Tracking stress and hydrothermal activity along the Eastern Lau Spreading Center using seismic anisotropy

Dunn, R. A.

doi:10.1016/j.epsl.2014.11.027

Cited by 10 publications

(14 citation statements)

References 62 publications

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“…The oriented cracks would need to be aligned perpendicular to the paleospreading direction. This alignment would be consistent with the stress field experienced by the lithosphere near the ridge (Dunn, 2015), but horizontal extensional stress due to thermal contraction may be at a maximum normal to the plate spreading direction at older ages (e.g., Sandwell & Fialko, 2004;Sasajima & Ito, 2017). Joints and other types of layering, such as spatial variation in the density of microcracks or gabbroic dikes (e.g., Francheteau et al, 1990;Hekinian et al, 1993), can also produce an extrinsic transverse isotropy for the wavelengths typical of active-source seismic experiments (e.g., Backus, 1962).…”

Section: Depth Variation Of Anisotropysupporting

confidence: 76%

“…The mantle experiences large shear strains during corner flow at the ridge, and laboratory experiments show that this can impart an anisotropic fabric that can be locked into the lithospheric mantle as minerals are aligned into a crystallographic preferred orientation (CPO) by shear (e.g., Nicolas et al, 1973;Turner, 1942;Zhang & Karato, 1995). Off-axis, plate structure continues to evolve: as plates cool, they undergo tensional cracking and serpentinization (e.g., Cormier et al, 2011;Dunn, 2015;Korenaga, 2007;Mishra & Gordon, 2016;Sandwell & Fialko, 2004).…”

Section: Introductionmentioning

confidence: 99%

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Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

et al. 2019

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Plate formation and evolution processes are predicted to generate upper mantle seismic anisotropy and negative vertical velocity gradients in oceanic lithosphere. However, predictions for upper mantle seismic velocity structure do not fully agree with the results of seismic experiments. The strength of anisotropy observed in the upper mantle varies widely. Further, many refraction studies observe a fast direction of anisotropy rotated several degrees with respect to the paleospreading direction, suggesting that upper mantle anisotropy records processes other than 2‐D corner flow and plate‐driven shear near mid‐ocean ridges. We measure 6.0 ± 0.3% anisotropy at the Moho in 70‐Ma lithosphere in the central Pacific with a fast direction parallel to paleospreading, consistent with mineral alignment by 2‐D mantle flow near a mid‐ocean ridge. We also find an increase in the strength of anisotropy with depth, with vertical velocity gradients estimated at 0.02 km/s/km in the fast direction and 0 km/s/km in the slow direction. The increase in anisotropy with depth can be explained by mechanisms for producing anisotropy other than intrinsic effects from mineral fabric, such as aligned cracks or other structures. This measurement of seismic anisotropy and gradients reflects the effects of both plate formation and evolution processes on seismic velocity structure in mature oceanic lithosphere, and can serve as a reference for future studies to investigate the processes involved in lithospheric formation and evolution.

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Section: Depth Variation Of Anisotropysupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

et al. 2019

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“…While the tectonic fracturing has maximum effects near the seafloor, the thermally driven fracturing should be strongest around the magma body. Dunn [] used similar mechanisms to explain the increased amplitude of anisotropy in the upper crust at more magmatically robust segments of the East Lau spreading center. He suggested that the hydrofracturing combined with other processes like thermal contraction and fluid overpressure, could increase the tensile stress and porosity above the magma body.…”

Section: Discussionmentioning

confidence: 97%

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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“…In addition, the 37 airgun pulses of 21 MCS seismic lines (nominal source spacing of 37.5 m) were recorded 38 by the inner 20 OBSs of the array. Seismic tomographic imaging was carried out using 39 P-wave travel time data (~152,000 measurements) from both sets of seismic lines and an 40 iterative technique that computes 3D velocity structure (Dunn, 2015;Dunn et al, 2005). 41…”

Section: Data Repository 1 ) 124mentioning

confidence: 99%

Seismic imaging of magma sills beneath an ultramafic-hosted hydrothermal system

Canales

Dunn

Arai

et al. 2017

Geology

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10Hydrothermal circulation at mid-ocean ridge volcanic segments extracts heat from 11 crustal magma bodies. However, the heat source driving hydrothermal circulation in 12 ultramafic outcrops, where mantle rocks are exhumed in low-magma supply 13 environments, has remained enigmatic. Here we use a three-dimensional P-wave velocity 14 model derived from active-source wide-angle refraction/reflection ocean bottom 15 seismometer data and pre-stack depth-migrated images derived from multichannel 16 seismic reflection data to investigate the internal structure of the Rainbow ultramafic 17 massif, which is located in a non-transform discontinuity of the Mid-Atlantic Ridge. 18Seismic imaging reveals that the ultramafic rocks composing the Rainbow massif have 19 been intruded by a large number of magmatic sills, distributed throughout the massif at 20 depths of ~2-10 km. These sills, which appear to be at varying stages of crystallization, 21can supply the heat needed to drive high-temperature hydrothermal circulation, and thus 22

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Tracking stress and hydrothermal activity along the Eastern Lau Spreading Center using seismic anisotropy

Cited by 10 publications

References 62 publications

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

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

Seismic imaging of magma sills beneath an ultramafic-hosted hydrothermal system

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