Single-crystal elastic properties of the modified spinel (Beta) phase of magnesium orthosilicate

The single-crystal elastic moduli of the modified spinel structure (beta phase) of magnesium orthosilicate (Mg(2)SiO(4)) have been measured by Brillouin spectroscopy under ambient conditions. Single crystals with dimensions up to 500 micrometers were grown at 22 gigapascals and 2000 degrees C over a period of 1 hour. Growth of crystals larger than 100 micrometers was achieved only when the pressure was within 5 percent of the pressure of the phase boundary separating the beta- and gamma-phase stability fields. A comparison of the elastic properties of the modified spinel phase with those of the olivine phase suggests that the 400-kilometer seismic discontinuity in the earth's mantle can be described by a mantle with 40 percent olivine. These results confirm that the 400-kilometer discontinuity can be due to the transition from olivine to modified spinel. The amount of olivine that must be present is less than that in a pyrolite model, although the results do not exclude pyrolite as a possible mantle model.     

Cordierite-spinel troctolite, a new magnesium-rich lithology from the lunar highlands

A clast of spinel troctolite containing 8 percent cordierite (Mg(2)Al(4)Si(5)O(18)) has been identified among the constituents of Apollo 15 regolith breccia 15295. The cordierite and associated anorthite, forsteritic olivine, and pleonaste spinel represent a new, Mg-rich lunar highlands lithology that formed by metamorphism of an igneous spinel cumulate. The cordierite-forsterite pair in the assemblage is stable at a maximum pressure of 2.5 kilobars, equivalent to a depth of 50 kilometers, or 10 kilometers above the lunar crust-mantle boundary. The occurrence of the clast indicates that spinel cumulates are a more important constituent of the lower lunar crust than has been recognized. The rarity of cordierite-spinel troctolite among lunar rock samples suggests that it is excavated only by large impact events, such as the one that formed the adjacent Imbrium Basin.     

Modified spinel, Beta-manganous orthogermanate: stability and crystal structure

A new high-pressure polymorph with a modified spinel structure, beta-Mn(2)GeO(4), is stable in a pressure range intermediate between the field of the polymorph with the olivine structure and that of another high-pressure polymorph. Oxygen atoms are located approximately in cubic close packing with manganese and germanium atoms in octahedral and tetrahedral interstices, respectively, as in the spinel structure; however, germanium atoms form Ge(2)O(7) groups instead of isolated GeO(4) groups.     

Catalysis of the olivine to spinel transformation by high clinoenstatite

Although enstatite is a major constituent of the Earth's upper mantle and subducting lithosphere, most kinetic studies of olivine phase transformations have typically involved single-phase polycrystalline aggregates. Transmission electron microscopy investigations of olivine to spinel and modified spinel (beta phase) reactions in the (Mg, Fe)(2)SiO(4)-(Mg,Fe)SiO(3) system show that transformation of olivine in the stability field of spinel plus phase begins with coherent nucleation of spinel on high-clinoenstatite grains. These observations demonstrate that high clinoenstatite can catalyze the transformation by enhancing nucleation kinetics and therefore imply that secondary phases can influence reaction kinetics during high-pressure mineral transformations.     

Electrical conductivity of olivine, wadsleyite, and ringwoodite under upper-mantle conditions

Geophysical models show that electrical conductivity in Earth's mantle rises about two orders of magnitude through the transition zone in the depth range 410 to 660 kilometers. Impedance measurements obtained on Mg1.8Fe0.2SiO4 olivine, wadsleyite, and ringwoodite at up to 20 gigapascals and 1400 degreesC show that the electrical conductivities of wadsleyite and ringwoodite are similar and are almost two orders of magnitude higher than that of olivine. A conductivity-depth profile to 660 kilometers, based on these laboratory data, shows a conductivity increase of almost two orders of magnitude across the 410-kilometer discontinuity; such a profile favors a two-layer model for the upper mantle. Activation enthalpies of 1.2 to 1.7 electron volts permit appreciable lateral variations of conductivity with lateral temperature variations.     

Pyroxene-garnet transformation in coorara meteorite

Majorite is a new garnet in a veinlet of the Coorara meteorite. Its chemical composition is compatible with derivation mostly from original pyroxene, not from olivine as originally reported. Silicon is partly in sixfold coordination. Ringwoodite, a spinel of olivine composition, occurs as purple grains set in a matrix of fine-grained garnet. The similar mineralogy and texture of the Coorara and Tenham meteorites suggest a common parent body.     

Cumulate xenolith in oahu, hawaii: implications for deep magma chambers and hawaiian volcanism

The maximum depth at which large (>1000 km(3)) terrestrial mafic magma chambers can form has generally been thought to be the Moho, which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins. However, the presence of layers of cumulus magnesium-rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from Oahu, Hawaii, suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers; Hawaiian shield-building magmas may pond and fractionate in such magma chambers before continuing their ascent. This depth is at or near the base of the 90-million-year-old lithosphere beneath Oahu; thus, rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere.     

Electrical anisotropy below slow- and fast-moving plates: paleoflow in the upper mantle?

Upper mantle electrical conductivities can be explained by hydrogen diffusivity in hydrous olivine. Diffusivity enhances the conductivity of olivine anisotropically, making the a axis the most conductive of the three axes. Therefore, the hypothesis that plate motion induces lattice-preferred orientation of olivine can be tested with the use of long-period electromagnetic array measurements. Here, we compared electrical anisotropies below the slow-moving Fennoscandian and fast-moving Australian plates. The degree of olivine alignment is greater in the mantle below the Fennoscandian plate than below the Australian plate. This finding may indicate that convection rather than plate motion is the dominant deformation mechanism.     

Electrical conductivity in the precambrian lithosphere of western canada

The subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada is at least one order of magnitude more electrically conductive than the lithosphere beneath adjacent Paleoproterozoic crust. The measured electrical properties of the lithosphere underlying most of the Paleoproterozoic crust can be explained by the conductivity of olivine. Mantle xenolith and geological mapping evidence indicate that the lithosphere beneath the southern ACP was substantially modified as a result of being trapped between two nearly synchronous Paleoproterozoic subduction zones. Tectonically induced metasomatism thus may have enhanced the subcrustal lithosphere conductivity of the southern ACP.     

Seismic evidence for olivine phase changes at the 410- and 660-kilometer discontinuities

The view that the seismic discontinuities bounding the mantle transition zone at 410- and 660-kilometer depths are caused by isochemical phase transformations of the olivine structure is debated. Combining converted-wave measurements in East Asia and Australia with seismic velocities from regional tomography studies, we observe a correlation of the thickness of, and wavespeed variations within, the transition zone that is consistent with olivine structural transformations. Moreover, the seismologically inferred Clapeyron slopes are in agreement with the mineralogical Clapeyron slopes of the (Mg,Fe)2SiO4 spinel and postspinel transformations.     

Mineral chemistry of lunar samples

Glass spherules, glass fragments, augite, ferroaugite, titanaugite, pyroxmangite, pigeonite, hypersthene, plagioclase, potassium feldspar, maskelynite, olivine, silica, ilmenite, TiO(2), "ferropseudobrookite," spinel, ulv?spinel, native iron, nickel-iron, troilite, and chlorapatite were analyzed with the electron microprobe. There are no indications of large-scale chemical differentiation, chemical weathering, or hydrous minerals. Contributions of meteoritic material to lunar surface rocks are small. Rocks with igneous textures originated from a melt that crystallized at or near the surface, and oxygen fugacities have been low. Shock features indicate that at least some surface material is impact-produced.     

滨海盐土全盐量与电导率之间最佳曲线方程研究

滨海盐土的主要特征是全盐含量高,也是作物生长的障碍因子。电导率的测定是测定土壤中水可溶性盐快速而简单的方法。国内标准方法是在25℃温度下用土水比为1:5的澄清悬液测定,但计算方法不统一。为了研究滨海盐土中可溶性全盐(Y)与电导率(X)之间本质上关系,比较了10种曲线回归方程。结果表明：在砂涂中全盐与电导率之间最佳曲线回归方程为线性方程：Y=0.045+2.935X(R2=1.000),而其幂函数曲线方程R2=0.998。在黏涂中全盐与电导率之间最佳曲线回归方程为三次曲线方程：Y=0.194+0.3096X-0.253X2+0.046X3(R2=1.000),但其幂函数曲线方程的R2也为0.998。     

不同贮藏条件下成熟椰子水品质变化规律研究

以成熟椰子水为试验材料,以吸光度、pH、白利糖度和电导率为指标,结合感官评价对4个贮藏温度下的椰子水品质变化特点进行分析。结果表明,各处理随贮藏时间延长,吸光值均逐渐增大,pH值均逐渐减小,电导率呈增大趋势;温度越低,吸光值增大越缓慢和pH维持稳定的时间段越长,说明低温更有利于椰子水的贮藏;相同贮藏温度,密封和非密封保存时间无差别,37℃可保存5 h,24℃可保存8 h,14℃可保存22 h,4℃可保存7 d。椰子水的吸光值和p H值剧变时间点与椰子水变质时间节点最接近,其中吸光值变化最为显著,吸光值和pH变化可作为反映椰子水变质的主要指标;椰子水收集后迅速降至4℃可满足工业生产要求。     

草坪草海滨雀稗的抗寒机理研究

[目的]研究海滨雀稗（Paspalum vaginatum Swartz）的抗寒机理。[方法]对海滨雀稗进行低温处理（15、10、5℃）,以常温（25℃）为对照;以6个暖季型草坪草种作对照,通过测定各草种叶片内的可溶性糖、脯氨酸、丙二醛、叶绿素和电导率等生理指标,进行海滨雀稗的抗寒性和抗寒机理研究。[结果]海滨雀稗在适当低温（10℃左右）时的抗寒力强,生长旺盛,各抗寒生理指标变化小;但极度低温（5℃左右）时骤然死亡。原因是低温时抗寒物质（如脯氨酸和可溶性糖）增量少。[结论]海滨雀稗的抗寒性可能受少数几个主基因控制,诱变育种的效果可能较好。     

Phase Transitions Between beta and ggr (Mg, Fe)2SiO4 in the Earth's Mantle: Mechanisms and Rheological Implications

The mechanisms of the phase transformations between the spinel (gamma) and modified spinel (beta) polymorphs of Mg(2)SiO(4) have been studied experimentally between 15 and 20 gigapascals and 800 degrees to 950 degrees C. The gamma to beta transformation occurs by a shear mechanism, whereas the beta to gamma transformation involves grain-boundary nucleation and interface-controlled growth. These contrasting mechanisms are a consequence of the number of independent slip systems that are available in the respective crystal structures. This result leads to the prediction that in subduction zones and perhaps also rising plumes in the Earth's mantle, the gamma to beta transformation should be accompanied by a transient reduction in strength.     

Selected Elastic Moduli of Single-Crystal Olivines from Ultrasonic Experiments to Mantle Pressures

Ultrasonic interferometric measurements, developed for polycrystalline samples in a multi-anvil apparatus, were extended to single-crystal samples of San Carlos olivine and forsterite. The elastic moduli, C22 and C55 of San Carlos olivine and C55 of pure forsterite, were measured to about 13 gigapascals. These data on C22 for San Carlos olivine and C55 for forsterite are consistent with earlier measurements and extrapolations. The C55 for San Carlos olivine increases linearly as a function of increasing pressure, unlike the earlier nonlinear behavior observed at high pressure with impulsive stimulated scattering techniques.     

Lunar and martian surfaces: petrologic significance of absorption bands in the near-infrared

A reflection minimum at 1 micron, reported for Moon and for Mars, indicates olivine or iron- and calcium-bearing clinopyroxene, or both-major constituents of many basaltic rocks. If the 1-micron absorption features are real, both chondritic and acidic rocks are ruled out as primary constituents of the surfaces of the bodies. The reflectance spectrum of Mars matches closely that of an oxidized basalt.     

Major element variation and possible source materials of apollo 12 crystalline rocks

Nine different crystalline rocks of the Apollo 12 samples have been analyzed with conventional chemical rock analysis methods. Five of the rocks have normative quartz, whereas the others have normative olivine and hypersthene. The rocks show a wide range in the ratio of iron to magnesium, and their compositions fall on relatively smooth curves in the oxide variation diagram. It is suggested that these rocks, with one exception, represent different parts of a differentiated magmatic body, in which magmatic differentiation by crystallization and settling of olivine was most effective. The source material of the original magma may be peridotite with or without minor amounts of plagioclase or spinel or garnet, with the presence or absence of these minerals dependent on the depth of magma generation.     

A High-Temperature Electrical Conduction Mechanism in the Lower Mantle Phase (Mg,Fe)1-xO

Measurements of electrical conductivity at high pressure and temperature were taken on the lower mantle phase magnesiowustite with varying Fe3+ content. Although previous measurements at atmospheric pressure suggest Fe2+-Fe3+ hopping (small polaron) as the dominant conductivity mechanism, the present experiments show a change in charge transport mechanism with temperature. The lower temperature measurements are consistent with small polaron conduction, but at higher temperatures, which are more applicable to the lower mantle, a large polaron mechanism is suggested. Because these mechanisms have different temperature and compositional dependencies, this transition has important implications for extrapolation to mantle conditions.     

热处理对小麦品种发芽和种子活力的影响

以晋农207、农大2322个小麦品种为材料,测定了种子经高温高湿老化处理后的发芽指标、种子活力、电导率的变化。结果表明,高温((54±1)℃)、高湿(相对湿度100%)、密闭老化处理24h后,晋农207、农大232多数发芽指标下降,种子活力降低,而种子的相对电导率升高。2个小麦品种耐老化能力存在差异,晋农207比农大232相对耐高温老化。