scholarly journals Quasi-3-D Seismic Reflection Imaging and Wide-Angle Velocity Structure of Nearly Amagmatic Oceanic Lithosphere at the Ultraslow-Spreading Southwest Indian Ridge

2017 ◽  
Vol 122 (12) ◽  
pp. 9511-9533 ◽  
Author(s):  
Ekeabino Momoh ◽  
Mathilde Cannat ◽  
Louise Watremez ◽  
Sylvie Leroy ◽  
Satish C. Singh
Keyword(s):  
Seismic Reflection ◽  
Velocity Structure ◽  
Oceanic Lithosphere ◽  
Southwest Indian Ridge ◽  
Wide Angle ◽  
Reflection Imaging ◽  
Indian Ridge

Rifting and magmatism in the northeastern South China Sea from wide‐angle tomography and seismic reflection imaging

2014 ◽  
Vol 119 (3) ◽  
pp. 2305-2323 ◽  
Author(s):  
Ryan Lester ◽  
Harm J. A. Van Avendonk ◽  
Kirk McIntosh ◽  
Luc Lavier ◽  
C.‐S. Liu ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Seismic Reflection ◽  
Wide Angle ◽  
China Sea ◽  
Reflection Imaging ◽  
Northeastern South China Sea

scholarly journals Structure of the ultraslow-spreading Southwest Indian Ridge at 64°30’E from coincident multichannel and wide-angle seismic data

2020 ◽  
Author(s):  
Ana Corbalan ◽  
Mladen Nedimović ◽  
Ingo Grevemeyer ◽  
Keith Louden ◽  
Lousie Watremez
Keyword(s):  
Complex Structure ◽  
Vertical Gradient ◽  
Velocity Model ◽  
Southwest Indian Ridge ◽  
Gradual Transition ◽  
Ocean Bottom Seismometer ◽  
Wide Angle ◽  
Subsurface Structure ◽  
Indian Ridge ◽  
Spreading Rates

<p>Ultraslow-spreading oceanic ridges (<20 mm/yr) constitute about 35% of the global ridge system and yet the lithospheric structure that accretes at these spreading rates is little understood. At these ridges, the interplay between plate- and mantle-driven processes produces complex relationships between intermittent volcanic seafloor and extensive non-volcanic seafloor domains, with a subsurface structure that differs significantly from the traditional 3-layer crust topping the uppermost mantle that forms at faster-spreading rates. We present new constraints on the velocity and reflectivity structure of the oceanic lithosphere at the ultraslow-spreading Southwest Indian Ridge (SWIR) at 64°30’E. The eastern SWIR has a full-spreading rate of <14 mm/yr and represents a magma-poor endmember. In this area, broad serpentinized mantle domains are exposed with little interference of igneous rocks that can make their identification and geophysical characterization challenging. We use coincident wide-angle ocean bottom seismometer (OBS) and multichannel seismic (MCS) data collected during the SISMOSMOOTH 2014 survey along two long (~150 km) orthogonal profiles, one along the ridge valley (EW direction) and one across it (NS direction). We first run traveltime tomography using picks of first arrivals recorded by 16 OBS placed on the NS profile and 16 OBS on the EW profile. The computed models show that seismic velocities increase rapidly with depth, changing from 3.5-4 km/s at the seafloor to 7 km/s at 2-5 km and that the vertical gradient reduces for velocities greater than 7 km/s. We suggest that the changes in velocity with depth are related to changes in the degree of serpentinization and interpret the subsurface structure to be composed of highly fractured and fully serpentinized peridotites at the top with a gradual decrease in pore space and serpentinization to unaltered peridotites at depth. The NS velocity model shows greater lateral velocity variations than the EW profile, which indicates a more complex structure for the former. Next we perform MCS data analysis to produce reflection sections for the two profiles. Time-migrated sections are converted to depth using the velocities derived from the tomographic models. We observe steep south-dipping reflections around the highest topographic feature on the NS profile, coincident with a sharp lateral change in the velocities and a high vertical gradient in the velocity model, which we interpret as the seismic expression of an active axial detachment fault. Clear Moho arrivals are not identified either in the OBS or the MCS record sections, consistent with our interpretation of the subsurface being composed of a gradual transition from serpentinized peridotites to fresh mantle peridotites.</p>

scholarly journals A new peltospirid snail (Gastropoda: Neomphalida) adds to the unique biodiversity of Longqi vent field, Southwest Indian Ridge

2021 ◽  
Vol 55 (13-14) ◽  
pp. 851-866
Author(s):  
Chong Chen ◽  
Yuru Han ◽  
Jonathan T. Copley ◽  
Yadong Zhou
Keyword(s):  
Southwest Indian Ridge ◽  
Indian Ridge

scholarly journals Microbial ecology of the newly discovered serpentinite-hosted Old City hydrothermal field (southwest Indian ridge)

2020 ◽  
Author(s):  
Aurélien Lecoeuvre ◽  
Bénédicte Ménez ◽  
Mathilde Cannat ◽  
Valérie Chavagnac ◽  
Emmanuelle Gérard
Keyword(s):  
Microbial Ecology ◽  
New Caledonia ◽  
Southwest Indian Ridge ◽  
Hydrothermal Field ◽  
Metagenomic Sequencing ◽  
Lost City ◽  
Old City ◽  
Mid Atlantic Ridge ◽  
Indian Ridge ◽  
Geochemical Analyses

Abstract Lost City (mid-Atlantic ridge) is a unique oceanic hydrothermal field where carbonate-brucite chimneys are colonized by a single phylotype of archaeal Methanosarcinales, as well as sulfur- and methane-metabolizing bacteria. So far, only one submarine analog of Lost City has been characterized, the Prony Bay hydrothermal field (New Caledonia), which nonetheless shows more microbiological similarities with ecosystems associated with continental ophiolites. This study presents the microbial ecology of the ‘Lost City’-type Old City hydrothermal field, recently discovered along the southwest Indian ridge. Five carbonate-brucite chimneys were sampled and subjected to mineralogical and geochemical analyses, microimaging, as well as 16S rRNA-encoding gene and metagenomic sequencing. Dominant taxa and metabolisms vary between chimneys, in conjunction with the predicted redox state, while potential formate- and CO-metabolizing microorganisms as well as sulfur-metabolizing bacteria are always abundant. We hypothesize that the variable environmental conditions resulting from the slow and diffuse hydrothermal fluid discharge that currently characterizes Old City could lead to different microbial populations between chimneys that utilize CO and formate differently as carbon or electron sources. Old City discovery and this first description of its microbial ecology opens up attractive perspectives for understanding environmental factors shaping communities and metabolisms in oceanic serpentinite-hosted ecosystems.

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