A different pattern of ridge segmentation and mantle Bouguer gravity anomalies along the ultra-slow spreading Southwest Indian Ridge (15°30′E to 25°E)

Grindlay, N. R.; Madsen, John A.; Rommevaux-Jestin, Céline; Sclater, John G.

doi:10.1016/s0012-821x(98)00154-x

Cited by 74 publications

(84 citation statements)

References 29 publications

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“…Most regions of the axis display a succession of along-axis highs and lows with typical half-wavelengths of 30-100 km (Fig. 11;Rommevaux-Jestin et al 1997;Grindlay et al 1998) similar to the second-order segmentation found at slow-spreading ridges ( Fig. 8; Sempéré et al 1990).…”

Section: Ultraslow-spreading Ridgesmentioning

confidence: 65%

“…These ridges had been largely unexplored until the 1990s, but significant portions are now mapped, both on and off axis (e.g. Mendel et al 1997;Rommevaux-Jestin et al 1997;Grindlay et al 1998;Sauter et al 2001;Okino et al 2002;Cannat et al 2003Cannat et al , 2006Cochran et al 2003;Dick et al 2003;Michael et al 2003). Because the MidCayman, Mohns and Knipovich ridges are relatively short (,400 km), the range of ultraslow segmentation scales is best investigated on the SWIR and Gakkel ridges.…”

Section: Ultraslow-spreading Ridgesmentioning

confidence: 99%

“…9). The ends of these segments on ultraslowspreading ridges typically display elongated basins that trend sub-parallel to the regional orientation of the ridge (Mendel et al 1997;Grindlay et al 1998;Okino et al 2002;Michael et al 2003). This contrasts with segment ends at the slow-spreading MAR, which typically exhibit semi-circular nodal basins adjacent to the discontinuities ).…”

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confidence: 99%

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Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Carbotte

Smith

Cannat

et al. 2015

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Mid-ocean ridges display tectonic segmentation defined by discontinuities of the axial zone, and geophysical and geochemical observations suggest segmentation of the underlying magmatic plumbing system. Here, observations of tectonic and magmatic segmentation at ridges spreading from fast to ultraslow rates are reviewed in light of influential concepts of ridge segmentation, including the notion of hierarchical segmentation, spreading cells and centralized v. multiple supply of mantle melts. The observations support the concept of quasi-regularly spaced principal magmatic segments, which are 30-50 km long on average at fast-to slow-spreading ridges and fed by melt accumulations in the shallow asthenosphere. Changes in ridge properties approaching or crossing transform faults are often comparable with those observed at smaller offsets, and even very small discontinuities can be major boundaries in ridge properties. Thus, hierarchical segmentation models that suggest large-scale transform fault-bounded segmentation arises from deeper level processes in the asthenosphere than the finer-scale segmentation are not generally supported. The boundaries between some but not all principal magmatic segments defined by ridge axis geophysical properties coincide with geochemical boundaries reflecting changes in source composition or melting processes. Where geochemical boundaries occur, they can coincide with discontinuities of a wide range of scales.Discovery and interpretations of mid-ocean ridge (MOR) segmentation: historical review

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Section: Ultraslow-spreading Ridgesmentioning

confidence: 65%

Section: Ultraslow-spreading Ridgesmentioning

confidence: 99%

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confidence: 99%

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Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Carbotte

Smith

Cannat

et al. 2015

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“…Brandon et al [2000] Os and a high Pt/Os ratio. Open system behavior of sulfides with respect to Os has also been documented in a suite of peridotitic xenoliths [Handler et al, 1999]. Further understanding of these complex processes will require microbeam Os isotope analysis of sulfides [Alard et al, 2000].…”

Section: Geochemistry Geophysicsmentioning

confidence: 95%

The influence of ridge geometry at the ultraslow-spreading Southwest Indian Ridge (9º-25ºE) : basalt composition sensitivity to variations in source and process

Standish¹

2006

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Between 9º-25º E on the ultraslow-spreading Southwest Indian Ridge lie two sharply contrasting supersegments. One 630 km long supersegment erupts N-MORB that is progressively enriched in incompatible element concentrations from east to west. The second 400 km long supersegment contains three separate volcanic centers erupting E-MORB and connected by long amagmatic accretionary segments, where mantle is emplaced directly to the seafloor with only scattered N-MORB and E-MORB erupted. Rather than a major break in mantle composition at the discontinuity between the supersegments, this sharp contrast in geometry, physiography, and chemistry reflects "source" versus "process" dominated generation of basalt.Robust along-axis correlation of ridge characteristics (i.e. morphology, upwelling rate, lithospheric thickness), basalt chemistry, and crustal thickness (estimated from gravity) provides a unique opportunity to compare the influence of spreading geometry and rate on MORB generation. What had not been well established until now is the importance of melting processes rather than source at spreading rates < 20 mm/yr. Along the orthogonally spreading supersegment (14 mm/yr) moderate degrees of partial melting effectively sample the bulk mantle source, while on the obliquely spreading supersegment (7-14 mm/yr) suppression of mantle melting to low degrees means that the bulk source is not uniformly sampled, and thus "process" rather than "source" dominates melt chemistry. AcknowledgementsThere are so many people to thank when reaching a milestone such as this, so let me start with those that have had the most recent impact on this accomplishment, my thesis committee; Henry Dick, Stan Hart, Ken Sims, Fred Frey, Anton le Roex, Mark Kurz, Jian Lin, and my thesis defense chairperson, Hans Schouten. With both Hans and Jian I have gained a new appreciation for and understanding of real-time seagoing geophysics, and I think all four of us (including Henry) have witnessed some pretty amazing human efforts and as a result grown together as people and scientists during the many days bouncing around the South Atlantic. Mark's analytical expertise, continuing support and encouraging words, and attention to detail, has kept my path over the last 6 years straight and narrow, and in the right direction. Anton has been a great source of information both regarding trace elements and more importantly the SW Indian Ridge. As one of the first geochemists to study the South Atlantic spreading ridges in detail, his early work through the 80's and 90's set the bar (and quite a high bar it was) for which all of my work will be gauged. It is a shame that our schedules did not coincide so that he could be here at WHOI for the defense, but I know much discussion will come from my work. Learning trace element geochemistry from Fred Frey was special. Fred's ability to get back to the basics and stress the importance to understanding "why" in the most fundamental terms is important in geochemistry. I very much appreciated his willingness to ...

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“…It is characterized by 17 individual magmatic segments, 10-35 km in length and elevated by 500-1000 m at their midpoints (Grindlay et al, 1998;Dulaney, 2002). This is important because it indicates limited along-axis communication of magmatic systems, and therefore a low probability of large-scale magma mixing.…”

Section: Case B: the Very-slow-spreading Sw Indian Ridgementioning

confidence: 99%

Scale length of mantle heterogeneities: Constraints from helium diffusion

Hart

Kurz

Wang

2008

Earth and Planetary Science Letters

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A model of coupled He production/diffusion is used to constrain the question of whether Earth's peridotitic mantle contains ubiquitous mesoscale veins or slabs of other lithologies. The high diffusion rates of helium preclude survival of He isotope heterogeneities on scales smaller than a few tens of meters, especially if they represent long term in-growth of 4 He in the mantle. He variability for these 3 areas is very small, and independent of spreading rate: 0. 13, 0.19 and 0.21 Ra (±1σ). Since these ridges range from ultraslow to very fast-spreading, the variability in size of along-axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are not sampling mantle that contains enriched veins or recycled oceanic crust slabs of significant size (> tens of meters). It appears difficult to sustain a view of the upper mantle as a ubiquitous mixture of veins and depleted matrix, with MORB always representing an averaging of this mixture.

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A different pattern of ridge segmentation and mantle Bouguer gravity anomalies along the ultra-slow spreading Southwest Indian Ridge (15°30′E to 25°E)

Cited by 74 publications

References 29 publications

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

The influence of ridge geometry at the ultraslow-spreading Southwest Indian Ridge (9º-25ºE) : basalt composition sensitivity to variations in source and process

Scale length of mantle heterogeneities: Constraints from helium diffusion

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