The nature of subslab slow velocity anomalies beneath South America

Portner, D. E.; Beck, S. L.; Zandt, G.; Scire, A. C.

doi:10.1002/2017gl073106

Cited by 51 publications

(82 citation statements)

References 60 publications

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“…of Portner et al [2017] that mantle material is being advected through the opening in the subducting slab. In order to develop plate-motion-parallel shear wave splitting, entrainment of asthenospheric material by the subducting plate is needed.…”

Section: /2017gl074312mentioning

confidence: 99%

“…The South American subduction zone is one of the geographically longest continuous regions of active subduction and is characterized by lateral variations in slab dip angle [e.g., Kay and Coira, 2009;Scire et al, 2016;Portner et al, 2017]. In particular, two prominent regions of flat slab subduction are observed beneath Peru and beneath central Chile and Argentina.…”

Section: Introductionmentioning

confidence: 99%

“…Individual shear wave splitting measurements made at ESP and SIEMBRA stations plotted atop the P wave teleseismic tomography model ofPortner et al [2017] at a depth of 320 km. Stations are colored by average station delay time.…”

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confidence: 99%

“…Raypaths of all individual splitting measurements made at ESP and SIEMBRA stations through a schematic of the subducting Nazca plate derived from a combination of the +0.5% contour from thePortner et al [2017] model and Slab 1.0[Hayes et al, 2012]. The exact boundaries of the slab tear are therefore poorly constrained.…”

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confidence: 99%

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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: /2017gl074312mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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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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“…At the Peru‐Chile trench, the oblique subduction of the Nazca Ridge, traced inland, correlates with a 600 km near‐horizontal extension of the slab over a wide segment of the plate boundary beneath central Peru (Bishop et al, ; Hampel, ). The JFR points geographically into a narrower segment of elevated slab beneath central Chile, known as the Pampean flat slab, extending inland equally as far (Kay & Mpodozis, ; Nikulin et al, ; Portner et al, ).…”

Section: Aseismic Ridges and Flat‐slab Subductionmentioning

confidence: 99%

Broader Impacts of the Metasomatic Underplating Hypothesis

Park

Rye

2019

Geochem Geophys Geosyst

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The “metasomatic underplating” hypothesis argues that crustal fractures develop during hot spot magma ascent to allow seawater to infiltrate and to serpentinize the sub‐Moho mantle. Published seismic velocities and layer thicknesses support estimates that 1 km of seawater could be chemically bound within an underplated layer, which may require 2–4 Myr to mature. If a serpentinized mantle layer underlies hot spot tracks and/or aseismic ridges, their buoyancy can induce flat‐slab behavior within subduction zones (e.g., beneath central Chile and Peru), weaken slab rheology, and foster slab tears. During serpentinization, metasomatic underplating would produce more serpentine and talc and less brucite and magnetite, if seawater equilibrates with silica in the gabbroic oceanic crust as it descends to the Moho. The restricted solubility of carbonate with temperature may induce seawater CO2 to sequester in the crust as carbonate concretions or intergrowths. Consumption of seawater H2O by serpentinization raises its salinity so that Fe cations stabilize in chloride complexes and depart the open system. Alkali cations in seawater contribute to the sodic metasomatism of pyroxenes, analogous to alterations observed in abyssal peridotites.

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Subducted Lithosphere under South America from Multi-frequency P-wave Tomography

Mohammadzaheri

Sigloch

Hosseini

2021

Preprint

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We analyze mantle structure under South America in the DETOX-P1 seismic tomography model, a global-scale, multifrequency inversion of teleseismic P waves. DETOX-P1 inverts the most extensive data set of broadband, waveform-based traveltime measurements to date, complemented by analyst-picked traveltimes from the ISC-EHB catalog. The mantle under South America is sampled by ∼665,000 cross-correlation traveltimes measured on 529 South American broadband stations and on 5,389 stations elsewhere. By their locations, depths, and geometries, we distinguish four high-velocity provinces under South America, interpreted as subducted lithosphere ("slabs"). The deepest (∼1,800-1,200 km depth) and shallowest (<600 km) slab provinces are observed beneath the Andean Cordillera near the continent's northwest coast. At intermediate depths (1,200-900 km, 900-600 km), two slab provinces are observed farther east, under Brazil, Bolivia and Venezuela, with links to the Caribbean. We interpret the slabs relative to South America's paleo-position over time, exploring the hypothesis that slabs sank essentially vertically after widening by viscous deformation in the mantle transition zone. The shallowest slab province carries the geometric imprint of the continental margin and represents ocean-beneathcontinent subduction during Cenozoic times. The deepest, farthest west slab complex formed under intraoceanic trenches during late Jurassic and Cretaceous times, far west of South America's paleo-position adjoined to Africa. The two intermediate slab complexes record the Cretaceous transition from westward intra-oceanic subduction to eastward subduction beneath South America. This geophysical inference matches geologic records of the transition from Jura-Cretaceous, extensional "intra-arc" basins to basin inversion and onset of the modern Andean arc ∼85 Ma. Plain Language Summary Eastward subduction of the Pacific basin lithosphere beneathSouth America has generated arc magmatism and produced the modern Andes. However, extrapolation of the modern east-dipping subduction scenario to before the Late Cretaceous does not readily explain the contrasting history of the ancestral Andes. Subducted former seafloor continues to exist in the mantle and remains visible to seismic tomography because P waves travel faster in it than in ambient mantle. We analyze such seismically fast domains, that is, "slabs" of interpreted paleo-seafloor, at depths of ∼300-1,800 km in our global tomography model DETOX-P1. Combining these observations with quantitative plate reconstructions and geological observations, we attempt to reconstruct the subduction history under South America. The slab that dips eastward down beneath the present-day Andes is relatively continuous to ∼900 km depth. Deeper down, slab geometries completely change. Voluminous slabs are unexpectedly imaged thousands of kilometers west of South America's reconstructed paleo-margin. We argue that in the simplest explanation all slabs sank essentially in place, and a trans-American, tectonic reconfigu...

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The nature of subslab slow velocity anomalies beneath South America

Cited by 51 publications

References 60 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

Broader Impacts of the Metasomatic Underplating Hypothesis

Subducted Lithosphere under South America from Multi-frequency P-wave Tomography

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