scholarly journals The role of water in Earth's mantle

2019 ◽  
Vol 7 (1) ◽  
pp. 224-232 ◽  
Author(s):  
Eiji Ohtani
Keyword(s):  
Solid Solution ◽  
Transition Zone ◽  
Lower Mantle ◽  
Water Solubility ◽  
High Pressures ◽  
Low Velocity ◽  
The Core ◽  
Velocity Anomalies ◽  
Oceanic Sediment

Abstract Geophysical observations suggest that the transition zone is wet locally. Continental and oceanic sediment components together with the basaltic and peridotitic components might be transported and accumulated in the transition zone. Low-velocity anomalies at the upper mantle–transition zone boundary might be caused by the existence of dense hydrous magmas. Water can be carried farther into the lower mantle by the slabs. The anomalous Q and shear wave regions locating at the uppermost part of the lower mantle could be caused by the existence of fluid or wet magmas in this region because of the water-solubility contrast between the minerals in the transition zone and those in the lower mantle. δ-H solid solution AlO2H–MgSiO4H2 carries water into the lower mantle. Hydrogen-bond symmetrization exists in high-pressure hydrous phases and thus they are stable at the high pressures of the lower mantle. Thus, the δ-H solid solution in subducting slabs carries water farther into the bottom of the lower mantle. Pyrite FeO2Hx is formed due to a reaction between the core and hydrated slabs. This phase could be a candidate for the anomalous regions at the core–mantle boundary.

scholarly journals The sound velocity of wüstite at high pressures: implications for low-velocity anomalies at the base of the lower mantle

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Ryosuke Tanaka ◽  
Tatsuya Sakamaki ◽  
Eiji Ohtani ◽  
Hiroshi Fukui ◽  
Seiji Kamada ◽  
...  
Keyword(s):  
Sound Velocity ◽  
Lower Mantle ◽  
High Pressures ◽  
Low Velocity ◽  
Velocity Anomalies

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.

scholarly journals Teleseismic Tomography for Imaging the Upper Mantle Beneath Northeast China

2020 ◽  
Vol 10 (13) ◽  
pp. 4557
Author(s):  
Zhuo Jia ◽  
Gongbo Zhang
Keyword(s):  
Travel Time ◽  
Transition Zone ◽  
Upper Mantle ◽  
Northeast China ◽  
Time Data ◽  
Low Velocity ◽  
Mantle Transition Zone ◽  
Teleseismic Tomography ◽  
Travel Time Data ◽  
Velocity Anomalies

Tomographic imaging technology is a geophysical inversion method. According to the ray scanning, this method carries on the inversion calculation to the obtained information, and reconstructs the image of the parameter distribution rule of elastic wave and electromagnetic wave in the measured range, so as to delineate the structure of the geological body. In this paper, teleseismic tomography is applied by using seismic travel time data to constrain layered crustal structure where Fast Marching Methods (FMM) and the subspace method are considered as forward and inverse methods, respectively. Based on the travel time data picked up from seismic waveform data in the study region, the P-wave velocity structure beneath Northeast China down to 750 km is obtained. It can be seen that there are low-velocity anomalies penetrating the mantle transition zone under the Changbai volcano group, Jingpohu Volcano, and Arshan Volcano, and these low-velocity anomalies extend to the shallow part. In this paper, it is suggested that the Cenozoic volcanoes in Northeast China were heated by the heat source provided by the dehydration of the subducted Pacific plate and the upwelling of geothermal matter in the lower mantle. The low-velocity anomaly in the north Songliao basin does not penetrate the mantle transition zone, which may be related to mantle convection and basin delamination. According to the low-velocity anomalies widely distributed in the upper mantle and the low-velocity bodies passing through the mantle transition zone beneath the volcanoes, this study suggests that the Cenozoic volcanoes in Northeast China are kindred and have a common formation mechanism.

scholarly journals Features of the velocity structure of the mantle under the Precambrian structures on the example of the Indian platform (according to seismic tomography)

2021 ◽  
Vol 43 (1) ◽  
pp. 211-226
Author(s):  
L.N. Zaiets ◽  
I.V. Bugaienko ◽  
T.A. Tsvetkova
Keyword(s):  
Transition Zone ◽  
Seismic Tomography ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Velocity Structure ◽  
Initial Approximation ◽  
Low Velocity ◽  
Tectonic Zone ◽  
Lower Velocity ◽  
Northern Border

The paper presents additional data, approaching to understanding the driving forces in the formation of geological structures and the development of the Indian platform. The results of seismic tomography are attracted here and their analysis is presented. A 3-dimensional P-velocity model of the mantle of the Indian platform was obtained according to the Taylor approximation method developed by V. Geyko. The undeniable advantages of the method are independence from the initial approximation (reference model) and the best approximation of nonlinearity. According to the data, the mantle under the Indian platform is influenced by both plumes and fluid systems. The influence of plumes is observed in the form of low-velocity subvertical exits from the lower mantle to the transition zone; fluids — in the form of interbedding of high and low velocity anomalies from the lower mantle (or from the transition zone of the upper mantle) to the upper mantle. An analysis is presented of both general velocity structure of the platform mantle and the velocity structure of the mantle under individual cratons (Bandelkand, Singhbum, Bastar and Darvar), the totality of which forms the Indian platform and the trap provinces. At lower velocity, an area is distinguished in the mantle that corresponds to the surface of the Narmada-Son lineament moving into the Central Indian Tectonic Zone. The mantle high-velocity structures under the Deccan trap province, together with their spreading area in the transitional zone of the mantle, subdivide the platform into two parts at depths of 375 km. Areas in the mantle with inclined layers were identified and analyzed: under the cratons Bandelkand and Singbum, the Rajmahal traps and the northern border of the Deccan traps. According to the model, an area bordering the Himalayas is well distinguished in the mantle. It is shown how, when the Indian platform collides with the Eurasian margin, the upper mantle stratifies into plates capable of independent motions, including subduction.

Prominent thermal anomalies in the mantle transition zone beneath the Transantarctic Mountains

Geology ◽  
2020 ◽  
Vol 48 (7) ◽  
pp. 748-752
Author(s):  
Erica L. Emry ◽  
Andrew A. Nyblade ◽  
Alan Horton ◽  
Samantha E. Hansen ◽  
Jordi Julià ◽  
...  
Keyword(s):  
Transition Zone ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Low Velocity ◽  
Mantle Transition Zone ◽  
Thermal Anomalies ◽  
Victoria Land ◽  
Convective Thermal ◽  
Mantle Processes ◽  
Transantarctic Mountains

Abstract The Transantarctic Mountains (TAMs), Antarctica, exhibit anomalous uplift and volcanism and have been associated with regions of thermally perturbed upper mantle that may or may not be connected to lower mantle processes. To determine if the anomalous upper mantle beneath the TAMs connects to the lower mantle, we interrogate the mantle transition zone (MTZ) structure under the TAMs and adjacent parts of East Antarctica using 12,500+ detections of P-to-S conversions from the 410 and 660 km discontinuities. Our results show distinct zones of thinner-than-global-average MTZ (∼205–225 km, ∼10%–18% thinner) beneath the central TAMs and southern Victoria Land, revealing throughgoing convective thermal anomalies (i.e., mantle plumes) that connect prominent upper and lower mantle low-velocity regions. This suggests that the thermally perturbed upper mantle beneath the TAMs and Ross Island may have a lower mantle origin, which could influence patterns of volcanism and TAMs uplift.

scholarly journals Mantle Evolution of Asia Inferred from Pb Isotopic Signatures of Sources for Late Phanerozoic Volcanic Rocks

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 739
Author(s):  
Sergei Rasskazov ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Elena Saranina
Keyword(s):  
Upper Mantle ◽  
Lower Mantle ◽  
Volcanic Rocks ◽  
Solid Core ◽  
Magma Ocean ◽  
Low Velocity ◽  
Isotopic Signatures ◽  
Mantle Evolution ◽  
Mantle Sources

We present a systematic study of Pb isotope ages obtained from sources of the late Phanerozoic volcanic rocks from unstable Asia and also volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents. In the mantle sources, we have recorded events of the Early, Middle, and Late epochs of the Earth’s evolution. Evidence on the Early epoch are preserved in sources of the protolithosphere and viscous lower protomantle likely generated from the Hadean magma ocean about 4.51 and 4.44 Ga and in sources of the viscous upper mantle that acquired low µ and elevated µ (LOMU and ELMU) signatures in the early Archean (4.0–3.7 Ga). The Middle and Late epochs are denoted by sources of the viscous upper mantle that was generated, respectively, in the late Archean-Paleoproterozoic (2.9–2.6 Ga and 2.0–1.8 Ga) and in the Neoproterozoic-late Phanerozoic (0.7–0.6 Ga and < 0.25 Ga). Our results show the specific role of the mantle beneath unstable Asia in terms of globally varied µ signatures and the same mantle epochs in sources of the late Phanerozoic volcanic rocks and kimberlites from stable regions of the Siberian and Indian paleocontinents, but with high μ (HIMU) signatures that are distributed worldwide and explained by sulfide sequestration of Pb from the mantle to the core. We refer the LOMU-ELMU mantle sources to the Asian high-velocity lower mantle domain and propose that the HIMU generating processes were focused mainly in the South Pacific and African low-velocity lower mantle domains in the Middle Mantle Epoch of the Earth’s evolution due to influence of the unbalanced solid core.

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