Internal deformation of the subducted Nazca slab inferred from seismic anisotropy

Eakin, C. M.; Long, Maureen D.; Scire, A. C.; Beck, S. L.; Wagner, L. S.; Zandt, G.; Tavera, Hernando

doi:10.1038/ngeo2592

Cited by 36 publications

(53 citation statements)

References 34 publications

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“…These splitting directions are similar to those observed to the south of our study area by Anderson et al [2004] and MacDougall et al [2012]. Eakin et al [2016] demonstrated that deformation along the edges of flat slabs can induce strong slab-internal anisotropy with trench-parallel orientations. The variable northeasternmost ESP stations do not lie directly updip from the slab tear.…”

Section: 1002/2017gl074312supporting

confidence: 91%

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

Lynner

Anderson

Portner

et al. 2017

Geophysical Research Letters

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A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate‐motion‐parallel fast splitting directions, indicative of plate‐motion‐parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate‐motion‐parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate‐motion‐parallel flow in both the subslab mantle and mantle wedge.

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Section: 1002/2017gl074312supporting

confidence: 91%

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

Lynner

Anderson

Portner

et al. 2017

Geophysical Research Letters

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“…This lateral mantle flow may contribute to the low shear wave velocities we observe beneath the inboard easternmost corner of the flat slab. We find evidence for modified slab fabric along the southern edge of the flat slab, consistent with previous results and interpretations of Eakin et al [], but preserved fossil spreading fabric within the torn slab to the north. The contrast in slab fabric along the strike supports the hypothesis that the extension due to change in slab geometry from steep to flat may alter the internal slab anisotropy upon subduction.…”

Section: Introductionsupporting

confidence: 92%

“…The model for upper mantle anisotropy obtained in this study provides constraints complementary to those provided by shear wave splitting, which has previously been studied in this region by Eakin et al [, , ] and Long et al []. Here we briefly discuss the comparison between the two types of studies, illustrated in Figure .…”

Section: Discussionsupporting

confidence: 66%

Effects of change in slab geometry on the mantle flow and slab fabric in Southern Peru

et al. 2016

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The effects of complex slab geometries on the surrounding mantle flow field are still poorly understood. Here we combine shear wave velocity structure with Rayleigh wave phase anisotropy to examine these effects in southern Peru, where the slab changes its geometry from steep to flat. To the south, where the slab subducts steeply, we find trench‐parallel anisotropy beneath the active volcanic arc that we attribute to the mantle wedge and/or upper portions of the subducting plate. Farther north, beneath the easternmost corner of the flat slab, we observe a pronounced low‐velocity anomaly. This anomaly is caused either by the presence of volatiles and/or flux melting that could result from southward directed, volatile‐rich subslab mantle flow or by increased temperature and/or decompression melting due to small‐scale vertical flow. We also find evidence for mantle flow through the tear north of the subducting Nazca Ridge. Finally, we observe anisotropy patterns associated with the fast velocity anomalies that reveal along strike variations in the slab's internal deformation. The change in slab geometry from steep to flat contorts the subducting plate south of the Nazca Ridge causing an alteration of the slab petrofabric. In contrast, the torn slab to the north still preserves the primary (fossilized) petrofabric first established shortly after plate formation.

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“…In order to investigate variations in seismic anisotropy in the subducting Hikurangi slab we selected earthquakes that had a station–earthquake raypath that was approximately parallel to the dip of the subducting slab (∼300°). By doing this, the anisotropy measurements will originate from earthquake raypaths that sample large portions of the downgoing slab, as the fast internal velocities of the slab will act as a waveguide (Eakin et al, ). We confirm this behavior by comparing the S‐wave frequencies of these deep earthquakes at stations in the Hikurangi arc and in the NW of the North Island (Supporting information Figure S1).…”

Section: Resultsmentioning

confidence: 99%

Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

Illsley‐Kemp

Savage

Wilson

et al. 2019

Geochem Geophys Geosyst

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We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW‐SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep‐rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench‐parallel fast orientation, reflecting the pervasive presence of plate‐bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E‐W compression, oblique to the stress field in the subducting slab. The north‐south variation in fore‐arc stress is likely related to differing subduction‐interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large‐scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

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Internal deformation of the subducted Nazca slab inferred from seismic anisotropy

Cited by 36 publications

References 34 publications

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

Effects of change in slab geometry on the mantle flow and slab fabric in Southern Peru

Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

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