scholarly journals CaSiO3 perovskite in diamond indicates the recycling of oceanic crust into the lower mantle

Nature ◽  
2018 ◽  
Vol 555 (7695) ◽  
pp. 237-241 ◽  
Author(s):  
F. Nestola ◽  
N. Korolev ◽  
M. Kopylova ◽  
N. Rotiroti ◽  
D. G. Pearson ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Lower Mantle ◽  
Casio3 Perovskite

scholarly journals Seismic scatterers in the lower mantle near subduction zones

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S2-S20 ◽  
Author(s):  
Satoshi Kaneshima
Keyword(s):  
Oceanic Crust ◽  
Lower Mantle ◽  
Subduction Zones ◽  
P Waves ◽  
Waveform Data ◽  
Basaltic Rocks ◽  
Short Period ◽  
Subducted Oceanic Crust ◽  
Conversion Depth ◽  
Seismic Networks

SUMMARY We investigate the global distribution of S-to-P scatterers in the shallow to mid-lower mantle beneath subduction zones, where deep seismicity extends down to the bottom of the upper mantle. By array processing broadband and short period waveform data obtained at seismic networks, we seek anomalous later phases in the P coda within about 15–150 s after direct P waves. The later phases usually arrive along off-great circle paths and significantly later than S-to-P conversion from the ‘660 km’ discontinuity, often show positive slowness anomalies relative to direct P, and do not show a conversion depth that is consistent among nearby events. They are thus adequately regarded as scattered waves, rather than conversion at a global horizontal discontinuity. The S-to-P scattered waves often show amplitudes comparable to ‘S660P’ waves, which indicates that a spatial change in elastic properties by several percent occurs at the scatterers as abruptly as the post-spinel transformation and should arise from compositional heterogeneity. We locate prominent S-to-P scatterers beneath Pacific subduction zones and beneath southern Spain. Nearly half of 137 S-to-P scatterers located in this study and previous studies by the authors are shallower than 1000 km, and the number of scatterers decreases with depth. Scatterers deeper than 1800 km are rare and mostly weak. We examine relations between the locations of the scatterers and recently subducted slabs inferred from seismic tomography. The scatterers of mid-mantle depths, deeper than about 1000 km, are located distant from tomographic slabs. On the other hand, the majority of shallower scatterers are located beneath the slabs rather than near their fastest portions, which would indicate that chemically heterogeneous materials are not extensively entrained within thickened and folded slabs when the slabs impinge on the lower mantle. We also find scatterers near the locations where basaltic rocks of recently subducted oceanic crust are expected to exist, which suggests that oceanic crust is not delaminating when slabs impinge on the lower mantle.

scholarly journals Velocity and density characteristics of subducted oceanic crust and the origin of lower-mantle heterogeneities

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenzhong Wang ◽  
Yinhan Xu ◽  
Daoyuan Sun ◽  
Sidao Ni ◽  
Renata Wentzcovitch ◽  
...  
Keyword(s):  
Phase Transition ◽  
Oceanic Crust ◽  
Seismic Tomography ◽  
Lower Mantle ◽  
Shear Velocity ◽  
Calcium Ferrite ◽  
Velocity Anomaly ◽  
Mantle Heterogeneities ◽  
Subducted Oceanic Crust ◽  
Low Shear

AbstractSeismic heterogeneities detected in the lower mantle were proposed to be related to subducted oceanic crust. However, the velocity and density of subducted oceanic crust at lower-mantle conditions remain unknown. Here, we report ab initio results for the elastic properties of calcium ferrite‐type phases and determine the velocities and density of oceanic crust along different mantle geotherms. We find that the subducted oceanic crust shows a large negative shear velocity anomaly at the phase boundary between stishovite and CaCl2-type silica, which is highly consistent with the feature of mid-mantle scatterers. After this phase transition in silica, subducted oceanic crust will be visible as high-velocity heterogeneities as imaged by seismic tomography. This study suggests that the presence of subducted oceanic crust could provide good explanations for some lower-mantle seismic heterogeneities with different length scales except large low shear velocity provinces (LLSVPs).

scholarly journals Confirming a pyrolitic lower mantle using self-consistent pressure scales and new constraints on CaSiO3 perovskite

2016 ◽  
Vol 121 (7) ◽  
pp. 4876-4894 ◽  
Author(s):  
Ningyu Sun ◽  
Zhu Mao ◽  
Shuai Yan ◽  
Xiang Wu ◽  
Vitali B. Prakapenka ◽  
...  
Keyword(s):  
Lower Mantle ◽  
Self Consistent ◽  
Casio3 Perovskite

scholarly journals Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth’s lower mantle

Nature ◽  
2019 ◽  
Vol 572 (7771) ◽  
pp. 643-647 ◽  
Author(s):  
A. R. Thomson ◽  
W. A. Crichton ◽  
J. P. Brodholt ◽  
I. G. Wood ◽  
N. C. Siersch ◽  
...  
Keyword(s):  
Lower Mantle ◽  
Seismic Velocities ◽  
Casio3 Perovskite

scholarly journals Author Correction: Velocity and density characteristics of subducted oceanic crust and the origin of lower-mantle heterogeneities

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenzhong Wang ◽  
Yinhan Xu ◽  
Daoyuan Sun ◽  
Sidao Ni ◽  
Renata Wentzcovitch ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Lower Mantle ◽  
Mantle Heterogeneities ◽  
Subducted Oceanic Crust

Super-deep diamond from Central African Republic

2020 ◽  
Author(s):  
Sofia Lorenzon ◽  
Fabrizio Nestola ◽  
Steven Jacobsen ◽  
Thomassot Emilie ◽  
Prosperi Loredana ◽  
...  
Keyword(s):  
Transition Zone ◽  
Oceanic Crust ◽  
Lower Mantle ◽  
Central African Republic ◽  
Isotope Composition ◽  
Heavy Isotope ◽  
Aggregation State ◽  
Mineral Inclusions ◽  
C And N ◽  
The One

<p><strong>Key-words: </strong>Super-deep diamond, Central African Republic, hydrous ringwoodite, Insitu C- and N- isotope composition, subduction, N aggregation state.</p><p>Diamonds and their inclusions are key geological materials that provide a unique opportunity to directly investigate the deepest regions of our planet.</p><p>Based on their formation depth, diamonds are classified in lithospheric, which formed between about 120 and 220 km depth and represent about 99% of worldwide diamond population, and sub-lithospheric or super-deep diamonds, extremely rare samples which crystallized from about 300 to more than 800 km depth (Stachel et al., 2008).</p><p>Here, we have investigated a 1.3 carats diamond, Type IaAB (determined by FTIR), from an alluvial deposit located in Central African Republic, close to the Ubangy River. As far as we know, this is the first study dedicated to inclusions in diamonds from this country.</p><p>The investigated diamond contains the second world finding of hydrous ringwoodite after the one found within a Brazilian diamond by Pearson et al. (2014). This finding indicates that our diamond is certainly a super-deep diamond coming from the lower part of the transition zone (between 525 and 660 km depth). Carbon isotope composition of the host diamond (δ<sup>13</sup>C<sub>mean</sub> = -2.2 ± 0.3 ‰, n=16, analytical error = 0.3‰ (2σ)) is significantly enriched in heavy isotope when compare to the canonical mantle value (δ<sup>13</sup>C = -5‰). It is nitrogen poor (N < 44 ± 23 at.p.p.m., mean = 15 at p.p.m.) and partially aggregated (%B= 88.5 %). For N content greater that our analytical precision (23 p.p.m.) we performed N-isotope measurement and the values, although associated to large analytical uncertainties, are all positive, (d<sup>15</sup>N = 3.48 ± 3.5 ‰) and significantly enriched in heavy isotope compare with the mantle values (-5‰). These geochemical signatures are similar with those previously found in super-deep diamonds (Stachel et al., 2002). These data are consistent with a diamond forming fluid originating from a N-poor subducted source, such as carbonates, (e.g. Walter et al., 2011), in agreement with studies reporting transition-zone and lower-mantle diamonds (Nestola et al., 2018).</p><p> </p><p><strong>References</strong></p><p> </p><p>Nestola F., Korolev N., Kopylova M., Rotiroti N., Pearson D.G., Pamato M.G., Alvaro M., Peruzzo L., Gurney J.J., Moore A.M. & Davidson J. 2018. CaSiO<sub>3</sub> perovskite in diamond indicates the recycling of oceanic crust into the lower mantle. Nature, 555, 237-241.</p><p>Pearson D.G., Brenker F.E., Nestola F., McNeill J., Nasdala L., Hutchison M.T., Matveev S., Mather K., Silversmith G., Schmitz S., Vekemans B. & Vincze L. 2014. Hydrous mantle transition zone indicated by ringwoodite included within diamond. Nature, 507, 221-224.</p><p>Stachel T., Harris J.W., Aulbach S. & Deines P. 2002. Kankan diamonds (Guinea) III: δ<sup>13</sup>C and nitrogen characteristics of deep diamonds. Contrib. Mineral. Petrol., 142, 465-475.</p><p>Stachel T. & Harris J.W. 2008. The origin of cratonic diamonds -Constraints from mineral inclusions. Ore Geol. Rev., 34, 5-32.</p><p>Walter M.J., Kohn S.C., Araujo D., Bulanova J.P., Smith C.B., Gaillou E., Wang J., Steele A. & Shirey S.B. 2011. Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions. Science, 334, 54-57.</p><p> </p><p> </p>

scholarly journals Hydrous SiO2 in subducted oceanic crust and water transport to the core-mantle boundary

2020 ◽  
Author(s):  
Yanhao Lin ◽  
Qingyang Hu ◽  
Jing Yang ◽  
Yue Meng ◽  
Yukai Zhuang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Mantle ◽  
Oceanic Lithosphere ◽  
Low Velocity ◽  
Water Storage Capacity ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Subducted Oceanic Crust

Abstract Subduction of oceanic lithosphere transports surface water into the mantle where it can have remarkable effects, but how much can be cycled down into the deep mantle, and potentially to the core, remains ambiguous. Recent studies show that dense SiO2 in the form of stishovite, a major phase in subducted oceanic crust at depths greater than ~300 km, has the potential to host and carry water into the lower mantle. We investigate the hydration of stishovite and its higher-pressure polymorphs, CaCl2-type SiO2 and seifertite, in experiments at pressures of 44–152 GPa and temperatures of ~1380–3300 K. We quantify the water storage capacity of these dense SiO2 phases at high pressure and find that water stabilizes CaCl2-type SiO2 to pressures beyond the base of the mantle. We parametrize the P-T dependence of water capacity and model H2O storage in SiO2 along a lower mantle geotherm. Dehydration of slab mantle in cooler slabs in the transition zone can release fluids that hydrate stishovite in oceanic crust. Hydrous SiO2 phases are stable along a geotherm and progressively dehydrate with depth, potentially causing partial melting or silica enrichment in the lower mantle. Oceanic crust can transport ~0.2 wt% water to the core-mantle boundary region where, upon heating, it can initiate partial melting and react with the core to produce iron hydrides, providing plausible explanations for ultra-low velocity regions at the base of the mantle.

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