et al ., ; Sato et al ., ; Okino et al ., ]. These results suggest that the Yokoniwa Rise formed during the Brunhes normal chron (<0.78 Ma).…”

“…Bathymetry data are from Okino et al . []. The circles and the square show sampling done with SHINKAI 6500 dives and a dredge haul, respectively.…”

“…The spreading axes have a right lateral offset of 26 km between the CIR-S1 and S2. Ridge-parallel abyssal hill patterns are distributed along the trace of this NTO, where several domed highs composed of ultramafic rocks are present, such as the 258S OCC, Uraniwa Hills, and Phoenix knoll [Kumagai et al, 2008;Morishita et al, 2009Morishita et al, , 2015Nakamura et al, 2009;Sato et al, 2009;Okino et al, 2015] Between two nodal basins of CIR-S1 Figure 1. Sample locations illustrated with a seafloor bathymetric map of the Central Indian Ridge (CIR) segments 1 and 2.…”

“…All samples were collected on a nontransform massif of the Yokoniwa Rise near a nontransform discontinuity. Bathymetry data are from Okino et al [2015]. The circles and the square show sampling done with SHINKAI 6500 dives and a dredge haul, respectively.…”