Seismic observation of an extremely magmatic accretion at the ultraslow spreading Southwest Indian Ridge

We present results from an ocean bottom seismometer experiment surveying the fossil spreading centre in the Southwest Sub‐basin of the South China Sea. The detailed velocity model shows that oceanic layer 2 exhibits across‐axis variations in thickness and velocity, whereas oceanic layer 3 displays a variation in crustal thickness. A low‐angle (24°) SE‐dipping oceanic detachment fault is proposed to explain the anomalous structure on the NW side of the spreading centre, which exhibits uplifting of the upper mantle beneath a thinned oceanic crust. The inferred oceanic detachment fault was at its initial stage, localized within the basaltic crust and did not exhume lower crust. We suggest that the low‐velocity (7.6–7.9 km/s) body located within the upper mantle beneath the footwall of the detachment fault is caused by both mantle serpentinization and partial melting. The difference in crustal thickness in the Southwest Sub‐basin indicates that the magma supply varied in time and space during or even after the seafloor spreading. Compared with other fossil spreading ridges, the fossil spreading centre of the northeast Southwest Sub‐basin studied here represents a third type of fossil spreading ridge, characterized by a reduced melt supply at the waning stage of spreading and a strong post‐spreading magmatism. Copyright © 2016 John Wiley & Sons, Ltd.

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“…Morgan and Ghen, 1993;Canales et al, 1998;Li et al, 2015). Morgan and Ghen, 1993;Canales et al, 1998;Li et al, 2015).…”

Section: Variations In the Magma Supply In The Swsbunclassified

The velocity structure of a fossil spreading centre in the Southwest Sub‐basin, South China Sea

Zhang

Ruan

et al. 2016

Geological Journal

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“…(a) Bathymetry map of the central Southwest Indian Ridge (SWIR), fracture zones (FZ), and off‐axis high‐topography edifices modified from Li et al . []. Black dots represent sample locations in this study.…”

Section: Introductionmentioning

confidence: 99%

“…There is a bathymetric high and a mantle Bouguer anomaly (MBA) low between the Indomed (IFZ) and Gallieni (GFZ) fracture zones (46°E and 52°20′E, Figure a) [ Georgen et al ., ]. At 50°28′E with the shallowest water depth and the only axial high along this region (Figure b), seismic studies indicate the thickest oceanic crust along ultraslow‐spreading ridges [ Carbotte et al ., ] up to 10 km thick [ Niu et al ., ] and off axis [ Li et al ., ], suggesting that robust magmatism at this particular location has lasted at least 3 Ma [ Li et al ., ]. Off‐axis topographic and gravimetric studies further extend such a melting anomaly to persist for 10 Ma [ Sauter et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Isotopically enriched N‐MORB: A new geochemical signature of off‐axis plume‐ridge interaction—A case study at 50°28′E, Southwest Indian Ridge

et al. 2017

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Interaction between the Southwest Indian Ridge (46°E and 52°20′E) and Crozet hotspot has been proposed by geophysical studies but remains controversial mostly due to the lack of E‐MORB (enriched mid‐ocean ridge basalts). Forty‐seven new samples collected from this region, including 15 from segment 27 centered at 50°28′E with a 10 km thick crust, are all N‐MORB (normal MORB) and can be classified into two groups: a high‐Al group only at 50°28′E and a Main group widespread. The former, with higher Al2O3 and lower TiO2 and SiO2, have slightly enriched Sr‐Nd‐Hf‐Pb isotopic compositions. We propose that their major and trace elemental signatures were modified by reaction with primitive cumulate in the crust, whereas the enriched isotopic compositions indicate the contribution of Crozet plume materials. During upslope flow of the Crozet plume to the ridge, decompression melting would occur along the path, which would deplete the plume in incompatible elements but not significantly change the isotopic compositions. Thus, when they finally reach the ridge, the depleted residue would remelt due to further decompression at MOR and produce isotopically enriched N‐MORB at segment 27. Isotopically enriched N‐MORB are known elsewhere, mostly at slower‐spreading ridges possibly influenced by plumes with large plume‐ridge distances. In particular, the constant Nd isotopic compositions with decreasing (La/Sm)N ratios for off‐axis magmatism between the Réunion hotspot toward the CIR perfectly match such a plume‐ridge interaction model. Therefore, aside from E‐MORB, isotopically enriched N‐MORB can also be considered as the geochemical signature for off‐axis plume‐ridge interaction.

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“…A unique segment centered at 50°28 0 E shows obviously low magnetic anomaly at its center. Li et al (2015) used three-dimensional seismic tomography at 50°28 0 E and revealed a low-velocity anomaly (*0.6 km/s) which was accompanied by an unusually thick crust (*9.5 km). Niu et al (2015) also identified the thick crust (*10 km) beneath the segment center by wide-angle seismic reflection.…”

Section: Introductionmentioning

confidence: 99%

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

Yang

Tao

et al. 2016

Mar Geophys Res

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Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zones at the central volcano, at 50°28 0 E in the ultraslow-spreading Southwest Indian Ridge (SWIR). Twenty-eight subsamples from a relict chimney and massive sulfides were dated using the 230 Th/ 238 U method. Four main episodes of hydrothermal activity were determined according to the restricted results: 68. 9-84.3, 43.9-48.4, 25.3-34.8, and 0.7-17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. The periodic character of hydrothermal activity may be related to the heat source provided by the interaction of local magmatism and tectonism. The estimated mean growth rate of the sulfide chimney is \0.02 mm/yr. This study is the first to estimate the growth rate of chimneys in the SWIR. The maximum age of the relict chimney in Duanqiao hydrothermal filed is close to that of the chimneys from Mt. Jourdanne (70 kyrs). The hydrothermal activity in Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfides are younger than the sulfides from other hydrothermal fields such as Rainbow, Sonne and Ashadze-2. The preliminarily estimated reserves of sulfide ores of Duanqiao are approximately 0.5-2.9 million tons.

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Seismic observation of an extremely magmatic accretion at the ultraslow spreading Southwest Indian Ridge

Cited by 62 publications

References 40 publications

The velocity structure of a fossil spreading centre in the Southwest Sub‐basin, South China Sea

The velocity structure of a fossil spreading centre in the Southwest Sub‐basin, South China Sea

Isotopically enriched N‐MORB: A new geochemical signature of off‐axis plume‐ridge interaction—A case study at 50°28′E, Southwest Indian Ridge

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

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