Skip to main content

Main menu

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
    • Front Matter Portal
    • Journal Club
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses
  • Submit
  • Submit
  • About
    • Editorial Board
    • PNAS Staff
    • FAQ
    • Accessibility Statement
    • Rights and Permissions
    • Site Map
  • Contact
  • Journal Club
  • Subscribe
    • Subscription Rates
    • Subscriptions FAQ
    • Open Access
    • Recommend PNAS to Your Librarian

User menu

  • Log in
  • My Cart

Search

  • Advanced search
Home
Home
  • Log in
  • My Cart

Advanced Search

  • Home
  • Articles
    • Current
    • Special Feature Articles - Most Recent
    • Special Features
    • Colloquia
    • Collected Articles
    • PNAS Classics
    • List of Issues
  • Front Matter
    • Front Matter Portal
    • Journal Club
  • News
    • For the Press
    • This Week In PNAS
    • PNAS in the News
  • Podcasts
  • Authors
    • Information for Authors
    • Editorial and Journal Policies
    • Submission Procedures
    • Fees and Licenses
  • Submit
Research Article

Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle

Yanhao Lin, Qingyang Hu, Yue Meng, Michael Walter, and Ho-Kwang Mao
  1. aGeophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015;
  2. bCenter for High Pressure Science and Technology Advanced Research, Shanghai 201203, People’s Republic of China;
  3. cHigh-Pressure Collaborative Access Team (HPCAT), X-Ray Science Division, Argonne National Laboratory, Lemont, IL 60439

See allHide authors and affiliations

PNAS January 7, 2020 117 (1) 184-189; first published December 16, 2019; https://doi.org/10.1073/pnas.1914295117
Yanhao Lin
aGeophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: yhlin@carnegiescience.edu qingyang.hu@hpstar.ac.cn maohk@hpstar.ac.cn
Qingyang Hu
bCenter for High Pressure Science and Technology Advanced Research, Shanghai 201203, People’s Republic of China;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: yhlin@carnegiescience.edu qingyang.hu@hpstar.ac.cn maohk@hpstar.ac.cn
Yue Meng
cHigh-Pressure Collaborative Access Team (HPCAT), X-Ray Science Division, Argonne National Laboratory, Lemont, IL 60439
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Michael Walter
aGeophysical Laboratory, Carnegie Institution for Science, Washington, DC 20015;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Ho-Kwang Mao
bCenter for High Pressure Science and Technology Advanced Research, Shanghai 201203, People’s Republic of China;
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: yhlin@carnegiescience.edu qingyang.hu@hpstar.ac.cn maohk@hpstar.ac.cn
  1. Contributed by Ho-Kwang Mao, November 20, 2019 (sent for review August 19, 2019; reviewed by Arianna E. Gleason and Jin S. Zhang)

  • Article
  • Figures & SI
  • Info & Metrics
  • PDF
Loading

Significance

The great abundance of water on Earth’s surface makes it different from other terrestrial planets, and it may be linked to a deep interior water cycle. How water is transported into Earth’s deep interior and in which phases it is held are still a matter of much debate. Stishovite is known as a major component of subducted oceanic basalt, and recent experiments have reported that it can incorporate significant amounts of water in its crystal structure. Here, we show that, at the pressure–temperature conditions of a mantle geotherm, stishovite may be a key phase for transporting water into the deep mantle, providing important information on the water cycle in the deep earth.

Abstract

The distribution and transportation of water in Earth’s interior depends on the stability of water-bearing phases. The transition zone in Earth’s mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H2O in their structures at mantle temperatures. The extent to which water can be transported beyond the transition zone deeper into the mantle depends on the water carrying capacity of minerals stable in subducted lithosphere. Stishovite is one of the major mineral components in subducting oceanic crust, yet the capacity of stishovite to incorporate water beyond at lower mantle conditions remains speculative. In this study, we combine in situ laser heating with synchrotron X-ray diffraction to show that the unit cell volume of stishovite synthesized under hydrous conditions is ∼2.3 to 5.0% greater than that of anhydrous stishovite at pressures of ∼27 to 58 GPa and temperatures of 1,240 to 1,835 K. Our results indicate that stishovite, even at temperatures along a mantle geotherm, can potentially incorporate weight percent levels of H2O in its crystal structure and has the potential to be a key phase for transporting and storing water in the lower mantle.

  • ultrahydrous stishovite
  • water transporting
  • deep mantle
  • high pressure–temperature

Liquid water covering Earth’s surface is a unique feature among the terrestrial planets. Plate tectonics, through the continuous subduction of rocks that have interacted with the surface hydrosphere, may regulate surface water through a deep water cycle that involves mineral phases capable of storing water at the high-pressure and -temperature conditions of Earth’s mantle. The presence of water in the mantle can affect significantly the chemical and physical properties of the rock-forming minerals, including mineral phase relations, melting temperatures, rheological properties, electrical conductivity, and seismic velocities (1⇓⇓⇓⇓⇓⇓⇓–9). Water transport and storage in the mantle may also regulate the surface water reservoir over geological time through a deep water cycle.

Water is transported into the mantle at subduction zones in hydrous phases (10⇓⇓–13), in nominally anhydrous minerals (14⇓⇓⇓–18), or as a fluid captured in disconnected interstitial patches in mantle rocks (19). In basaltic oceanic crust and sediment, hydrous phases destabilize at the temperatures of the slab top during subduction with models indicating nearly complete dehydration by ∼200 km (20), leading to melting in the mantle wedge that produces primary arc magmas with an average of ∼4 wt % H2O (21). Hydrous phases (e.g., serpentine, chlorite, clinohumite, chondrodite) and dense hydrous magnesium silicates (DHMSs; DHMS phases: Phase A, superhydrous B, D, and H) that are stable in the peridotitic portion of the lithosphere can potentially transport significant quantities of water into the deeper mantle in colder subducting slabs but are predicted to destabilize either within the transition zone or on entry into the lower mantle, and they are certainly not stable at the temperatures of the mantle geotherm (11, 13, 22, 23). This deeper mantle dehydration of the slab perhaps makes the transition zone the largest potential reservoir for water in Earth’s mantle because its main constituent minerals, wadsleyite and ringwoodite, can incorporate up to ∼1 to 1.5 wt % H2O in their structures at mantle temperature (24).

The potential for water to be transported and remain stable in minerals in the deeper, lower mantle will depend on the capacity of nominally anhydrous minerals to incorporate water into their structures. Here, we focus on the mineral stishovite, a high-pressure polymorph of silica (SiO2) that is a major component of subducted oceanic crust (∼23% by volume) (25, 26). Up to ∼9 GPa (∼300 km), all forms of silica, like quartz, are built up of SiO4 tetrahedra, with coesite being the highest-pressure polymorph of this type. At higher pressures, stishovite, a tetragonal phase with a rutile structure (P42/mnm) and with silicon in octahedral coordination with oxygen, is stable up to ∼70 GPa along a mantle geotherm, where it transforms through a second-order displacive phase transition to an orthorhombic CaCl2-structured phase (27⇓–29). Recent high-pressure experiments have shown up to ∼3.2 wt % H2O in stishovite synthesized at ∼10 GPa and 723 K (18, 30), a temperature far too low to be appropriate for Earth’s mantle. If such quantities of water can be accommodated at higher pressures and temperatures, stishovite may become a potentially important phase for subducting water into the deeper mantle. Here, we investigate whether such large amounts of water can be accommodated by stishovite at high temperatures and pressures appropriate for the mantle beyond the transition zone (∼27 to 58 GPa and ∼1,240 to 1,835 K).

Results and Discussion

The starting material for our experiments was a mixture of amorphous SiO2 and goethite (α-FeOOH) in the molar ratio of 4:1, with goethite serving as a source of water. About 2 wt % Pt black powder was added to the mixture for infrared laser absorption in laser-heating experiment (Methods has more details). The sample assembly consisted of the SiO2–goethite mixture sandwiched between 2 layers of amorphous SiO2 (Methods). The sample was first compressed to ∼30 GPa (Run 1) at room temperature. We used both ruby and Pt as internal pressure standards (Methods has details). The sample was then heated using a double-sided laser system and held at target temperatures for ∼10 min each: 1,240 K at 32.5 GPa (27 GPa), 1,450 K at 33.1 GPa (34 GPa), and 1,775 K at 34 GPa (37 GPa), where Pt pressures are in parentheses. In situ X-ray diffraction (XRD) spectra were acquired at each pressure and temperature condition and also, after quenching to ambient temperature. Subsequently, the sample was compressed to 39 GPa (Run 2) at room temperature and then heated in a different location to temperatures of 1,310 K at 48.3 GPa (37 GPa), 1,410 K at 49 GPa (52 GPa), and 1,835 K at 52 GPa (58 GPa). The diffraction data show that our heated sample was dominated by stishovite with a minor amount of Fe2O3 and FeOOH in the high-pressure ε phase (Fig. 1). At high pressure and 300 K, we find that sharp diffraction lines agree well with the expected diffraction pattern of anhydrous stishovite (31), except that they are systematically shifted to higher d spacings. Unit cell parameters acquired at 300 K and high pressure are summarized in Fig. 2 and Table 1. The much larger volumes of stishovite synthesized under hydrous conditions relative to volumes of anhydrous stishovite calculated from its equation of state at the same pressures (29, 31, 32) provide primary evidence for considerable hydration.

Fig. 1.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 1.

XRD patterns at 34 and 52 GPa (ruby pressures) and 300 K after laser heating. At the center of the heated area, the majority of diffraction peaks belong to stishovite. The transition from stishovite to CaCl2-type SiO2 was not observed in our experiment. Data were acquired using an X-ray wavelength of 0.4066 Å.

Fig. 2.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 2.

Measured stishovite unit cell volumes at high pressure and 300 K. Solid squares (Run 1) and solid circles (Run 2) show pressure based on the ruby pressure calibration [the error bar based on stress anisotropy (51)], whereas open squares and open circles show pressure based on the Pt pressure calibration (the error bar of ±2 GPa). The solid black curve shows the equation of state for anhydrous stishovite of Andrault et al. (31). The solid green curve shows the equation of state of stishovite with 3.2 wt % H2O from Nisr et al. (34). The dashed green line is an estimated equation of state for stishovite with 10 wt % H2O on the basis of a linear extrapolation of the bulk moduli for the anhydrous stishovite and stishovite with 3.2% H2O (31, 34). The decompression data are shown in SI Appendix, Fig. S3.

View this table:
  • View inline
  • View popup
Table 1.

Summary of experimental results

Spektor et al. (18, 33) and Nisr et al. (30) reported on the synthesis of hydrous Al-free stishovite samples grown at 9 and 10 GPa under hydrothermal, low-temperature conditions (350 °C to 550 °C). The water content of their samples was calibrated based on thermogravimetric analysis and secondary ion mass spectrometry, with reported water contents of up to 3.2 wt % H2O. These authors suggest H incorporation into SiO2 through an octahedral “hydrogarnet”-type defect mechanism with hydroxyl groups around a silicon vacancy, equivalent to direct cation substitution of the form 4H+ → Si4+ (18, 30). Spektor et al. (33) provided a calibration for the water content of stishovite on the basis of the observed volume change relative to anhydrous stishovite in samples quenched to 1 bar and 300 K. To make an initial estimate of the water content in our samples, we assume that the slope of the observed linear relationship at 1 bar is constant with pressure and use the equation of state of Andrault et al. (31) to determine the volume of anhydrous stishovite at high pressure. On this basis, the changes in unit cell volume observed in our study would indicate about 4.5 to 10 wt % H2O in stishovite at high pressure (Table 1). However, this approach may not be reliable if the compression behaviors of hydrous and anhydrous stishovite are different. Nisr et al. (34) measured the equation of state of hydrous stishovite with ∼3.2 wt % H2O, which is shown relative to the equation of state of anhydrous stishovite on Fig. 2. The higher compressibility of hydrous stishovite indicates that the change in volume at higher pressures with the addition of H2O is expected to be less than at 1 bar as shown in Fig. 2. Thus, our estimates based on the 1-bar data would be minimal. On the basis of a linear extrapolation of the difference in observed bulk moduli from these studies (31, 34) to higher water contents, our samples could contain as much as 10 wt % or more H2O (Fig. 2).

When using the ruby pressure calibration, where the ruby was off center to the heated area, the results apparently indicate that the water contents in stishovite are very high (e.g., 10 wt % H2O or more) but decrease systematically with temperature. However, when using the Pt pressure calibration, where the Pt is in the same location as the X-ray spot, the data fan out nearly parallel to a compression curve, possibly indicating synthesis of stishovite with a relatively constant but still very high water content (Table 1). The remarkably high water content predicted for our stishovite samples based on the volume change may be explicable when considering that other rutile-structured high-pressure hydrous phases, like δ-AlOOH and Phase H (MgSiH2O4), contain ∼15 wt % H2O in their structures. We note that Phase H becomes stable at ∼35 to 40 GPa in the MgO–SiO2–H2O system at the temperatures in our study (13). Whether or not the stishovite we observe is a fully hydrated stoichiometric phase or a high but limited solid solution remains an open question that we cannot address further with our data.

The extremely high amounts of water estimated for the stishovite samples in this study based on their expanded unit cell volumes are much higher than observed in any previous study (summarized in SI Appendix, Table S1). For example, the stishovite samples synthesized at ∼9 to 10 GPa and 723 K by Spektor et al. (18) (∼1.3 wt %) and Nisr et al. (30) (∼3.2 wt %) and at 15 GPa and 1,500 °C by Bolfan-Casanova et al. (14) (72 ppm) in the pure SiO2 system have much lower water contents, especially at high temperature. Previous results have indicated that the incorporation of alumina (<2.3 wt % Al) in stishovite promotes the substitution of water in stishovite through the cation substitution mechanism (Al3+ + H+ → Si4+), which includes the Al-bearing stishovites synthesized at 10 GPa and 1,200 °C by Pawley et al. (35) (82 ppm for 1.51 wt % Al2O3), 15 GPa and 1,400 °C by Chung and Kagi (36) (844 ppm for 1.32 wt % Al2O3), ∼32 GPa and 2,577 °C by Panero et al. (37) (∼460 ppm for 3 wt % Al2O3), and 20 GPa and 1,400 °C by Litasov et al. (17) (3,010 ppm for 4.4 wt % Al2O3).

Stishovite is not expected to be a stable phase in peridotite bulk compositions either in ambient mantle or in the mantle portion of subducted lithosphere (14, 38, 39). However, in subducted basaltic compositions, like midocean ridge basalt (MORB), stishovite becomes a modally abundant phase at transition zone depths where it coexists with majorite garnet. At lower mantle conditions, stishovite comprises ∼23 modal % in MORB, coexisting with aluminous bridgmanite (∼22 modal %), Na–Al phase phase (∼35 modal %), and Ca–ferrite-structured phase (∼20 modal %) (17). Among these nominally anhydrous phases in basaltic compositions at lower mantle pressures, stishovite stands out as a phase that can potentially contain a large amount of water while remaining stable along the mantle geotherm. In contrast, bridgmanite can accommodate perhaps 2 orders of magnitude less water (∼1,000 ppm water) (40), and there are no data on the water storage capacities of the Na–Al phase and Ca–ferrite phases.

Dense hydrous phases can also potentially be stable in basaltic compositions, like Phase D in the transition zone and upper lower mantle or Phase H in the midlower mantle to the base of the mantle (15). However, these phases are not stable along a mantle geotherm and would only stabilize at lower temperatures in cold slabs after the nominally anhydrous phases, like stishovite in oceanic crust, exceed their storage capacity (13). Because of its potential to store exceptionally large amounts of water at high temperatures, stishovite is potentially the most important host of water in basaltic compositions in the transition zone and lower mantle.

Subducted oceanic crust is considered to be largely dehydrated in the upper mantle (20). However, water may be subducted into the transition zone in the peridotitic lithosphere in postserpentine dense hydrous phases, like Phase A, superhydrous Phase B, or Phase D (41). These phases may break down in the transition zone if subducting lithosphere founders and heats up. The discovery of hydrous ringwoodite as an inclusion in “superdeep” diamond (42) as well as boron-rich diamonds originating from around 700-km depth (43) indicates that at least locally water-enriched regions of diamond formation may be linked to slab dehydration. Furthermore, seismic velocity anomalies observed in the uppermost lower mantle have been ostensibly attributed to the melting caused by dehydration of hydrous ringwoodite when it breaks down to nominally anhydrous bridgmanite and ferropericlase (6) or alternatively, due to melting caused by breakdown of Phase D or Phase H (13). These observations indicating release of water from subducted lithosphere via dehydration or hydrous melting also suggest that stishovite, even if it were effectively anhydrous in oceanic crust that had previously dehydrated, could become an important carrier for water into the lower mantle on rehydration (Fig. 3).

Fig. 3.
  • Download figure
  • Open in new tab
  • Download powerpoint
Fig. 3.

Transporting water into the lower mantle by ultrahydrous SiO2. Dehydration of basaltic crust produces melting in the mantle wedge beneath island arcs and effectively dehydrates the crust. However, colder slabs may transport water in subducted mantle lithosphere to transition zone depths where dehydration occurs. Infiltration of fluids or melts through the crust may rehydrate stishovite in the crust to form ultrahydrous stishovite, which can then be transported into the deep lower mantle.

Water or hydrous melts from dehydration of ringwoodite or dense hydrous silicates in peridotitic subducted lithosphere in the transition zone or the upper lower mantle may infiltrate subducted basaltic oceanic crust where they can be accommodated in hydrous stishovite. With further subduction into the lower mantle, stishovite would remain stable, even if the slab heats up to the mantle geotherm. Stishovite undergoes a transition to CaCl2-structered phase at ∼70 GPa along a mantle geotherm, and it is not known if this phase can also accommodate abundant water (28). In addition, Lakshtanov et al. (5) suggested that the rutile–CaCl2 transition pressure in stishovite with ∼5 wt % Al2O3 can be as low as ∼24 GPa. However, as the transition is second order resulting from a small distortion of the unit cell from tetragonal to orthorhombic with only a minor volume change (44), we predict it may also accommodate significant H through protonation.

As a modally abundant phase in subducted oceanic crust, stishovite has the potential to transport a significant quantity of water into the deep mantle. Assuming current values for the average subduction rate (5 cm y−1), length of subduction zones (46,000 km), and crustal thickness (6 km) (37), we estimate that, for an abundance of 23% in a subducted MORB, 4.6 × 1022 kg of stishovite would be subducted into the deep mantle per year. Although we cannot constrain the water content in deeply subducted oceanic crust, with the addition of each 1 wt % H2O to stishovite, subducted oceanic crust could transport ∼1011 kg of water per year into the deep mantle. To put that quantity into perspective, current estimates for the water content of the mantle are about 0.75 oceans masses based on geochemical arguments (45) or about 1021 kg. This entire quantity of water could be transported to the mantle by stishovite over 4 billion y of subduction if the average stishovite water content was ∼2 wt %. If water in stishovite is partially released during the transportation, stishovite is requested to contain water more than ∼2 wt % at the start to reach the geochemical estimation (45).

In conclusion, our results indicate that stishovite can accommodate weight percent levels of water in its structure. As a modally abundant phase in subducted oceanic crust, stishovite is a potential carrier of significant quantities of water into the deep earth even at the high temperatures along a mantle geotherm. Our results have not yet quantified precisely the storage capacity of water in stishovite in oceanic crustal assemblages, and more work is needed to understand how water partitions among coexisting phases as well as the thermodynamic and physical properties of hydrous stishovite (e.g., seismic velocities) as a function of temperature, pressure, and minor element concentrations (Al3+, Fe3+).

Methods

Starting Materials and Experimental Design.

A mixture of SiO2 (amorphous, 1-μm grain size, purity 99.999%), FeOOH (goethite), and Pt black were ground in a ball mill for 1.5 h. The starting material was cold pressed into a thin foil ∼60 × 60 μm2 in size and ∼10 μm in thickness. The sample foil was loaded in a 150-μm-diameter hole in a rhenium gasket indented by diamond anvils with 200-μm culet diameter and embedded between 2 layers of SiO2 that served as a thermal insulator and solid pressure medium in a symmetric diamond-anvil cell (46). We loaded a ruby chip peripheral to the sample on the cylinder side that was used as a pressure calibrant. Samples were heated in a double-sided laser-heated diamond-anvil cell and examined in situ at high pressures and temperatures by synchrotron X-ray powder diffraction at beamline 16-IDB of the Advanced Photon Source, Argonne National Laboratory (47). The X-ray beam size was 4.8 × 5.3 μm2 with a wavelength of 0.4066 Å. For laser heating, the diameter of a laser-heating spot was up to ∼40 μm at ∼1,800 K in the flat top area created with a focused yttrium lithium fluoride laser using a double-sided heating technique that minimizes both radial and axial temperature gradients. Temperatures were determined by fitting the thermal radiation from the central portion of the heated spot to the Planck radiation function (48). The unit cell is calculated by indexing the 110, 101, 111, 210, and 211 diffraction peaks of stishovite by a nonlinear fitting program (details are in SI Appendix, Table S2) (49). Pressures were determined before and after heating using the calibrated ruby fluorescence line shift in an offline ruby system and in situ using the Pt pressure calibration (50). Because the Pt peaks were relatively weak due to the small amount of Pt in the starting material, here we report both the ruby and Pt pressures.

Pressure Uncertainty.

The precision in measuring the ruby pressure is estimated to be ±0.5 GPa, whereas for Pt pressures, uncertainty is estimated to be of the order 1 to 2 GPa due to the weak nature of the Pt peaks. Another source of pressure uncertainty is nonhydrostatic stress, which also can affect the measurement of stishovite unit cell volumes. As the ruby pressures are measured away from the heated spot, they may be subject to errors introduced by the stress gradient across the sample. Pt pressures are measured at the place where diffraction is taken and therefore, are more reliably linked to the stishovite unit cell volumes. We performed XRD mapping over the sample after the final heating to estimate the pressure gradient. In an XRD pattern taken close to the heating spot (SI Appendix, Fig. S1), the Pt pressure is about 6 GPa higher than the ruby pressure, but this difference varied systematically in the 2 runs as a function of temperature (Fig. 2). The variations in the pressure range in Runs 1 and 2 are 27 to 37 and 43 to 58 GPa, respectively, with pressure increasing after each heating. For stishovite, differential stress results from both the intrinsic lattice anisotropy and the nonhydrostatic conditions. The former is directly related to the tetragonal unit cell of stishovite and was previously quantified by a radial XRD, which showed that the differential stress is ∼4.5 GPa below 40 GPa and sharply decreases as it approaches 50 GPa (51).

Analytical Techniques.

The diamond anvil cell (DAC) samples, after heated, were prepared for electron microprobe analysis (EMPA) using a focused ion beam (FIB; 30 kV, Ga+ ions, Auriga; Zeiss Instruments) at the Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, which follows the method of ref. 52. Nano- to milliscale milling from the edge of the DAC sample to the heated spot until the quenched silicate phase (stishovite) was exposed and surrounded by iron oxide. A smooth and flat surface was prepared using a 2-nA beam for chemical composition analysis and energy-dispersive spectroscopy mapping. Experimental run products were polished by an FIB for back-scattered electron imagery used to assess the texture and mineralogy (SI Appendix, Fig. S2) and then, Ir coated for EMPA. The heating spots of the samples were analyzed by using a JEOL 8530F field emission microprobe at the Geophysical Laboratory, Carnegie Institution for Science. We used 2 different focused beams of 1- and 2-μm diameters for the silicate phase and iron oxide and for the unheated area, respectively. Analyses were done using an accelerating voltage of 15 kV and a beam current of 20 nA. Analyses were calibrated against primary standards of enstatite glass (Si) and basalt 812 glass (Fe). Compositions of the silicate phase and iron oxide (contained within and surrounding each heating spot) reported here are based on 1 to 7 analyses per phase. The EMPA data of DAC samples are shown in SI Appendix, Table S3.

Data Availability.

The authors declare that all relevant data supporting this study are available within the paper and SI Appendix or available on request from the corresponding authors.

Acknowledgments

We acknowledge Jinfu Shu, Emma Bullock, Suzy Vitale, Lili Zhang, Dongzhou Zhang, and Jingui Xu for experimental assistance and measurements help. This work was performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory (ANL). HPCAT operations are supported by the Department of Energy (DOE) National Nuclear Security Administration (NNSA)’s Office of Experimental Sciences. The APS is a US DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. XRD measurements were performed at the 16ID-B of HPCAT and 13BM-C of GeoSoilEnviroCARS (GSECARS), APS, ANL; the 13BM-C operation is supported by Consortium for Materials Properties Research in Earth Sciences through the Partnership for Extreme Crystallography project under NSF Cooperative Agreement EAR 11-57758. Y.L. and H.-K.M. are supported by NSF Grant EAR-1722515. The Center for High Pressure Science and Technology Advanced Research is supported by National Science Foundation of China Grants U1530402 and U1930401. Part of the experiment was performed at the BL15U1 beamline, Shanghai Synchrotron Radiation Facility in China.

Footnotes

  • ↵1To whom correspondence may be addressed. Email: yhlin{at}carnegiescience.edu, qingyang.hu{at}hpstar.ac.cn, or maohk{at}hpstar.ac.cn.
  • Author contributions: Y.L., Q.H., M.W., and H.-K.M. designed research; Y.L., Q.H., Y.M., M.W., and H.-K.M. performed research; Y.L., Q.H., Y.M., and M.W. analyzed data; and Y.L., Q.H., M.W., and H.-K.M. wrote the paper.

  • Reviewers: A.E.G., SLAC National Accelerator Laboratory; and J.S.Z., University of New Mexico.

  • The authors declare no competing interest.

  • This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1914295117/-/DCSupplemental.

Published under the PNAS license.

References

  1. ↵
    1. T. Inoue
    , Effect of water on melting phase relations and melt composition in the system Mg2SiO4–MgSiO3–H2O up to 15 GPa. Phys. Earth Planet. Inter. 85, 237–263 (1994).
    OpenUrl
  2. ↵
    1. S. Karato,
    2. M. S. Paterson,
    3. J. D. FitzGerald
    , Reology of synthetic olivine aggregates: Influence of grain size and water. J. Geophys. Res. 91, 8151–8176 (1986).
    OpenUrl
  3. ↵
    1. Y. Lin,
    2. E. J. Tronche,
    3. E. S. Steenstra,
    4. W. van Westrenen
    , Evidence for an early wet Moon from experimental crystallization of the lunar magma ocean. Nat. Geosci. 10, 14–18 (2017).
    OpenUrl
  4. ↵
    1. T. Yoshino,
    2. T. Matsuzaki,
    3. S. Yamashita,
    4. T. Katsura
    , Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere. Nature 443, 973–976 (2006).
    OpenUrlCrossRefPubMed
  5. ↵
    1. D. L. Lakshtanov et al
    ., The post-stishovite phase transition in hydrous alumina-bearing SiO2 in the lower mantle of the earth. Proc. Natl. Acad. Sci. U.S.A. 104, 13588–13590 (2007).
    OpenUrlAbstract/FREE Full Text
  6. ↵
    1. B. Schmandt,
    2. S. D. Jacobsen,
    3. T. W. Becker,
    4. Z. Liu,
    5. K. G. Dueker
    , Earth’s interior. Dehydration melting at the top of the lower mantle. Science 344, 1265–1268 (2014).
    OpenUrlAbstract/FREE Full Text
  7. ↵
    1. E. Boulard et al
    ., CO2-induced destabilization of pyrite-structured FeO2Hx in the lower mantle. Natl. Sci. Rev. 5, 870–877 (2018).
    OpenUrl
  8. ↵
    1. J. Zhang,
    2. J. D. Bass
    , Sound velocities of olivine at high pressures and temperatures and the composition of Earth’s upper mantle. Geophys. Res. Lett. 43, 9611–9618 (2016).
    OpenUrl
  9. ↵
    1. H. Mao et al
    ., When water meets iron at Earth’s core–Mantle boundary. Natl. Sci. Rev. 4, 870–878 (2017).
    OpenUrl
  10. ↵
    1. E. Ohtani
    , The role of water in Earth’s mantle. Natl. Sci. Rev., doi:10.1093/nsr/nwz071 (2019).
    OpenUrlCrossRef
  11. ↵
    1. M. Nishi et al
    ., Stability of hydrous silicate at high pressures and water transport to the deep lower mantle. Nat. Geosci. 7, 224–227 (2014).
    OpenUrl
  12. ↵
    1. M. G. Pamato et al
    ., Lower-mantle water reservoir implied by the extreme stability of a hydrous aluminosilicate. Nat. Geosci. 8, 75–79 (2015).
    OpenUrl
  13. ↵
    1. M. J. Walter et al
    ., The stability of hydrous silicates in Earth’s lower mantle: Experimental constraints from the systems MgO–SiO2–H2O and MgO–Al2O3–SiO2–H2O. Chem. Geol. 418, 16–29 (2015).
    OpenUrl
  14. ↵
    1. N. Bolfan-Casanova,
    2. H. Keppler,
    3. D. C. Rubie
    , Water partitioning between nominally anhydrous minerals in the MgO–SiO2–H2O system up to 24 GPa: Implications for the distribution of water in the Earth’s mantle. Earth Planet. Sci. Lett. 182, 209–221 (2000).
    OpenUrl
  15. ↵
    1. H. Keppler,
    2. J. R. Smyth
    1. H. Skogby
    , “Water in natural mantle minerals. I. Pyroxenes” in Water in Nominally Anhydrous Minerals, H. Keppler, J. R. Smyth, Eds. (Reviews in Mineralogy & Geochemistry, de Gruyter, 2006), vol. 62, pp. 155–167.
  16. ↵
    1. H. Keppler,
    2. J. R. Smyth
    1. A. Beran,
    2. E. Libowitzky
    , “Water in natural mantle minerals. II. Olivine, garnet, and accessory minerals” in Water in Nominally Anhydrous Minerals, H. Keppler, J. R. Smyth, Eds. (Reviews in Mineralogy & Geochemistry, de Gruyter, 2006), vol. 62, pp. 169–191.
  17. ↵
    1. K. D. Litasov et al
    ., High hydrogen solubility in Al-rich stishovite and water transport in the lower mantle. Earth Planet. Sci. Lett. 262, 620–634 (2007).
    OpenUrl
  18. ↵
    1. K. Spektor et al
    ., Ultrahydrous stishovite from high-pressure hydrothermal treatment of SiO2. Proc. Natl. Acad. Sci. U.S.A. 108, 20918–20922 (2011).
    OpenUrlAbstract/FREE Full Text
  19. ↵
    1. K. Mibe,
    2. T. Yoshino,
    3. S. Ono,
    4. A. Yasuda,
    5. T. Fujii
    , Connectivity of aqueous fluid in eclogite and its implications for fluid migration in the Earth’s interior. J. Geophys. Res. 108, 2295 (2003).
    OpenUrl
  20. ↵
    1. P. E. van Keken,
    2. B. R. Hacker,
    3. E. M. Syracuse
    , Subduction factory. 4. Depth-dependent flux of H2O from subducting slabs worldwide. J. Geophys. Res. Solid Earth 116, B01401 (2011).
    OpenUrl
  21. ↵
    1. T. Plank,
    2. K. A. Kelley,
    3. M. M. Zimmer,
    4. E. H. Hauri,
    5. P. J. Wallace
    , Why do mafic arc magmas contain ∼4 wt% water on average? Earth Planet. Sci. Lett. 364, 168–179 (2013).
    OpenUrl
  22. ↵
    1. P. Ulmer,
    2. V. Trommsdorff
    , Serpentine stability to mantle depths and subduction-related magmatism. Science 268, 858–861 (1995).
    OpenUrlAbstract/FREE Full Text
  23. ↵
    1. K. D. Litasov,
    2. E. Ohtani
    , Stability of various hydrous phases in CMAS pyrolite–H2O system up to 25 GPa. Phys. Chem. Miner. 30, 147–156 (2003).
    OpenUrl
  24. ↵
    1. D. L. Kohlstedt,
    2. H. Keppler,
    3. D. C. Rubie
    , Solubility of water in the α, β, and γ phases of (Mg,Fe)2SiO4. Contrib. Mineral. Petrol. 123, 345–357 (1996).
    OpenUrlCrossRef
  25. ↵
    1. S. Ono,
    2. E. Ito,
    3. T. Katsura
    , Mineralogy of subducted basaltic crust (MORB) from 25 to 37 GPa, and chemical heterogeneity of the lower mantle. Earth Planet. Sci. Lett. 190, 57–63 (2001).
    OpenUrl
  26. ↵
    1. K. Hirose,
    2. N. Takafuji,
    3. N. Sata,
    4. Y. Ohishi
    , Phase transition and density of subducted MORB crust in the lower mantle. Earth Planet. Sci. Lett. 237, 239–251 (2005).
    OpenUrl
  27. ↵
    1. K. J. Kingma,
    2. R. E. Cohen,
    3. J. Russell,
    4. H. K. Mao
    , Transformation of stishovite to a denser phase at lower-mantle pressures. Nature 374, 243–245 (1995).
    OpenUrlCrossRef
  28. ↵
    1. R. A. Fischer et al
    ., Equations of state and phase boundary for stishovite and CaCl2-type SiO2. Am. Mineral. 103, 792–802 (2018).
    OpenUrl
  29. ↵
    1. A. E. Gleason et al
    ., Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2. Nat. Commun. 6, 8191 (2015).
    OpenUrl
  30. ↵
    1. C. Nisr,
    2. S. H. Shim,
    3. K. Leinenweber,
    4. A. Chizmeshya
    , Raman spectroscopy of water-rich stishovite and dense high-pressure silica up to 55 GPa. Am. Mineral. 102, 2180–2189 (2017).
    OpenUrlAbstract/FREE Full Text
  31. ↵
    1. D. Andrault,
    2. R. J. Angel,
    3. J. L. Mosenfelder,
    4. T. L. Bihan
    , Equation of state of stishovite to lower mantle pressures. Am. Mineral. 88, 301–307 (2003).
    OpenUrlAbstract/FREE Full Text
  32. ↵
    1. J. S. Pigott et al
    ., High-pressure, high-temperature equations of state using nanofabricated controlled-geometry Ni/SiO2/Ni double hot-plate samples. Geophys. Res. Lett. 42, 239–247 (2015).
    OpenUrl
  33. ↵
    1. K. Spektor et al
    ., Formation of hydrous stishovite from coesite in high pressure hydrothermal environments. Am. Mineral. 101, 2514–2524 (2016).
    OpenUrlAbstract/FREE Full Text
  34. ↵
    1. C. Nisr et al
    ., Phase transition and equation of state of dense hydrous silica up to 63 GPa. J. Geophys. Res. Solid Earth 122, 6972–6983 (2017).
    OpenUrl
  35. ↵
    1. A. R. Pawley,
    2. P. F. McMillan,
    3. J. R. Holloway
    , Hydrogen in stishovite, with implications for mantle water content. Science 261, 1024–1026 (1993).
    OpenUrlAbstract/FREE Full Text
  36. ↵
    1. J. I. Chung,
    2. H. Kagi
    , High concentration of water in stishovite in the MORB system. Geophys. Res. Lett. 29, 2020 (2002).
    OpenUrlCrossRef
  37. ↵
    1. W. R. Panero,
    2. L. R. Benedetti,
    3. R. Jeanloz
    , Transport of water into the lower mantle: Role of stishovite. J. Geophys. Res. 108, 2039 (2003).
    OpenUrl
  38. ↵
    1. N. Bolfan-Casanova
    , Water in the Earth’s mantle. Mineral. Mag. 69, 229–257 (2005).
    OpenUrlAbstract/FREE Full Text
  39. ↵
    1. N. Bolfan-Casanova,
    2. H. Keppler,
    3. D. C. Rubie
    , Water partitioning at 660 km depth and evidence for very low water solubility in magnesium silicate perovskite. Geophys. Res. Lett. 30, 1905 (2003).
    OpenUrlCrossRef
  40. ↵
    1. S. Fu et al
    ., Water concentration in single-crystal (Al,Fe)-Bearing bridgmanite grown from the hydrous melt: Implications for dehydration melting at the topmost lower mantle. Geophys. Res. Lett. 46, 10346–10357 (2019).
    OpenUrl
  41. ↵
    1. T. Komabayashi,
    2. S. Omori,
    3. S. Maruyama
    , Petrogenetic grid in the system MgO-SiO2-H2O up to 30 GPa, 1600 °C: Applications to hydrous peridotite subducting into the Earth’s deep interior. J. Geophys. Res. 109, B03206 (2004).
    OpenUrl
  42. ↵
    1. D. G. Pearson et al
    ., Hydrous mantle transition zone indicated by ringwoodite included within diamond. Nature 507, 221–224 (2014).
    OpenUrlCrossRefPubMed
  43. ↵
    1. E. M. Smith et al
    ., Blue boron-bearing diamonds from Earth’s lower mantle. Nature 560, 84–87 (2018).
    OpenUrl
  44. ↵
    1. Y. Tsuchida,
    2. T. Yagi
    , A new, post-stishovite high-pressure polymorph of silica. Nature 340, 217–220 (1989).
    OpenUrlCrossRef
  45. ↵
    1. M. M. Hirschmann,
    2. R. Dasgupta
    , The H/C ratios of Earth’s near-surface and deep reservoirs, and consequences for deep Earth volatile cycles. Chem. Geol. 262, 4–16 (2009).
    OpenUrlCrossRef
  46. ↵
    1. A. P. Jephcoat,
    2. H. K. Mao,
    3. P. M. Bell
    , Hydrothermal Experiment Techniques (Wiley-Interscience, 1987), chap. 11.
  47. ↵
    1. H. Yuan,
    2. L. Zhang
    , In situ determination of crystal structure and chemistry of minerals at Earth’s deep lower mantle conditions. Matter Radiat. Extremes 2, 117–128 (2017).
    OpenUrl
  48. ↵
    1. Y. Meng,
    2. G. Shen,
    3. H. K. Mao
    , Double-sided laser heating system at HPCAT for in situ x-ray diffraction at high pressures and high temperatures. J. Phys. Condens. Matter 18, S1097–S1103 (2006).
    OpenUrlCrossRefPubMed
  49. ↵
    1. T. J. B. Holland,
    2. S. A. T. Redfern
    , Unit cell refinement from powder diffraction data: The use of regression diagnostics. Min. Mag. (Lond.) 61, 65–77 (1997).
    OpenUrlAbstract
  50. ↵
    1. Y. Fei et al
    ., Toward an internally consistent pressure scale. Proc. Natl. Acad. Sci. U.S.A. 104, 9182–9186 (2007).
    OpenUrlAbstract/FREE Full Text
  51. ↵
    1. S. R. Shieh,
    2. T. S. Duffy,
    3. B. Li
    , Strength and elasticity of SiO2 across the stishovite-CaCl2-type structural phase boundary. Phys. Rev. Lett. 89, 255507 (2002).
    OpenUrlCrossRefPubMed
  52. ↵
    1. C. R. M. Jackson,
    2. N. R. Bennett,
    3. Z. Du,
    4. E. Cottrell,
    5. Y. Fei
    , Early episodes of high-pressure core formation preserved in plume mantle. Nature 553, 491–495 (2018).
    OpenUrl
PreviousNext
Back to top
Article Alerts
Email Article

Thank you for your interest in spreading the word on PNAS.

NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

Enter multiple addresses on separate lines or separate them with commas.
Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle
(Your Name) has sent you a message from PNAS
(Your Name) thought you would like to see the PNAS web site.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Citation Tools
Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle
Yanhao Lin, Qingyang Hu, Yue Meng, Michael Walter, Ho-Kwang Mao
Proceedings of the National Academy of Sciences Jan 2020, 117 (1) 184-189; DOI: 10.1073/pnas.1914295117

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Request Permissions
Share
Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle
Yanhao Lin, Qingyang Hu, Yue Meng, Michael Walter, Ho-Kwang Mao
Proceedings of the National Academy of Sciences Jan 2020, 117 (1) 184-189; DOI: 10.1073/pnas.1914295117
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
  • Tweet Widget
  • Facebook Like
  • Mendeley logo Mendeley

Article Classifications

  • Physical Sciences
  • Earth, Atmospheric, and Planetary Sciences
Proceedings of the National Academy of Sciences: 117 (1)
Table of Contents

Submit

Sign up for Article Alerts

Jump to section

  • Article
    • Abstract
    • Results and Discussion
    • Methods
    • Acknowledgments
    • Footnotes
    • References
  • Figures & SI
  • Info & Metrics
  • PDF

You May Also be Interested in

Smoke emanates from Japan’s Fukushima nuclear power plant a few days after tsunami damage
Core Concept: Muography offers a new way to see inside a multitude of objects
Muons penetrate much further than X-rays, they do essentially zero damage, and they are provided for free by the cosmos.
Image credit: Science Source/Digital Globe.
Water from a faucet fills a glass.
News Feature: How “forever chemicals” might impair the immune system
Researchers are exploring whether these ubiquitous fluorinated molecules might worsen infections or hamper vaccine effectiveness.
Image credit: Shutterstock/Dmitry Naumov.
Venus flytrap captures a fly.
Journal Club: Venus flytrap mechanism could shed light on how plants sense touch
One protein seems to play a key role in touch sensitivity for flytraps and other meat-eating plants.
Image credit: Shutterstock/Kuttelvaserova Stuchelova.
Illustration of groups of people chatting
Exploring the length of human conversations
Adam Mastroianni and Daniel Gilbert explore why conversations almost never end when people want them to.
Listen
Past PodcastsSubscribe
Horse fossil
Mounted horseback riding in ancient China
A study uncovers early evidence of equestrianism in ancient China.
Image credit: Jian Ma.

Similar Articles

Site Logo
Powered by HighWire
  • Submit Manuscript
  • Twitter
  • Facebook
  • RSS Feeds
  • Email Alerts

Articles

  • Current Issue
  • Special Feature Articles – Most Recent
  • List of Issues

PNAS Portals

  • Anthropology
  • Chemistry
  • Classics
  • Front Matter
  • Physics
  • Sustainability Science
  • Teaching Resources

Information

  • Authors
  • Editorial Board
  • Reviewers
  • Subscribers
  • Librarians
  • Press
  • Cozzarelli Prize
  • Site Map
  • PNAS Updates
  • FAQs
  • Accessibility Statement
  • Rights & Permissions
  • About
  • Contact

Feedback    Privacy/Legal

Copyright © 2021 National Academy of Sciences. Online ISSN 1091-6490