首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 547 毫秒
1.
The processes of solar wind sputtering and meteoritic impact vaporization have created materials in the lunar regolith which were deposited from a vapor phase. Although the quantity of such exotic condensed substances should theoretically be comparable with that of materials which have been melted by impacts, their existence in the fines has not been generally recognized. We have investigated the physical and chemical properties of materials deposited from vapors generated by hydrogen-ion sputtering and thermal evaporation of lunar and artificial ferrosilicates. Both processes are highly reducing. The deposits are enriched in Fe, have large, nonselective, optical absorptivities, and contain abundant sub-microscopic, superparamagnetic grains of metallic Fe which exhibit the characteristicg=2.1 ESR resonance. The sputter-deposited films are enriched in heavy elements. Thus the hypothesis that the lunar fines contain several percent of materials deposited from the vapor phase accounts in a natural manner for many of the unusual optical, physical and chemical properties of lunar soils. The vapor-deposits are probably concentrated in the agglutinate particles of the regolith.  相似文献   

2.
Space weathering is now generally accepted to modify the optical and magnetic properties of airless planetary regoliths such as those on the Moon and Mercury. Under micrometeorite and ion bombardment, ferrous iron in such surfaces is reduced to metallic iron spheres, found in amorphous coatings on almost all exposed regolith grains. The size and number distribution of these particles and their location in the regolith all determine the nature and extent of the optical and magnetic changes. These parameters in turn reflect the formation mechanisms, temperatures, and durations involved in the evolution of the regolith. Studying them in situ is of intrinsic value to understanding the weathering process, and useful for determining the maturity of the regolith and providing supporting data for interpreting remotely sensed mineralogy. Fine-grained metallic iron has a number of properties that make it amenable to magnetic techniques, of which magnetic susceptibility is the simplest and most robust. The magnetic properties of the lunar regolith and laboratory regolith analogues are therefore reviewed and the theoretical basis for the frequency dependence of magnetic susceptibility presented. Proposed here is then an instrument concept using multi-frequency measurements of magnetic susceptibility to confirm the presence of fine-grained magnetic material and attempt to infer its quantity and size distribution. Such an instrument would be invaluable on a future mission to an asteroid, the Moon, Mercury or other airless rocky Solar System body.  相似文献   

3.
This paper synthesizes information on the size distribution and physical properties of interplanetary dust grains obtained from analyses of lunar microcraters performed until 1979. The different aspects of these analyses (counting methods, simulation, calibrations) are summarized and a large amount of data is collected and discussed in order to clarify past contradictions. The number of small microcraters (Dc < 5 μm) is found to be higher than previously derived and the ratio P/Dc (depth to crater diameter) to depend upon their sizes. All results converge to a two-component dust population: Population 1 consists principally of large grains (d > 2 μm) with density typical of silicates while Population 2 consists of small grains (d < 2 μm) with higher density typical of iron, with a minor component of silicates. The conclusion appears to be further supported by spatial measurements and collection experiments. Fluffy grains of very low density (0.3 g/cm3) are probably not present to a large extent.  相似文献   

4.
Many of the breccias returned by the Apollo missions are capable of acquiring a substantial viscous remanent magnetization (VRM) which is of two forms. The first one has an upper limit to the relaxation times of about 100 to 1000min which corresponds to a grain diameter of about 145 Å. This suggests that the maximum relaxation time is determined by the transition from superparamagnetic to stable single domain particles. The second form of VRM follows the classical logt dependence typical for multidomain grains with a wide distribution of relaxation times. Hysteresis loop measurements yield the same kind of grain size distributions. In addition the analysis shows a fivefold enrichment of native iron in the breccias and soils as compared to the igneous rocks. In spite of a large VRM some breccias contain a stable remanent magnetization. Its intensity is typically 10–6emu/gm, the same value found for igneous rocks. It is possible, therefore, to use some of the breccias to reconstruct the history of the lunar magnetic field.  相似文献   

5.
Abstract— We present the results of irradiation experiments aimed at understanding the structural and chemical evolution of silicate grains in the interstellar medium. A series of He+ irradiation experiments have been performed on ultra‐thin olivine, (Mg,Fe)2SiO4, samples having a high surface/volume (S/V) ratio, comparable to the expected S/V ratio of interstellar dust. The energies and fluences of the helium ions used in this study have been chosen to simulate the irradiation of interstellar dust grains in supernovae shock waves. The samples were mainly studied using analytical transmission electron microscopy. Our results show that olivine is amorphized by low‐energy ion irradiation. Changes in composition are also observed. In particular, irradiation leads to a decrease of the atomic ratios O/Si and Mg/Si as determined by x‐ray photoelectron spectroscopy and by x‐ray energy dispersive spectroscopy. This chemical evolution is due to the differential sputtering of atoms near the surfaces. We also observe a reduction process resulting in the formation of metallic iron. The use of very thin samples emphasizes the role of surface/volume ratio and thus the importance of the particle size in the irradiation‐induced effects. These results allow us to account qualitatively for the observed properties of interstellar grains in different environments, that is, at different stages of their evolution: chemical and structural evolution in the interstellar medium, from olivine to pyroxene‐type and from crystalline to amorphous silicates, porosity of cometary grains as well as the formation of metallic inclusions in silicates.  相似文献   

6.
We detail the production of metallic spherules in laboratory oblique shock impact experiments, and their applicability (1) to textures in a partly shock‐melted chondritic meteorite and (2) to the occurrence of palaeomagnetically important fine iron or iron alloy particles in the lunar regolith. Samples recovered from 29–44 GPa, 800 ns, experiments revealed melting and textures reminiscent of metallic spherules in the Yanzhuang H‐chondrite, including “dumbbell” forms and other more complex morphologies. Our experiments demonstrate that metallic spherules can be produced via oblique impact sliding at lower velocities (1.85 km s?1) than are generally assumed in previous work associated with bulk‐shock melting, and that oblique impact sliding is a viable mechanism for producing spherules in shock‐induced veins in moderately shocked meteorites. Significantly, our experiments also produced fine metallic (iron alloy) spherules within the theoretical narrow size range (a few tens of nanometers for slightly ellipsoidal particles) for stable single‐domain (SSD) particles, which are the most important palaeomagnetically, since they can record lunar and planetary magnetic fields over geological time periods. The experiments also produced spherules consistent with superparamagnetic (SP) and multidomain (MD) particle sizes. The fine SSD and SP particles on the lunar surface are currently thought to have been formed predominantly by space weathering processes. Our experiments suggest that oblique shock impact sliding may be a further means of producing the SSD and SP iron or iron alloy particles observed in the lunar regolith, and which are likely to occur in the regoliths of Mercury and other planetary bodies.  相似文献   

7.
Pulsed‐laser irradiation causes the visible‐near‐infrared spectral slope of olivine (Fo90 and Fo99+) and SiO2 to increase (redden), while the olivine samples darken and the SiO2 samples brighten slightly. XPS analysis shows that irradiation of Fo90 produces metallic Fe. Analytical SEM and TEM measurements confirm that reddening in the Fo90 olivine samples correlates with the production of “nanophase” metallic Fe (npFe0) grains, 20–50 nm in size. The reddening observed in the SiO2 sample is consistent with the formation of SiO or other SiOx species that absorb in the visible. The weak spectral brightening induced by laser irradiation of SiO2 is consistent with a change in surface topography of the sample. The darkening observed in the olivine samples is likely caused by the formation of larger npFe0 particles, such as the 100–400 nm diameter npFe0 identified during our TEM analysis of Fo90 samples. The Fo90 reflectance spectra are qualitatively similar to those in previous experiments suggesting that in all cases formation of npFe0 is causing the spectral alteration. Finally, we find that the accumulation of successive laser pulses cause continued sample darkening in the Vis‐NIR, which suggests that repeated surface impacts are an efficient way to darken airless body surfaces.  相似文献   

8.
Magnetic observations yield information about the amount and nature of the magnetic phases present in a sample. They reveal that the predominant magnetic phase in the lunar samples is metallic iron which is sometimes alloyed with nickel and cobalt. In the mare basalts less than 0.1% of metallic iron is present, whereas in the non-mare crystalline rocks several percent of iron has been found in some samples. The soils have approximately 0.5% of iron, which is fine grain, rather pure iron occurring in impact glass. In the recrystallized breccias and the igneous rocks the iron is coarser. Systematic minor variations in metallic iron content in the soils reveal soil maturity trends. Mixing between highland and mare soils can be traced with the Fe2+ content. Mare soils differ from highland soils in having a higher value of reduced remanence. The magnetic characteristics of the Apollo 14 breccias are not consistent with the progressive metamorphism of a common starting material. Shock welding in the range of tens of kbs can account for the characteristics of some of the ‘unmetamorphosed’ breccias. Greater shock accompanied by recovery can account for the magnetic characteristics of the ‘recrystallized’ breccias.  相似文献   

9.
The near-IR spectral properties of minerals, meteorites, and lunar soil vary with temperature. The manner in which these materials vary is diagnostic of aspects of their composition. We quantify the spectral dependence on temperature by reporting the change in relative reflectance with temperature as a function of wavelength. We call this quantity, ΔR/ΔT (in units of K−1), as a function of temperature the “thermo-reflectance spectrum.” The thermo-reflectance spectra of olivine and pyroxene are distinct, and most of the observable structure in thermo-reflectance spectra of the ordinary and carbonaceous chondrites can be understood in terms of a mixture of the thermo-reflectance spectra of olivine and pyroxene. The magnitude of thermo-reflectance spectra of meteorites and lunar soils is much less than that of pure minerals. Lunar soils are particularly subdued. While conventional analysis of remotely obtained spectra of the Moon can neglect temperature effects, spatially resolved measurements of the surface of the asteroid Vesta will likely have a strong temperature-dependent component based on measurements of a eucrite and a howardite.  相似文献   

10.
Abstract— A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid nitrogen temperature Mössbauer measurements, X‐ray diffraction (XRD), and electron probe microanalysis (EPMA) in conjunction with energy dispersive X‐ray microscopy. The Mössbauer spectra exhibited strong paramagnetic doublets with magnetic sextets. The doublets are assigned to olivine and pyroxene, while the magnetic sextets are assigned to troilite and kamacite. Based on microprobe analyses and textural studies, olivine is the most abundant phase and occurs as fine to medium grained laths both in the groundmass and in barred olivine chondrules. Both orthopyroxenes and clinopyroxenes are present and these tend to be granular. Plagioclase is an abundant interstitial groundmass phase. Chromites were detected in some groundmass olivine and are highly chromiumand iron‐rich with no Fe3+ detected. The kamacite contains small amounts of Co. The mole fraction of the Fe end‐member of olivine (fayalite) and orthopyroxene (ferrosilite) are found to be about 28% and 23%, respectively. These values are compared with that obtained from two chondritic meteorites. Based on these results, the studied meteorite is classified as an ordinary LL5 chondrite.  相似文献   

11.
For fayalite formation times of several thousand years, and systems enriched in water by a factor of ten relative to solar composition, 1 μm radius olivine grains could reach 2 mole% fayalite and 0.1 μm grains 5 mole% by nebular condensation, well short of the values appropriate for precursors of most chondrules and the values found in the matrices of unequilibrated ordinary chondrites. Even 10 μm olivine crystals could reach 30 mole% fayalite above 1100 K in solar gas if condensation of metallic nickel‐iron were delayed sufficiently by supersaturation. Consideration of the surface tensions of several phases with equilibrium condensation temperatures above that of metallic iron shows that, even if they were supersaturated, they would still nucleate homogeneously above the equilibrium condensation temperature of metallic iron. This phenomenon would have provided nuclei for heterogeneous nucleation of metallic nickel‐iron, thus preventing the latter from supersaturating significantly and preventing olivine from becoming fayalitic. Unless a way is found to make nebular regions far more oxidizing than in existing models, it is unlikely that chondrule precursors or the matrix olivine grains of unequilibrated ordinary chondrites obtained their fayalite contents by condensation processes. Perhaps stabilization of FeO occurred after condensation of water ice and accretion of icy planetesimals, during heating of the planetesimals and/or in hot, dense, water‐rich vapor plumes generated by impacts on them. This would imply that FeO is a relatively young feature of nebular materials.  相似文献   

12.
Abstract— Yamato 000593, a nakhlite, was analyzed in terms of its magnetic record and magnetomineralogy. The natural remanent magnetization (NRM: 3.55–6.07 times 10?5 Am2/kg) was thermally demagnetized at ～320 °C, and it was unstable against alternating field demagnetization. Based on analyses of thermomagnetic curves, the temperature dependence of hysteresis parameters, and microscopic observations, the magnetic minerals mainly consist of magnetite (0.68 wt% of the sample, including ～5% Fe2TiO4) of less than 100 μm in size, associated with minor amounts of monoclinic pyrrhotite (<0.069 wt% of the sample) and goethite. Thermal demagnetization of NRM at ～330 °C is explained due to an offset of magnetization of antipodal NRM components of magnetite, whereas it is not due to a pyrrhotite Curie point. Large magnetite grains show exsolution texture with ilmenite laths, and are cut by silicate (including goethite) veins that formed along cracks. Numerous single‐domain (SD) and pseudo‐single‐domain (PSD) magnetite grains are scattered in the mesostasis and adjacent olivine grains. Moderate coercive forces of HC = 6.8 mT and HRC = 31.1 mT suggest that Yamato 000593 is fundamentally able to carry a stable NRM; however, NRM was found to be unstable. Accordingly, the meteorite was possibly crystallized at 1.3 Ga under an extremely weak or absent magnetic field, or was demagnetized by impact shock at 12 Ma (ejection age) on Mars. This finding differs from the results of previous paleomagnetic studies of SNC (shergottites, nakhlites, chassignites, and orthopyroxenite) Martian meteorites. The significant dipole magnetic field resulting from the molten metallic core was probably absent during the Amazonian Epoch (after 1.8 Ga) on Mars.  相似文献   

13.
A new meteorite find, named Khatyrka, was recovered from eastern Siberia as a result of a search for naturally occurring quasicrystals. The meteorite occurs as clastic grains within postglacial clay‐rich layers along the banks of a small stream in the Koryak Mountains, Chukotka Autonomous Okrug of far eastern Russia. Some of the grains are clearly chondritic and contain Type IA porphyritic olivine chondrules enclosed in matrices that have the characteristic platy olivine texture, matrix olivine composition, and mineralogy (olivine, pentlandite, nickel‐rich iron‐nickel metal, nepheline, and calcic pyroxene [diopside‐hedenbergite solid solution]) of oxidized‐subgroup CV3 chondrites. A few grains are fine‐grained spinel‐rich calcium‐aluminum‐rich inclusions with mineral oxygen isotopic compositions again typical of such objects in CV3 chondrites. The chondritic and CAI grains contain small fragments of metallic copper‐aluminum‐iron alloys that include the quasicrystalline phase icosahedrite. One grain is an achondritic intergrowth of Cu‐Al metal alloys and forsteritic olivine ± diopsidic pyroxene, both of which have meteoritic (CV3‐like) oxygen isotopic compositions. Finally, some grains consist almost entirely of metallic alloys of aluminum + copper ± iron. The Cu‐Al‐Fe metal alloys and the alloy‐bearing achondrite clast are interpreted to be an accretionary component of what otherwise is a fairly normal CV3 (oxidized) chondrite. This association of CV3 chondritic grains with metallic copper‐aluminum alloys makes Khatyrka a unique meteorite, perhaps best described as a complex CV3 (ox) breccia.  相似文献   

14.
J. Warell  D.T. Blewett 《Icarus》2004,168(2):257-276
We present new optical (0.4-0.65 μm) spectra of Mercury and lunar pure anorthosite locations, obtained quasi-simultaneously with the Nordic Optical Telescope (NOT) in 2002. A comparative study is performed with the model of Lucey et al. (2000, J. Geophys. Res. 105, 20297-20305, and references therein) between iron-poor, mature, pure anorthosite (>90% plagioclase feldspar) Clementine spectra from the lunar farside and a combined 0.4-1.0 μm mercurian spectrum, obtained with the NOT, calculated for standard photometric geometry. Mercury is located at more extreme locations in the Lucey ratio-reflectance diagrams than any known lunar soil, specifically with respect to the extremely iron-poor mature anorthosites. Though quantitative prediction of FeO and TiO2 abundances cannot be made without a more generally applicable model, we find qualitatively that the abundances of both these oxides must be near zero for Mercury. We utilize the theory of Hapke (2002, Icarus 157, 523-534, and references therein), with realistic photometric parameters, to model laboratory spectra of matured mineral powders and lunar soils, and remotely sensed spectra of lunar anorthosites and Mercury. An important difference between fabricated and natural powders is the high value for the internal scattering parameter necessary to interpret the spectra for the former, and the requirement of rough and non-isotropically scattering surfaces in the modelling of the latter. The mature lunar anorthosite spectra were well modelled with binary mixtures of calcic feldspars and olivines, grain sizes of 25-30 μm and a concentration of submicroscopic metallic iron (SMFe) of 0.12-0.15% in grain coatings. The mercurian spectrum is not possible to interpret from terrestrial mineral powder spectra without introducing an average particle scattering function for the bulk soil that increases in backscattering efficiency with wavelength. The observed spectrum is somewhat better predicted with binary mixture models of feldspars and pyroxenes, than with single-component regoliths consisting of either albite or diopside. Correct spectral reflectance values were predicted with a concentration of 0.1 wt% SMFe in coatings of 15-30 μm sized grains. Since reasonable cosmogonical formation scenarios for Mercury, or meteoritic infall, predict iron concentrations at least this high, we draw the conclusion that the average grain size of Mercury is about a factor of two smaller than for average returned lunar soil samples. The 0.6-2.5 μm spectrum of McCord and Clark (1979, J. Geophys. Res. 178, 745-747) is used to further limit the possible range of mineralogical composition of Mercury. It is found that an intimately mixed and matured 3:1 labradorite-to-enstatite regolith composition best matches both the optical and near-infrared spectra, yielding an abundance of ∼1.2 wt% FeO and ∼0 wt% TiO2.  相似文献   

15.
M.J. Loeffler  R.A. Baragiola 《Icarus》2008,196(1):285-292
We present quantitative laboratory studies that simulate the effect of redeposition of impact-ejecta on mineral surfaces. We produced deposits of natural olivine (Fo90) and forsterite on olivine and forsterite powder samples by ns-pulsed laser ablation. The deposits produce changes in the optical reflectance (0.66-2.5 μm). We show that significant darkening and reddening of the surface occurs when the deposit is olivine but not if it is forsterite. This is attributed to the formation of metallic iron nanoparticles in the olivine deposits. We also characterized structural and chemical changes using scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). In situ XPS measurements show that the olivine deposits are reduced, with 50% of the iron becoming metallic. Transmission electron microscope studies confirm the presence of 2-3 nm crystalline iron nanoparticles in the olivine deposits. The scanning electron microscope shows that both olivine and forsterite deposits smoothen the topography of the powder surface, which could have effects on processes such as exosphere-surface interactions and sputtering. We conclude that the effect of coatings produced by micrometeorite impacts will not be uniform on airless bodies but will depend on the composition of the terrain.  相似文献   

16.
To compare the spectra of main-belt S-type asteroids and ordinary chondrites, we investigated the correlation between the reflectance peak position near 750 nm, the bend of the spectral curves in the 359–701 nm region, the linear gradient in the 359–853 nm range, and the absorption band position near 950 nm. In the diagrams of spectral parameters, the regions occupied by S-type asteroids and ordinary chondrites are separated. The modeling of the optical effect of maturation of ordinary-chondrite samples, which leads to variations in the meteorite spectral parameters, was carried out under the following conditions: (1) the increase of the concentration of reduced-iron grains (SMFe) in particles without any change in their size; (2) the increase/decrease of the size of particles at a constant concentration of SMFe in them; (3) we also examined different relations between the concentration and the size of SMFe in particles. But, under no conditions did we manage to bring into coincidence the asteroid and meteorite regions simultaneously in all spectral-parameter diagrams. Hence, the conclusion was made that the difference between the reflectance spectra of ordinary chondrites and those of large main-belt S-type asteroids is determined not only by space weathering of asteroidal surfaces but also by systematic differences in the material composition.  相似文献   

17.
Martian meteorites, in particular shergottites, contain darkened olivine (so‐called “brown olivine”) whose color is induced by iron nanoparticles formed in olivine during a shock event. The formation process and conditions of brown olivine have been discussed in the Northwest Africa 2737 (NWA 2737) chassignite. However, formation conditions of brown olivine in NWA 2737 cannot be applied to shergottites because NWA 2737 has a different shock history from that of shergottites. Therefore, this study observed brown olivine in the NWA 1950 shergottite and discusses the general formation process and conditions of brown olivine in shergottites. Our observation of NWA 1950 revealed that olivine is heterogeneously darkened between and within grains different from brown olivine in NWA 2737. XANES analysis showed that brown olivine contains small amounts of Fe3+ and TEM/STEM observation revealed that there is no SiO‐rich phase around iron metal nanoparticles. These observations indicate that iron nanoparticles were formed by a disproportionation reaction of olivine (3Fe2+olivine → Fe0metal + 2Fe3+olivine + Volivine, where Volivine means a vacancy in olivine). Some parts of brown olivine show lamellar textures in SEM observation and Raman peaks in addition to those expected for olivine, implying that brown olivine experienced a phase transition (to e.g., ringwoodite). In order to induce heterogeneous darkening, heterogeneous high temperature of about 1500–1700 K and shock duration of at least ~90 ms are required. This heterogeneous high temperature resulted in high postshock temperature (>900 K) inducing back‐transformation of most high‐pressure phases. Therefore, in spite of lack of high‐pressure phases, NWA 1950 (= Martian meteorites with brown olivine) experienced higher pressure and temperature compared to other highly shocked meteorite groups.  相似文献   

18.
Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.  相似文献   

19.
Abstract— We have used the Manchester ISOLAB 54 ion microprobe to make in situ measurements of the 17O/16O and 18O/16O ratios of olivine grains in the Julesburg (L3.6) and Allende (CV3) chondrites. We have discovered a population of olivines in Julesburg characterised by (1) the most 16O-rich compositions yet reported for olivine from an ordinary chondrite; (2) cores of low-Fa olivine, which frequently shows blue cathodoluminesce; (3) thick coats of more Fa-rich (Fa ～20) olivine, which is also 16O-enriched. In an O isotopic plot, the Julesburg 16O-rich grains form a roughly linear array that is offset from the Allende mixing line. The presence of very low Fa olivine and, sometimes, well-defined Fa-rich coats indicates that these grains experienced significantly less thermal metamorphism than most of the olivine in the meteorite. Some 16O-rich Julesburg grains are associated with minor feldspar or pyroxene and are probably chondrule fragments. They are isotopically indistinguishable from forsterite in Allende; however, Allende forsterite grains do not have the thick Fa20 coats typical of those in Julesburg. These 16O-rich forsterite grains appear to be related to the “blue olivine” of Steele (1986). Both cores and coats of 16O-rich grains in Julesburg are isotopically distinct from olivine in Semarkona group A and group B chondrules.  相似文献   

20.
Kuebler et al. (2006) identified variations in olivine Raman spectra based on the composition of individual olivine grains, leading to identification of olivine composition from Raman spectra alone. However, shock on a crystal lattice has since been shown to result in a structural change to the original material, which produces a shift in the Raman spectra of olivine grains compared with the original unshocked olivine (Foster et al. 2013). This suggests that the use of the compositional calculations from the Raman spectra, reported in Kuebler et al. (2006), may provide an incorrect compositional value for material that has experienced shock. Here, we have investigated the effect of impact speed (and hence peak shock pressure) on the shift in the Raman spectra for San Carlos olivine (Fo91) impacting Al foil. Powdered San Carlos olivine (grain size 1–10 μm) was fired at a range of impact speeds from 0.6 to 6.1 km s?1 (peak shock pressures 5–86 GPa) at Al foil to simulate capture over a wide range of peak shock pressures. A permanent change in the Raman spectra was found to be observed only for impact speeds greater than ~5 km s?1. The process that causes the shift is most likely linked to an increase in the peak pressure produced by the impact, but only after a minimum shock pressure associated with the speed at which the effect is first observed (here 65–86 GPa). At speeds around 6 km s?1 (peak shock pressures ~86 GPa), the shift in Raman peak positions is in a similar direction (red shift) to that observed by Foster et al. (2013) but of twice the magnitude.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号