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1.
We performed ion irradiation on olivine and ilmenite to simulate solar-wind exposure effects in lunar soil. The surface morphology and microstructure after ion irradiation were characterized by field emission scanning electron microscopy. Sputtering erosion significantly modified the surface of irradiated Luobusha olivine grains. All irradiated grains show smooth surface and round shape. The cleavage fractures on the unirradiated olivine surface were widened and deeply etched after He＋ irradiation. Both of these are the consequence of ion sputtering erosion. There are no bubbles or voids foundin the irradiated olivine grains, because He＋ dose in this study is lower than saturated fluence. Irradiated Panzhihua ilmenite grains are all covered with smooth flakes with the thickness of about 400 nm. The formation of the flakes should be related with helium bubbles and their growth during He＋ implantation. Some columnar-shaped particles are found at the surface of irradiated Panzhihua ilmenite. We speculate that these particles should be sulfide because of significantly high sulfur contents. 相似文献
2.
月壤介电常数是当前月球微波遥感探测的基础, 是月壤厚度、成分等信息提取不可或缺的参数.为了实现全月介电常数反演, 通过对嫦娥二号卫星微波辐射计亮温数据进行时角校正, 得到同一时角的全月微波亮温图.全月微波亮温表现出随月球地形、月壤成分及纬度变化的特征.基于校正后的微波辐射亮温, 结合辐射传输模型, 通过解算相关参数, 反演得到3GHz频率下全月介电常数分布.其中, 月海地区的介电常数实部高于月陆地区, 且月球极地区域介电常数实部偏低; 而介电常数虚部则在月海区域和艾肯盆地较高.通过模拟月表介电常数实验对反演结果进行温度校正, 得到22℃下全月介电常数.将反演结果和月壤真实样品的介电常数测量值进行比较评价.结果表明介电常数实部相对误差都低于11%;虚部相对误差偏大, 但其差值最大仅为0.02.因此, 基于嫦娥二号卫星微波辐射计亮温数据反演月表介电常数的方法是可行的. 相似文献
3.
Brightness temperature is a main index to reflect the energy of microwave radiation of an object. Using lunar brightness temperature data, physical properties of lunar regolith, such as thickness, heat flow and dielectric permittivity, could be interpreted. There are two methods to study brightness temperature distribution of the moon: the first is used to measure lunar brightness temperature by radio observation or spaceborne microwave radiometers, and the second is used to simulate calculation by the physical model. On the basis of the measurements of lunar brightness temperature in the history, this study analyzed the main physical model of lunar brightness temperature, also including its theory and influence factors. The authors concluded that surface and subsurface temperatures of the moon, dielectric properties and layered structure of lunar regolith were the main factors affecting the global brightness temperature of the moon. These factors should be quantified in detail in the future research. 相似文献
4.
月壤钛铁矿微波烧结制备月球基地结构材料的初步设想 总被引：2，自引：0，他引：2
月球基地建设是当前"重返月球"的一个重要目标,为满足其建设需要大量结构材料.部分学者通过对真实月壤样品和模拟月壤进行各种高温烧结实验,分析了就地利用月壤矿物资源制备各种材料的方法.但由于月壤成分较为复杂,烧结产物的性能还很难满足实际需求.微波烧结技术作为一项新技术,具有传统烧结技术无法比拟的优势,更适合作为月球资源利用中的烧结加热技术.结合月壤中钛铁矿的含量,通过热力学分析,作者认为利用钛铁矿进行微波烧结实验来制备月球基地所需结构材料是一个值得深入研究的方案. 相似文献
5.
6.
非均匀月壤介质的被动微波辐射传输模拟 总被引：1，自引：1，他引：0
基于非均匀月壤物理模型和辐射传输方程,模拟月壤介质中的微波辐射传输特性,探讨频率、月壤厚度等与月表亮温的关系。结果表明:在低频段,月壤微波辐射亮温的动态变化范围较大,可探测的月壤厚度大,3 GHz时的最大可探测月壤厚度达12.4 m;在高频段对应的可探测月壤厚度较小,特别是从50GHz往后的频率段内,最大可探测月壤厚度均小于2 m。不同频率的亮温-厚度变化曲线没有交叉点,且频率越高,所能探测的月壤厚度越小。根据模拟结果,建立了月壤厚度与亮温的查找表。基于查找表,利用单个波段的亮温数据即可得到月壤厚度信息。 相似文献
7.
O Eugster N Grögler M.D Mendia P Eberhardt J Geiss 《Geochimica et cosmochimica acta》1973,37(9):1991-2003
He, Ne, Ar, Kr and Xe concentrations and isotopic abundances were measured in three bulk grain size fractions prepared from sample L-16-19, No. 120 (C level, 20–22 cm depth) returned by the Luna 16 mission. The expected anticorrelation between the concentrations of trapped solar wind noble gases and grain size is observed. Elemental abundances of solar wind trapped noble gases are similar to those previously found in corresponding grain size fractions of the Apollo 11 and 12 fines. The trapped ratio varies in the soils from different lunar maria due to diffusion losses. A rough correlation of with the proportion of ilmenite in these samples is apparent. The elemental and isotopic ratios of the surface correlated noble gases in Luna 16 resemble those previously found in Apollo fines. Based on 21Ne, 78Kr and 126Xe a cosmic ray exposure age of 360 my was determined. This age is similar to those obtained for the soils from other lunar maria. 相似文献
8.
Regional soil moisture retrievals and simulations from assimilation of satellite microwave brightness temperature observations 总被引：4，自引：2，他引：2
Xiaokang Shi Jun Wen Lei Wang Tangtang Zhang Hui Tian Xin Wang Rong Liu Jinghui Zhang 《Environmental Earth Sciences》2010,61(6):1289-1299
Low-frequency microwave satellite observations are sensitive to land surface soil moisture (SM). Using satellite microwave
brightness temperature observations to improve SM simulations of numerical weather, climate and hydrological predictions is
one of the most active research areas of the geoscience community. In this paper, Yan and Jins’ (J Radio Sci 19(4):386–392,
2004) theory on the relationship between satellite microwave remote sensing polarization index and SM is used to estimate land
surface SM values from the advanced microwave scanning radiometer-E (AMSR-E) brightness temperature data. With consideration
of soil texture, surface roughness, optical thickness, and the monthly means of NASA AMSR-E SM data products, the regional
daily land surface SM values are estimated over the eastern part of the Qinghai-Tibet Plateau. The resulting SM retrievals
are better than the NASA daily AMSR-E SM product. The retrieved SM values are generally lower than the ground measurements
from the Maqu Station (33.85°N, 102.57°E) and the Tanglha Station (33.07°N, 91.94°E) and the US NCEP reanalysis data, but
the temporal variations of the retrieved SM demonstrate more realistic response to the observed precipitation events. In order
to improve the land surface SM simulating ability of the weather research and forecasting model, the retrieved SM was assimilated
into the Noah land surface model by the Newtonian relaxation (NR) method. A direct insertion method was also applied for comparison.
The results indicate that fine-tuning the quality factor in the NR method improves the simulated SM values most for desert
areas, followed by grasslands, and shrub and grass mixed zones at the regional scale. At the temporal scale, the NR method
decreased the root mean square error between the simulated SM and actual observed SM by 0.03 and 0.07 m3/m3 at the Maqu and Tanglha Stations, respectively, and the temporal variation of simulated SM values was much closer to the
ground-measured SM values. 相似文献
9.
Abhijit Basu 《Journal of Earth System Science》2005,114(3):375-380
Back scattered electron and transmission electron imaging of lunar soil grains reveal an abundance of submicrometer-sized
pure Fe0 globules that occur in the rinds of many soil grains and in the submillimeter sized vesicular glass-cemented grains called
agglutinates. Grain rinds are amorphous silicates that were deposited on grains exposed at the lunar surface from transient
vapors produced by hypervelocity micrometeorite impacts. Fe0 may have dissociated from Fe-compounds in a high temperature (>3000°C) vapor phase and then condensed as globules on grain
surfaces. The agglutinitic glass is a quenched product of silicate melts, also produced by micrometeorite impacts on lunar
soils. Reduction by solar wind hydrogen in agglutinitic melts may have produced immiscible droplets that solidified as globules.
The exact mechanism of formation of such Fe0 globules in lunar soils remains unresolved. 相似文献
10.
B. B. Krissinel’ 《Astronomy Reports》2005,49(11):939-945
The radio brightness distribution at 5.2 cm has been obtained along the entire solar limb down to a level of 0.01 of brightness temperature at the disk center T 0 c during the solar minimum. The measurements are based on strip scans from the Siberian Solar Radio Telescope. Data reduction included model fitting of an actual solar scan for each position angle. The maximum limb brightness, 1.37 T 0 c , in the derived distribution is at equatorial direction, where the radio radius exceeds the photosphere radius by 7%. Toward the poles, the brightness peak and radio radius gradually decrease to 1.01 T 0 c and 1.005 R0. The derived two-dimensional brightness distribution was used to calculate radio radius as a function of position angle for several wavelengths from 4 to 31.6 cm. These dependences are consistent with RATAN-600 observations at position angles 0° and 25°. 相似文献
11.
L.J. Hallis M. Anand R.C. Greenwood I.A. Franchi 《Geochimica et cosmochimica acta》2010,74(23):6885-6899
To investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition, titanium content and modal mineralogy of a suite of lunar basalts. Our sample set included eight low-Ti basalts from the Apollo 12 and 15 collections, and 12 high-Ti basalts from Apollo 11 and 17 collections. In addition, we have determined the oxygen isotopic composition of an Apollo 15 KREEP (K - potassium, REE - Rare Earth Element, and P - phosphorus) basalt (sample 15386) and an Apollo 14 feldspathic mare basalt (sample 14053). Our data display a continuum in bulk-rock δ18O values, from relatively low values in the most Ti-rich samples to higher values in the Ti-poor samples, with the Apollo 11 sample suite partially bridging the gap. Calculation of bulk-rock δ18O values, using a combination of previously published oxygen isotope data on mineral separates from lunar basalts, and modal mineralogy (determined in this study), match with the measured bulk-rock δ18O values. This demonstrates that differences in mineral modal assemblage produce differences in mare basalt δ18O bulk-rock values. Differences between the low- and high-Ti mare basalts appear to be largely a reflection of mantle-source heterogeneities, and in particular, the highly variable distribution of ilmenite within the lunar mantle. Bulk δ18O variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases. Thus, ilmenite fractionation is important in the case of high-Ti Apollo 17 samples, whereas olivine plays a more dominant role for the low-Ti Apollo 12 samples.Consistent with the results of previous studies, our data reveal no detectable difference between the Δ17O of the Earth and Moon. The fact that oxygen three-isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated. 相似文献
12.
Dominique Lattard 《Contributions to Mineralogy and Petrology》1987,97(2):264-278
An experimental study of the system Zr-Fe-Ti-O in equilibrium with metallic iron has been conducted at atmospheric pressure and in the temperature range 950–1300° C, with the purpose of modelling sub-solidus relations between Zr-bearing Fe-Ti oxide phases in lunar rocks. The phase relations are governed by the coexistence of the Fe-Ti oxides with ZrO2 at temperatures below 1247° C, but with the new cubic ZFT phase at higher temperatures. ZFT, approximately Zr Fe Ti O5, is probably related to the so-called stabilized cubic zirconia and could represent a synthetic equivalent of some lunar Zr-Fe-Ti rich oxide minerals.The zirconium contents in all Fe-, Ti and Fe-Ti-oxide phases increase with increasing temperature. At each temperature, Zr is incorporated preferentially in the Ti-oxide (up to 11 wt% ZrO2), followed by ferropseudobrookite (up to 6 wt% ZrO2), ilmenite (max. 4 wt%) and wüstite (max. 2.5 wt%). Ulvöspinel coexisting with ilmenite (+Fe0+ ZrO2 and/or ZFT) always contains less than 1.2 wt% ZrO2, whereas the same mineral in assemblage with wüstite-ZrO2-Fe0 displays even higher ZrO2 contents than ilmenite (above 4 wt%). Considering that the values determined here in the synthetic parageneses represent saturation concentrations at high temperatures in a simple model system, the ZrO2 concentrations in the corresponding lunar minerals should generally be significantly lower. This is realized, except for the so-called Cr-Zr-Ca armalcolites which display ZrO2 contents in the range 3.5–7 wt% and are thus probably related rather to Zr-rich oxide minerals than to armalcolite itself. 相似文献
13.
He, Ne, Ar, Kr and Xe were measured mass spectrometrically in eight bulk fines and one sample of 2–4 mm fines (15603) from stations LM-ALSEP, 2, 6, 61, 7a, and 9. We have also measured these gases in size fractions of samples 15091 and 15601. These samples come from three morphologically distinct selenographic settings: the Appenine Front, the Mare and Hadley Rille. Measured gas contents in these samples are comparable to those from previous Apollo missions. He4 and the other trapped gases are inversely proportional to grain diameter in the size fractions of 15091 and 15601. More than 90 per cent of the trapped gas in 15601 is surface correlated; hence is probably directly implanted solar wind. Size fractions of 15091 contain large volume correlated amounts of He4, Ne20 and Ar36. He4/Ne20 ranges from about 20 to 60; Ne20/Ar36 from 5 to 8: Ar36/Kr84 from 2400 to 3200; and Kr84/Xe132 from 3·2 to 7·3. The lowest He4/Ne20 ratios occur in samples rich in green glass spherules which have He4/Ne20 ≤ 10 (Lakatos, Heymann, and Yaniv, unpublished). He4/He3 ranges from about 210 to 2700; Ne20/Ne22 from 12·7 to 13·2; Ne21/Ne22 from 0·035 to 0·041; and Ar36/Ar38 from 5·26 to 5·45. The measured Ar40/Ar36 ratios range from 0·757 to 3·56; when corrected for radiogenic Ar40, the range becomes 0·6 to 3·4. The largest corrected Ar40/Ar36 ratios occur in samples from the Apennine Front, the smallest occur in the Mare. This could be due to slope effects between the front as opposed to the mare terrain. An alternative possibility is that the Front fines acquired their atmospheric Ar40 at a time when the concentration of neutral Ar40 in the lunar atmosphere was relatively large.Ne21 radiation ages were calculated for all samples. There is evidence in the landing area for debris from craters with ages less than 100 × 106 yr, but these craters cannot be firmly identified from the data. 相似文献
14.
Maria Schönbächler Der-Chuen Lee Mark Rehkämper Bodo Hattendorf 《Geochimica et cosmochimica acta》2005,69(3):775-785
A comprehensive Zr isotopic study was conducted on eleven lunar basalts and highland rocks to search for evidence of the extinct nuclide 92Nb, which decays to 92Zr with a half-life of 36 Ma. Internal isochrons were determined for two early highland rocks, 77215 and 60025. No resolvable Zr isotopic variations were detected in this wide range of lunar samples and thus there is no evidence for the former existence of live 92Nb on the Moon. The Nb/Zr ratios of lunar ilmenites and bulk rock samples vary by only a factor of two to three relative to the chondritic Nb/Zr ratio. No evidence for larger Nb/Zr fractionation was found. This limited fractionation and late isotopic closure of the source region prevents the formation of measurable 92Zr anomalies in high-Ti mare basalts. As a consequence, it is not possible to draw conclusions from the 92Nb-92Zr chronometer about the timing of early lunar differentiation and to constrain the role of ilmenite in the source region of high-Ti mare basalts. However, the fractionation is still sufficient to deduce an upper limit for the initial 92Nb/93Nb ratio of the solar system of <5 × 10−4. 相似文献
15.
LIU Bin LIU Jianzhong ZHANG Guangliang LING Zongcheng ZHANG Jiang HE Zhiping YANG Benyong ZOU Yongliao 《中国地球化学学报》2014,33(1):86-94
In 2013, Chang＇E-3 program will develop lunar mineral resources in-situ detection. A Visible and Near-infrared Imaging Spectrometer （VNIS） has been selected as one payload of CE-3 lunar rover to achieve this goal. It is critical and urgent to evaluate VNIS＇ spectrum data quality and validate quantification methods for mineral composition before its launch. Ground validation experiment of VNIS was carried out to complete the two goals, by simulating CE-3 lunar rover＇s detection environment on lunar surface in the laboratory. Based on the hyperspectral reflectance data derived, Correlation Analysis and Partial Least Square （CA-PLS） algorithm is applied to predict abundance of four lunar typical minerals （pyroxene, plagioclase, ilmenite and olivine） in their mixture. We firstly selected a set of VNIS＇ spectral parameters which highly correlated with minerals＇ abundance by correlation analysis （CA）, and then stepwise regression method was used to find out spectral parameters which make the largest contri- butions to the mineral contents. At last, functions were derived to link minerals＇ abundance and spectral parameters by partial least square （PLS） algorithm. Not considering the effect of maturity, agglutinate and Fe~, we found that there are wonderful correlations between these four minerals and VNIS＇ spectral parameters, e.g. the abundance of pyroxene correlates positively with the mixture＇s absorption depth, the value of absorption depth added as the in- creasing of pyroxene＇s abundance. But the abundance of plagioclase correlates negatively with the spectral parame- ters of band ratio, the value of band ratio would decrease when the abundance of plagioclase increased. Similar to plagioclase, the abundance of ilmenite and olivine has a negative correlation with the mixture＇s reflectance data, if the abundance of ilmenite or olivine increase, the reflectance values of the mixture will decrease. Through model validation, better estimates of pyroxene, plagioclase and ilmenite＇s abundances are given. It is concluded that VNIS has the capability to be applied on lunar minerals＇ identification, and CA-PLS algorithm has the potential to be used on lunar surface＇s in-situ detection for minerals＇ abundance prediction. 相似文献
16.
Lawrence M. Anovitz Allan H. Treiman Eric J. Essene Bruce S. Hemingway Edgar F. Westrum Victor J. Wall Ramón Burriel Steven R. Bohlen 《Geochimica et cosmochimica acta》1985,49(10):2027-2040
Low temperature adiabatic calorimetry and high temperature differential scanning calorimetry have been used to measure the heat-capacity of ilmenite (FeTiO3) from 5 to 1000 K. These measurements yield S2980 = 108.9 J/(mol · K). Calculations from published experimental data on the reduction of ilmenite yield Δ2980(I1) = ?1153.9 kJ/(mol · K). These new data, combined with available experimental and thermodynamic data for other phases, have been used to calculate phase equilibria in the system Fe-Ti-O. Calculations for the subsystem Ti-O show that extremely low values of are necessary to stabilize TiO, the mineral hongquiite reported from the Tao district in China. This mineral may not be TiO, and it should be re-examined for substitution of other elements such as N or C. Consideration of solid-solution models for phases in the system Fe-Ti-O allows derivation of a new thermometer/oxybarometer for assemblages of ferropseudobrookite-pseudobrookitess and hematite-ilmenitess. Preliminary application of this new thermometer/oxybarometer to lunar and terrestrial lavas gives reasonable estimates of oxygen fugacities, but generally yields subsolidus temperatures, suggesting re-equilibration of one or more phases during cooling. 相似文献
17.
Ilmenite has played an important role in the petrogenesis of lunar high-Ti picritic magmas, and armalcolite is another high-Ti oxide that was first discovered on the moon. In this study, we examined the thermodynamic stability of ilmenite and armalcolite in the context of lunar cumulate mantle overturn. Two starting compositions were explored, an ilmenite-bearing dunite (olivine + ilmenite) and an ilmenite-bearing harzburgite (olivine + orthopyroxene + ilmenite). Experiments were conducted using a 19.05 mm piston-cylinder apparatus at temperatures of 1235-1475 °C and pressures of 1-2 GPa. In runs with the ilmenite-bearing dunite mixture, ilmenite is stable in the subsolidus assemblage at least up to 1450 °C and 2 GPa. In runs with the ilmenite-bearing harzburgite starting mixture, ilmenite is stable at pressures greater than 1.4 GPa, and armalcolite is stable at lower pressures. Solidi for both starting compositions were determined, and the phase boundary between ilmenite- and armalcolite-bearing harzburgite was shown to have little dependence on temperature. During lunar cumulate overturn, sinking ilmenite formed near the end of lunar magma ocean solidification transforms into armalcolite when in contact with harzburgite cumulates at depths of less than 280 km in the lunar mantle. Inefficient overturn could leave isolated, inhomogeneously distributed pockets of armalcolite-bearing harzburgite in the upper lunar mantle, underlain by an ilmenite-bearing lower lunar mantle. These high-Ti oxide-bearing harzburgitic pockets can serve as potential sources for the generation of high-Ti magmas through partial melting or through assimilation of high-Ti minerals during transport of low-Ti picritic magmas in the lunar mantle.FeO-MgO exchange between olivine and either ilmenite or armalcolite was also examined in this study. We found the FeO-MgO distribution coefficient to be effectively independent of temperature for the pressures, temperatures, and compositions explored, with an average value of 0.179 ± 0.008 for olivine/ilmenite and 0.319 ± 0.021 for olivine/armalcolite. Given the bulk composition of an overturned lunar cumulate mantle, our measured FeO-MgO distribution coefficients can be used to estimate the Mg# of coexisting minerals in armalcolite- or ilmenite-bearing harzburgite and dunite in the overturned lunar mantle. Finally, the transformation from ilmenite-bearing harzburgite to armalcolite-bearing harzburgite results in a density increase of up to 2%. Large armalcolite-bearing cumulate bodies in the upper lunar mantle may be detectable in future lunar geophysical experiments. 相似文献
18.
我国嫦娥三号着陆于雨海北部的年轻玄武岩熔岩平原上,该区域的物质成分和矿物组成对于理解月球年轻的火山活动具有重要研究价值。月球全球勘探者(Lunar Prospector,LP)探测的元素数据揭示着陆区附近岩石类型主要为高铁中钛玄武岩(19.5%FeO;5.2%TiO_2)。本研究利用月球矿物绘图仪(Moon Mineralogy Mapper,M~3)获取的嫦娥三号着陆区附近的新鲜撞击坑高光谱数据,采用Hapke辐射传输模型和修正高斯模型(MGM)联合分析,对其年轻月海玄武岩铁镁质矿物进行了定量反演。研究表明该区域玄武岩中矿物组成以单斜辉石矿物为主,存在较高比例的橄榄石。基于光谱库匹配方法和MGM优化分析,我们反演出单斜辉石,斜方辉石,橄榄石和钛铁矿四种矿物的相对体积比为57.6:18.0:15.3:9.1,这一研究结果有待于与嫦娥三号玉兔号月球车上搭栽的红外成像光谱仪数据进行比对,以期从遥感和就位探测两个角度获得对于该地区矿物和岩石类型的全面认识。 相似文献
19.
Lunar mare basalts are a product of partial melting of the lunar mantle under more reducing conditions when compared to those expected for the Earth’s upper mantle. Alongside Fe, Ti can be a major redox sensitive element in lunar magmas, and it can be enriched by up to a factor of ten in lunar basaltic glasses when compared to their terrestrial counterparts. Therefore, to better constrain the oxidation state of Ti and its coordination chemistry during lunar magmatic processes, we report new X-ray absorption near edge structure (XANES) spectroscopy measurements for a wide range of minerals (pyroxene, olivine, Fe–Ti oxides) and basaltic melt compositions involved in partial melting of the lunar mantle. Experiments were conducted in 1 bar gas-mixing furnaces at temperatures between 1100 and 1300 °C and oxygen fugacities (fO2) that ranged from air to two orders of magnitude below the Fe–FeO redox equilibrium. Run products were analysed via electron microprobe and XANES Ti K-edge. Typical run products had large (>?100 µm) crystals in equilibrium with quenched silicate glass. Ti K-edge XANES spectra show a clear shift in energy of the absorption edge features from oxidizing to reducing conditions and yield an average valence for Fe–Ti oxides (armalcolite and ilmenite) of 3.6, i.e., a 40% of the overall Ti is Ti3+ under fO2 conditions relevant to lunar magmatism (IW ??1.5 to ??1.8). Pyroxenes and olivine have average Ti valence of 3.75 (i.e., 25% of the overall Ti is trivalent), while in silicate glasses Ti is exclusively tetravalent. Pre-edge peak intensities also indicate that the coordination number of Ti varies from an average V-fold in silicate glass to VI-fold in the Fe–Ti oxides and a mixture between IV and VI-fold coordination in the pyroxenes and olivine, with up to 82% [IV]Ti4+ in the pyroxene. In addition, our results can help to better constrain the Ti3+/∑Ti of the lunar mantle phases during magmatic processes and are applied to provide first insights into the mechanisms that may control Ti mass-dependent equilibrium isotope fractionation in lunar mare basalts. 相似文献
20.
Vacuum crushing is an efficient technique to selectively release the mantle-derived helium component trapped within olivine and pyroxene phenocrysts. However, contrary to previous assumptions, recent studies have shown that this method may liberate significant matrix-sited cosmogenic 3He (3Hec) or radiogenic 4He (4He∗). Because this loss may bias both the determination of magmatic 3He/4He ratios and the accuracy of 3Hec measurements, it is essential to understand what mechanism is responsible and under what conditions matrix helium loss is manifest. To address this question, olivines and pyroxenes with various amounts of matrix-sited 3He (from 107 to 1011 at. g−1) were crushed in air or in vacuum using several crushing devices. Sample temperature was controlled during each crushing experiment, and ranged from 25 to 325 °C. The resulting powders were then sieved to obtain several homogeneous grain fractions ranging between <10 and >300 μm. The 3Hec concentrations measured in each fraction clearly show that significant 3Hec loss (>20%) affects only the finest fraction (<10 μm) and, importantly, only under hot conditions (here T ?300 °C). Even the smallest fractions (<10 μm) quantitatively retain matrix-sited 3Hec when crushed under cold conditions (T ?25 °C), regardless of the duration and energy of crushing. These results invalidate the model previously proposed by (Yokochi R., Marty B., Pik R. and Burnard P. (2005) High 3He/4He ratios in peridotite xenoliths from SW Japan revisited: evidence for cosmogenic 3He released by vacuum crushing. Geochem. Geophys. Geosyst.6, doi:10.1029/2004GC000836) that involved spallation tracks and implied that the magnitude of loss was mainly controlled by the grain size. Moreover, new diffusion experiments were carried out to constrain the diffusivity of matrix-sited helium in crushed olivines. When used to model diffusive 3Hec loss as a function of grain size during crushing, these new data predict the observed release fairly well. Therefore, we conclude that temperature-enhanced volume diffusion is one of the main mechanisms controlling the release of 3Hec during crushing. For future applications, special attention should thus be paid to control the grain size, the crushing duration, and the temperature of the sample. 相似文献