Crustal thickness and earthquake distribution south of the Logachev Seamount, Knipovich Ridge

Jokat, Wilfried; Kollofrath, Jochen; Geissler, Wolfram; Jensen, Laura

doi:10.1029/2012gl051199

Cited by 35 publications

(38 citation statements)

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“…The most significant difference as compared to previously studied ultraslow‐spreading segments [e.g., Jokat et al , ; Minshull et al , ; Zhao et al , ] is the presence of a much thicker crust and the crustal magma system, both indicating an excess melt supply to this segment that has been persistent for more than 3 Ma [ Li et al , ]. In addition, the maximum crustal thickness beneath the segment center (∼9.5 km) is even larger than those at the slow‐spreading MAR segments that also contain similar lower crustal magma chambers [ Seher et al , ; Dunn et al , ].…”

Section: Discussionmentioning

confidence: 78%

“…A general way is to generate a 1‐D starting model from previous studies in the same area or similar areas [ Seher et al , ]. However, the gravimetric observations [ Sauter et al , ] at this study area suggest that the crustal thickness is more than the global average of ∼6 km [ Chen , ], much larger than any other seismically studied segments at ultraslow‐spreading ridges [ Jokat et al , ; Minshull et al , ]. As the morphology shows a similarity to the slow‐spreading segments, we first constructed a velocity‐depth profile similar to the MAR type velocity profiles at segment centers [ Canales et al , ; Hooft et al , ; Seher et al , ].…”

Section: Resultsmentioning

confidence: 99%

“…We have presented the 3‐D crustal seismic image of the ultraslow‐spreading ridge segment with excess melt supply [ Li et al , ; Sauter et al , ]. It is significantly different from previous seismic images at the ultraslow‐spreading ridge segments [e.g., Minshull et al , ; Jokat and Schmidt‐Aursch , ; Jokat et al , ], which found much thinner crusts as compared to the global average of 6 km [ Chen , ; Bown and White , ] and the lack of the lower crustal velocities (between 6.5 km/s and 7.2 km/s). Li et al [] has demonstrated that the thick crust at the segment center rapidly decreases toward the segment ends, suggesting an enhanced focusing mechanism of the melt supply to the segment center from the mantle.…”

Section: Discussionmentioning

confidence: 98%

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Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

et al. 2017

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We present a three‐dimensional crustal structure of a magmatically robust segment of the ultraslow‐spreading Southwest Indian Ridge at 50°28'E based on tomographic inversions of an ocean bottom seismometer data set. Our results show an upper crustal low‐velocity band in the axial zone, which is attributed to increased porosities due to active extensions, leading to anisotropy in the upper crust with a fast direction subperpendicular to the spreading direction. In the lower crust, the results reveal a round‐shaped low‐velocity anomaly at the segment center, indicative of high temperatures and/or a small amount of melt, suggestive of the presence of an axial magma chamber. At the midcrustal depth, an along‐axis asymmetry is observed with respect to the segment center. While a small low‐velocity anomaly indicates lateral magma redistribution toward the western segment end, the deep‐penetrating low velocities and high velocity gradients toward the eastern end suggest that the crust is colder and contains a thicker fractured layer. This asymmetry occurs very close to the axial magma chamber (<5 km) and seems to be related to the fact that the oblique‐spreading domain at the eastern end offsets the ridge axis by a larger distance than that at the western end. We suggest that an along‐axis deep‐penetrating hydrothermal circulation develops on the east side of the axial magma chamber, in response to the rapid change from orthogonal‐ to oblique‐spreading domains and cools the crust.

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Section: Discussionmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 98%

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Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

et al. 2017

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“…One-dimensional velocity model. To derive a minimum one-dimensional velocitydepth profile, as commonly used in earthquake location 33 , we used the results of refraction seismic surveys 15,34,35 conducted within each of the study sites (Extended Data Figs 1a, 2a and 3a). We extracted smoothed average velocity-depth profiles for the upper 5 km, where the refraction seismic data provided sufficient ray cover.…”

Section: Methodsmentioning

confidence: 99%

Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere

Schlindwein

Schmid

2016

Nature

127

142

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Along ultraslow-spreading ridges, where oceanic tectonic plates drift very slowly apart, conductive cooling is thought to limit mantle melting and melt production has been inferred to be highly discontinuous. Along such spreading centres, long ridge sections without any igneous crust alternate with magmatic sections that host massive volcanoes capable of strong earthquakes. Hence melt supply, lithospheric composition and tectonic structure seem to vary considerably along the axis of the slowest-spreading ridges. However, owing to the lack of seismic data, the lithospheric structure of ultraslow ridges is poorly constrained. Here we describe the structure and accretion modes of two end-member types of oceanic lithosphere using a detailed seismicity survey along 390 kilometres of ultraslow-spreading ridge axis. We observe that amagmatic sections lack shallow seismicity in the upper 15 kilometres of the lithosphere, but unusually contain earthquakes down to depths of 35 kilometres. This observation implies a cold, thick lithosphere, with an upper aseismic zone that probably reflects substantial serpentinization. We find that regions of magmatic lithosphere thin dramatically under volcanic centres, and infer that the resulting topography of the lithosphere-asthenosphere boundary could allow along-axis melt flow, explaining the uneven crustal production at ultraslow-spreading ridges. The seismicity data indicate that alteration in ocean lithosphere may reach far deeper than previously thought, with important implications towards seafloor deformation and fluid circulation.

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“…A brief microseismicity study at SWIR volcano 11 (Fig. 11;Yamada et al 2002) suggested hypocentres depths up to 8 km below the seafloor, while a more comprehensive microseismicity study on the Knipovich ridge found maximum hypocentral depths c. 20 km beneath the axial basins, and c. 8 km beneath the volcanic centres (Jokat et al 2012;Schlindwein et al 2013). The results for axial basins suggest a brittle lithospheric thickness in excess of the 8 -10 km that is typically inferred from hypocentre depths at the MAR (Toomey et al 1988;Wolfe et al 1995;de Martin et al 2007).…”

mentioning

confidence: 99%

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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Crustal thickness and earthquake distribution south of the Logachev Seamount, Knipovich Ridge

Cited by 35 publications

References 38 publications

Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

Seismic structure and magmatic construction of crust at the ultraslow‐spreading Southwest Indian Ridge at 50°28'E

Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere

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

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