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We investigated the stability of the Al‐rich dense hydrous magnesium silicate Phase D (PhD) in a MgO‐Al2O3‐SiO2‐H2O system between 14 and 25 GPa at 900–1,500 °C. Al‐rich PhD has a very wide stability ...region from 900 °C and 14 GPa to at least 1,500 °C and 25 GPa, showing strong temperature stability with increasing pressure. Al‐rich PhD decomposes to Phase Egg at pressure of the mantle transition zone, whereas it decomposes to δ‐AlOOH phase with a temperature increase at pressure of the uppermost lower mantle. X‐ray diffraction and Raman spectroscopy measurements of Al‐rich PhD show that the unit‐cell volume is slightly larger, but the Raman spectra resemble that of Al‐free PhD. The wide stability region of Al‐bearing PhD would contribute an important storage site for water in the mantle transition zone, suggesting that it can deliver a certain amount of water into the lower mantle along hot subduction and even at the normal mantle geothermal P‐T condition. Furthermore, the dehydration of Al‐bearing PhD might be responsible for a series of observed seismic discontinuities from the transition zone to the uppermost lower mantle and even for deep earthquakes in some typical locations.
Key Points
Stability of the Al‐rich dense hydrous magnesium silicate Phase D (PhD) was investigated under high pressure‐temperature conditions
The maximum stability of Al‐rich Phase D is above 1,500 °C at 25 GPa, which decomposed further to Phase Egg or δ‐AlOOH with elevated temperature
Dehydration of these Al‐bearing hydrous minerals might strongly affect physical and chemical properties of surrounding materials
Melting experiments on a carbonated pelite were performed at 5.5–15.5 GPa, 800–1875 °C using multi-anvil apparatuses to determine the melting phase relations and the P–T stability fields of various ...phases, which may shed some light on the source of silica-undersaturated magmas and the deep Earth carbon and water cycles. The subsolidus assemblages contain garnet, clinopyroxene, coesite/stishovite at all investigated pressures. Phengite, aragonite or magnesite, and topaz-OH occur below 9.5 GPa. Phase egg, K-hollandite, Ti-oxide, and CAS phase appear at 12–15.5 GPa. Phengite is stable up to 6 GPa and 800 °C, with the phengite-out boundary overlapping with the carbonate-out curve. Thus, the initial melt is carbonatitic and extremely potassium-rich, with K
2
O/Na
2
O weight-ratios larger than 40 at fluid-present conditions. The melting reaction phase egg + magnesite + aragonite + (clinopyroxene) + stishovite → melt + garnet + kyanite defines the solidus at 9.5 GPa, 1000–1100 °C. With increasing pressure, the composition of the near-solidus melts gradually evolves from potassium-rich to sodium-rich due to the formation of K-hollandite and the destabilization of clinopyroxene, and as a result of the clinopyroxene-out, the near-solidus melt has the lowest K
2
O/Na
2
O value and partitioning coefficient of sodium between clinopyroxene and melt
D
Na
cpx/melt
at 15.5 GPa. In addition, phase egg remains stable up to 1400 °C at 15.5 GPa. Thus, phase egg is a good candidate as a deep-water carrier during subduction of pelitic sediments. This study concludes that low degree partial melting of carbonated pelite produces alkali-rich carbonatite melts evolving from potassium-rich (6–12 GPa) to sodium-rich (above 12 GPa) with increasing pressure, and if a slab stagnates at depth, and/or subduction slows down, the produced carbonatite melts will be more silicate-rich with increasing temperature. Moreover, the produced melts generally evolve from relatively silicate-rich to carbonatite-rich with increasing pressure. These alkali-rich carbonatite melts are compositionally similar to those in diamond inclusions, which provides strong evidence for the origin of deep-seated silica-undersaturated carbonatitic magma. Such magma is an ideal metasomatic agent that can give rise to mantle heterogeneity.
Superhydrous phase B is an important dense hydrous magnesium silicate (DHMS) phase in a hydrous peridotite system for understanding the deep water cycle in the Earth’s interior. A large amount of Al ...can be substituted in the crystal structure of superhydrous phase B, but its position in the crystal structure has yet to be determined. Here, we investigated the crystal structure of Al-bearing superhydrous phase B (Mg
8.1
Si
2.0
Al
1.9
H
5.9
O
18
) by single-crystal X-ray diffraction (SC-XRD), together with Raman and Fourier-transform infrared (FT–IR) spectroscopies to determine the positions of Al and predict the positions of H. From crystal structure refinement, we clarified that Al was located in the octahedral Mg1, Mg2, and Si1 sites with a
Pnnm
space group. Furthermore, the result is consistent with a previously proposed substitution reaction: 2Mg
2+
+ Si
4+
⇄ 2Al
3+
+ 2H
+
+ □
Mg
. The obtained FT–IR spectra, difference Fourier maps, and bond-valence revealed new H positions at (1) O
6
–H⋯O
4
, which is a part of the AlO
6
octahedron; (2) O
5
–H⋯O
3
, which is the same as the Mg-endmember superhydrous phase B, and (3) O4-H⋯O1, which is the shared edge of the Mg2O
6
and Mg4O
6
octahedra. By summarizing the present study together with the previous studies, it is predicted that the cause of the phase transition between
Pnnm
and
Pnn
2 occurs at ~ 1300 ℃ due to the synthesis temperature, which is not due to the substitution of metal elements.
Nitrogen is a crucial volatile element in the early Earth's evolution and the origin of life. Despite its importance, nitrogen's behavior in the Earth's interior remains poorly understood. Compared ...to other volatile elements, nitrogen is depleted in the Earth's atmosphere (the so-called "missing nitrogen"), calling for a hidden deep reservoir. To investigate nitrogen's behavior in the deep Earth including how the reservoir formed, high-pressure and high-temperature experiments were conducted at 28 GPa and 1,400-1,700 °C. To reproduce the conditions in the lower mantle, the redox was controlled using a Fe-FeO buffer. We observed that depending on the temperature conditions, stishovite can incorporate up to 90-404 ppm nitrogen, experimentally demonstrating that stishovite has the highest nitrogen solubility among the deep mantle minerals. Stishovite is the main mineral component of subducted nitrogen-rich sedimentary rocks and eroded continental crust that are eventually transported down to the lower mantle. Our results suggest that nitrogen could have been continuously transported into the lower mantle via subduction, ever since plate tectonics began.
In recent times, therapy for renal anemia has changed dramatically in that iron administration has increased and doses of erythropoiesis-stimulating agents (ESAs) have decreased. Here we used a ...prospective, observational, multicenter design and measured the serum ferritin and hemoglobin levels every 3 months for 2 years in 1086 patients on maintenance hemodialysis therapy. The associations of adverse events with fluctuations in ferritin and hemoglobin levels and ESA and iron doses were measured using a Cox proportional hazards model for time-dependent variables. The risks of cerebrovascular and cardiovascular disease (CCVD), infection, and hospitalization were higher among patients who failed to maintain a target-range hemoglobin level and who exhibited high-amplitude fluctuations in hemoglobin compared with patients who maintained a target-range hemoglobin level. Patients with a higher compared with a lower ferritin level had an elevated risk of CCVD and infectious disease. Moreover, the risk of death was significantly higher among patients with high-amplitude ferritin fluctuations compared with those with a low ferritin level. The risks of CCVD, infection, and hospitalization were significantly higher among patients who were treated with high weekly doses of intravenous iron compared with no intravenous iron. Thus, there is a high risk of death and/or adverse events in patients with hemoglobin levels outside the target range, in those with high-amplitude hemoglobin fluctuations, in those with consistently high serum ferritin levels, and in those with high-amplitude ferritin fluctuations.
Patients with high serum ferritin and low transferrin saturation (TSAT) levels could be considered as presenting with dysutilization of iron for erythropoiesis. However, the long-term safety of iron ...administration in these patients has not been well established. An observational multicenter study was performed over 3 years. In 805 patients undergoing maintenance hemodialysis (MHD), we defined dysutilization of iron for erythropoiesis in patients with lower TSAT (20%) and higher ferritin (greater than or equal to100 ng/mL) levels. A time-dependent Cox hazard model was used for the evaluation of the association between dysutilization of iron for erythropoiesis and adverse events and survival. Patients with low TSAT levels showed an increased risk of cerebrovascular and cardiovascular disease (CCVD) and death compared to patients with normal or higher TSAT levels. Patients with low ferritin and high TSAT levels had a significantly lower risk of CCVD and death compared with patients with high ferritin and low TSAT levels. Higher TSAT levels were associated with male gender, age, the absence of diabetes, low levels of high-sensitivity CRP, and low beta2 microglobulin levels, but not with intravenous iron administration or ferritin levels. Although patients with low TSAT levels had a significantly higher risk of CCVD or death, high TSAT levels were not linked with iron administration. Patients, who were suspected of dysutilization of iron for erythropoiesis, had a higher risk of CCVD and death. The administration of iron should be performed cautiously for improving TSAT levels, as iron administration could sustain TSAT levels for a short term.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Although the induced melting of pelitic sediments, i.e., the devolatilization of hydrous and carbonate minerals, has been widely studied at fluid-undersaturated conditions, the flush ...dissolution of carbonated pelite has not been fully understood. In addition, the role of iron in the melting of carbonated pelite has not received much attention. To address these issues, we conducted two sets of experiments for carbonated pelite with an iron-bearing (LH-gloss) and an iron-free (LHIF-gloss) starting bulk composition at 5.5 to 6 GPa, 800 to 1600 °C at fluid-saturated conditions. The phase assemblages for both experiments at 800 °C are composed of garnet + clinopyroxene + coesite + kyanite + phengite + aragonite + magnesite ± lawsonite ± rutile. Higher jadeite component and lower diopside–hedenbergite solid solution (Di–Hdss) in omphacitic clinopyroxene are observed in the LH-gloss experiments; also, garnet remains stable to higher temperatures (800–1400 °C) in the LH-gloss than in the LHIF-gloss (900–1200 °C). Carbonate- and phengite-out temperature boundaries are overlapping in the respective system, with the temperature boundary in the LH-gloss (800–900 °C) slightly lower than that in the LHIF-gloss experiments (900–1000 °C). The different stability fields of volatile-bearing minerals can be ascribed not only to variable bulk XH2O molar ratio H2O/(H2O + CO2), which in turn depends on bulk H2O, CO2 and K2O contents, but also to bulk FeO*(Total Fe as FeO) content. Both the characteristic “fish egg” texture and the strong increase in the amount of dissolved solids in the liquid phase over a narrow temperature interval at 6 GPa testify to the possible existence of supercritical fluid. The marked solvent power of supercritical fluid can explain the earlier disappearance of experimental products including phengite, aragonite and magnesite. For the produced liquid phase (supercritical fluid or melt), the K2O/Na2O weight ratio decreases, whereas that of the SiO2/CaO increases with increasing temperature, placing potassium-rich carbonatitic supercritical fluids in the low-temperature and sodium-rich (carbonated) silicate melts in the high-temperature sections of both systems. The produced ultrapotassic (supercritical) liquid, when liberated from the subducting slab, may evolve into a melt parental to carbonatites and possibly result in the formation of diamonds. While those (carbonated) silicate melts, especially the more oxidized and buoyant ones produced by the melting of ferrous iron-depleted carbonated pelite, are expected to intensely interact with the overlying peridotite during the upward migration, which could lead to the formation of the metasomatic garnet pyroxenite.
A series of experiments was conducted on the decomposition of natural and chemically mixed chlorites to examine the stable hydrous phases in the MgO–FeO–Al2O3–SiO2–H2O (MFASH) system under 5–12GPa ...and 700–1100°C. The upper pressure and temperature limits of the stability region of chlorite are consistent with those observed in previous studies. The hydrous aluminum bearing pyroxene (phase HAPY) and Mg-sursassite (Sur) were observed just above the temperature stability region of chlorite (Chl); clinohumite (cHm) was observed coexisting with phase HAPY at 6GPa and 800°C and coexisting with the 23-Å phase at 7GPa and 800°C, which may suggest the transportation of water through Chl→(HAPY→cHm)→23-Å phase along a relatively warm slab. The 23-Å phase has a wider stability region in the pure MASH system (up to 12GPa and 1100°C) than it does in the MFASH system (7–10GPa, up to 1000°C). The stability of the 23-Å phase beyond the chlorite breakdown pressure indicates that it may play an important role in transporting water into the deep Earth and even into the mantle transition zone.
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