Regional mantle heterogeneity regulates melt production along the Réunion hotspot-influenced Central Indian Ridge

Machida, Shiki; Orihashi, Yuji; Magnani, M.; Neo, Natsuki; Wilson, Samantha Clare; Tanimizu, Masaharu; Yoneda, Shigekazu; Yasuda, Atsushi; Tamaki, Kensaku

doi:10.2343/geochemj.2.0320

Cited by 13 publications

(12 citation statements)

References 64 publications

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“…In addition, our new samples from segments 5 and 6 present uniform Ce/Pb (∼17–21) and Nb/U (∼35–41) (Figure 3). The variations in these trace element ratios are of the same order of magnitude as previously reported for samples from segments 5 and 6 (and those encountered along the Rodrigues segment, south of MCFZ (Füri et al., 2011; Kim et al., 2017; Machida et al., 2014; Murton et al., 2005; Nauret et al., 2006). Overall, segment 6 shows higher variability in Ce/Pb with ratios from ∼15 to 28 compared to segment 5 (Ce/Pb = 17 to 23).…”

Section: Resultssupporting

confidence: 81%

Heterogeneous Fossil Réunion Plume Component in the Source Region of Enriched MORB Along the Central Indian Ridge Between 12° and 17°S

et al. 2022

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Mid‐ocean ridge basalts (MORB) from the Central Indian Ridge (CIR) between 12° and 17°S show a wide range of geochemical and isotopic variations. Particularly, MORB from a segment between 14° and 15°S are more enriched in incompatible trace elements with more radiogenic Sr and Pb isotope and unradiogenic Nd isotope values than the lavas between 15° and 16°S with geochemical features of normal MORB. However, the causes for the enrichment between 14° and 15°S are poorly constrained. In this study, we re‐examined the CIR MORB from 12° to 17°S with new geochemical data obtained based on high spatial resolution sampling to better understand the nature of the enriched mantle source. Our new geochemical data show that the MORB between 14° and 15°S, with maximum values for (La/Sm)N = 1.95, 87Sr/86Sr = 0.703526 and 206Pb/204Pb = 18.7558, are more enriched than those from the southern segments (16° to 20°S) known to be influenced by the Réunion mantle component. The new trace element and isotopic compositions of MORB suggest that three mantle end‐members are required to explain the geochemical variations shown between 14° and 16°S: the depleted Indian‐type MORB mantle, Réunion Plume (RP), and Seychelles/Madagascar‐like continental crust components. Moreover, our mixing model suggests that the differences in enriched MORB signature from 14° to 20°S are due to variable proportions of continental material previously mixed with the RP. Our study implies that a continental component interacted with the plume into the asthenosphere, possibly beneath Madagascar or below Mauritius Island and the Mascarene plateau.

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Section: Resultssupporting

confidence: 81%

Heterogeneous Fossil Réunion Plume Component in the Source Region of Enriched MORB Along the Central Indian Ridge Between 12° and 17°S

et al. 2022

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“…The axial valley seafloor of segments 15 and 16 has little terrigenous sediment. It has been revealed that potassium and helium-3 are enriched in the basalts collected from the spreading axes and off axes of these segments, although the cause of such petrological characteristics is under debate (Murton et al 2005;Nauret et al 2006;F€ uri et al 2011;Machida et al 2014).…”

Section: Observation Geological Backgroundmentioning

confidence: 99%

Fluid chemistry in the Solitaire and Dodo hydrothermal fields of the Central Indian Ridge

et al. 2016

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Fluid chemistry and microbial community patterns in chimney habitats were investigated in two hydrothermal fields located at the Central Indian Ridge. Endmember hydrothermal fluid of the Solitaire field, located ~3 km away from the spreading center, was characterized by moderately high temperature (307°C), Cl depletion (489 mm), mildly acidic pH (≥4.40), and low metal concentrations (Fe ≤ 105 μm and Mn = 78 μm). Chloride depletion indicates that the subseafloor source fluid had undergone phase separation at temperatures higher than ~390°C while the metal depletion was likely attributable to fluid alteration occurring at a venting temperature of around 307°C. These different temperature conditions suggested from fluid chemistry might be associated with an off‐spreading center location of the field that allows subseafloor fluid cooling prior to seafloor discharge. The microbial community in the chimney habitat seemed comparable to previously known patterns in typical basalt‐hosted hydrothermal systems. Endmember hydrothermal fluid of the Dodo field, standing on center of the spreading axis, was characterized by high H2 concentration of 2.7 mm. The H2 enrichment was likely attributable to fresh basalt–fluid interaction, as suggested by the nondeformed sheet lava flow expansion around the vents. Thermodynamic calculation of the reducing pyrite–pyrrhotite–magnetite (PPM) redox buffer indeed reproduced the H2 enrichment. The quantitative cultivation test revealed that the microbial community associated with the hydrothermal fluid hosted abundant populations of (hyper)thermophilic hydrogenotrophic chemolithoautotrophs such as methanogens. The function of subseafloor hydrogenotrophic methanogenic populations dwelling around the H2‐enriched hydrothermal fluid flows was also inferred from the 13C‐ and D‐depleted signature of CH4 in the collected fluids. It was observed that the hydrothermal activity of the Dodo field had ceased until 2013.

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“…() have interpreted this discordance as the result of interactions between the Réunion hotspot and the nearby Central Indian Ridge. Rodrigues is located in a tectonically undisturbed area some 900 km north‐east of the Rodrigues Triple Junction (Machida et al ., ), and the older estimate is actually the age of the tectonic evolution of the Rodrigues Triple Junction (Mendel et al ., ). Other SWIO volcanic islands include the Comoros, and Aldabra, an 8 m high coral atoll of Pleistocene age.…”

Section: Geologymentioning

confidence: 99%

Human translocation as an alternative hypothesis to explain the presence of giant tortoises on remote islands in the south‐western Indian Ocean

Wilmé

Waeber²,

Ganzhorn³

2016

Journal of Biogeography

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Giant tortoises are known from several remote islands in the Indian Ocean (IO). Our present understanding of ocean circulation patterns, the age of the islands, and the life history traits of giant tortoises makes it difficult to comprehend how these animals arrived on such small, remote and geologically young (8–1.5 Ma) landmasses. For colonization to have occurred by dispersal, giant tortoises must either have originated in Madagascar or Africa and swum for hundreds of km against the ocean currents, or have launched themselves from the eastern IO margin and drifted with the currents over several thousands of km of open ocean. After these navigational feats, the tortoises would have needed to found new, viable populations on potentially inhospitable volcanic or coral outcrops. Geologically recent sea level changes are likely to have eliminated terrestrial life from islands like Aldabra, complicating the scenario. We reviewed information relating to IO geology, the evolution and ecology of giant tortoises, and the spread of humans within the region, and propose an alternative explanation: we posit that giant tortoises were introduced to the IO islands by early Austronesian sailors, possibly to establish provisioning stations for their journeys, just as European sailors did in more recent historical times.

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Regional mantle heterogeneity regulates melt production along the Réunion hotspot-influenced Central Indian Ridge

Cited by 13 publications

References 64 publications

Heterogeneous Fossil Réunion Plume Component in the Source Region of Enriched MORB Along the Central Indian Ridge Between 12° and 17°S

Heterogeneous Fossil Réunion Plume Component in the Source Region of Enriched MORB Along the Central Indian Ridge Between 12° and 17°S

Fluid chemistry in the Solitaire and Dodo hydrothermal fields of the Central Indian Ridge

Human translocation as an alternative hypothesis to explain the presence of giant tortoises on remote islands in the south‐western Indian Ocean

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