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1.
Paleoproterozoic carbonaceous shales in the Tim-Yastrebovskii ancient rift, which underwent zonal metamorphism at 350–550°C,
contain REE mineralization of silicates (allanite, thorite, and Ce-P huttonite) fluorcarbonates (bastnaesite and synchysite),
phosphates (monazite and xenotime), and REE-bearing apatite. The reason for the wide occurrence of bastnaesite and other REE
minerals is relatively high REE concentrations in the sulfide-bearing carbonaceous shales, with these elements accumulated
in the organic matter in the course of diagenesis. Reaction textures with REE-bearing chlorite, bastnaesite, and allanite
suggest that REE-bearing chlorite and bastnaesite provided REE for the forming of higher temperature allanite and monazite.
This is corroborated by the REE patterns of the monazite, allanite, and bastnaesite, which are almost identical and are characterized
by the strong predominance of LREE. The replacements of REE minerals during metamorphism at 350–550°C took place via a number
successive transitions: (1) Mnz → Aln, Chl
REE → Bst, Chl
REE → Aln, Bst → Aln and (2) Bst → Mnz and Ap
LREE → Mnz. These replacements can be accounted for by prograde metamorphic reactions. 相似文献
2.
T. M. Will 《Mineralogy and Petrology》2001,72(1-3):229-247
Summary Geometric data of fault planes and fault plane lineations, together with the observed sense of shear on the slip planes,
were used to calculate paleostress tensors and fields responsible for the post metamorphic peak D3 and D4 deformation events
in the four Odenwald units sensu Krohe (1991). The paleostress fields were calculated using the method of Will and Powell (1991). As inferred from the paleostress analysis, the D3 strike-slip deformation west of the Otzberg fault zone was caused
by a, ± N-S directed, compressional regional stress field, with shallowly plunging σ1 axes and σ3 directions that plunge at shallow to moderate angles to the E or W; the calculated mean orientations are: σ1 06 → 350, σ2 77 → 234 and σ3 12 → 085. The B?llsteiner Odenwald east of the Otzberg fault zone was not affected by this stress field. This implies that
the Bergstr?sser and B?llsteiner Odenwald were spatially separated and formed independent crustal blocks during D3. The D4
faulting event is recognised in all areas investigated, even though most prominently in units III and IV, and juxtaposed the
Bergstr?sser and B?llsteiner Odenwald. This faulting episode was caused by a paleostress field with a steeply westerly plunging
σ1 axis and a shallowly southsoutheasterly plunging σ3 axis. The orientations of the principal stresses are: σ1 52 → 270, σ2 38 → 085 and σ3 06 → 174. With continued deformation from D3 to D4, there was a progressive change in the orientation of the stress field
indicating a change from a N-S compressional to extensional stress field, accompanied by the progressive development of strike-slip
faults and late normal faults. Paleostress field orientations in the Pfalz Forest, SW of the Odenwald, determined by Fl?ttmann and Oncken (1992) are very similar to those obtained for the Odenwald region and indicate a regionally consistent stress pattern in
the southwestern part of the Mid-German Crystalline Rise (MGCR) during strike-slip and normal faulting deformations.
Received July 8, 1999; revised version accepted March 28, 2000 相似文献
Zusammenfassung Paleostress-Tensor Analyse sp?ter Deformationsereignisse im Odenwald-Kristallin und ein Vergleich mit anderen Einheiten der Mitteldeutschen Kristallinzone, Deutschland Für die vier Odenwald-Einheiten im Sinne von Krohe (1991) wurden Pal?ostressfelder für die Blattverschiebungs- und Abschiebungsereignisse D3 und D4 mit der Methode von Will und Powell (1991) berechnet. Die Analyse ergibt, da? das regionale Spannungsfeld, das westlich der Otzberg-Zone im Bergstr?sser Odenwald zum D3-Ereignis führte, ein ± N-S gerichtetes kompressives Stresssfeld war. Die σ1-Achse f?llt flach nach N bzw. S ein, die σ3-Achse mit kleinen bis moderaten Winkeln nach E bzw. W; die berechneten Orientierungen der Hauptspannungsrichtungen sind: σ1 08 → 350, σ2 77 → 234 and σ3 12 → 085. Der B?llsteiner Odenwald, ?stlich der Otzberg-Zone, wurde von diesem Spannungsfeld nicht erfa?t. Dies impliziert, da? Bergstr?sser und B?llsteiner Odenwald w?hrend des D3-Ereignisses voneinander getrennt waren und separate Krusteneinheiten darstellten. Auswirkungen der D4-Deformation k?nnen im gesamten Untersuchungsgebiet erkannt werden, am st?rksten jedoch in den Einheiten III und IV. Dieses Ereignis wurde von einem Pal?ostressfeld mit einer steil nach W einfallenden σ1- und einer flach nach SSE einfallenden σ3-Achse verursacht und führte zum Zusammenschlu? von Bergstr?sser und B?llsteiner Odenwald. Die berechneten Orientierungen der Hauptspannungsrichtungen sind: σ1 52 → 270, σ2 38 → 085 und σ3 06 → 174. Die Rotation der Hauptspannungsrichtungen war mit einer ?nderung von einem kompressionalen N-S gerichteten (D3) hin zu einem extensionalen (D4) Stressfeld verbunden. Die erzielten Ergebnisse sind sehr ?hnlich mit Resultaten, die Fl?ttmann und Oncken (1992) im Pf?lzer Wald ermittelten. Dies weist auf ein regional übereinstimmendes Spannungsfeld im SW-Teil der Mitteldeutschen Kristallinzone hin.
Received July 8, 1999; revised version accepted March 28, 2000 相似文献
3.
On the basis of mineral paragenesis and the chemistry and homogenization temperatures of fluid inclusions, the physicochemical
parameters were calculated for the formation of the Dalingkou Ag-Pb-Zn deposit in Zhejiang. From the early to the late stage
of mineralization the ore-forming temperature venation was found to be 298.5 °C → 267.0 °C → 217.6 °C → 167.3 °C, with a corresponding
pH change of 3.0 ∼ 5.8 → 6.1 → 6.7→ 5.0 ∼ 7.3. The pressure changed from 403.8 to 128.5 atm, andlogf S2-9.9 → -11.2 → < -15; logf o2< -44→ -45.6 ∼ -42.6 → > -44.2; and logf co2 around -1.55.
In conjunction with geological observations, the deposit is considered to be of meso-epithermal origin, i.e., it was formed
after continental volcanic-subvolcanic activity. The major factors affecting ore precipitation are the decreasing temperature
and the increasing pH of ore-forming solutions. 相似文献
4.
Polarization and radiation measurements and microwave studies show that the planets and the great majority of asteroids in the solar system are covered by soils similar to regolith on the moon surface.The soils repesent the composition of the asteroids and the geological elements of the planets. The spectral reflectance shows a tendency of decreasing from near ultraviolet,visible to near-infrared in order of LL→L→H→H with increasing Fe^0/Fet rato and toward to absorption for Jilin,Xinyang and Zanoyang ordinary chondrites and Qinzhen enstatite chondrite recently fallen in China,The same chemical group of meteorites feature deeper absorption valleys with increasing metamorphic grade.The spectal reflectance of igneous rocks varies from strong to what is like that of H-group chondrites in order of acid→basic→ultrabasic rocks. 相似文献
5.
Magnesian metamorphic rocks with metapelitic mineral assemblage and composition are of great interest in metamorphic petrology for their ability to constrain P–T conditions in terranes where metamorphism is not easily visible. Phase–assemblage diagrams for natural and model magnesian metapelites in the system KFMASH are presented to document how phase relationships respond to water activity, bulk composition, pressure and temperature. The phase assemblages displayed on these phase diagrams are consistent with natural mineral assemblages occurring in magnesian metapelites. It is shown that the equilibrium assemblages at high pressure conditions are very sensitive to a(H2O). Specifically, the appearance of the characteristic HP assemblage chloritoid–talc–phengite–quartz (with excess H2O) in the magnesian metapelites of the Monte Rosa nappe (Western Alps) is due to the reduction of a(H2O). Furthermore, the mineral assemblages are determined by the whole-rock FeO/(FeO+MgO) ratio and effective Al content X
A as well as P and T. The predicted mineral associations for the low- and high-X
A model bulk compositions of magnesian metapelites at high pressure are not dependent on the X
A variations as they show a similar sequence of mineral assemblages. Above 20 kbar, the prograde sequence of assemblages associated with phengite (with excess SiO2 and H2O) for low- and high-X
A bulk compositions of magnesian metapelites is: carpholite–chlorite → chlorite–chloritoid → chloritoid–talc → chloritoid–talc–kyanite → talc–garnet–kyanite → garnet–kyanite ± biotite. At low to medium P–T conditions, a low-X
A stabilises the phengite-bearing assemblages associated with chlorite, chlorite + K-feldspar and chlorite + biotite while a high-X
A results in the chlorite–phengite bearing assemblages associated with pyrophyllite, andalusite, kyanite and carpholite. A high-X
A magnesian metapelite with nearly iron-free content stabilises the talc–kyanite–phengite assemblage at moderate to high P–T conditions. Taking into account the effective bulk composition and a(H2O) involved in the metamorphic history, the phase–assemblage diagrams presented here may be applied to all magnesian metapelites that have compositions within the system KFMASH and therefore may contribute to gaining insights into the metamorphic evolution of terranes. As an example, the magnesian metapelites of the Monte Rosa nappe have been investigated, and an exhumation path with P–T conditions for the western roof of the Monte Rosa nappe has been derived for the first time. The exhumation shows first a near-isothermal decompression from the Alpine eclogite peak conditions around 24 kbar and 505°C down to approximately 8 kbar and 475°C followed by a second decompression with concomitant cooling.M. Frey: deceased 相似文献
6.
Helen Newton Stuart A. Hayward Simon A. T. Redfern 《Physics and Chemistry of Minerals》2008,35(1):11-16
The thermal anomalies associated with the Ia3d → I41/acd → I41/a transition sequence of phase transitions in leucite have been studied by differential scanning calorimetry and interpreted
with Landau theory. Both transitions are close to the tricritical point. The coupling between the two transitions is biquadratic,
and reduces the stability of the I41/a phase. 相似文献
7.
Daisuke Nishio-Hamane Asa Shimizu Ritsuko Nakahira Ken Niwa Asami Sano-Furukawa Taku Okada Takehiko Yagi Takumi Kikegawa 《Physics and Chemistry of Minerals》2010,37(3):129-136
The stability and equation of state for the cotunnite phase in TiO2 were investigated up to a pressure of about 70 GPa by high-pressure in situ X-ray diffraction measurements using a laser-heated
diamond anvil cell. The transition sequence under high pressure was rutile → α-PbO2 phase → baddeleyite phase → OI phase → cotunnite phase with increasing pressure. The cotunnite phase was the most stable
phase at pressures from 40 GPa to at least 70 GPa. The equation of state parameters for the cotunnite phase were established
on the platinum scale using the volume data at pressures of 37–68 GPa after laser annealing, in which the St value, an indicator of the magnitude of the uniaxial stress component in the samples, indicates that these measurements were
performed under quasi-hydrostatic conditions. The third-order Birch-Murnaghan equation of state at K
0′ = 4.25 yields V
0 = 15.14(5) cm3/mol and K
0 = 294(9), and the second-order Birch-Murnaghan equation of state yields V
0 = 15.11(5) cm3/mol and K
0 = 306(9). Therefore, we conclude that the bulk modulus for the cotunnite phase is not comparable to that of diamond. 相似文献
8.
Li Guowu Shi Nicheng Xiong Ming Ma Zhesheng Bai Wenji Fang Qingsong 《Frontiers of Earth Science》2007,1(1):21-25
The origin of native Si-Fe alloy mineral is thought to be related with mantle and aerolite. The native Si-Fe alloy minerals
from podiform chromites of the Luobusha ophiolite in the Yarlong Zangbo suture zone were examined by a new method for powder-like
diffractograms of small single crystals, using an SMART APEX-CCD area-detector X-ray diffractometer. The powder diffraction
pattern shows that the minerals are composed of FeSi, FeSi2, β-FeSi2 and native silicon. The association of these minerals suggests that the crystallization order of the mineral may be from
early to late FeSi→FeSi2→native silicon, accompanied by gradually increasing deoxidization.
Translated from Acta Petrologica et Mineralogica, 2005, 24(5): 453–456 [译自: 岩石矿物学杂志] 相似文献
9.
F, Cl, S and P were determined, using electron microprobe, in magmatic inclusions trapped within minerals and glass mesostasis
from Wudalianchi volcanic rocks. The initial volcanic magma from Wudalianchi corresponds to the basanitic magma crystallized
near the surface ( pressure < 91 Mpa ). The potential H2O content of this magma is in the range 2 — 4 wt. %. The initial composition of volcanic magmas varies regularly from early
to late volcanic events. From the Middle Pleistocene to the recent eruptions (1719 – 1721 yr.), the basicity of volcanic magma
tends to increase, as reflected by an increase in MgO and CaO contents and by a progressive decrease in SiO2 and K2O contents. Meanwhile. from early (Q2 ) to late (Q3) episodic eruptions of the Middle Pleistocene, the initial concentrations of chlorine in volcanic magmas range from 1430
– 1930 ppm to 1700 ppm and decrease to 700 — 970 ppm for the first episodic eruption during the Holocene (Q
4
1
). The chlorine concentrations of volcanic magmas of recent eruption (Q
4
2
) are increased again to 2600 – 2870 ppm. A parallel evolution trend for phosphorus and chlorine concentrations in magmas
has been certified: 1500 – 5970 ppm (Q2)→ 3500 – 4210 ppm (Q3)→ 1100– 3500 ppm (Q
4
1
)→ 6800– 7900 ppm (Q
4
2
). The fluorine contents of volcanic magmas, from early to late volcanic events, show the same trend: 770 – 2470 ppm → 200–700
ppm → 700 – 800 ppm.
During the crystallization-evolution of volcanic magmas, fluorine and phosphorus tend to be enriched in residual magmas as
a result of crystal-melt differentiation. for example. the fluorine contents reach 5000– 6800 ppm and the phosphorus contents,
2.93wt.% in residual magmas. An appreciable amount of chlorine may be lost from water rich volcanic magmas prior to eruption
as a result of degassing. Apparently, water serves as a gas carrier for the chlorine. The chlorine contents of residual magmas
may decrease to 100 – 300 ppm.
The volcanic magmas from Wudalianchi are poor in sulfur, normally ranging from 200 to 400ppm. On account of the behavior of
sulfur in magmas and the strontium and oxygen isotopic analyses ((87Sr /86Sr)i=0.70503– 0.70589; δ18O = + 5.50 – + 6.89 ‰ ), it can be considered that the basanitic magmas in the Wudalianchi volcanic area came from the upper
mantle and have not yet been contaminated probably by continental crust materials. 相似文献
10.
Björn Winkler Mark J. Harris Roger S. Eccleston Karsten Knorr Bernard Hennion 《Physics and Chemistry of Minerals》1997,25(1):79-82
Inelastic magnetic neutron scattering has been used to determine the energy of the 4
A
2→4
T
2 transition in CoAl2O4 spinel and the δ1 transition in Co2[Al4Si5]O18 cordierite. The observed crystal field splitting in Co-spinel is 485 meV (3900 cm−1), which corresponds to a crystal field stabilization energy of 56.2 kJmol−1. The transition energy of the δ1 transition in Co-cordierite has been determined to be 21 meV (170 cm−1). The present data demonstrate that magnetic neutron scattering can be used to measure crystal field transitions at energies
of interest in the study of 3d-containing silicates. It may be used to measure transition energies when the use of optical spectroscopy is inappropriate.
Received: 30 January 1997 / Accepted: 5 July 1997 相似文献
11.
Paul Karabinos 《Contributions to Mineralogy and Petrology》1985,90(2-3):262-275
During prograde metamorphism garnet and, in some higher grade samples, staurolite were produced in a chlorite-chloritoid schist,
part of the Precambrian Z to Cambrian Hoosac Formation near Jamaica, VT. Garnet grew during two prograde events separated
by a retrogression. This sequence resulted in distinctive inclusion textures and zoning anomalies in garnet produced by diffusive
alteration. Textures, reaction space analysis, and mineral compositional variations constrain the possible sequence of reactions
in these rocks. Below the staurolite isograd, and to some unknown extent above it, garnet grew by the reaction chloritoid+chlorite+quartz→garnet+H2O. With increasing grade the mineral compositions are displaced towards lower Mn/Fe and higher Mg/Fe ratios. The data are
compatible with equilibrium with respect to exchange reactions for the matrix assemblages on a thin section scale and with
minerals having closely followed equilibrium paths during reaction. The staurolite isograd coincides with the reaction chloritoid+quartz→garnet+staurolite+chlorite+H2O. This reaction is continuous and trivariant with ZnO becoming an additional component concentrated in staurolite. During
this reaction both the Mn/Fe and Mg/Fe ratios of the phases appear to have decreased. This new chemical trend is recorded by garnet zoning profiles
and is compatible with trends predicted from phase diagrams. Thus there are two distinct types of garnet zoning reversals
in these samples. One is near the textural unconformity and is best explained by diffusive alteration during partial resorption
of first stage garnet. The other occurs near the outer rim of garnet in staurolite zone samples and marks the onset of a new
prograde garnet producing reaction. 相似文献
12.
Time-resolved luminescence spectra of natural and synthetic hydrous volcanic glasses with different colors and different
Fe, Mn, and H2O content were measured, and the implications for the glass structure are discussed. Three luminescence ranges are observed
at about 380–460, 500–560, and 700–760 nm. The very short-living (lifetimes less than 40 ns) blue band (380–460 nm) is most
probably due to the 4T2(4D) →6A1(6S) and 4A1(4G) →6A1(6S) ligand field transitions of Fe3+. The green luminescence (500–560 nm) arises from the Mn2+ transition 4T1(4G) →6A1(6S). It shows weak vibronic structure, short lifetimes less than 250 μs, and indicates that Mn2+ is tetrahedrally coordinated, occupying sites with similar distortions and ion–oxygen interactions in all samples studied.
The red luminescence (700–760 nm) arising from the 4T1(4G) →6A1(6S) transition of Fe3+ has much longer lifetimes of the order of several ms, and indicates that ferric iron is also mainly tetrahedrally coordinated.
Increasing the total water content of the glasses leads to quenching of the red luminescence and decrease of the distortions
of the Fe3+ polyhedra.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
13.
Thermal behaviour of γ-anhydrite (γ-CaSO4, soluble anhydrite) has been investigated in situ real-time using laboratory parallel-beam X-ray powder diffraction data.
Thermal expansion has been analysed from 303 to 569 K with temperature steps of 4 K. Lattice parameters and volume were fitted
with a second-order polynomial to calculate thermal expansion coefficients. Thermal expansion of γ-anhydrite is anisotropic
being larger along the c axis. Within the 343–383 K thermal range, γ-anhydrite has been found to partially re-hydrate to bassanite CaSO4·0.5H2O. At 455 K the transformation γ-CaSO4 → β-CaSO4, insoluble anhydrite, starts reaching completion at 653 K. 相似文献
14.
Michail N. Taran Haruo Ohashi Monika Koch-Müller 《Physics and Chemistry of Minerals》2008,35(3):117-127
Six synthetic NaScSi2O6–CaNiSi2O6 pyroxenes were studied by optical absorption spectroscopy. Five of them of intermediate (Na1−x
, Ca
x
)(Sc1−x
, Ni
x
)Si2O6 compositions show spectra typical of Ni2+ in octahedral coordination, more precise Ni2+ at the M1 site of the pyroxene structure. The common feature of all spectra is three broad absorption bands with maxima around
8,000, 13,000 and 24,000 cm−1 assigned to 3
A
2g → 3
T
2g, 3
A
2g → 3
T
1g and →3
T
1g (3
P) electronic spin-allowed transitions of VINi2+. A weak narrow peak at ∼14,400 cm−1 is assigned to the spin-forbidden 3
A
2g → 1
T
2g (1
D) transition of Ni2+. Under pressure the spin-allowed bands shift to higher energies and change in intensity. The octahedral compression modulus,
calculated from the shift of the 3
A
2g → 3
T
2g band in the (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6 pyroxene is evaluated as 85±20 GPa. The Racah parameter B of Ni2+(M1) is found gradually changing from ∼919 cm−1 at ambient pressure to ∼890 cm−1 at 6.18 GPa. The Ni end-member pyroxene [(Ca0.93 Ni0.07)NiSi2O6] has a spectrum different from all others. In addition to the above mentioned bands of Ni2+(M1) it displays several new relatively intense and broad extra bands, which were attributed to electronic transitions of
Ni2+ at the M2 site. In difference to CaO8 polyhedron geometry of an eightfold coordination, Ni2+(M2)O8 polyhedra are assumed to be relatively large distorted octahedra. Due to different distortions and different compressibilities
of the M1 and M2 sites the Ni2+(M1)- and Ni2+(M2)-bands display rather different pressure-induced behaviors, becoming more resolved in the high-pressure spectra than in
that measured at atmospheric pressure. The octahedral compression modulus of Ni2+(M1) in this end-member pyroxene is evaluated as 150 ± 25 GPa, which is noticeably larger than in Ni0.3 pyroxene. This is due to a smaller size and, thus, a stiffer character of Ni2+(M1)O6 octahedron in the (Ca0.93Ni0.07)NiSi2O6 pyroxene compared to (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6.
相似文献
Monika Koch-MüllerEmail: |
15.
Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam
X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The
high-temperature limits for the cell edges and for the cell volume, calculated using the Einstein equation, are 4.29 × 10−6, 4.94 × 10−5, 2.97 × 10−5, and 8.21 × 10−5. Thermal expansion of gypsum is strongly anisotropic being larger along the b axis mainly due to the weakening of hydrogen bond. Dehydration of gypsum has been investigated in isothermal conditions within the 348–403 K range with a temperature
increase of 5 K. Dehydration proceeds through the CaSO4·2H2O → CaSO4·0.5H2O → γ-CaSO4 steps. Experimental data have been fitted with the Avrami equation to calculate the empirical activation energy of the process.
No change in transformation mechanism has been observed within the analysed temperature range and the corresponding E
a is 109(12) kJ/mol. 相似文献
16.
M. N. Taran H. Ohashi K. Langer A. A. Vishnevskyy 《Physics and Chemistry of Minerals》2011,38(5):345-356
Comparison of polarized optical absorption spectra of natural Ca-rich diopsides and synthetic NaCrSi2O6 and LiCrSi2O6 clinopyroxenes, evidences as vivid similarities, as noticeable differences. The similarities reflect the fact that in all
cases Cr3+ enters the small octahedral M1-site of the clinopyroxene structure. The differences are due to some iron content in the natural
samples causing broad intense near infrared bands of electronic spin-allowed dd transitions of Fe2+(M1, M2) and intervalence Fe2+/Fe3+ charge-transfer transition, and by different symmetry and different local crystal fields strength of Cr3+ in the crystal structures. The positions of the spin-allowed bands of Cr3+, especially of the low energy one caused by the electronic 4
A
2g → 2
T
1g transition, are found to be in accordance with mean M1–O distances. The local relaxation parameter ε calculated for limCr
3+ → 0 from the spectra and interatomic
á Cr - O
ñ \left\langle {Cr - O} \right\rangle and
á Mg - O
ñ \left\langle {Mg - O} \right\rangle distances yields a very high value, 0.96, indicating that in the clinopyroxene structure the local lattice relaxation around
the “guest” ion, Cr3+, deviates greatly from the “diffraction” value, ε = 0, than in any other known Cr3+-bearing systems studied so far. Under pressure the spin-allowed bands of Cr3+ shift to higher energies and decrease in intensity quite in accordance with the crystal field theoretical expectations, while
the spin-forbidden absorption lines remain practically unshifted, but also undergo a strong weakening. There is no evident
dependence of the Racah parameter B of Cr3+ reflecting the covalence of the oxygen-chromium bond under pressure: within the uncertainty of determination it may be regarded
as practically constant. The values of CrO6 octahedral modulus,
k\textpoly\textloc k_{\text{poly}}^{\text{loc}} , derived from high-pressure spectra of natural chromium diopside and synthetic NaCrSi2O6 kosmochlor are very close, ~203 and ~196 GPa, respectively, being, however, nearly twice higher than that of MgO6 octahedron in diopside, 105(4) GPa, obtained by Thompson and Downs (2008). Such a strong stiffening of the structural octahedron, i.e. twice higher value of
k\textCr3 + \textloc k_{{{\text{Cr}}^{3 + } }}^{\text{loc}} comparing with that of
k\textMg2 + \textloc k_{{{\text{Mg}}^{2 + } }}^{\text{loc}} , may be caused by simultaneous substitution of Ca2+ by larger Na+ in the neighboring M2 sites at so-called jadeite-coupled substitution Mg2+ + Ca2+ → Cr3+ + Na+. It is also remarkable that the values of CrO6 octahedral modulus of NaCrSi2O6 kosmochlor obtained here are nearly twice larger than that of 90(16) GPa, evaluated by high-pressure X-ray structural refinement
by Origlieri et al. (2003). Taking into account that the overall compressibility of the clinopyroxene structure should mainly be due to the compressibility
of M1- and M2-sites, our
k\textCr3 + \textloc k_{{{\text{Cr}}^{3 + } }}^{\text{loc}} -value, ~196 GPa, looks much more consistent with the bulk modulus value, 134(1) GPa. 相似文献
17.
A. N. Platonov A. N. Tarashchan K. Langer M. Andrut G. Partzsch S. S. Matsyuk 《Physics and Chemistry of Minerals》1998,25(3):203-212
A selected set of five different kyanite samples was analysed by electron microprobe and found to contain chromium between <0.001 and 0.055 per formula unit (pfu). Polarized electronic absorption spectroscopy on oriented single crystals,
R1, R2-sharp line luminescence and spectra of excitation of λ3- and λ4-components of R1-line of Cr3+-emission had the following results: (1) The Fe2+–Ti4+ charge transfer in c-parallel chains of edge connected M(1) and M(2) octahedra shows up in the electronic absorption spectra
as an almost exclusively c(||Z′)-polarized, very strong and broad band at 16000 cm−1 if <, in this case the only band in the spectrum, and at an invariably lower energy of 15400 cm−1 in crystals with ≥ . The energy difference is explained by an expansion of the Of–Ok, and Ob–Om edges, by which the M(1) and M(2) octahedra are interconnected (Burnham 1963), when Cr3+ substitutes for Al compared to the chromium-free case. (2) The Cr3+ is proven in two greatly differing crystal fields a and b, giving rise to two sets of bands, derived from the well known
dd transitions of Cr3+
4A2g→4T2g(F)(I), →4T1g(F)(II), and →4T1g(P)(III). Band energies in the two sets a and b, as obtained by absorption, A, and excitation, E, agree well: I: 17300(a, A),
17200(a, E), 16000(b, A), 16200(b, E); II: 24800(a, A), 24400(a, E); 22300(b, A), 22200(b, E); III: 28800(b,A) cm−1. Evaluation of crystal field parameters from the bands in the electronic spectra yield Dq(a)=1730 cm−1, Dq(b)=1600 cm−1, B(a)=790 cm−1, B(b)=620 cm−1 (errors ca. ±10 cm−1), again in agreement with values extracted from the λ3, λ4 excitation spectra. The CF-values of set a are close to those typical of Cr3+ substituting for Al in octahedra of other silicate minerals without constitutional OH− as for sapphirine, mantle garnets or beryl, and are, therefore, interpreted as caused by Cr3+ substituting for Al in some or all of the M(1) to M(4) octaheda of the kyanite structure, which are crystallographically
different but close in their mean Al–O distances, ranging from 1.896 to 1.919 A (Burnham 1963), and slight degrees of distortion.
Hence, band set a originates from substitutive Cr3+ in the kyanite structural matrix. The CF-data of Cr3+ type b, expecially B, resemble those of Cr3+ in oxides, especially of corundum type solid solutions or eskolaite. This may be interpreted by the assumption that a fraction
of the total chromium contents might be allocated in a precursor of a corundum type exsolution.
Received: 3 January 1997 / Revised, accepted: 2 May 1997 相似文献
18.
This paper deciphers the late stress systems involved in the development of kink bands in the perspective of thrust regime.
In kink bands, the correlation coefficient for α–β plots is positive near thrusts and negative away from thrusts. The plots show nearly linear relationship near thrusts and
non-linear relationship away from thrusts. The rotation was prominent mechanism of kink band formation near thrusts and rotation
coupled with shearing, along the kink planes away from thrusts. Along thrusts σ
1 is horizontal E–W trend and it rotates to horizontal N–S trend away from the thrust. The proposed model establishes that
(1) the shearing along kink planes led to angular relationship, β < α and (2) the kink planes of conjugate kinks could be used for paleostress analysis even in those cases where shearing along
these planes has occurred. 相似文献
19.
Discussed in this paper are the processes of albitization and iron activation during the formation of iron deposits, the transport
and hydrolysis of iron, chemical reaction characteristic of wall-rock alteration responsible for the localization of iron
deposits, the dynamic factors affecting these reactions and systematic variations in pH of ore-forming solutions. A metasomatic
series of Na→ Ca→ Fe is noticed when diorite and dark minerals + anorthite + quartz react with 1–3m NaCl solutions at 400°–500°C.
Hydrolysis of FeCl2 has been experimentally studied as a function of temperature and pressure. It is suggested that the pH of ore-forming solutions
varies in the direction of alkalic→intermediate→acid→intermediate←kalic from early to late stages. 相似文献
20.
The kinetics of monodomain order-disorder processes in monoclinic (I2/c) BaAl2Ge2O8-feldspar have been investigated by X-ray powder diffraction, Hard Mode IR Spectroscopy, and TEM darkfield imaging on quenched
samples. Compared to the behaviour predicted by the TDGL approximation ordering kinetics observed at low temperatures slow
down significantly when equilibrium is approached. Such a delay is not observed in disordering experiments starting from essentially
ordered cation distributions. The deviation from TDGL behaviour is interpreted in terms of partial order parameter conservation
in a non-uniformly ordered phase. Modifications to the uniform TDGL rate equation are tested against the available data. An
activation energy of 352 ± 28 kJ/mol is obtained for Al,Ge ordering. The mixing coefficient ξc
2/ξ2, which describes the degree of order parameter conservation, is obtained as a function of temperature. While this coefficient
vanishes in the vicinity of the transformation temperature T
tr, it saturates towards a level of ξc
2/ξ2≈0.4 for T→0. ξ
c
2/ξ2 determines the kinetic stability of ordered clusters quenched from T≈T
tr.
Received: 21 April 1999 / Revised, accepted: 19 July 1999 相似文献