Melting of plagioclase-quartz assemblages at 2 kbar water pressure

The melting of plagioclase and quartz has been investigated at P _H2O =2kb. A single crystal of plagioclase was surrounded by quartz powder and water. A reaction rim consisting of glass and of An-rich plagioclase developed around unchanged starting plagioclase. Microprobe determinations of melt and coexisting plagioclase compositions reveal a strong fractionation of plagioclase components between melt and new plagioclase. For example at 850° C the approximate X _An of melt is 0.3 and that of plagioclase is 0.8. The temperature interval between beginning of melting and complete melting of cotectic compositions is 100° C or more for quartz-plagioclase mixtures with plagioclases between An 40 and An 75. In comparison to the system Ab-An-H₂O the plagioclase melting loop is somewhat wider in the investigated system Qz-Ab-An-H₂O but the temperature interval is much smaller (100° C) than in the system Ab-An-H₂O (200° C). The solidus data indicated by the new plagioclase compositions are practically identical with those observed in beginning of melting experiments. The results show that fractionation of plagioclase components between partial melts and restite plagioclase can be more pronounced in multi-component rocks than in the pure plagioclase system. This finding is important for the development of albite rich rocks from more basic compositions.     

同步辐射激光加温DAC技术及在地球深部物质研究中的应用

实验室模拟地球深部的温度和压力环境,研究地球相关材料的物理和化学性质,是解释地震波数据、进一步了解地球内部结构和动力学过程的重要途径。用高功率的红外激光光束,加温金刚石对顶砧压腔(DAC)中的样品,可以获得深部地幔乃至地核的极端温度和压力条件,已广泛地用于地球深部矿物的相变、熔融和状态方程研究。同步辐射微束技术的发展,为激光加温DAC技术的应用开辟了新的领域,也使地幔及地核条件下的矿物研究有了重要的突破。文章介绍激光加温DAC技术的发展;阐述高温高压原位的同步辐射X射线衍射方法;例举激光加温DAC技术在地球深部物质研究中的一些应用;并对一些关键的技术问题加以分析和讨论。     

The compressibility of FeO measured by energy dispersive X-ray diffraction in a diamond anvil squeezer up to 200 kbar

The compressibility of Fe_0.941O has been measured by energy-dispersive X-ray diffraction methods in a diamond anvil squeezer up to 200 kbar. The data points can be described by the Murnaghan equation with K ₀=1,540±50 kbar and K'=4. An analysis of previous investigations, X-ray diffraction and ultrasonic measurements yields for the general composition Fe_1?xO a regression line K ₀=5,438(1?x)?3,595 kbar for all known measurements.     

Melting of carbon at 50 to 300 kbar

Diamond (～1 μm) and graphite (1–10 μm) in NaCl were melted at 50 to 300 kbar in a diamond anvil cell using a pulsed YAG laser. The samples were removed from the cell and the structures of the quenched phases were studied by transmission electron microscopy. The melted regions of the samples were found to consist of nearly perfect spheres of carbon ranging in size from ～1 μm down to less than a few nanometers. In the diamond sample melted at 300 kbar, the larger spherules (>0.2 μm) are polycrystalline diamond with either a granular or radial texture. The smaller spherules (<0.2 μm) give electron diffraction patterns with four diffuse rings that correspond to the 002, 100, 004 and 110 of graphite. This diffraction pattern is typical of disordered graphite randomly oriented about the c-axis. Dark field imaging, using a portion of the 002 ring, produces a “bow tie” figure in each of the smaller spherules. The orientation of the “bow tie” figure depends on the portion of the ring used to form the image, and indicates a radial orientation of the c-axis of the disordered graphite. The spacing between the 002 layers depends on the pressure at the time of melting. We interpret this to indicate that there is some sp³ bonding between layers in the disordered graphite in the smaller spherules. The smaller spherules may have the disordered graphite structure because of the effect of the size on the free energy relationship between the phases, or they may have been quenched more rapidly than the larger spherules thus preserving some of the character of the melt. If the latter explanation is correct, then our results may indicate that the diamond melt contains significant sp² bonding. Lattice images (Fig. 12) of the internal structure of the smallest spherules observable (～50 A) clearly show that the carbon layers are parallel to the surface of the spherules and that there is a great deal of disorder in the layers. These observations are entirely consistent with our conclusions based on the dark field images.     

Melting of wüstite and iron up to pressures of 600 kbar

The effect of pressure on melting temperature of wüstite and iron has been measured with laser-heated diamond anvil cell. The temperature was determined by measuring the thermal radiation emitted by the sample as a function of wavelength in the range from 600 nm to 900 nm to which Planck's radiation function was fitted; the pressure was measured by ruby-fluorescence technique. The melting curve of wüstite in this study when extrapolated to low pressures agrees with Lindsley's (1966) data. Our data are similar to the recent data of Boehler (1992) and close to that of Ringwood and Hibberson (1990) at pressure of 160 kbar, but the melting temperature does not rise as rapidly with increasing pressure as reported by Knittle and Jeanloz (1991). If tungsten emissivity is used in the temperature calculation, the melting curve of iron matches those of Boehler et al. (1990). Use of emissivity of iron in the temperature calculation results in somewhat higher temperatures than those reported by Boehler et al. (1990).     

Melting experiments on the enstatite-diopside join at 70–224 kbar,including the melting of diopside

 Melting relations on the enstatite−diopside (En, Mg₂Si₂O₆−Di, CaMgSi₂O₆) join, including the compositions of crystalline phases and melts coexisting along the solidi, were experimentally determined in the pressure range 70–224 kbar with a split-sphere anvil apparatus (USSA-2000). Melting is peritectic in enstatite-rich compositions at 70–124 kbar (1840–2100° C) and eutectic at higher pressures, while the diopside-rich clinopyroxene melts azeotropically at 70–165 kbar and up to 300° C lower temperatures than the eutectic. Orthopyroxene is replaced with enstatite-rich clinopyroxene at 120 kbar and 2090°C. First garnet with 17 mol% Di forms on the solidus at 158 kbar and 2100° C. Two garnets coexist on the solidus at 165–183 kbar and 2100° C, garnet coexists with CaSiO₃ perovskite at 183–224 kbar (2100–2230° C) and two coexisting perovskites are stable at higher pressures. The melting curve of diopside was determined at 80–170 kbar; the slope becomes negative at 140 kbar and 2155° C. At 170 kbar and 2100° C, diopside with 96% Di breaks down to garnet with 89% Di and CaSiO₃ perovskite. The new data were used to calculate an improved temperature-pressure phase diagram for the CMAS system, which can be useful for estimating the mineralogy of the Earth's upper mantle. Received: 15 October 1994 / Accepted: 15 October 1995     

金刚石压腔（DAC）技术及其在地球科学中的应用

近几十年来金刚石压腔（DAC）技术被广泛应用于高温高压实验研究领域,它可以达到550GPa的压力和6 000K的温度。与其他静高压实验技术（大压力机、高压釜等）相比,金刚石压腔具有独特的优势,它不仅可以进行极端温压条件下物质的结构性质、相变及状态方程等研究,而且可以原位观测整个实验过程。文中简述了金刚石压腔装置的结构及温压测量方法,然后分别从物质相变、矿物溶解度、流体性质和组成、油气成因、稳定同位素分馏系数和布里渊声学测量等方面简要介绍了金刚石压腔技术在地球科学中的研究进展。随着实验技术的不断发展和更新,金刚石压腔技术将具有更广阔的应用前景。     

Development of density measurement for metals at high pressures and high temperatures using X-ray absorption imaging combined with externally heated diamond anvil cell

A technique for density measurement under high pressure and high temperature was developed using the X-ray absorption imaging method combined with an externally heated diamond anvil cell. The densities of solid and liquid In were measured in the pressure and temperature ranges of 3.2–18.6 GPa and 294–719 K. The densities obtained through the X-ray absorption imaging method were in good agreement (less than 2.0% difference) with those obtained through X-ray diffraction. Based on the measured density, the isothermal bulk modulus of solid In is determined as 48.0 ± 1.1?40.9 ± 0.8 GPa at 500 K, assuming K′ = 4 to 6. The compression curve of liquid In approaches that of solid In at higher pressures and does not cross over the solid compression curve in the measurement range. The present technique enables us to determine the densities of both solids and liquids precisely in a wide pressure and temperature range.     

Dehydration Melting of Metabasalt at 8-32 kbar: Implications for Continental Growth and Crust-Mantle Recycling

We report the results of partial melting experiments between8 and 32 kbar, on four natural amphibolites representative ofmetamorphosed Archean tholeiite (greenstone), high-alumina basalt,low-potassium tholeiite and alkali-rich basalt. For each rock,we monitor changes in the relative proportions and compositionof partial melt and coexisting residual (crystalline) phasesfrom 1000 to 1150C, within and beyond the amphibole dehydrationreaction interval. Low percentage melts coexisting with an amphiboliteor garnet amphibolite residue at 1000–1025C and 8–16kbar are highly silicic (high-K₂O granitic at 5%; melting, low-Al₂O₃trondhjemitic at 5–10%). Greater than 20% melting is onlyachieved beyond the amphibole-out phase boundary. Silicic tointermediate composition liquids (high-Al₂O₃ trondhjemitic-tonalitic,granodioritic, quartz dioritic, dioritic) result from 20–40%melting between 1050 and 1100C, leaving a granulite (plagioclase+ clinopyroxene orthopyroxene olivine) residue at 8 kbarand garnet granulite to eclogite (garnet + clinopyroxene) residuesat 12–32 kbar. Still higher degrees of melting ( 40–60%)result in mafic liquids corresponding to low-MgO, high-Al₂O₃basaltic and basaltic andesite compositions, which coexist withgranulitic residues at 8 kbar and edogitic or garnet granulitic(garnet + clinopyroxene + plagioclase orthopyroxene) residuesat higher pressures (12–28 kbar). As much as 40% by volumehigh-Al₂O₃ trondhjemitic-tonalitic liquid coexists with an eclogiticresidue at 1100–1150C and 32 kbar. The experimental datasuggest that the Archean tonalite-trondhjemite-granodiorite(TTG) suite of rocks, and their Phanerozoic equivalents, thetonalite-trondhjemite-dacite suite (including ‘adakites’and other Na-rich granitoids), can be generated by 10–40%melting of partially hydrated metabasalt at pressures abovethe garnet-in phase boundary (12 kbar) and temperatures between1000 and 1100C. Anomalously hot and/or thick metabasaltic crustis implied. Although a rare occurrence along modern convergentplate margins, subductionrelated melting of young, hot oceaniccrust (e.g. ocean ridges) may have been an important (essential)element in the growth of the continental crust in the Archean,if plate tectonic processes were operative. Coupled silicicmelt generation-segregation and mafic restite disposal may alsooccur at the base of continental or primitive (sub-arc?) crust,where crustal overthickening is a consequence of underplatingand overaccretion of mafic magmas. In either setting, net growthof continental crust and crustmantle recycling may be facilitatedby relatively high degrees of melting and extreme density contrastsbetween trondhjemitictonalitic liquids and garnet-rich residues.Continuous chemical trends are apparent between the experimentalcrystalline residues, and mafic migmatites and garnet granulitexenoliths from the lower crust, although lower-crustal xenolithsin general record lower temperatures (600–900C) and pressures(5–13 kbar) than corresponding residual assemblages fromthe experiments. However, geo-thermobarometry on eclogite xenolithsin kimberlites from the subcontinental mantle indicates conditionsappropriate for melting through and beyond the amphibole reactioninterval and the granulite-eclogite transition. If these samplesrepresent ancient (eclogitized) remnants of subducted or otherwisefoundered basaltic crust, then the intervening history of theirprotoliths may in some cases include partial melting. KEY WORDS: dehydration melting; metabasalt; continental growth; crust–mantle recycling ^*Corresponding author. Present address: Mineral Physics Institute and Center for High Pressure Research, Department of Earth and Space Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA     

In situ determination of crystal structure for high pressure phase of ZrO2 using a diamond anvil and single crystal X-ray diffraction method

Combining a miniature diamond-anvil pressure cell with a single crystal four-circle diffractometer, the crystal structure of a synthetic ZrO₂ has been studied in situ up to 51 kbar at room temperature. The space group of the unquenchable orthorhombic high pressure phase is Pbcm. The directions of the b and c axes are preserved through the transition and the transformation is displacive. The coordination configurations of the Zr atoms and oxygen atoms are the same in the high pressure and low pressure phases. The orthorhombic high pressure phase has a higher entropy than that of low pressure monoclinic phase.     

Silicic Magma Formation in Overthickened Crust: Melting of Charnockite and Leucogranite at 15, 20 and 25 kbar

Two models of silicic magma formation have been experimentallytested: (1) generation of A-type granite magma by partial meltingof crustal source rocks at depths >50 km; (2) productionof syenite magma by partial melting of quartzofeldspathic rocksat pressures >15 kbar. Melting experiments at 15, 20 and25 kbar were performed on Archaean biotite-bearing charnockiteof opx-bearing granodiorite composition, and on leucogranite.Most experiments were conducted with oxalic acid (OA) to provide2 wt % H₂O and     

High-pressure and high-temperature in situ X-ray diffraction study of iron and corundum to 68 GPa using an internally heated diamond anvil cell

Using powder X-ray diffraction of heated solids to pressures reaching 68 GPa, the pressure-volume-temperature (PVT) data on corundum Al₂O₃ and ɛ-Fe were determined with the following results: *Corundum,*Iron, *Al₂O₃*ɛ-Fe Isothermal bulk*258 (2)*164 (3)  modulus K'_{300, 1} (GPa) Pressure derivative K_{300, 1}*4.88 (4)*5.36 (16) Temperature derivative*–0.020 (2)*–0.043 (3)  (∂K _T,1 /∂T) _P (GPa/K) Molar volume V_300,1*25.59 (2)*6.76 (2)  (cm³/mol) Isobaric thermal expansion at 1 atm (0.101 MPa) is given by (K^–1): α _T =2.6 (2) 10^–5+1.81 (9) 10^–9 T–0.67 (6)/T ² for corundum, and α _T =5.7 (4) 10^–5+4.2 (4) 10^–9 T–0.17 (7)/T ² for iron ɛ-Fe. Received: 1 March 1997 / Revised, accepted: 21 August 1997     

Tridymite: Effect of hydrostatic pressure to 6 kbar on temperatures of two rapidly reversible transitions

Trajectories of two reversible phase transitions in a low-Na synthetic tridymite have been determined to 6 kbar by differential thermal analysis (DTA) in hydrostatic apparatus using Ar or CO₂. The temperature of the lower transition increases from 111 ° C at 1 bar linearly with pressure with slope 1₅ deg kbar^–1. Pressure raises the temperature of the upper transition from 157 ±2 ° or 159 ° C (independently determined) at 1 bar wit a slope of 53 deg kbar^–1, up to 0.7 kbar; for the data above that pressure, the initial slope is 64 deg kbar^–1. Above 2–1/2 kbar, the variation is linear with slope 70 deg kbar^–1. No evidence for other transitions was found at any of the apparent changes of slope. Hystereses for both transitions decreased at high pressures compared to 1-bar. Preferred values for the transition enthalpies, together with these slopes and the Clausius-Clapeyron equation, yield estimates for the volume changes at the transitions of 0.01 (lower) and 0.15 to 0.25 (upper) cm³ gfw^–1. These calculated volume changes are not consonant with many of the high temperature volumetric data on tridymites of varying origins.     

地球内部极端条件下流体和物质相互作用:透过金刚石窗口探测地球深部流体

报道关于地球内部极端条件下的流体实验研究的最新进展。使用金刚石压砧结合各种谱学方法及同步辐射光源技术,在高温超高压条件下原位直接测量物质的结构和性质,已经获得分子-原子尺度信息新的实验数据。本项工作使用金刚石压砧对高压(10GPa)和高温高压(800℃,3GPa)条件下的NaCl-H2O进行红外谱原位直测,研究了高压和高温高压下水分子结构,发现水分子的O—H振动特征峰频率随温度向高波数变化,而且,在临界态区域时水分子间的氢键网格被破坏。实验说明:地球内部流体性质由深到浅不断变化,如水的密度、介电常数等物理参数随温度压力而改变,在临界态出现突变。这些变化可以用高压高温的物质的各种谱学特征来表征。水的性质与它的分子结构、分子振动有关。在跨越临界区时水的性质异常涨落是由水分子结构异常变化、分子振动形式变化和氢键网格破坏所导致的。从分子尺度认识地球内部流体在极端条件下的性质和高压原位实验观测有助于我们进一步了解地球深部物质的性质及其相互作用,有助于认识深部过程。     

Melting of albite and dehydration of brucite in H2O–NaCl fluids to 9 kbars and 700–900°C: implications for partial melting and water activities during high pressure metamorphism

 The melting reaction: albite_(solid)+ H₂O_(fluid) =albite-H₂O_(melt) has been determined in the presence of H₂O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H₂O–CO₂ fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X _(H2O) ) melting relations in the two systems are almost coincident. By contrast, H₂O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 ^°C higher in H₂O–NaCl brines than in H₂O–CO₂ fluids for X _(H2O) =0.8 and ∼100 ^°C higher for X _(H2O) =0.5. The melting temperature of albite in H₂O–NaCl fluids of X _(H2O)=0.8 is ∼100 ^°C higher than in pure water. The P–T curves for albite melting at constant H₂O–NaCl show a temperature minimum at about 5 kbar. Water activities in H₂O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H₂O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but may be due to the presence of low a _(H2O) brines. Received: 17 March 1995/Accepted: 9 April 1996     

Simulation of the fluorescence evolution of “live” oils from kerogens in a diamond anvil cell: Application to inclusion oils in terms of maturity and source

The evolution of fluorescence has been measured for “live” oils generated from 14 oil-prone kerogens or coals from varying depositional environments during closed system pyrolysis in a diamond anvil cell at three heating rates (3, 8, and 25 °C/min), and temperatures up to 600 °C. The measured fluorescence intensities of the samples, employing using violet excitation at 405 nm, increases significantly during maturation intervals within the oil window, while the fluorescence spectra of oils generated from all studied kerogens exhibit progressive blue-shift of peak wavelengths (λ_max) and red/green quotients (I₆₅₀/I₅₀₀) upon increasing maturity. The observed trend is consistent with a maturity dependence of the spectral shift, which is widely recognized in natural hydrocarbon inclusions and crude oils using ultraviolet (UV) excitation (365 nm). The data presented herein suggest that the λ_max of spectra for inclusion oils shift in similar direction despite differences in composition or source kerogen. This implies that the reverse or anomalous trends reported for inclusion oils in nature may be attributed to other processes, which significantly alters the fluorescence properties of oils subsequent to their generation. Oils with the similar color (λ_max or I₆₅₀/I₅₀₀) can be derived from diverse kerogens with maturities that vary by ±0.3% Ro, suggesting that the fluorescent colors of crude and inclusion oils are both maturity- and source-dependent, and therefore cannot be used as universal maturity indicators. In addition, the blue-shifts observed for cumulative oils generated from all kerogens approaches similar minima λ_max values around the green-yellow wavelength (564 nm) and at I₆₅₀/I₅₀₀ values around 0.6, at maturities close to the middle or late stage of oil generation. This suggests that most late-stage cumulative oils will exhibit similar colors. Oils generated during late-stage maturity intervals, however, can exhibit colors with shorter wavelengths.     

Compressibility and structure behaviour of maruyamaite (K-tourmaline) from the Kokchetav massif at high pressure up to 20 GPa

Mineralogy and Petrology - The structural behaviour of maruyamaite (K-dominant tourmaline) X(K0.54Na0.28Ca0.19)Y(Mg1.3Al1.17Fe0.39Ti0.14)Z(Al5Mg)[Si5.95Al0.05O18](BO3)3V,W[O1.69(OH)2.31] from the...