A dynamic lithosphere–asthenosphere boundary near the equatorial Mid-Atlantic Ridge

Rychert, C.; Tharimena, S.; Harmon, Nicholas; Wang, Shunguo; Constable, Steven; Kendall, J. M.; Bogiatzis, Petros; Agius, Matthew; Schlaphorst, David

doi:10.1016/j.epsl.2021.116949

Cited by 42 publications

(44 citation statements)

References 56 publications

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“…In addition, our observed low average crustal velocities in the south may be explained by thicker sediment, as also supported by P-to-S converted phases that found > 2 km of sediment south of Martinique in both the Grenada basin and the Tobago Trough, and generally thinner sediments to the north . A companion study, using shorter period Rayleigh wave data from ambient noise also has good general agreement with our findings, but provides greater detail of the regional crustal structure (Schlaphorst et al, 2021). General agreement with a range of independent observations gives us confidence in our crustal model, which in turn increases our confidence that our mantle structures are not biased by the shallow structure.…”

Section: Crustsupporting

confidence: 85%

Widespread Hydration of the Back Arc and the Link to Variable Hydration of the Incoming Plate in the Lesser Antilles From Rayleigh Wave Imaging

Harmon

Rychert

Goes

et al. 2021

Geochem Geophys Geosyst

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Subduction zone dynamics are important for a better understanding of natural hazards, plate tectonics, and the evolution of the planet. Despite this, the factors dictating the location and style of volcanism are not well-known. Here we present Rayleigh Wave imaging of the Lesser Antilles subduction zone using ocean bottom and land seismic data collected as part of the VoiLA experiment. This region is an important global endmember that represents a slow (<19 mm/yr) convergence rate of old (80-120 Ma), Atlantic lithosphere formed at a slow spreading ridge. We image the fast slab, the fast-overriding plate and the slow mantle wedge across the entire arc. We find slow velocity anomalies (~4.1 km/s) in the mantle wedge directly beneath the arc with local minima beneath Dominica/Martinique, Montserrat and the Grenadines. We observe that slow velocities in the wedge extend 200 km into the back arc west of Martinique. The slowest mantle wedge velocity anomaly is more muted than several global wedges, likely reflecting the lower temperatures and less partial melt predicted for the Antilles. Subducted fracture zones and plate boundaries are a potential source of hydration, since they are located nearby the anomalies, although not directly beneath them. To match our observations, geodynamic models with a broadly hydrated mantle wedge are required, which can be achieved via deep hydration of the slab, and fluid release further into the back arc. In addition, 3-D flow and melt migration or ponding are required to explain the shape and location of our anomalies. KeypointsWe image a fast slab and upper plate with slow anomalies found in the wedge beneath the central part of the arc and the backarc Low velocity wedge anomalies are associated with projected fracture zones and tectonic plate boundaries on the downgoing slab Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

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Section: Crustsupporting

confidence: 85%

Widespread Hydration of the Back Arc and the Link to Variable Hydration of the Incoming Plate in the Lesser Antilles From Rayleigh Wave Imaging

Harmon

Rychert

Goes

et al. 2021

Geochem Geophys Geosyst

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“…However, this can be explained by two main differences: (a) The anomalies in the new shear velocity model presented here are up to 1% slower than those of the previous study (Harmon et al, 2020) and (b) we used the Takei (1998) relationship between melt and velocity here, which corresponds to about a 2% velocity reduction for 0.01 melt fraction in comparison to the 7.9% reduction for 0.01 melt fraction from the work of (Hammond & Humphreys, 2000) used by Harmon et al (2020). Our melt fraction result of up to 0.04 is also consistent with the 6%-11% velocity drop with depth required by receiver functions after correcting for the maximum effect of temperature (Rychert et al, 2021), which would require melt fractions of 0.03-0.06 assuming the same melt-velocity relationship from Takei (1998) that we used here.…”

Section: Discussionsupporting

confidence: 72%

“…The Imaging the Lithosphere-Asthenosphere Boundary (I-LAB) experiments including: (a) Passive Imaging of the Lithosphere Asthenosphere Boundary (PI-LAB) experiment, (b) Experiment to Unearth the Rheological Lithosphere-Asthenosphere Boundary (EURO-LAB), and (c) the Central Atlantic Lithosphere-Asthenosphere Boundary (CA-LAB) experiment presented a unique opportunity for interpretation of MT and seismic data in order to understand the oceanic lithosphere-asthenosphere system at the equatorial Mid-Atlantic Ridge. We deployed 39 ocean bottom seismometers (OBS) and 39 ocean bottom magnetotelluric (OBMT) instruments on 0-80 Myr seafloor across the long offset Chain and Romanche as (Agius et al, 2018(Agius et al, , 2021Harmon et al, 2018Harmon et al, , 2020Hicks et al, 2020;Rychert et al, 2021;Saikia et al, 2020Saikia et al, , 2021Wang et al, 2019Wang et al, , 2020, allowing us to sample a wide seafloor age range in one experiment. The OBS and OBMT were co-located (within 1-2 km), in three lines perpendicular to the ridge (Figure 1).…”

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confidence: 99%

Shear Velocity Inversion Guided by Resistivity Structure From the PI‐LAB Experiment for Integrated Estimates of Partial Melt in the Mantle

et al. 2021

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Plate tectonic theory is predicated on the idea of a rigid lithosphere that overrides a weaker underlying asthenosphere (McKenzie & Parker, 1967), but the nature of the lithosphere-asthenosphere system remains the subject of vigorous debate. The oceanic lithosphere comprises the majority of the surface of the Earth and has the simplest evolution and history. It is classically thought to be thermally defined as a boundary layer in a simple thermal model (Parker & Oldenburg, 1973). In this model, increasing temperature with depth causes mantle rocks to weaken, creating the asthenosphere (e.g.,

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“…The method is advantageous over P-receiver functions since the Sp converted phases are free from interferences by free-surface multiples. Because of its promised feature, numerous studies have employed this method to detect LAB (Kumar et al 2005;Rychert et al 2005;Lekic et al 2011;Zhang et al 2014;Hopper et al 2020), and some of them have applied the method to the oceanbottom environment (Kawakatsu et al 2009;Kumar et al 2011;Rychert et al 2018Rychert et al , 2021Mark et al 2021). However, the effects of unconsolidated sediments at the ocean bottom on S-RF waveforms have not been fully understood yet, which is another focus of this paper.…”

Section: Yamato Basinmentioning

confidence: 99%

Lithosphere–asthenosphere boundary beneath the Sea of Japan from transdimensional inversion of S-receiver functions

Akuhara

Nakahigashi

Shinohara

et al. 2021

Earth Planets Space

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The evolution history of the Sea of Japan back-arc basin remains under debate, involving the opening of sub-basins such as the Japan and Yamato Basins. Detailed knowledge of the lithospheric structure will provide the key to understanding tectonic history. This study identifies the lithosphere–asthenosphere boundary (LAB) beneath the Sea of Japan back-arc basin using S-receiver functions (S-RFs). The study area, including the Japan and Yamato Basins, has been instrumented with broadband ocean-bottom seismometers (OBSs). S-RFs from these OBSs show negative Sp phases preceding the direct S arrivals, suggesting the LAB. The S-RFs also show abnormally reduced amplitudes. For further qualitative interpretation of these findings, we conduct transdimensional Bayesian inversion for S-wave velocity models. This less-subjective Bayesian approach clarifies that the low-velocity seafloor sediments and damped deconvolution contribute to the amplitude reduction, illuminating the necessity of such considerations for similar receiver function works. Inverted velocity structures show a sharp velocity decrease at the mantle depths, which we consider the LAB. The obtained LAB depths vary among sites: ~ 45 km beneath the Japan and Yamato Basins and ~ 70 km beneath the Yamato Rise, a bathymetric high between the two basins. The thick lithosphere beneath the Yamato Rise most likely reflects its continental origin. However, the thickness is still thin compared to that of eastern Asia, suggesting lithosphere extension by rifting. Notably, the Japan and Yamato Basins show a comparable lithospheric thickness, although the crustal thickness beneath the Yamato Basin is known to be anomalously thick. This consistency in the lithospheric thickness implies that both basins undergo similar back-arc opening processes.

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A dynamic lithosphere–asthenosphere boundary near the equatorial Mid-Atlantic Ridge

Cited by 42 publications

References 56 publications

Widespread Hydration of the Back Arc and the Link to Variable Hydration of the Incoming Plate in the Lesser Antilles From Rayleigh Wave Imaging

Widespread Hydration of the Back Arc and the Link to Variable Hydration of the Incoming Plate in the Lesser Antilles From Rayleigh Wave Imaging

Shear Velocity Inversion Guided by Resistivity Structure From the PI‐LAB Experiment for Integrated Estimates of Partial Melt in the Mantle

Lithosphere–asthenosphere boundary beneath the Sea of Japan from transdimensional inversion of S-receiver functions

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