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T. Gasparik 《Physics and Chemistry of Minerals》2002,29(3):170-180
Multianvil experiments were carried out at 10–15 GPa and 1600–1700 °C to match the compositions of majoritic garnet inclusions
from diamonds, and to determine the compositions of other phases potentially coexisting with these inclusions in the source.
Most experiments produced coexisting majoritic garnet, diopsidic clinopyroxene, one or more (Mg,Fe)2SiO4 polymorphs, and quenched carbonatic melt. The experimental garnets had relatively high Ca and Fe contents similar to the
observed Ca and Fe contents of the inclusions. The resulting Si contents confirmed that the depth of origin of the inclusion
with the highest Si content did not exceed 410 km, thus none of the majoritic garnet inclusions found so far originated in
the transition zone (410–660 km). The evidence from inclusions and experiments is consistent with the presence of an eclogite
layer occurring globally between 200 and 410 km. Compositional variations observed among more than 100 majoritic garnet inclusions
with their Si content, which is a measure of pressure and depth, are consistent with the origin of the eclogite layer by crystal
fractionation in a magma ocean. The compositions of olivine coexisting with majoritic garnet in the experimental products
had the average Fe/(Fe + Mg) ratios between 0.16 and 0.28. Inclusions with such high Fe contents have not been found; the
Fe/(Fe + Mg) ratio of the olivine inclusions in diamonds usually varies between 0.05 and 0.09. Hence, the mantle between 200
and 410 km may not contain olivine. In the absence of olivine, the discontinuity at 410 km is most likely a chemical boundary
between the 200-km-thick eclogite layer and a more mafic transition zone.
Received: 15 March 2001 / Accepted: 14 September 2001 相似文献
2.
The tried and tested multianvil apparatus has been widely used for high-pressure and high-temperature experimental studies in Earth science. As a result, many important results have been obtained for a better understanding of the components, structure and evolution of the Earth. Due to the strength limitation of materials, the attainable multianvil pressure is generally limited to about 30 GPa (corresponding to about 900 km of the depth in the Earth) when tungsten carbide cubes are adopted as second-stage anvils. Compared with tungsten carbide, the sintered diamond is a much harder material. The sintered diamond cubes were introduced as second-stage anvils in a 6–8 type multianvil apparatus in the 1980s, which largely enhanced the capacity of pressure generation in a large volume press. With the development of material synthesis and processing techniques, a large sintered diamond cube (14 mm) is now available. Recently, maximum attainable pressures reaching higher than 90 GPa (corresponding to about 2700 km of the depth in the Earth) have been generated at room temperature by adopting 14-mm sintered diamond anvils. Using this technique, a few researches have been carried out by the quenched method or combined with synchrotron radiation in situ observation. In this paper we review the properties of sintered diamond and the evolution of pressure generation using sintered diamond anvils. As-yet unsolved problems and perspectives for uses in Earth Science are also discussed. 相似文献
3.
H.-R. Wenk G. Ischia N. Nishiyama T. Uchida 《Physics of the Earth and Planetary Interiors》2005,152(3):191-199
Ringwoodite Mg2SiO4 with spinel structure is an important phase in the earth's mantle transition zone. Controlled deformation experiments showed that ringwoodite underwent ductile deformation when compressed axially at 6-10 GPa and at room temperature in a multianvil D-DIA deformation apparatus. Texture evolution during cyclic compression has been recorded in situ using X-ray transparent anvils with monochromatic synchrotron X-ray diffraction and a two-dimensional detector. Quantitative analysis of the images with the Rietveld method revealed a 1 1 0 fiber texture. By comparing this texture pattern with polycrystal plasticity simulations, it is inferred that {1 1 1}〈 1 0〉 slip is the dominant deformation mechanism in ringwoodite, consistent with high temperature mechanisms observed in other spinel-structured materials. Although strong ringwoodite textures may develop in the transition zone, the contribution to bulk anisotropy is minimal due to the weak single-crystal anisotropy. 相似文献
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Experimental investigation of the effect of metasomatism by carbonatic melt on the composition and structure of the deep mantle 总被引：2，自引：0，他引：2
The compositions of various transition-zone and lower-mantle phases and coexisting carbonatic melts were determined by exploratory melting experiments in chemically complex CO2-bearing systems at 20–24.5 GPa and 1600–2000 °C. The melts are highly ultramafic, enriched in K, Na, Ca, Fe, and Mg, and depleted in Al and Si. Melting experiments were also carried out with the compositions on the join Mg2SiO4–Na2CO3 at 3.7 GPa and 1200–1600 °C. The solidus assemblage of MgCO3 and Na2MgSiO4 melts incongruently to produce forsterite and Na-rich melt. The new results and other recent studies in CO2-bearing systems suggest that carbonatic melt could be present, either transiently or permanently, in the whole Earth's upper mantle and at least the uppermost lower mantle. Carbonate-melt metasomatism is recognized as a process that could have a major effect on the composition and structure of the deep mantle, and thus play an important role in its evolution. Due to the unique properties of the carbonatic melt, its circulation in an otherwise static mantle could be a more efficient process than the solid-state convection for maintaining equilibrium in most of the mantle not involved directly in plate tectonics. 相似文献
5.
J. L. Mosenfelder 《Physics and Chemistry of Minerals》2000,27(9):610-617
The solubility of hydroxyl in coesite was investigated in multianvil experiments performed at 1200 °C over the nominal pressure
range 5–10 GPa, at an f
O2 close to the Ni-NiO buffer. The starting material for each experiment was a cylinder of pure silica glass plus talc, which
dehydrates at high P and T to provide a source of water and hydrogen (plus enstatite and excess SiO2). Fourier-transform infrared (FTIR) spectra of the recovered coesite crystals show five sharp bands at 3606, 3573, 3523,
3459, and 3299 cm−1, indicative of structurally bonded hydrogen (hydroxyl). The concentration of hydrogen increases with pressure from 285 H/106 Si (at 5 GPa) to 1415 H/106 Si (at 10 GPa). Assuming a model of incorporation by (4H)Si defects, the data are fit well by the equation C
OH=Af
2
H2<\INF>Oexp(−PΔV/RT), with A=4.38 H/106 Si/GPa, and ΔV=20.6 × 10−6 m3 mol−1. An alternative model entailing association of hydrogen with cation substitution can also be used to fit the data. These
results show that the solubility of hydroxyl in coesite is approximately an order of magnitude lower than in olivines and
pyroxenes, but comparable to that in pyropic garnet. However, FTIR investigations on a variety of ultrahigh pressure metamorphic
rocks have failed in all cases to detect the presence of water or hydrogen in coesite, indicating either that it grew in dry
environments or lost its hydrogen during partial transformation to quartz. On the other hand, micro-FTIR investigations of
quartz crystals replacing coesite show that they contain varying amounts of H2O. These results support the hypothesis that preservation of coesite is not necessarily linked to fast exhumation rates but
is crucially dependent on limited fluid infiltration during exhumation.
Received: 23 August 1999 / Accepted: 10 April 2000 相似文献
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