Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow

Bodmer, Miles; Toomey, D. R.; Hooft, E. E.; Nábělek, J.; Braunmiller, Jochen

doi:10.1130/g37181.1

Cited by 27 publications

(77 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Basal shear stresses may be small, but they can amount to a significant force when integrated over a substantial area (∼10 14−16 N assuming strain rates of 10 −15 s −1 , asthenosphere viscosity of 10 19 Pa s, and plate area of 10 10−12 m 2 ). In support of this view, shear wave splitting observations made at sites throughout the JdF plate are consistent with a clockwise rotation of asthenospheric flow relative to absolute plate motion 25 . A skewed mantle flow field would generate transtensional stresses at the ridge.…”

Section: Tectonic Segmentation Of Mid-ocean Ridgesmentioning

confidence: 64%

Segmentation of mid-ocean ridges attributed to oblique mantle divergence

et al. 2016

Self Cite

View full text Add to dashboard Cite

The origin of mid-ocean ridge segmentation-the systematic along-axis variation in tectonic and magmatic processesremains controversial. It is commonly assumed that mantle flow is a passive response to plate divergence and that between transform faults magma supply controls segmentation. Using seismic tomography, we constrain the geometry of mantle flow and the distribution of mantle melt beneath the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge. Our results, in combination with prior studies, establish a systematic skew between the mantle-divergence and plate-spreading directions. In all three cases studied, mantle divergence is advanced with respect to recent changes in the plate-spreading direction and the extent to which the flow field is advanced increases with decreasing spreading rate. Furthermore, seismic images show that large-o set, non-transform discontinuities are regions of enhanced mantle melt retention. We propose that oblique mantle flow beneath mid-ocean ridges is a driving force for the reorientation of spreading segments and the formation of ridge-axis discontinuities. The resulting tectonic discontinuities decrease the e ciency of upward melt transport, thus defining segment-scale variations in magmatic processes. We predict that across spreading rates mid-ocean ridge segmentation is controlled by evolving patterns in asthenospheric flow and the dynamics of lithospheric rifting.S ince the discovery that Earth's mid-ocean ridge system is divided into segments 1-3 a wealth of observations have shown that there are systematic, along-axis variations in tectonic and magmatic processes 2,4-6 . Between transform faults, the boundaries of ridge segments are defined by long-lived, non-transform tectonic offsets or second-order ridge crest discontinuities 2,3 ( Fig. 1) that often occur at axial depth maxima and that migrate along the plate boundary. These second-order discontinuities include overlapping spreading centres (OSCs) at fast-and intermediate-spreading rates, and oblique shear zones at slow-spreading rates. The origin of non-transform tectonic offsets and their relations to segment-scale magmatic processes remains actively debated 1,2,5-9 .The prevailing hypothesis for segmentation of spreading centres attributes second-order offsets to variations in magma supply from the upwelling mantle. In this view, segment centres overlie sites of increased melt supply and magma is redistributed along axis at crustal or mantle depths toward magma-starved segment ends 1,2,8,10 . Alternatively, competing hypotheses suggest that changes in the plate-spreading direction are related to the formation of tectonic offsets 7 and to a misalignment between sub-ridge mantle and crustal processes 9 . Here, we seismically image the geometry of mantle flow and the distribution of shallow mantle melt beneath the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge (JdFR). We synthesize our results with observations from other spreading environments to identify the mechanisms responsible ...

show abstract

Section: Tectonic Segmentation Of Mid-ocean Ridgesmentioning

confidence: 64%

Segmentation of mid-ocean ridges attributed to oblique mantle divergence

et al. 2016

Self Cite

View full text Add to dashboard Cite

show abstract

“…6) is stronger than for the intermediate coupling case, with off-axis splitting ∼1.2 s at 20 Myr compared to ∼0.6 s. This difference is within detection limits for discrimination using a quiet, well-oriented ocean bottom seismometer station (Wolfe & Solomon 1998) but is near the limit for noisy stations or small data sets (Bodmer et al 2015;Menke et al 2015). Reduced anisotropy within ∼75 km of the axis might be discernible, and a dense station spacing across the plate boundary with analysis of both P and S waves could help discriminate between models.…”

Section: Power-law Polycrystalmentioning

confidence: 81%

Effects of crystal preferred orientation on upper-mantle flow near plate boundaries: rheologic feedbacks and seismic anisotropy

Blackman¹,

Boyce

Castelnau

et al. 2017

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…Blue arrows show the orientation of Pn anisotropy beneath the JdF plate interior and in the Blanco transform fault region (BTF; outlined by blue box) measured in this study. The orientation of mantle anisotropy from Pn travel times measured beneath the northern JdF Ridge (green arrow; VanderBeek et al, ) and from SKS splits measured beneath the plate interior and the BTF region (red arrows; Bodmer et al, ) is also shown. White and black arrows parallel Pacific and JdF APM and JdF‐Pacific RPM, respectively.…”

Section: Methodsmentioning

confidence: 99%

Shallow Mantle Anisotropy Beneath the Juan de Fuca Plate

VanderBeek

Toomey

2017

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

The anisotropic fabric of the oceanic mantle lithosphere is often assumed to parallel paleo‐relative plate motion (RPM). However, we find evidence that this assumption is invalid beneath the Juan de Fuca (JdF) plate. Using travel times of seismic energy propagating through the topmost mantle, we find that the fast direction of P wave propagation is rotated 18° ± 3° counterclockwise to the paleo‐spreading direction and strikes between Pacific‐JdF relative and JdF absolute plate motion (APM). The mean mantle velocity is 7.85 ± 0.02 km/s with 4.6% ± 0.4% anisotropy. Synthesis of the plate‐averaged Pn anisotropy signal with measurements of Pn anisotropy beneath the JdF Ridge and SKS splits across the JdF plate suggests that the anisotropic structure of the topmost mantle continues to evolve away from the spreading center to more closely align with APM. We infer that the oceanic mantle lithosphere may record the influence of both paleo‐RPM and paleo‐APM.

show abstract

Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow

Cited by 27 publications

References 22 publications

Segmentation of mid-ocean ridges attributed to oblique mantle divergence

Segmentation of mid-ocean ridges attributed to oblique mantle divergence

Effects of crystal preferred orientation on upper-mantle flow near plate boundaries: rheologic feedbacks and seismic anisotropy

Shallow Mantle Anisotropy Beneath the Juan de Fuca Plate

Contact Info

Product

Resources

About