高温高压下电导-温度曲线方法进行蛇纹石的脱水温度测量及其意义

在1．0～5．0GPa压力范围内，运用高温同时高压下电导测量方法确定了蛇纹石的脱水温度。实验结果表明，压力小于2.0GPa时叶蛇纹石的脱水温度随压力的增大呈微弱升高趋势，压力大于2．0GPa时其脱水温度随压力的增大明显降低，意味着较高压力下有利于脱水反应的发生，是俯冲带岩浆作用及地幔交代作用流体的重要来源。蛇纹石脱水后，由于自由水的存在导致其电导明显增加，可能是高导层产生的原因之一。     

十字石的原位高压X射线衍射研究

利用原位高压同步辐射能量色散X射线衍射技术,在室温下对采自新疆阿尔泰地区冲乎尔递增变质带的天然十字石进行高压晶体结构测定,测量的压力范围为0.0001~3.9GPa,共11组有效数据。实验表明,在实验压力范围内,随着压力的增加晶胞参数β值逐渐增大,表明了十字石的结构对称性随压力增加而有所降低;同时,在1.5~2.7GPa压力范围内,十字石的晶体结构也发生了改变。     

透视石的原位高压单晶X射线衍射研究

采用同步辐射光源和金刚石对顶砧(DAC)技术,对透视石进行了室温下的原位高压单晶X射线衍射研究。实验的最高压力为11.7 GPa,在实验压力范围内,未观察到透视石发生相变。随着压力的升高,晶胞体积逐步被压缩,体积压缩率符合三阶Birch-Murnaghan状态方程,拟合获得体模量K0为114.6(5.3)GPa。压力低于9.3 GPa时,c轴的压缩率大于a轴;在9.3~11.7 GPa压力范围内,限制于透视石结构中的水分子在高压下会阻碍硅氧四面体六元环沿c轴方向的扭曲变形,导致c轴的抗压性增强,最终a轴与c轴的被压缩程度趋于一致。通过分析多种含水环状硅酸盐矿物的高压行为,发现高压下结构中水的存在形式对含水环状硅酸盐矿物的弹性性质有重要的影响。     

钛闪石的高压结构及其地质意义

利用同步辐射EDXD方法和DAc高压技术对采于新疆天山碱性玄武岩地幔捕虏体中的钛闪石进行了原位高压(达25．4GPa)结构研究：在室温下，随着压力的增加，钛闪石的轴长a、b、c被逐渐压缩；当压力为18、9GPa时，钛闪石可能由于“脱水”而导致结构发生相变，此相变应属于可逆的二级相变。结合钛闪石的地质产状，我们认为，钛闪石在上地幔一定深度范围内可以保持稳定，是上地幔中重要的含水矿物相之一，其被携带到地表是一个非常快速的过程，本文的结果对某些含钛矿物的高压行为研究提供了一定的参考。     

南大别太湖地区榴辉岩峰期变质温压条件及所揭示的构造含义

通过岩石学、矿物成分和峰期变质温压条件的研究表明，南大别变质块体由超高压带、高压/超高压“混合”带和高压带3个变质单元组成，具有区域上的温压渐变趋势。应用5个Grt-Cpx温度计和Grt-Cpx-Phe压力计。对榴辉岩的峰期变质温压条件计算显示，自北向南，可分为4个温压域，温度压力逐渐降低：760～950℃，3．5～4．1GPa→660-750℃，2．7～3．1GPa→640-780℃，2．0～2．7GPa→550～680℃，1．5～2．3GPa，这表明南大别变质块体在俯冲过程中是一个连续的块体。然而，超高压带和高压带之间的压力差异以及不同变质带内相邻榴辉岩之间的压力差、无序分布特征及其与围岩的构造接触关系显示，南大别变质块体经历了强烈的缩短过程，现今榴辉岩的分布特征反映的是折返至地表的状态。     

白钨矿的原位高压X射线衍射研究

使用金刚石对顶砧高压装置(DAC)和同步辐射光源,对天然白钨矿进行了原位高压能量色散X射线衍射(EDXD)研究,实验最高压力为16.0 GPa.在实验压力范围内观察到了一次白钨矿结构→钨锰铁矿结构的可逆相变:压力小于5.3 GPa时为白钨矿结构(I4_1/a),在5.3～12.3 GPa压力区间内为白钨矿结构与钨锰铁矿结构(P2/c)并存,大于12.3 GPa时完全相变为钨锰铁矿结构.从键长、配位数和配位多面体角度对白钨矿→钨锰铁矿结构的相变机制进行了解释.     

天然黝帘石原位高压X射线衍射和拉曼光谱

黝帘石属于绿帘石族矿物[Ca2(Al,Fe)3Si3O12(OH)],产出于各种不同地质环境(比如大陆碰撞带和俯冲带)的高压和超高压变质岩中。不同于其他绿帘石族矿物属于单斜晶系矿物,黝帘石属于斜方晶系(空间群Pnma)。本文采用金刚石压腔装置(DAC)结合同步辐射X射线衍射及拉曼光谱技术对天然黝帘石[Ca2(Al2.71Fe0.29)(Si O4)(Si2O7)O(OH)]进行了原位常温高压实验研究,以期增进对黝帘石在常温高压下的稳定性以及Fe含量的不同对于其弹性性质影响的认识。原位常温高压X射线衍射实验在上海同步辐射装置(SSRF)的BL15U线站上完成。实验采用DAC高压装置结合单晶X射线衍射实验技术,实验最高压力约为30 GPa,衍射谱图采用黝帘石标准谱(JCPDS85-1631)进行指标化,衍射斑点的位置用来计算其在不同压力下的晶胞参数。随着实验压力的升高,所有的衍射晶面间距逐渐减小,当压力达约15.2 GPa,在衍射图谱上出现一新的衍射晶面信号(晶面间距d=2.238 3),并在之后的压力范围内一直存在。此外当压力达约22.6 GPa,又有一晶面间距d=2.689 6的新衍射信号出现,并一直保持存在到最高压力。据此推断黝帘石在压力约15 GPa时存在结构的变化。同时,在常温最高压力约为40 GPa条件下,对黝帘石进行了拉曼光谱测量。随着实验压力的增加,黝帘石的拉曼振动峰向着高波数方向移动,在压力约为15.7 GPa,低压下存在的波数为1 083 cm-1和1 098 cm-1的两个振动峰消失,与此同时,在波数为247 cm-1、303 cm-1、339 cm-1、和379 cm-1位置分别出现了新的拉曼谱峰,其中,339 cm-1峰于27.6 GPa时消失,其余新峰一直保持到实验最高压力值。因此,本文推测天然黝帘石样品在15~16 GPa压力范围内存在有结构的变化。对于变化后的结构和性质还有待于进一步研究。另外,本文利用三阶Birch-Murnaghan状态方程拟合了发生结构变化前(0~14.4 GPa)的p-V数据,得到V0=908.1(9)3、K0=108(2)GPa和K'0=6.5(6),其中V0、K0和K'0分别表示零压晶胞体积、等温体积模量及其压力导数值。综合上述获得的实验结果并结合前人对黝帘石的研究成果,本文探讨了含Fe量的不同对于黝帘石弹性性质以及晶体结构性质的影响。与不含Fe黝帘石的等温体积模量[Ca2Al3Si3O12OH(]122.1(7)GPa,123.4(4)GPa)以及低含Fe量的黝帘石[Ca2Al2.88Fe0.12Si3O12OH]的体积模量(119.1(7)GPa)相比,本次实验样品黝帘石[Ca2(Al2.71Fe0.29)(Si O4)(Si2O7)O(OH)]的体积模量(108(2)GPa)明显偏小,说明含Fe会增加黝帘石矿物的可压缩性,并且,含铁量越大其体积模量越小。     

橄榄石的等温状态方程

利用金刚石对顶砧(DAC)高压装置产生高压,使用16∶3∶1的甲醇、乙醇和水混合液体作为传压介质,在室温下,40 GPa的压力范围内,对橄榄石(olivine)进行了原位高压同步辐射能量色散X射线衍射(EDXRD)研究。实验结果表明,在所研究压力范围内,采自张家口大麻坪天然新鲜橄榄石的结构稳定,未见相变和压致非晶现象发生。用Birch-Murnaghan方程对测得的V-p数据进行了数值拟合,当K′T0=4时,橄榄石的零压体弹模量为KT0=141.3±3.2 GPa。     

高压下天然菱铁矿的压缩性和电子结构研究

采用同步辐射光源和金刚石对顶砧(DAC)技术,对天然菱铁矿的压缩性和电子结构进行了原位X射线衍射(XRD)和X射线吸收近边结构谱(XANES)测试研究。在室温下随着压力逐渐升高至50.2 GPa,菱铁矿保持方解石型结构不变,但是逐渐向Na Cl型结构转变;刚性[CO3]2-基团平行于ab-平面定向排列使c轴的压缩性大于a轴。菱铁矿在44.6~47.1 GPa之间发生电子由高自旋态(HS)向低自旋态(LS)的转变,表现为体积塌陷8%。HS菱铁矿的等温状态方程参数为K0=112(5)GPa和K'0=4.6(3)。首次采用XANES技术对菱铁矿中Fe2+的电子结构进行了研究,结果表明:随着压力升高至37.3 GPa,Fe2+的配位和局域对称并未发生明显变化;此后电子结构开始转变,Fe2+的3d轨道分裂能降低,电子跃迁概率增大,呈现LS特性。     

锡石的原位高压X射线衍射研究

利用同步辐射能量色散X射线衍射(EDXD)方法和金刚石对顶砧(DAC)高压技术对采于四川平武的锡石进行原位高压(达24.0 GPa)结构研究发现:压力加载过程中,锡石在13.8 GPa时发生了从金红石型结构(P 42/m nm)到C aC l2型结构(P nnm)的位移式相变;在19.9 GPa时又由C aC l2型结构相变为黄铁矿型结构(P a3),此相变为重构式相变。对于第Ⅳ主族元素氧化物(S iO2,G eO2,SnO2和PbO2)及过渡金属氧化物(M nO2和R uO2)的高压行为进行了讨论,它们具有相似的高压相变序列,这些成果对与斯石英同构氧化物的高压行为研究提供了有价值的参考。     

The strength of ruby from X-ray diffraction under non-hydrostatic compression to 68 GPa

Polycrystalline ruby (α-Al₂O₃:Cr³⁺), a widely used pressure calibrant in high-pressure experiments, was compressed to 68.1 GPa at room temperature under non-hydrostatic conditions in a diamond anvil cell. Angle-dispersive X-ray diffraction experiments in a radial geometry were conducted at beamline X17C of the National Synchrotron Light Source. The stress state of ruby at high pressure and room temperature was analyzed based on the measured lattice strain. The differential stress of ruby increases with pressure from ~3.4 % of the shear modulus at 18.5 GPa to ~6.5 % at 68.1 GPa. The polycrystalline ruby sample can support a maximum differential stress of ~16 GPa at 68.1 GPa under non-hydrostatic compression. The results of this study provide a better understanding of the mechanical properties of this important material for high-pressure science. From a synthesis of existing data for strong ceramic materials, we find that the high-pressure yield strength correlates well with the ambient pressure Vickers hardness.     

Phase transitions in the system CaCO<Subscript>3</Subscript> at high P and T determined by in situ vibrational spectroscopy in diamond anvil cells and first-principles simulations

The stability of the high-pressure CaCO₃ calcite (cc)-related polymorphs was studied in experiments that were performed in conventional diamond anvil cells (DAC) at room temperature as a function of pressure up to 30 GPa as well as in internally heated diamond anvil cells (DAC-HT) at pressures and temperatures up to 20 GPa and 800 K. To probe structural changes, we used Raman and FTIR spectroscopy. For the latter, we applied conventional and synchrotron mid-infrared as well as synchrotron far-infrared radiation. Within the cc-III stability field (2.2–15 GPa at room temperature, e.g., Catalli and Williams in Phys Chem Miner 32(5–6):412–417, 2005), we observed in the Raman spectra consistently three different spectral patterns: Two patterns at pressures below and above 3.3 GPa were already described in Pippinger et al. (Phys Chem Miner 42(1):29–43, 2015) and assigned to the phase transition of cc-IIIb to cc-III at 3.3 GPa. In addition, we observed a clear change between 5 and 6 GPa that is independent of the starting material and the pressure path and time path of the experiments. This apparent change in the spectral pattern is only visible in the low-frequency range of the Raman spectra—not in the infrared spectra. Complementary electronic structure calculations confirm the existence of three distinct stability regions of cc-III-type phases at pressures up to about 15 GPa. By combining experimental and simulation data, we interpret the transition at 5–6 GPa as a re-appearance of the cc-IIIb phase. In all types of experiments, we confirmed the transition from cc-IIIb to cc-VI at about 15 GPa at room temperature. We found that temperature stabilizes cc-VI to lower pressure. The reaction cc-IIIb to cc-VI has a negative slope of ?7.0 × 10^?3 GPa K^?1. Finally, we discuss the possibility of the dense cc-VI phase being more stable than aragonite at certain pressure and temperature conditions relevant to the Earth’s mantle.     

Raman spectroscopic study of high-pressure phase transitions in cristobalite

The pressure dependence of the cristobalite Raman spectrum has been investigated to 22 GPa at room temperature, using single-crystal Raman spectroscopy with a diamond-anvil cell. We observe a rapid, first-order phase transition on increasing pressure, consistent with the cristobalite I?II transition revealed in previous x-ray diffraction experiments. The phase transition has been bracketed at 1.2±0.1 GPa on increasing pressure and 0.2±0.1 GPa on decreasing pressure. The pressure shifts II) of 11 Raman bands in the high-pressure phase (cristobalite have been measured. Evidence for an unusual hybridization of modes at 490–500 cm^?1 is found. Changes in the Raman spectra also reveal an additional phase transition to a new phase at P ≈ 11 GPa, which remains to be fully characterized.     

地幔不同深度单斜辉石含水量的高压实验

在1.5~5GPa、1100~1200℃条件下开展了含水大陆碱性玄武岩的熔融实验研究。通过红外光谱分析其中单斜辉石的结构水,计算得到其量为1173(153)×10-6～2049(197)×10-6。结果表明:当P<3GPa时,随着压力增大,单斜辉石的含水量逐渐增加,在3GPa附近达到峰值,之后随着压力的增大单斜辉石含水量又逐渐减少。单斜辉石含水量随压力的这种变化关系可能受单斜辉石中Al含量的影响。该研究为了解上地幔不同深度处水的分布提供了实验证据。     

An experimental study of Cl and S distribution between sodalite and fluid

S and Cl distribution between sodalite and fluid was experimentally studied at temperatures of 300–800°C and pressure of 0.5–3 kbar. It is demonstrated that S is preferably distributed into fluid in equilibrium with sodalite of the composition X _S ^Sod > 0.05 throughout the whole temperature range. The distribution of S in the sodalite-fluid system is nonideal. An equation (derived from experimental data) is presented for evaluating the S mole fraction in fluid from the composition of sodalite at a known temperature. The S mole fractions in the fluid are evaluated for sodalite assemblages from nepheline syenites of the Lovozero Massif as being within the range of 0.036–0.23. The S mole fraction in the fluid is proved to increase with increasing mineral formation temperatures.     

Equilibrium and Fractional Crystallization Experiments at 0{middle dot}7 GPa; the Effect of Pressure on Phase Relations and Liquid Compositions of Tholeiitic Magmas

Two series of anhydrous experiments have been performed in anend-loaded piston cylinder apparatus on a primitive, mantle-derivedtholeiitic basalt at 0·7 GPa pressure and temperaturesin the range 1060–1270°C. The first series are equilibriumcrystallization experiments on a single basaltic bulk composition;the second series are fractionation experiments where near-perfectfractional crystallization was approached in a stepwise mannerusing 30°C temperature increments and starting compositionscorresponding to that of the previous, higher temperature glass.At 0·7 GPa liquidus temperatures are lowered and thestability of olivine and plagioclase is enhanced with respectto clinopyroxene compared with phase equilibria of the samecomposition at 1·0 GPa. The residual solid assemblagesof fractional crystallization experiments at 0·7 GPaevolve from dunites, followed by wehrlites, gabbronorites, andgabbros, to diorites and ilmenite-bearing diorites. In equilibriumcrystallization experiments at 0·7 GPa dunites are followedby plagioclase-bearing websterites and gabbronorites. In contrastto low-pressure fractionation of tholeiitic liquids (1 bar–0·5GPa), where early plagioclase saturation leads to the productionof troctolites followed by (olivine) gabbros at an early stageof differentiation, pyroxene still crystallizes before or withplagioclase at 0·7 GPa. The liquids formed by fractionalcrystallization at 0·7 GPa evolve through limited silicaincrease with rather strong iron enrichment following the typicaltholeiitic differentiation path from basalts to ferro-basalts.Silica enrichment and a decrease in absolute iron and titaniumconcentrations are observed in the last fractionation step afterilmenite starts to crystallize, resulting in the productionof an andesitic liquid. Liquids generated by equilibrium crystallizationexperiments at 0·7 GPa evolve through constant SiO₂ increaseand only limited FeO enrichment as a consequence of spinel crystallizationand closed-system behaviour. Empirical calculations of the (dry)liquid densities along the liquid lines of descent at 0·7and 1·0 GPa reveal that only differentiation at the baseof the crust (1·0 GPa) results in liquids that can ascendthrough the crust and that will ultimately form granitoid plutonicand/or dacitic to rhyodacitic sub-volcanic to volcanic complexes;at 0·7 GPa the liquid density increases with increasingdifferentiation as a result of pronounced Fe enrichment, renderingit rather unlikely that such differentiated melt will reachshallow crustal levels. KEY WORDS: tholeiitic magmas; experimental petrology; equilibrium crystallization; fractional crystallization     

Evaluation of the non-hydrostatic stress produced in a multi-anvil high pressure apparatus

Olivine single crystals have been deformed under high confining pressure (P=5?GPa) and temperature (T=1400?°C) conditions in a multi-anvil high pressure apparatus. NaCl, diamond and NaCl+diamond (2:1 by volume) powders were encapsulated along with the olivine single crystals in order to produce a range of stress states. The change of the non-hydrostatic stress transmitted to the olivine samples, enclosed within these three different media, during heating has been evaluated by observation of dislocation microstructure and density. A higher differential stress can be generated with diamond powder (0.1?GPa) than with NaCl powder (0.02?GPa). Although an intermediate differential stress between 0.1?GPa and 0.02?GPa had been expected to be generated using NaCl+diamond powder, the generation of non-hydrostatic stress in the olivine sample was unsuccessful. This may be caused by the fact that compaction (or sintering) proceeded in the capsule throughout the experiments. The most important finding of these experiments is that a constant non-hydrostatic stress can be applied to a sample under very high pressure and temperature conditions within the multi-anvil high pressure apparatus for the duration of the experiment. This approach is therefore suitable for investigating the steady-state rheological properties of mantle minerals at near-mantle conditions.     

New insights into the high-pressure polymorphism of SiO<Subscript>2</Subscript> cristobalite

Single-crystal X-ray diffraction experiments with SiO₂ α-cristobalite reveal that the well-known reversible displacive phase transition to cristobalite-II, which occurs at approximately 1.8 GPa, can be suppressed by rapid pressure increase, leading to an overpressurized metastable state, persisting to pressure as high as 10 GPa. In another, slow pressure increase experiment, the monoclinic high-pressure phase-II was observed to form at ~1.8 GPa, in agreement with earlier in situ studies, and its crystal structure has been unambiguously determined. Single-crystal data have been used to refine the structure models of both phases over the range of pressure up to the threshold of formation of cristobalite X-I at ~12 GPa, providing important constraints on the feasibility of the two competing silica densification models proposed in the literature, based on quantum mechanical calculations. Preliminary diffraction data obtained for cristobalite X-I reveal a monoclinic unit cell that contradicts the currently assumed model.     

Analysis of precipitates from reactions of hyperalkaline solutions with soluble silica

Cancrinite, sodalite, and zeolite A have been found to form upon contacting hyperalkaline simulated tank waste (STW) with vadose zone sediments from the Hanford Reservation. Here, soluble silica and STW are used to study mineral formation and transformation. Two Hanford sediment fractions (diameters <50 and >50 μm instead of soluble silica) are also used as silica sources for comparison. A series of batch experiments at 50 °C and 25 days duration were conducted by reacting 0.026 mol/kg soluble Si with 6 different STW solutions. The STW solutions differed in NaOH and Al concentrations. Cancrinite, sodalite, and zeolite A formed when soluble Si was used as the Si source. The minerals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS-NMR). Larger NaOH and Al concentrations favored formation of the more compact structures of cancrinite and sodalite. At larger NaOH concentration more Al for Si substitution occurred in the tetrahedral sites. A greater Al(4)/Al(6) ratio in the solids was found for the higher Si/Al ratio solutions based on NMR results. Mixtures of cancrinite and sodalite were characterized by particles with lepispheric morphology. At low Al concentration, increasing NaOH resulted in distinct hexagonal, prismatic particles common to crystalline cancrinite. At low Al/Si ratio, the characteristic cubic morphology of zeolite was observed in addition to cancrinite and sodalite.