Phase transformations of enstatite in spherical shock waves

The analysis of available theoretical evaluations and experimental data reveals discrepancies and makes it possible to formulate the goals for the comprehensive study of the behavior of enstatite MgSiO₃ in shock isentropic waves of various scale and intensity. The paper presents the layout and results of an explosion experiment on the compression of an enstatite sphere with spherical shock waves and the subsequent recovery of the experimental material and its examination in discrete zones (along the sphere radius) that were produced by shock waves in the material. The latter were examined with the application of scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis. The comparison of the systematic variations in the texture, chemistry, and phase composition of enstatite along the sphere radius with calculated pressure P(R, t) and temperature T(R, t) values led us to the following conclusions: enstatite starts melting on an isentrope upon pressure relief after shock wave compression at ?? _xx ?? 80 GPa and melts on the front of the spherically converging shock wave at ?? _xx ?? 160 GPa and T ?? 6300 K. Our laboratory experiments with shock waves were the world??s first in which enstatite was loaded with spherical converging shock isentropic waves and which provided evidence that shock wave-loaded MgSiO₃ shows certain morphological and mineralogical features never before detected in this mineral loaded with plane shock wave of smaller amplitude and duration. Goals are formulated for the further studying of shock wave-loaded materials, and the necessity is discussed for conducting an explosion experiment with a five to seven times greater spherical system in order to increase the duration of the shock wave loading impulse.     

Cluster type of silicate vaporization: Newly obtained experimental data

Impact cratering is usually associated with the partial or complete vaporization of the high-temperature impact melts. According to its chemical characteristics, the vaporization of major oxides, silicate minerals, and rock melts can be classified into the following four types: (1) congruent vaporization without decomposition of the compound in the vapor phase, (2) congruent vaporization with the decomposition of the compound in the vapor phase, (3) incongruent vaporization, and (4) cluster vaporization. The latter type of vaporization pertains to the transfer of material into vapor phase in the form of complicated atomicmolecular groups (clusters) of certain stoichiometry. Cluster vaporization takes place at superhigh temperatures typical of impact processes. The clusters can comprise compounds of different individual volatility, and this often results in the enrichment of the vapor phase in elements traditionally thought to be refractory. Examples of cluster vaporization are offered by lately obtained experimental results on laser-pulse vaporization of larnite, merwinite, and wollastonite. Condensed vapor generated at the vaporization of orthosilicates (larnite and merwinite) was proved to be dominated by chain bonds of Si-O tetrahedrons and to contain molecular groups of wollastonite and pseudowollastonite stoichiometry.     

Strain localization in sand: an overview of the experimental results obtained in Grenoble using stereophotogrammetry

Experimental results are presented from the extensive program of drained plane strain compression tests on sand carried out in Grenoble over the last two decades. Systematic analysis of photographs of the deforming specimen allowed for measuring deformations and determining strain fields throughout the test, that is: prior to, at, and after the onset of strain localization. The principles, details and accuracy of the procedure are described, as well as its suitability to properly depict the patterns of deformation. Findings concerning the occurrence and progression of strain localization are discussed. The issues of shear band orientation and thickness are addressed, as well as temporary and persistent complex localization patterns, and the volumetric behaviour inside a band after its formation. The influence of such variables as initial state of the sand (effective stress and relative density), specimen size and slenderness, as well as grain size, is discussed. Copyright © 2004 John Wiley & Sons, Ltd     

应力波在平台-桩系统中传播的实验研究

分析了应力波在平台－桩系统中的传播图案。对有限尺寸的平台来说，应力波在平台边界面上会发生反射，反射波不仅有同类波同时还有转换波，除此之外，平台表面的响应还受桩及桩土相互作用的影响。除非桩身反射波走时较长，可以避开平台上的各种干扰波，否则，由平台实测波形特征来分析平台下桩的完整性是很困难的。通过对平台上完整桩实测波形与异常桩波形进行比较，可以提高波形识别的准确度，此外，根据桩侧面测点及平台表面测点走时，相位、幅值间关系，将两者信号进行比较，可以从复杂的信号中辨别出桩身反射波信号。     

Newest results obtained in studying the Fennoscandian land uplift phenomenon

The Fennoscandian land uplift phenomenon has been studied using geodetic, gravimetric and seismologic material. Results obtained show that the greatest part of the phenomenon is of glaciological origin. In the geoid there is a depression approx. eight meters in depth. A seismic map showing data gathered over 500 years shows also a certain tectonic pattern.     

Subcritical crack propagation in rocks: theory,experimental results and applications

The micromechanisms of tensile fracture are reviewed, with particular emphasis on the influence of chemical effects on fracture controlled by pre-existing cracks (stress corrosion). A fracture mechanism map for quartz is presented which was constructed using a combination of theoretical insights and experimental data. The manner in which stress corrosion will modify the predictions of fracture mechanism maps is discussed by reviewing the numerous theories of stress corrosion. Experimental data are presented on stress corrosion in tensile deformation of quartz, quartz rocks, calcite rocks, basaltic rocks, granitic rocks and other geological materials. Although the experimental evidence for stress corrosion is overwhelming, very few data were obtained under conditions that simulate those in the bulk of the earth's crust and so the extent of its geophysical significance is yet to be fully established. Examples are given, however, of how invoking stress corrosion as a rate-controlling deformation mechanism sheds new light on extremely diverse geophysical phenomena, such as: predicting the strength and sliding friction properties of rocks, modelling earthquake rupture, the stability of hot, dry-rock geothermal reservoirs, stimulation of oil and gas reservoirs, the crack-seal mechanism of rock deformation and low stress dilatancy, fracture mechanics of lunar rocks, magmatic intrusions and the relaxation of internal stresses in rock.     

The olivine — clinopyroxene geobarometer: experimental results in the CaO-FeO-MgO-SiO2 system

The exchange of Ca and Mg between olivine and clinopyroxene has been studied in the CFMS system. Experiments were conducted in a piston-cylinder apparatus in the temperature range of 1,100–1,300° C and the pressure range 10–30 kbar. Results confirm the previous suggestion (Adams and Bishop 1982) that this reaction has a sufficiently large V° to be used as a geobarometer in several basic and ultrabasic systems. Experimental results were corrected for compositional effects using recent activity-composition models for quadrilateral pyroxenes and olivines. The corrected results indicate that the exchange reaction has aH _{1 bar} of 34,900 J, a S° of -7.25J/deg, and a V° of -0.489 J/bar. Corrected results agree well with calculations based on the thermodynamic properties of the endmembers.Application of the olivine-clinopyroxene geobarometer to many systems will require additional calibration of non CFMS components. Preliminary pressure estimates based on simple assumptions about the activity relations of these components have been made for spinel lherzolites from southwestern United States and coarse and porphyroclastic garnet lherzolites from southern Africa. A geotherm calculated from spinel lherzolites near the Rio Grande rift is consistent with a geophysical geotherm based on near-surface heat-flow measurements of 100 mW/m² or greater. Results on garnet lherzolites yield a southern African geotherm with no inflection which falls at somewhat higher temperatures than pyroxene geotherms calculated for the same area.     

Fracture sealing of quartzite under a temperature gradient: experimental results

Veined lithologies are formed by fracturing and sealing processes, with the veins representing former fluid conduits through the rock. Although detailed fieldwork and numerical simulations have provided a better understanding of vein growth, few studies have attempted to seal fractures and generate veins experimentally. In this pilot study, we subjected fractured quartzite to temperature gradients of 45–125 °C under hydrothermal conditions in a static fluid, with the aim of precipitating secondary quartz in the cooler portions of the fracture. Results show that secondary quartz precipitates due to the imposed temperature gradient, causing the initial fracture to seal locally. Although no systematic sealing pattern was observed along the fracture, samples subjected to higher temperatures exhibit a smaller fracture width and appear to have reacted more extensively. Electron microprobe mapping visualizes the spatial distribution of secondary quartz, which contains elevated concentrations of aluminium.     

青海小赛什腾山地区达肯大坂岩群中新解体出一套变火山岩系

达肯大坂岩群(Pt1D.)是柴北缘欧龙布鲁克地块的结晶基底,为一套变质程度达角闪岩相的深变质岩系,形成时代为古元古代.通过1 ∶ 5万专项地质调查,在柴北缘欧龙布鲁克地块苏干湖南小赛什腾山一带原划归达肯大坂岩群中,新填绘出一套糜棱岩化变中酸性火山岩系与达肯大坂岩群岩石组合存在明显差异.通过LA-ICP-MS锆石U-Pb...     

A possible manifestation of spiral shock waves in the accretion disks of cataclysmic variables

We present the results of three-dimensional numerical simulations of flow structures in binary systems with spiral shock waves. Variations of the mass-transfer rate perturb the equilibrium state of the accretion disk; consequently, a condensation (blob) behind the shock breaks away from the shock front and moves through the disk with variable speed. Our computations indicate that the blob is a long-lived formation, whose mean parameters do not vary substantially on timescales of several tens of orbital periods of the system. The presence of the spiral shocks maintains the compact blob in the disk: it prevents the blob from spreading due to the differential motion of matter in the disk, and dissipative spreading on this timescale is negligible. A number of cataclysmic variables display periodic or quasi-periodic photometric variations in their light curves with characteristic periods ～0.1–0.2P _orb, where P _orb is the orbital period. The blobs formed in systems with spiral shock waves are examined as a possible origin for these variations. The qualitative (and, in part, quantitative) agreement between our computations and observations of IP Peg and EX Dra provides evidence for the efficacy of the proposed model.     

Partial melting of two amphibolites: contrasting experimental results under fluid-absent conditions

A large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase. As a consequence, H₂O-undersaturated or fluid-absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events. In an attempt to determine the systematics of melting under fluid-absent conditions, a series of piston-cylinder experiments was conducted on two natural amphibolites; one, a meta-alkali basalt (ABA) with a total water content of ∼ wt% contained in hornblende, and the other, a meta-island-arc tholeiite (IAT) which has ∼1–1.3 wt% water contained in hornblende, cummingtonite and biotite. The experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures, and sta temperature interval over which amphibole was stable, were controlled by the amphibolites' different bulk compositions and their resulting metamorphic assemblages. The volume % of melt produced by melting of the two amphibolites were compared with estimated amounts, based on Burnham's (1979) water-melt solubility model and the fluid-absent melting model presented by Clemens and Vielzeuf (1987). The observed melt volumes were greater than estimated. As the water content of melt largely detemines the volume % of melt produced, independent measurements of the water-content of the glass formed during partial melting in the ABA were made by thermogravimetric analyses. The water content of the ABA glass is ∼2 wt%, which is less than the assumed “melt-water” content (water content of the melt) used in previous modeling of fluidabsent anatexis in mafic lithologies. As a consequence, more melt can be expected during fluid-absent partial melting of mafic lower crust, as is observed in the experiments. A modification of the Clemens and Vielzeuf (1987) fluid-absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5, 8 and 10 kbar. Tectonic scenarios in which the crust is thickened (i.e. by collision) then undergoes extension or where a previously thinned crust is later rethickened, provide enough heat so that amphibolite melting under fluid-absent conditions can become importan and hence responsible for some melts produced during post-collisional magmatism. The results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains.     

Three Alkali-Rich Intrusive Rock Belts Newly Discovered in the Mt. Kunlun-Mt. Altun Region, Xinjiang, China

The newly discovered three alkali-rich intrusive rock belts in the Mt. Kunlun Mt.Altun region of southern Xinjiang are the Lapeiquan-Yitunbulak alkali-rich intrusive rock belt,the Gez-Taxkorgan alkali-rich intrusive rock belt and the Beilisai-Abulash alkali-rich intrusive rock belt. The former two belts were formed during the Yanshanian period, and the third one was formed during the Himalayan period, which is the youngest alkali-rich intrusive rock belt in China. The discovery of the alkali-rich intrusive rock belts is of great significance in shedding light on the history of tectono-magmatic activities in this region.     

Mechanisms of formation of deep-sea ferromanganese nodules: Mathematical modeling and experimental results

Our study attempts to provide insight into the physicochemical processes operating in bottom seawater and to develop mathematical models for the formation of marine nodules owing to the diffusive transport of the major elements from ambient water to the nodule. A comparison of the model results with experimental data on the growth rates and the age of nodules provided an argument in favor of a rapid-growth concept (millimeters per thousand years). The distribution of trace elements in the nodules was derived from the limited source model and appeared to be related to the process of nodule formation; therefore, it is largely identical for many of the trace elements. These results are in line with the experimental data. Both stable and radioactive isotopes show an exponential concentration profile measured in the outer layers of the nodule, which has no bearing on radioactive decay. Given these results, the earlier conclusions on the slow growth of the nodules (millimeters per million years), which were based on the interpretation of the observed isotope distribution as a result of radioactive decay, appear questionable.     

TRANSIT,an experimental archaeological program in periglacial environment: Problem,methodology, first results

The aim of the experimental archaeological program TRANSIT is to improve the scientific study of Paleolithic sites. This program is based on studies and experiments carried out at high altitudes in the French Alps. One of its goals is to assess the effects of periglacial processes on spatial distributions within archaeological assemblages and on artifacts and bones. Research on sedimentary environments elucidates stratogenesis in periglacial contexts. In particular, sedimentary models that are useful for interpreting fossil deposits were identified. The first results obtained from experimental artifact test plots emphasize the importance and speed of changes that occur in such a climatic and morphodynamic context. Mean lateral displacements from 1.66 to 4.75 cm yr⁻¹ were measured. Moreover, analysis of osseous and dental pieces showed that they experienced important damage. Works on pollen assemblages have shown that most of the pollen deposited on the ground surface is quickly removed and that, owing to the very uneven preservation of pollen taxa, an important distortion of the initial spectrum occurs. A model of spatial arrangement of artifacts linked to the action of solifluction processes is also proposed. Finally, application of these results to some Paleolithic sites in the Massif Central and southwest France are discussed. © 1998 John Wiley & Sons, Inc.     

The Diavik Waste Rock Project: Design,construction, and instrumentation of field-scale experimental waste-rock piles

The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04 wt.% S; the second test pile contains waste rock with a target S content of >0.08 wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08 wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15 m high with bases of 50 m by 60 m, and the re-sloped test pile has a larger base of 80 m by 125 m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O₂ concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles.     

Oxygen diffusion in basalt and andesite melts: experimental results and discussion of chemical versus tracer diffusion

Chemical diffusion coefficients for oxygen in melts of Columbia River basalt (Ice Harbor Dam flow) and Mt. Hood andesite have been determined at 1 atm. The diffusion model is that of sorption or desorption of oxygen into a sphere of uniform initial concentration from a constant and semi-infinite atmosphere. The experimental design utilizes a thermogravimetric balance to monitor the rate of weight change arising from the response of the sample redox state to an imposed fO₂. Oxygen diffusion coefficients are approximately an order-ofmagnitude greater for basaltic melt than for andesitic melt. At 1260° C, the oxygen diffusion coefficients are: D=1.65×10^–6cm²/s and D=1.43×10^–7cm²/s for the basalt and andesite melts, respectively. The high oxygen diffusivity in basaltic melt correlates with a high ratio of nonbridging oxygen/tetrahedrally coordinated cations, low melt viscosity, and high contents of network-modifying cations. The dependence of the oxygen diffusion coefficient on temperature is: D=36.4exp(–51,600±3200/RT)cm²/s for the basalt and D=52.5exp(–60,060±4900/RT)cm²/s for the andesite (R in cal/deg-mol; T in Kelvin). Diffusion coefficients are independent of the direction of oxygen diffusion (equilibrium can be approached from extremely oxidizing or reducing conditions) and thus, melt redox state. Characteristic diffusion distances for oxygen at 1260° C vary from 10^-2 to 10² m over the time interval of 1 to 10⁶ years. A compensation diagram shows two distinct trends for oxygen chemical diffusion and oxygen tracer diffusion. These different linear relationships are interpreted as supporting distinct oxygen transport mechanisms. Because oxygen chemical diffusivities are generally greater than tracer diffusivities and their Arrhenius activation energies are less, transport mechanisms involving either molecular oxygen or vacancy diffusion are favored.