Upper mantle structure of the <scp>T</scp>onga‐<scp>L</scp>au‐<scp>F</scp>iji region from <scp>R</scp>ayleigh wave tomography

Wei, S. S.; Zha, Yang; Shen, Weisen; Wiens, Douglas A.; Conder, J. A.; Webb, Spahr C.

doi:10.1002/2016gc006656

Cited by 17 publications

(11 citation statements)

References 91 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Strong anomalies of high P ‐ and S ‐wave attenuation are imaged beneath the Lau Basin (Figure ), indicating perhaps the highest shear attenuation ( Q μ −1 = 0.047 ± 0.001) known in the mantle (Figure b). The high shear attenuation anomalies coincide with low‐velocity anomalies in the uppermost mantle wedge revealed by previous tomography work (Conder & Wiens, ; Wei et al, ; Wiens et al, ), suggesting high mantle temperature as well as the existence of partial melts. Hot materials of the Australian mantle upwell from the west along the mantle wedge corner flow pattern, triggering extensive decompression melting that generates a large amount of magma erupting at the back‐arc spreading centers.…”

Section: Discussionsupporting

confidence: 82%

“…The location of the cross section is shown as the straight line in Figure . The black contours show the local melt production rate modeled by Wei et al (), starting from 1%/Myr with a 2%/Myr increment. Other features are plotted in the same manner as Figure a.…”

Section: Resultsmentioning

confidence: 99%

“…Intensive melting of the Tonga-Lau mantle wedge generates extensive magmatism along the Lau back-arc spreading centers and the Tofua arc (Kelley et al, 2006). The region of partial melting within the mantle wedge has been previously imaged as a low-velocity zone beneath the Lau back-arc basin west of the high-velocity Tonga slab (Conder & Wiens, 2006;Wei et al, 2015;Wei et al, 2016;Wiens et al, 2008). Additionally, previous studies of seismic attenuation show a broad high-shear-attenuation zone beneath the Lau Basin, also indicating high temperature and partial melts in the mantle wedge (Barazangi & Isacks, 1971;Bowman, 1988;Roth et al, 1999).…”

Section: Tonga-lau Subduction Systemmentioning

confidence: 99%

“…Readers are referred to higher-resolution tomography results of SV-velocity and P-wave attenuation (Wei et al, 2016;Wei & Wiens, 2018) for details of melt distribution and mantle wedge dynamics.…”

Section: 1029/2019jb017527mentioning

confidence: 99%

See 3 more Smart Citations

High Bulk and Shear Attenuation Due to Partial Melt in the Tonga‐Lau Back‐arc Mantle

Wei

Wiens²

2020

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

Seismic attenuation measures energy loss during seismic wave propagation and quantifies the relaxation of rocks' elastic moduli. Abundant seismic studies have observed shear attenuation, but few have quantified bulk attenuation (bulk modulus relaxation), and these studies controversially locate finite bulk attenuation in different parts of the Earth, from the asthenosphere to the inner core. Here we present conclusive evidence localizing bulk attenuation to a specific region of the uppermost mantle. By analyzing amplitude spectral decay of P and S waves from Tonga earthquakes recorded at local seismic stations, we observe unusually low Q P /Q S ratios (<1.5) in the Tonga-Lau mantle wedge. All seismic raypaths with significant path-average bulk attenuation (Q κ −1 > 0.01 or Q κ < 100) are confined to the region immediately beneath the Lau back-arc spreading centers west of the Tonga Arc. Tomography results show that the highest bulk attenuation (Q κ −1 = 0.037 ± 0.008 or Q κ = 27.0 ± 0.2) is about 75% of the in situ shear attenuation. The observed high bulk attenuation anomalies coincide with an inferred zone of partial melting, suggesting that the causative mechanism involves either infinitesimal movement of melt through pores or changes in melt fraction in response to seismic waves.Key Points:• Low Q P /Q S ratios (<1.5) are observed beneath the Lau back-arc spreading centers • The low Q P /Q S ratios indicate bulk attenuation as high as 75% of the in situ shear attenuation • High bulk attenuation coincides with partial melt in the Tonga-Lau mantle wedgeSupporting Information:• Supporting Information S1

show abstract

Section: Discussionsupporting

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Section: Tonga-lau Subduction Systemmentioning

confidence: 99%

Section: 1029/2019jb017527mentioning

confidence: 99%

See 2 more Smart Citations

High Bulk and Shear Attenuation Due to Partial Melt in the Tonga‐Lau Back‐arc Mantle

Wei

Wiens²

2020

JGR Solid Earth

Self Cite

View full text Add to dashboard Cite

show abstract

“…At subduction zones, for example, a trench/fault-parallel polarization of seismic waves has been reported (e.g., Barak & Klemperer, 2016;Smith et al, 2001;Wei et al, 2016). At subduction zones, for example, a trench/fault-parallel polarization of seismic waves has been reported (e.g., Barak & Klemperer, 2016;Smith et al, 2001;Wei et al, 2016).…”

Section: Applicability To Naturementioning

confidence: 99%

Crystallographic Preferred Orientation of Olivine in Sheared Partially Molten Rocks: The Source of the “a‐c Switch”

Hansen

Wallis

et al. 2018

Geochem Geophys Geosyst

View full text Add to dashboard Cite

To investigate the mechanism that produces the crystallographic preferred orientations (CPO) characteristic of sheared partially molten rocks of mantle composition, we analyzed the microstructures of samples of olivine plus 7% basaltic melt deformed in torsion to shear strains as large as γ= 13.3. Electron backscattered diffraction (EBSD) observations reveal a CPO characterized by a weak a‐c girdle in the shear plane that develops by γ≈ 4. This CPO, which exhibits a slightly stronger alignment of [001] than [100] axes in the shear direction, changes little in both strength and distribution with increasing stress and with increasing strain. Furthermore, it is significantly weaker than the CPO observed for dry, melt‐free olivine aggregates. Orientation maps correlated with grain shape measurements from tangential, radial, and transverse sections indicate that olivine grains are longer along [001] axes than along [100] axes and shortest along [010] axes. This morphology is similar to that of olivine grains in a mafic melt. We conclude that the weak a‐c girdle observed in sheared partially molten rocks reflects contributions from two processes. Due to their shape‐preferred orientation (SPO), grains rotate to align their [001] axes parallel to the flow direction. At the same time, dislocation glide on the (010)[100] slip system rotates [100] axes into the flow direction. The presence of this CPO in partially molten regions of the upper mantle significantly impacts the interpretation of seismic anisotropy and kinematics of flow.

show abstract

A Visual Survey of Global Slab Geometries With ShowEarthModel and Implications for a Three‐Dimensional Subduction Paradigm

Jadamec

Kreylos

Chang

et al. 2018

Earth and Space Science

View full text Add to dashboard Cite

Increasing volumes of digital data, combined with advances in visualization, allow for a new three‐dimensional (3D) conceptualization of modern subduction systems. Here we present 16 visual exploration sessions with the ShowEarthModel program that interrogate modern slab morphologies on Earth. These virtual voyages through the Earth's interior provide a snapshot into the four‐dimensional evolution of plate tectonics, captured by the modern state of slab structure. Examining the modern subduction system in an interactive 3‐D framework provides an improved conceptualization of the morphology of slabs. The movies demonstrate that unlike the modern mid‐ocean ridge system, modern subduction systems are laterally discontinuous features, making lateral slab edges prevalent. The 3‐D visualizations elucidate the manner in which slabs intersect and overlap, processes that occur in at least six of the Earth's major subduction zones. The observed variability within a given subduction zone as well as the physical presence of intersecting slabs suggests that slab gaps and slab windows are common. The 3‐D rendering shows relative differences in the radius of curvature for arcuate slabs, as well as the variability in dip within a given subduction zone. Addressing the complex geometries of subducted lithosphere in this way can place constraints on outstanding questions of subduction dynamics including slab strength, mantle rheology, mantle flow circulation, and plate‐asthenosphere coupling. By conceptualizing the modern subduction system on Earth in 3‐D space, this paper contributes to the paradigm shift from a two‐dimensional (2‐D) to 3‐D framework for interpreting the subduction process.

show abstract

Upper mantle structure of the Tonga‐Lau‐Fiji region from Rayleigh wave tomography

Cited by 17 publications

References 91 publications

High Bulk and Shear Attenuation Due to Partial Melt in the Tonga‐Lau Back‐arc Mantle

High Bulk and Shear Attenuation Due to Partial Melt in the Tonga‐Lau Back‐arc Mantle

Crystallographic Preferred Orientation of Olivine in Sheared Partially Molten Rocks: The Source of the “a‐c Switch”

A Visual Survey of Global Slab Geometries With ShowEarthModel and Implications for a Three‐Dimensional Subduction Paradigm

Contact Info

Product

Resources

About