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101.
Prof.Dr. Kanenori Suwa Dr. Masaki Enami Mr. Isuzu Hiraiwa Mr. Tai-ming Yang 《Mineralogy and Petrology》1987,36(2):111-120
Summary Zn-Mn ilmenite occurs as a principal constituent of the miarolitic cavities in the Kuiqi granite from Fuzhou. In the cavities potassium feldspar, albite, quartz, fluorite, aegirine and arfvedsonite also occur with accessory zircon, magnetite, hematite and sphalerite. Zn-Mn ilmenite forms a trigonal platy euhedral crystal up to 30 mm in length. Its chemical composition ranges from 37.3 to 63.8 mol.% FeTiO3 (ilmenite molecule), 61.1 to 22.4 mol.% MnTiO3 (pyrophanite molecule) and 0.6 to 15.3 mol.% ZnTiO3 (Znmetatitanate molecule). ZnO content ranges from 0.34 wt.% to 7.63 wt.%. Zonal structure is noticeable in the Zn-Mn ilmenite. FeTiO3 and ZnTiO3 molecules increase towards the crystal rim, while MnTiO3 molecule decreases towards the rim. Unit cell parameters of the rim and the core area = 5.092(6)Å,c = 14.08(2)Å,V = 316.1Å3 anda = 5.106(7)Å,c = 14.02(3)Å,V = 316.6Å3, respectively. Coexisting minerals, except for arfvedsonite and sphalerite, are very low in ZnO content. It is suggested that complete isomorphous replacement between FeTiO3 MnTiO3 and ZnTiO3 may be possible. Oxygen fugacity conditions for crystallization of Zn-Mn ilmenite are considered to be in the vicinity of the magnetite-hematite and quartz-fayalite-magnetite buffers.
With 4 Figures 相似文献
Zn-Mn Ilmenit in dem Kuigi-Granit aus Fuzhou in der Provinz Fujian, Ostchina
Zusammenfassung Zn-Mn Ilmenit ist ein grundsätzlicher Bestandteil in miarolitischen Hohlräumen in den Kuiqi Graniten aus Fuzhou. Daneben treten Kalifeldspäte, Albit, Quarz, Fluorit, Ägirin und Arfvedsonit sowie akzessorisch Zirkon, Magnetit, Hämatit und Sphalerite in den Hohlräumen auf.Zn-Mn Ilmenit bildet idiomorphe, tabular trigonale Kristalle mit bis zu 30 mm Länge aus. Die chemische Zusammensetzung variiert zwischen 37,3 und 63,8 Mol.% FeTiO3 (Ilmenit) 61,1 und 22,4 Mol.% MnTiO3 (Pyrophanit) sowie zwischen 0,6 und 15,3 Mol.% ZnTiO3 (Zn-Metatitanat-Molekül). Die ZnO-Gehalte schwanken von 0,34 Gew.% bis 7,63 Gew.%. In dem Zn-Mn Ilmenit wurden Zonierungen beobachtet. FeTiO3 und ZnTiO3 Moleküle nehmen zum Rand des Kristalls hin zu, MnTiO3 Moleküle hingegen ab.Die Parameter der Elementarzelle sind am Randa = 5,092(6)Å,c = 14.08(2)Å,V = 316.1Å3 und im Kerna = 5,106(7)Å,c = 14.02(3)Å,V = 316,6Å3. Mit Ausnahme von Arfvedsonit und Sphalerit sind die ZnO Gehalte in koexistierenden Mineralen sehr niedrig.Es wird daher angenommen, daß zwischen FeTiO3, MnTiO3 und ZnTiO3 ein vollständiger isomorpher Ersatz möglich ist. Die Sauerstoff-Fugazitäten die während der Kristallisation von Zn-Mn Ilmenit herrschten, bewegten sich zwischen MagnetitHämatit und Quarz-Fayalit-Magnetit.
With 4 Figures 相似文献
102.
The structural and elastic properties of the ilmenite and perovskite phases of MgSiO3 are investigated with a computational model based on energy minimization. The potential energies of these two crystals are approximated by the sum of Coulomb, van der Waals, and repulsion terms between atoms. Required energy parameters are derived by fitting the parameters to the observed crystal structures of these two phases as well as to the measured elastic constants of the ilmenite phase. The resulting potential model is applied to predicting the elastic constants of the perovskite phase. The calculated bulk modulus of the perovskite phase compares favorably with the data obtained from volume-compression experiments as well as the values estimated from empirical elasticity systematics of perovskite type compounds. The predicted shear modulus of the perovskite phase is also in reasonable agreement with the values proposed from similar empirical elasticity systematics. Subsequently, the model is used to simulate the high pressure behaviors of the crystal structures and elastic constants of these two phases. 相似文献
103.
At high pressures, CdGeO3 pyroxenoid transforms to garnet, then to ilmenite, and finally to perovskite. Enthalpies of transition among the four phases were measured by high temperature calorimetry. The entropies of transition and slopes of the boundaries were calculated using the measured enthalpies and free energies calculated from the phase equilibrium data. Pyroxenoid and garnet are very similar energetically. However garnet is a high pressure phase because of its lower entropy and smaller volume. The pyroxenoid-garnet transition has a small positiveP-T slope. Ilmenite is intermediate in enthalpy between garnet and perovskite, but is lower in entropy than both phases. Therefore the garnet-ilmenite transition has a positivedP/dT, while a negativedP/dT is calculated for the ilmenite-perovskite transition. The thermochemical data for the CdGeO3 phases are generally consistent with the observed high pressure phase relations. The high entropy of perovskite relative to ilmenite, observed in several ABO3 comounds including CdGeO3, is related to the structural features of perovskite, in which relatively small divalent cations occupy the large sites of 8–12 fold coordination. The thermochemistry of the CdGeO3 polymorphs shows several similarities to that of the CaGeO3 system. 相似文献
104.
Hiroshi Satake Masahiko Ohashi Yoshimitsu Hayashi 《Pure and Applied Geophysics》1984,122(2-4):185-193
The concentration of H2 in soil gases has been measured weekly at five stations on the Atotsugawa and Ushikubi faults in northern central Main Island, Japan, since 1981 in search of possible relationship with earthquakes. The observed H2 concentration varies from lower than 1 ppm to 7.8% in time and place. When a large earthquake (M: 7.7, epicenter distance: 486 km) occurred on 26 May 1983, an outstanding discharge of H2 was observed at all five stations, preseismically at three of them, and coseismically at the other two. Simultaneous H2 emission was also observed at some stations in seven other occasions. These periods of unusual H2 discharge nearly coincided with occurrences of major earthquakes in Japan, but not of local minor earthquakes along the Atotsugawa fault. This fault, being a deep fracture zone, may be sensitive to large-scale crustal stress changes which incidentally cause the major earthquakes. Increased H2 may be produced by rock fracture caused by the increased stresses on the fault and by the earthquakes themselves. Local minor earthquakes along Atotsugawa fault with magnitude lower than 3 may be unable to cause sufficient rock fracture to produce significant H2. 相似文献
105.
Coexisting sodic augite and omphacite were found in a zoisite amphibolite from the Iratsu epidote amphibolite mass in the
Sanbagawa metamorphic terrain of central Shikoku, Japan. The occurrences of the sodic augite-omphacite pairs are classified
into four types by texture: independent, composite, intergrowth and exsolution types. Sodic augite and omphacite of the independent
and composite types (pair A) have X
Na (=Na/(Na + Ca)) = 0.15 and 0.35, respectively, and were stable in the epidote amphibolite facies during the Sanbagawa progressive
metamorphism. On the other hand, X
Na values of sodic augite and omphacite of the intergrowth and exsolution types (pair B) are 0.10 and 0.44, respectively. The
Na-poor augite and Na-rich omphacite of the pair B were formed by re-equilibration of the pair A at lower temperature. The
pair A of the Iratsu sample suggests that a compositional gap lies between sodic augite and C2/c omphacite under epidote amphibolite
facies conditions, and is in marked contrast to the coexistence of sodic augite and P2/n omphacite reported from some low-grade,
high-pressure metamorphic terrains. A possible phase diagram to explain the chemistry and mode of occurrence of the coexisting
sodic pyroxenes is proposed. 相似文献
106.
— We addressed effects of in situ stress on the formation of flow pathways in fractured rocks in geothermal reservoirs, especially for HDR projects. Here we focused on fractures which are critically-stressed, causing shear slip in a current stress field. The sliding is likely to break sealing in the fractures and, as a result, to increase their permeability. Such a mechanism is possibly significant under high-temperature conditions at geothermal fields because of temperature enhancement on chemical reactions for the sealing. We present a procedure to estimate the orientation of the critically-stressed fractures relative to axes of in situ principal stress with the aid of the Mohr diagram. The procedure allows us to evaluate intuitively how the orientation changes with factors such as magnitude of in situ principal stresses and pore pressure. We applied the procedure to estimate possible orientations of the critically-stressed fractures in major HDR test sites. Results show that overall alignments of microseismicity during hydraulic stimulation are within predicted ranges for possible orientations of the critically-stressed fractures. Furthermore, it was found that if the state of in situ stress is not favorable to cause sliding of natural fractures, it tends to lead a high wellhead pressure at hydraulic stimulation and a high recovery rate at circulation. On the other hand, if the state of in situ stress is favorable for sliding, it tends vice versa to lead a low wellhead pressure at hydraulic stimulation and a low recovery rate at circulation. 相似文献
107.
108.
Masaki Akaogi Akira TanakaEiji Ito 《Physics of the Earth and Planetary Interiors》2002,132(4):303-324
Phase relations in the system Mg4Si4O12-Mg3Al2Si3O12 were examined at pressures of 19-27 GPa and relatively low temperatures of 800-1000 °C using a multianvil apparatus to clarify phase transitions of pyroxene-garnet assemblages in the mantle. Both of glass and crystalline starting materials were used for the experiments. At 1000 °C, garnet solid solution (s.s.) transforms to aluminous ilmenite s.s. at 20-26 GPa which is stable in the whole compositional range in the system. In Mg4Si4O12-rich composition, ilmenite s.s. transforms to a single-phase aluminous perovskite s.s., while Mg3Al2Si3O12-rich ilmenite s.s. dissociates into perovskite s.s. and corundum s.s. These newly determined phase relations at 1000 °C supersede preliminary phase relations determined at about 900 °C in the previous study. The phase relations at 1000 °C are quite different from those reported previously at 1600 °C where garnet s.s. transforms directly to perovskite s.s. and ilmenite is stable only very close to Mg4Si4O12. The stability field of Mg3Al2Si3O12 ilmenite was determined at 800-1000 °C and 25-27 GPa by reversed phase boundaries. In ilmenite s.s., the a-axis slightly increases but the c-axis and molar volume decrease substantially with increasing Al2O3 content. Enthalpies of ilmenite s.s. were measured by differential drop-solution calorimetry method using a high-temperature calorimeter. The excess enthalpy of mixing of ilmenite s.s. was almost zero within the errors. The measured enthalpies of garnet-ilmenite and ilmenite-perovskite transitions at 298 K were 105.2±10.4 and 168.6±8.2 kJ/mol, respectively, for Mg4Si4O12, and 150.2±15.9 and 98.7±27.3 kJ/mol, respectively, for Mg3Al2Si3O12. Thermodynamic calculations using these data give rise to phase relations in the system Mg4Si4O12-Mg3Al2Si3O12 at 1000 and 1600 °C that are generally consistent with those determined experimentally, and confirm that the single-phase field of ilmenite expands from Mg4Si4O12 to Mg3Al2Si3O12 with decreasing temperature. The earlier mentioned phase relations in the simplified system as well as those in the Mg2SiO4-Fe2SiO4 system are applied to estimate mineral proportions in pyrolite as a function of depth along two different geotherms: one is a horizontally-averaged temperature distribution in a normal mantle, and the other being 600 °C lower than the former as a possible representative geotherm in subducting slabs. Based on the previously described estimated mineral proportions versus depth along the two geotherms, density and compressional and shear wave velocities are calculated as functions of depth, using available mineral physics data. Along a normal mantle geotherm, jumps of density and velocities at about 660 km corresponding to the post-spinel transition are followed by steep gradients due to the garnet-perovskite transition between 660 and 710 km. In contrast, along a low-temperature geotherm, the first steep gradients of density and velocities are due to the garnet-ilmenite transition between 610 and 690 km. This is followed by abrupt jumps at about 690 km for the post-spinel transition, and steep gradients between 700 and 740 km that correspond to the ilmenite-perovskite transition. In the latter profile along the low-temperature geotherm, density and velocity increases for garnet-ilmenite and ilmenite-perovskite transitions are similar in magnitude to those for the post-spinel transition. The likely presence of ilmenite in cooler regions of subducting slabs is suggested by the fact that the calculated velocity profiles along the low-temperature geotherm are compatible with recent seismic observations indicating three discontinuities or steep velocity gradients at around 600-750 km depth in the regions of subducting slabs. 相似文献
109.
Kuh Kim Young-Gyu Kim Yang-Ki Cho Masaki Takematsu Yuri Volkov 《Journal of Oceanography》1999,55(2):103-109
Analysis of CTD data from four CREAMS expeditions carried out in summers of 1993–1996 produces distinct T-S relationships
for the western and eastern Japan Basin, the Ulleung Basin and the Yamato Basin. T-S characteristics are mainly determined
by salinity as it changes its horizontal pattern in three layers, which are divided by isotherms of 5°C and 1°C; upper warm
water, intermediate water and deep cold water. Upper warm water is most saline in the Ulleung Basin and the Yamato Basin.
Salinity of intermediate water is the highest in the eastern Japan Basin. Deep cold water has the highest salinity in the
Japan Basin. T-S curves in the western Japan Basin are characterized by a salinity jump around 1.2–1.4°C in the T-S plane,
which was previously found off the east coast of Korea associated with the East Sea Intermediate Water (Cho and Kim, 1994).
T-S curves for the Japan Basin undergo a large year-to-year variation for water warmer than 0.6°C, which occupies upper 400
m. It is postulated that the year-to-year variation in the Japan Basin is caused by convective overturning in winter.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
110.
新疆阿勒泰地区发育了红柱石-矽线石型递增变质带,由绿泥石-黑云母带、黑云母-石榴石带、石榴石-十字石带、十字石-红柱石带和矽线石带组成,根据石榴石成分环带、变质与变形关系、矿物共生组合演化等特征,将变质作用分为峰前期、峰期和峰后期3个演化阶段。峰前期、峰期为连续的递增变质过程,形成典型的中-低压过渡型递增变质带,峰后期属于退变质过程。据石榴石一斜长石一黑云母-白云母-石英组合内部一致地质温压计估算出峰期温度-压力:T=580℃~670℃,P一0.4GPa~0.5GPa。变质作用演化具有顺时针的PTt轨迹,代表陆壳有一定程度的构造增厚,但幅度不大,没有大规模的陆壳俯冲或拆沉作用,这种增厚可能以陆壳的构造叠置机制为主。总体相当于地体间斜向走滑兼有一定垂直分量的拼合过程的地球动力学机制。 相似文献