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1.
Amy J.V. Riches Yang Liu James M.D. Day Igor S. Puchtel Douglas Rumble III Harry Y. McSween Jr. Richard J. Walker Lawrence A. Taylor 《Polar Science》2011,4(4):497-514
We report the petrography, mineral and whole-rock chemistry (major-, trace-, and highly-siderophile element abundances, and osmium and oxygen isotope compositions) of a newly recognized lherzolitic shergottite, Yamato (Y) 984028. Oxygen isotopes (Δ17O = 0.218‰) confirm a martian origin for this meteorite. Three texturally distinctive internal zones and a partially devitrified fusion crust occur in the polished section of Y 984028 studied here. The zones include: 1) a poikilitic region with pyroxene enclosing olivine and chromite (Zone A); 2) a non-poikilitic zone with cumulate olivine, interstitial pyroxene, maskelynite and Ti-rich chromite (Zone B) and; 3) a monomict breccia (Zone C). The pyroxene oikocryst in Zone A is chemically zoned from Wo3–7En76–71 in the core region to Wo33–36En52–49 at the rim, and encloses more Mg-rich olivine (Fo74–70) in the core, as compared with olivines (Fo69–68) located at the oikocryst rim. Constraints from Fe–Mg partitioning between crystals and melt indicate that constituent minerals are not in equilibrium with the corresponding bulk-rock composition, implying that Y 984028 represents a cumulate. The whole-rock major- and trace-element compositions, and initial 187Os/188Os value (0.1281 ± 0.0002) of Y 984028 are similar to other lherzolitic shergottites and this sample is probably launch-paired with Y 793602, Y 000027, Y 000047, and Y 000097. The Os isotopic composition and highly-siderophile element (HSE) abundances of Y 984028 and other lherzolitic shergottites are consistent with derivation from a martian mantle source that evolved with chondritic Re/Os. 相似文献
2.
南极陨石GRV052483样品为中国第22次南极科学考察队在蓝冰上发现的一块普通球粒陨石。初步研究发现,该样品中球粒结构并不发育。薄片中可见大量自形-半自形橄榄石斑晶镶嵌在细粒基质矿物中,具有典型的斑状结构。这些橄榄石斑晶大多为残留相,斑晶橄榄石和基质中主要矿物橄榄石、低钙辉石成分均一,平均橄榄石Fa值为24.7 mol%,而低钙辉石平均Fs值为21.1 mol%,斑晶中偶有粗粒长石玻璃化,根据岩相学及矿物成分特征,可确定此陨石为L6。不透明矿物含量较少,包括金属(铁纹石和镍纹石)与陨硫铁,此外可见少量的铬铁矿和磷灰石。冲击熔融脉发育、斑晶中粗粒长石玻璃化、基质中橄榄石、辉石、长石重结晶等现象说明该样品经历了强烈冲击,其冲击程度可能达到S6以上。因此,GRV052483可能为撞击熔融型L6普通球粒陨石。 相似文献
3.
M.D. Dyar T.D. Glotch M.D. Lane B. Wopenka J.M. Tucker S.J. Seaman G.J. Marchand R. Klima T. Hiroi J.L. Bishop C. Pieters J. Sunshine 《Polar Science》2011,4(4):530-549
Comprehensive spectroscopic characterization of interior and exterior chips of the lherzolitic shergottite Y-984028 has been performed using results from six techniques. Data from UV–visible–near-IR reflectance spectra, thermal (mid-IR) emission spectra, attenuated total reflectance (ATR) spectra, transmission FTIR spectra, Raman microprobe spectra, and Mössbauer spectra of whole rock and mineral separates from this meteorite are integrated and compared. Five of these analytical techniques accurately determined the ～Fo65 composition of the olivine within ±10 mol%. Both transmission FTIR and ATR spectra show broad features near 3500 cm?1 indicating the presence of OH/H2O that does not arise from surface water adsorption. The brown color of the Y-984028 olivine is likely due to the presence of nanophase metallic iron particles (npFe0) dispersed throughout the olivine during a major shock event on Mars. Y-984028 olivine also contains a significant amount of Fe3+, but this cannot be distinguished from Fe3+ that is present in pyroxene and possibly clay minerals. This meteorite and the nakhlite MIL03346 are the two most oxidized of the SNC meteorites studied to date, with Fe3+ contents consistent with high-temperature equilibration near the QFM oxygen buffer. 相似文献
4.
Amoeboid olivine aggregates (AOAs) are composed of forsteritic olivine, Fe,Ni-metal, and Ca,Al-rich nodules consisting mainly of Al-diopside, spinel, and anorthite. Although the textures, shapes, and mineralogy of AOAs are consistent with their being aggregates of nebular condensates, some textures are in conflict with equilibrium condensation calculations, indicating that AOAs were not produced by a simple one-stage condensation. To examine the origin of the constituent minerals within AOAs and their textural relationships, we performed heating experiments using mineral mixtures analogous to those in AOAs. Isothermal and cooling experiments on forsterite + anorthite mixtures reveal that a high-Ca pyroxene phase forms via the incipient melting of the two minerals. Comparative studies of heating experiments performed using the mineralogy of AOAs suggest that Al-diopside in AOAs can be produced from a small degree of melting of forsterite and anorthite. The formation of Al-diopside in this way is consistent with the annealing textures observed in AOAs, and it may account for the discrepancy between the observed mineralogy of AOAs and the results of equilibrium condensation calculations, the occurrence of two types of diopside (Al,Ti-rich diopside and Al-diopside), and the variable Al2O3 content of Al-diopside. 相似文献
5.
Freek van der Meer 《Natural Resources Research》1994,3(2):146-164
Laboratory reflectance spectra of synthetic mixtures of the carbonate minerals calcite and dolomite were measured in the visible and near-infrared wavelength region (0.4–2.5 m) using a high-spectral resolution laboratory spectrometer. The instrument measured reflectivity with an accuracy of 0.001 m, allowing detailed resolution of the carbonate spectrum. The spectra of calcite and dolomite could be characterized by the presence of a strong absorption band centered at 2.3465 m for pure calcite and at 2.3039 m for pure dolomite. Nine mixtures of intermediate composition were analyzed demonstrating that the position of the carbonate absorption band is semilinearly related to the calcite content of the sample. Theoretically, this model allows mapping of dolomitization from high-spectral resolution remotely sensed imagery, GER 63-channel imaging spectrometer data from southern Spain were used to attempt such a mapping. First, pixels of vegetation were removed. For the remaining pixels, the wavelength center of the carbonate absorption band was detected and converted to a category of calcite fraction. The percentage of calcite for the remaining pixels was estimated using direct indicator kriging (IK) and sequential conditional indicator simulation, assuming that the calcite content could be represented as a category variable (SCIS category variable) and as a continuous variable (SCIS continuous variable). Four realizations of an SCIS (category variable) showed that on the average, 60 percent of the data was simulated in the same class and over 90 percent of the data within one class difference. A comparison with field samples showed that IK estimates of calcite content were within 20 percent accurate. The SCIS (continuous variable) does not perform as well with differences between –45% and +26% calcite; however, simulation reproduces the spatial variability better. 相似文献
6.
Shin Ozawa Masaaki Miyahara Eiji Ohtani Makoto Kimura Yoshinori Ito 《Polar Science》2011,4(4):550-557
Yamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories. 相似文献
7.
《Polar Science》2007,1(1):45-53
NWA1241 is an unusual monomict ureilite, consisting mainly of pigeonite, olivine, suessite, and carbonaceous materials. The modal ratio of pyroxene/(olivine + pyroxene) is higher than those of common monomict ureilites. Metallic phases in NWA1241 are mainly suessite, although metals in common ureilites are mainly kamacite. The high ratio of pyroxene to olivine and the abundant occurrence of suessite make the meteorite unusual. The suessite coexists with magnesian olivine and pyroxene in NWA1241, and this mineral assemblage indicates that the suessite was produced from FeO-bearing olivine and Ni-bearing kamacite at temperatures around 1500–1400K and oxygen fugacity of 10−18–10−20 bars.Most ureilites experienced two-stage reduction. Stage-I reduction was a smelting process in ureilite parent bodies (UPB's) to form the framework of monomict ureilites. Stage-II reduction took place after catastrophic destruction of the UPB's to eject many fragmental blocks into space, where suessite (NWA1241) or Si-bearing kamacite (common ureilites) were produced together with the formation of reversely zoned olivines. 相似文献
8.
The study is aimed at investigating the response of the riffle–pool sequence to increased energy expenditure in the horizontal plane through meander development. It emphasizes field measurements of riffle–pool height and spacing and their links with meander morphology. River reaches in southern Ontario (Canada) were surveyed and statistical relations were established between parameters describing riffle–pool morphology (sequence length and amplitude) and planform curvature. The results indicate a lengthening of the sequence with increased total angular deflection along the measured reaches. Further analysis suggests that this lengthening occurs in the pool as a result of meander development. Apparently, as the path length extends beyond a critical threshold for a given bed material size, the transport capacity of the sequence is compromised. This may promote an initial shortening of the downstream riffle, with depositional processes ultimately forming a new riffle slightly upstream to achieve a new equilibrium. Additional extensive data sets provided by the Toronto and Region Conservation Authority on riffle–pool morphology also suggest that bed material size plays a significant role in controlling riffle–pool morphology. 相似文献
9.
Hidehiko Suzuki Kazuo Shiokawa Masaki Tsutsumi Takuji Nakamura Makoto Taguchi 《Polar Science》2008,2(1):1-8
Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2–6% in intensity and 0.5–2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474]. 相似文献
10.
西宁陨石具有典型的球粒结构,球粒轮廓依稀可辨-模糊,基质重结晶程度中-高等,次生斜长石粒度5-40μm,部分颗粒大于50μm。橄榄石和低钙辉石的化学成分均一：球粒中橄榄石Fa24.7-25.2,平均Fa24.9,相对标准偏差PMD值0.64%;低钙辉石Fs21.3-21.9 En 77.6-78.2 Wo 0.46-0.57,平均Fs21.5,Fs的PMD值0.84%。说明该陨石已达热力学平衡状态,为平衡型普通球粒陨石。根据该陨石结构构造特征、金属含量、矿物化学组成特征和热变质特征（平衡温度为778℃）,西宁陨石被划分为L群普通球粒陨石,岩石类型为5型,但已开始向6型过渡。该陨石的冲击变质程度为S3,风化程度W0。陨石母体形成之后遭受了冲击变质作用和热变质作用,导致原始球粒破碎、脱玻化和基质重结晶。 相似文献
11.
本文主要报道了南极格罗夫山新回收的100块陨石的岩石学和矿物化学特征。并根据矿物-岩石学特征,划分了它们的化学-岩石类型:6块属于非平衡型普通球粒陨石(H3和L3群各3块);92块属于平衡型普通球粒陨石,包括:H群24块(13块H4,10块H5,1块H6),L群64块(2块L4,44块L5,18块L6),LL群4块(3块LL4,1块LL5);另外两块属于石-铁陨石。6块非平衡型普通球粒陨石保存了原始的岩石学和矿物化学特征,包括:清晰的球粒结构、橄榄石和低钙辉石具有明显的成分环带以及极不均一的化学组成等。92块平衡型普通球粒陨石中的橄榄石和低钙辉石显示出均一的化学组成,表明它们达到了一定的热力学平衡。这些普通球粒陨石受到的风化作用以W1和W2为主,所占比例高于90%,表明南极陨石受到的风化作用不强烈。有约40%的陨石样品受到了强烈的冲击作用,并产生冲击脉或者冲击囊,它们是研究高压冲击矿物和冲击作用的理想样品。 相似文献
12.
Probability of occurrence, hazard intensity and encounter probability are key parameters in the quantitative risk analysis (QRA) of landslides. All are strongly dependent on magnitude of the landslides. As a result, magnitude–frequency analysis should be a part of QRA. Deriving representative magnitude–frequency relationships for debris avalanches and debris flows, however, is difficult. One key problem is illustrated with the example of a unique database from the coastal region of British Columbia, Canada, which was compiled entirely from detailed ground investigations. The magnitude of debris avalanches and debris flows is not an independent statistical quantity, but a function of the scale of a given slope, as characterized by the slope length. Thus, attempting to derive probability and magnitude for a given location or sub-region from a regionally-derived magnitude–frequency curve may lead to incorrect predictions. The same problem is pertinent to the application of the same approach to any type of landslide in which the largest combined dimension of the source volume (including entrainment) is of the same order as the length of the slope. It is recommended that greater emphasis be placed on site-specific geological observations, at the expense of generalized statistics. 相似文献
13.
Summary. The mantle between 700 and 1200 km is modelled using mixed oxides (MgO + FeO + SiO2 (stishovite)) having olivine, pyroxene, and peridotite (67 per cent ol-33 per cent px) stoichiometries and third-order finite strain theory. It is possible to satisfy the densities, compressional and shear velocities, and bulk and shear moduli of seismic models B1 and PEM and to obtain adiabatic temperature profiles consistent with literature profiles with olivine and peridotite stoichiometries, but not with pyroxenes. Estimates of K and μ for stishovite satisfying Bl and PEM profiles indicate that the stishovite data of Mizutani, Hamano & Akimoto and Liebermann, Ringwood & Major are inconsistent with the assumed mixed-oxide assemblages, even with a large range of pressure and temperature derivatives for K and μ. Assuming perovskite structure materials below 700 km shows that pyroxenes transformed to the perovskite structure are too dense by 1–2.5 per cent. Taking a wide range of P and T derivatives for the K and μ of MgSiO3 (perovskite) indicates that the seismic models can be satisfied with olivines and peridotites transformed to perovskites and oxides. The MgSiO3 (perovskite) K and μ estimates bracket the systematics estimates of Liebermann, Jones & Ring-wood. We find only marginal evidence for relaxation of the shear modulus. The mean atomic weight calculated for the mixed-oxide models agrees with the results of Watt, Shankland & Mao for the same region and with previous estimates for the upper mantle. Thus, an increase in iron content below 700 km appears unlikely. This result and the corresponding temperatures (lower than the Clark & Ringwood conduction geotherm) are consistent with convection below 700 km. 相似文献
14.
Sara Lucía Camargo-Ricalde Shivcharn S. Dhillion Vernica García-García 《Journal of Arid Environments》2004,58(4):1043
We report on the phenology, seed production, and three assays (field, greenhouse and laboratory) to detect the optimal temperature for germination (OPT) and the temperature with fastest germination rate (TFASG) of seven Mimosa species, all endemic to Mexico: Mimosa adenantheroides (M. Martens and Galeotti) Benth., M. calcicola B. L. Rob., M. lacerata Rose, M. luisana Brandegee, M polyantha Benth., M. purpusii Brandegee and M. texana (A. Gray) Small var. filipes (Britton and Rose) Barneby. Flowering and fruiting take place during the wet season (May–September). Though flowering periods overlap among species, no hybrid species were found. The reproductive strategy includes a large number of seeds produced (4000–15000 per plant); however, a high percentage (30–75%) is not viable due to bruchid predation (Acanthoscelides mexicanus (Sharp) and Stator pruininus Horn). In the laboratory, OPT was established at (23°C)24°C(27–28°C) and TFASG at (20°C)25°C(30°C), with 100% of germination in six of the seven Mimosa species. In the field, the maximum germination rate (MAXG) was 92% to 100%, whereas in the greenhouse this value was 56% to 80%. Our results show that heat and moisture do not necessarily stress Mimosa seedling germination, but shade seems to be an important factor influencing germination. 相似文献
15.
主要介绍GRV 022888和GRV 052408两块南极陨石的岩相学和矿物化学特征,并在此基础上探讨其成因。GRV 052408陨石主要由橄榄石(~60 vol%)和辉石(~35 vol%)组成,含少量富碳质填隙物(~5 vol%);而GRV022888陨石基本由橄榄石(~98 vol%)构成,仅有很少量辉石,富碳质不透明填隙物含量也较低(~2 vol%)。这两块陨石中的橄榄石都可以见到明显的核部富铁边部富镁的反环带结构。结合岩相学和矿物化学特征,将它们划分为单矿Ⅰ型橄辉无球粒陨石。根据橄榄石-易变辉石-熔体温度计,计算得到两块陨石的形成温度在1 220℃左右。我们的研究结果支持橄辉无球粒陨石为球粒陨石质母体部分熔融后的残余物成因假说。 相似文献
16.
In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region. 相似文献
17.
The geological and meteorological setting of the Jianghan–Dongting lake area leads to high precipitation and siltation, but poor water discharge, thus the area is frequently flooded. In the past the river–lake relationship of the Middle Yangtze has been variable but has deteriorated recently under increasing human influence. The Jianghan Plain of the Middle Yangtze becomes a waterlogged lowland under the constant threat of flooding from the perched Jingjiang River. Due to siltation and land reclamation the Dongting Lake has lost most of its regulatory function for the river and has become increasingly vulnerable to flood disasters. The Middle Yangtze River has been undergoing siltation, resulting from a downstream decline of sediment transport capacity, resulting in the elevation of the flood level above the lowlands. Heightening of the levees has caused further siltation of the channel.The Three Gorges Reservoir will provide a buffering period of 50–80 years, during which much of the silt will be trapped in the reservoir and scouring downstream may occur. We should utilize this period to work out an overall resolution to the problem. Construction of a water and silt diversion project in the Honghu Lake and surrounding areas may resolve this problem in the dangerous Chenglingji–Wuhan Segment of the Yangtze. Widening the canals connecting the Middle Yangtze and Han Rivers may function as a discharge-dividing channel of the Yangtze, which may prove to be beneficial. 相似文献
18.
Beach–dune seasonal elevation changes, aeolian sand transport measurements, bathymetric surveys and shoreline evolution assessments were used to investigate annual and seasonal patterns of dune development on Sfântu Gheorghe beach, the Danube delta coast, from 1997 to 2004. Dune volume increased consistently (1.96 m3 m− 1 y− 1 to 5.1 m3 m− 1 y− 1) over this 7-year period with higher rates in the southward (downdrift) direction. Dune aggradation is periodically limited by storms, each of which marks a new evolutionary phase of the beach–dune system. As a consequence of the variable beach morphology and vegetation density during a year, foredune growth occurs during the April–December interval while between December and April a slightly erosive tendency is present. The pattern of erosion and deposition shown by the topographical surveys is in good agreement with the sand transport measurements and demonstrates the presence of a vigorous sand flux over the foredunes which is 20–50% smaller than on the beach. This high sand flux, due to low precipitation and sparse vegetation cover, creates an aerodynamically efficient morphology on the seaward dune slope. The seaward dune face accretes during low to medium onshore winds (5.5–12 m s− 1) and erodes during high winds (> 12 m s− 1). 相似文献
19.
EET 96008是一块发现于南极Elephant地区的玄武岩质角砾岩月球陨石。本文对该陨石的矿物岩石学特征进行了详细的观察和描述。EET 96008具有典型的碎屑结构,其角砾浑圆度低,角砾大小一般为0.1-2mm,它主要由角砾（50.2vol%）和基质（49.8vol%）组成,该陨石角砾类型多样：（1）晶屑：主要为辉石、橄榄石、长石以及石英;（2）岩屑：主要为变粒岩岩屑、基性岩岩屑、苏长岩质斜长岩岩屑;（3）玻屑：主要为斜长岩质。基质和角砾在颗粒上是连续过渡的,基质主要是由粒度小于0.1mm的矿物碎屑和玻屑组成。该陨石辉石类型多样,成分变化大Fs18.0-58.0Wo3.9-45.2En3.5-79.1,出溶现象普遍,出溶条纹达到1μm宽;橄榄石中Fa值主要分为两个区域,Fa50-70以及Fa80-95,铁含量较高,平均Fa71.8;长石成分以钙长石为主（An84.9-97.9）,部分斜长石已熔长石化。该陨石与QUE 94281同为月球玄武岩质角砾岩,在结构及矿物组成上具有类似性,但是在岩屑类型及橄榄石矿物成分上存在着明显不同,为非成对陨石,且源区可能不同。EET 96008具有三个典型的冲击暗化区域,有大量的玻璃质以及冲击熔融囊的产生,冲击程度达到S5以上。该陨石在冲击作用下,富铁辉石分解产生钙铁辉石-铁橄榄石-石英,该现象为了解月球表面冲击历史提供了重要的科学依据。 相似文献
20.
Constructal view of scaling laws of river basins 总被引：1，自引：0，他引：1
River basins are examples of naturally organized flow architectures whose scaling properties have been noticed long ago. Based on data of geometric characteristics, Horton [Horton, R.E., 1932. Drainage basin characteristics. EOS Trans. AGU 13, 350–361.], Hack [Hack, J.T., 1957. Studies of longitudinal profiles in Virginia and Maryland. USGS Professional Papers 294-B, Washington DC, pp. 46–97.], and Melton [Melton, M.A, 1958. Correlation structure of morphometric properties of drainage systems and their controlling agents. J. of Geology 66, 35–56.] proposed scaling laws that are considered to describe rather accurately the actual river basins. What we show here is that these scaling laws can be anticipated based on Constructal Theory, which views the pathways by which drainage networks develop in a basin not as the result of chance but as flow architectures that originate naturally as the result of minimization of the overall resistance to flow (Constructal Law). 相似文献