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1.
陨石撞击地球表面往往产生灾难性的影响,然而这种影响往往很快地被地表活跃的地质与生物营力所抹去。撞击事件所产生的烟柱,携带大量气体、液滴和尘埃抛溅到距离撞击坑很远的地方,这些烟柱冷凝后成为球形颗粒被保存到地层中,为还原地球早期撞击事件、评估其对环境的影响提供了重要证据。本研究聚焦于撞击烟柱中高温矿物气体冷凝而成的气凝球粒,仔细分析了其中原生尖晶石相的化学成分特征,并以此为窗口推测了烟柱中的气体成分、氧逸度等。我们的研究表明,由于气凝球粒中尖晶石Fe3+/FeTOT的比值往往很高,而单纯矿物气液平衡本身过于还原,因此气凝球粒的形成需要有撞击烟柱中混杂的空气参与作用。气凝球粒也因而在一定程度上提供了地球早期大气中氧逸度变化以及撞击烟柱不均一性的记录。这一推断与前人依据实验和地球化学分析得到的推测一致,为关于气凝球粒形成机制的数值模拟研究提供了重要启示。 相似文献
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撞击角砾岩是陨石撞击过程形成的特有岩石种类,是研究撞击成坑过程、陨石坑定年、矿物岩石冲击变质的理想对象。岫岩陨石坑是一个直径1800m的简单陨石坑,坑内有大量松散堆积的撞击角砾岩。本研究通过光学显微镜、费氏台、电子探针、X射线荧光光谱仪、电感耦合等离子质谱仪等分析测试手段,主要研究了岫岩陨石坑撞击角砾岩的岩相学和冲击变质特征,并在此基础上讨论了撞击角砾岩的形成过程和陨石坑的形貌特征。岫岩陨石坑内产出有三种撞击角砾岩,分别是来自上部的玄武质角砾岩和复成分岩屑角砾岩,以及底部的含熔体角砾岩。组成玄武质角砾岩和复成分岩屑角砾岩的碎屑受到的冲击程度较低,仅有少量石英发育面状变形页理,指示不超过20GPa的冲击压力。而组成含熔体角砾岩的碎屑受到了很强的冲击,发育了熔融硅酸盐玻璃、石英面状变形页理、柯石英、二氧化硅玻璃、击变长石玻璃、莱氏石等冲击变质特征,指示的峰值压力超过50GPa。本研究证实了含熔体角砾岩通常产出在简单陨石坑底部,由瞬间坑的坑缘和坑壁垮塌的岩石碎屑与坑底的冲击熔体混合形成。岫岩坑的真实深度是495m,真实深度与直径的比值为0.275,符合简单陨石坑的尺寸特征。陨石坑内的撞击角砾岩中心厚度为188m,与直径之比为0.104,略低于其它简单坑,可能是受丘陵地貌影响导致改造阶段垮塌到坑内的岩石角砾偏少。 相似文献
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Mineralogy and Petrology - Complementary nano- and atomic-scale data from SEM, FIB, HRTEM, and EELS observations of after-coal impact diamonds from the giant Kara astrobleme are described,... 相似文献
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《Chemie der Erde / Geochemistry》2021,81(1):125683
Since the Apollo 14 mission delivered samples of the Fra Mauro formation, interpreted as ejecta of the Imbrium impact, defining the age of this impact has emerged as one of the critical tasks required for the complete understanding of the asteroid bombardment history of the Moon and, by extension, the inner Solar System. Significant effort dedicated to this task has resulted in a substantial set of ages centered around 3.9 Ga and obtained for the samples from most Apollo landing sites using a variety of chronological methods. However, the available age data are scattered over a range of a few tens of millions of years, which hinders the ability to distinguish between the samples that are truly representative of the Imbrium impact and those formed/reset by other, broadly contemporaneous impact events. This study presents a new set of U-Pb ages obtained for the VHK (very high K) basalt clasts found in the Apollo 14 breccia sample 14305 and phosphates from (i) several fragments of impact-melt breccia extracted from Apollo 14 soil sample 14161, and (ii) two Apollo 15 breccias 15455 and 15445. The new data obtained for the Apollo 14 samples increase the number of independently dated samples from this landing site to ten. These Apollo 14 samples represent the Fra Mauro formation, which is traditionally viewed as Imbrium ejecta, and therefore should record the age of the Imbrium impact. Using the variance of ten ages, we propose an age of 3922 ± 12 Ma for this event. Samples that yield ages within these limits can be considered as possible products of the Imbrium impact, while those that fall significantly outside this range should be treated as representing different impact events. Comparison of this age for Imbrium (determined from Apollo 14 samples) with the ages of another eleven impact-melt breccia samples collected at four other landing sites and a related lunar meteorite suggests that they can be viewed as part of Imbrium ejecta. Comprehensive review of 40Ar/39Ar ages available for impact melt samples from different landing sites and obtained using the step-heating technique, suggests that the majority of the samples that gave robust plateau ages are indistinguishable within uncertainties and altogether yield a weighted average age of 3916 ± 7 Ma (95 % conf., MSWD = 1.1; P = 0.13) and a median average age of 3919 + 14/-12 Ma, both of which agree with the confidence interval obtained using the U-Pb system. These samples, dated by 40Ar/39Ar method, can be also viewed as representing the Imbrium impact. In total 36 out of 41 breccia samples from five landing sites can be interpreted to represent formation of the Imbrium basin, supporting the conclusion that Imbrium material was distributed widely across the near side of the Moon. Establishing temporal limits for the Imbrium impact allows discrimination of ten samples with Rb-Sr and 40Ar/39Ar ages about 50 Ma younger than 3922 ± 12 Ma. This group may represent a separate single impact on the Moon and needs to be investigated further to improve our understanding of lunar impact history. 相似文献
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The largest known terrestrial impact melt sheet occurs within the 1850 Ma Sudbury Structure, Ontario. In order to evaluate the relative contributions of different target lithologies to the melt sheet, we have investigated the Pb isotope compositions of feldspar separates from early-formed quartz diorite magmas within Offset Dykes from around the impact structure. The samples define a linear array on plots of age-corrected 206Pb/204Pb versus 207Pb/204Pb. Samples from Offset Dykes hosted by the Huronian Supergroup (South Range) have a range of 206Pb/204Pb1850 from 15.424 to 17.255 and 207Pb/204Pb1850 from 15.390 to 15.801, whilst those hosted by Archean gneisses of the Superior Province (North Range) cluster around 206Pb/204Pb1850 ≈ 14.8 and 206Pb/204Pb1850 ≈ 15.1. These values can be approximated by binary mixing between the two major groups of target lithologies. A mix of 60-70% of Superior Province gneisses with 30-40% of Huronian metasedimentary material closely matches the Pb isotope compositions of North Range Offset Dyke samples, whereas in the South Range the required Huronian component is up to ca. 80%.These mixing proportions are consistent with Sr, Nd and Os isotope and trace element constraints. A third minor component, either locally-exposed Paleoproterozoic mafic rocks or the lower crust is also required. However, the isotopic, trace element and Ni-Cu-platinum group element characteristics of the melt sheet can be accommodated without the involvement of an average lower crustal or meteoritic component.A major contribution of Huronian supracrustal material, which had a pre-impact thickness of up to 12 km, is required to explain the chemical characteristics of the impact melts, which also have a strong upper crustal affinity (e.g. Eu/Sm = 0.22, Rb/Sr = 0.2-0.35). As such, a shallower level of melting is apparent than that predicted by many previous impact models for the Sudbury event. This can be accommodated by considering approach trajectories for the impactor oblique to the Earth’s surface. In addition, the isotopic and trace element variability identified indicates that the melt sheet was heterogeneous at an early stage, and may not have been completely homogenised during crater formation. Our findings have significant implications for the nature of the Sudbury impact event, the evolution of the melt sheet and the crustal sources of metals contained in Sudbury’s world class Ni-Cu-PGE sulphide ores. 相似文献
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针对常规单弯螺杆马达钻进硬岩层效率低、钻头和钻具消耗大的问题,采用在马达万向轴与钻头之间增加冲击机构的方法,研制了冲击螺杆马达,其具有冲击和定向双重功能。介绍了冲击螺杆马达冲击机构结构组成和工作原理、关键零部件设计、分析了冲击螺杆马达的特点。对φ89 mm冲击机构进行了室内试验,测得其冲击力峰值达到5 000~9 000 N,与理论计算结果基本一致,由硬质合金与轴承钢组成的复合结构的冲锤和砧体的耐磨性能达到了工业性使用要求。在晋煤集团寺河煤矿进行了现场工业性试验,钻进效率较常规单弯螺杆马达提高20%~30%。 相似文献
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《Comptes Rendus Geoscience》2005,337(10-11):897-907
The hydrological impact of the massive iceberg discharges during Heinrich events has been quantified for Heinrich 4 about 37 kyr ago. This event took place in a context of relatively stable orbital forcing and global ice volume. In this article, we propose to quantify the hydrological impact of the Heinrich event 1 which occurred at about 16 kyr BP. This time period is particularly interesting because orbital forcing was strong and it marks the onset of the last deglaciation. The results obtained here show that Heinrich event 1 has a larger isotopic amplitude than Heinrich event 4 when considering the cores located near the melting source. Concerning surface circulation, the northward progression of the North Atlantic Drift is affected only by Heinrich event 4, possibly because of the latitudinal extension of the melting area during this event. To cite this article: E. Cortijo et al., C. R. Geoscience 337 (2005). 相似文献
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A characteristic feature of ureilite meteorites is reduction of FeO. But the reduction is usually confined to the rims of olivine. In the LAR 04315, LAP 03587 and Almahata Sitta ureilites, pyroxene was extensively reduced by impact smelting. In LAR 04315, the impact caused nearly all of the original pigeonite to melt or otherwise become sufficiently structurally compromised to allow smelting, and yet a minor proportion of the pyroxene escaped smelting and survived with its original composition (En74.1Wo10.2). Olivine mosaicism confirms that LAR 04315 experienced a major shock event. The smelted pyroxenes also show a distinctive patchiness in their interference colors (although each grain’s basic optical continuity, often including twinning, is still discernible). They also have reduced compositions, are ubiquitously porous (∼15%), and contain sprinklings of Fe-metal and felsic glass. For the most part the olivine underwent only very slight reduction. Much of the (small) pyroxene component of LAP 03587 shows the same oddly porous texture. LAR 04315 also contains large traces of silica and felsic glass (with a typical composition of, in wt%, 61 SiO2, 23 Al2O3, 11 CaO, 3.7 Na2O) glass; these two phases together form selvages that line the walls of many of the largest voids in the rock. Silica is a by-product of pyroxene smelting. The felsic glass probably derives largely from interstitial basaltic melt that predated the impact. However, the comparatively stiff surrounding/included silica may have promoted unusually high melt retention within LAR 04315 through the smelting episode (one aspect of which was a major stream-out, through the same large voids, of COx gas). The impact-smelted pyroxene of LAP 03587 is enigmatic because this ureilite also features little-shocked euhedral graphite laths and no olivine mosaicism. The fine-grained ureilitic component of Almahata Sitta appears to have likewise formed by impact smelting, but with more extensive melting of pyroxene (especially a Ca-rich pyroxene component), more pulverization and melting of olivine, and more displacement of both. However, in places the original coarse-equant ureilite texture is still discernible in relict form. Ordinarily, an impact shock melts olivine before, or at least no later than, pyroxene. But in the case of LAR 04315 and LAP 03587, the great shock event evidently occurred when the material was already anatectic or very nearly so; and thus the difference in melting temperature between pyroxene and olivine, ∼300 degrees lower for pyroxene, was decisive. If literature inferences of extremely fast cooling rates, implying shallow burial depths, are accurate, the proportion of COx gas generated by ureilite smelting exceeded by a very large factor (of order 103 but possibly much greater) the volume represented as porosity in the final ureilites. The outflow of so much gas may have, by near-surface explosive expansion and jetting, enhanced the thoroughness of the impact-triggered catastrophic impact disruption of the parent asteroid. 相似文献
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冻土的冲击韧度与试块破坏断口的平整度反映了冻土的冲击特性。冻土凿碎比能是表示凿碎单位体积冻土所消耗的功,它反映了冲击破碎冻土的能力。以冻结粘土为试样,利用摆锤式冲击试验仪进行不同温度、不同冲击能量的带缺口的冲击实验,利用凿测器进行了冻土凿碎比能试验。实验结果表明,冻结粘土的冲击韧度随温度降低而增大,随冲击能量的增加而增大。随温度的降低,试样的破坏断口的凹凸不平度增大,其范围在±3mm之间。随着温度的降低,冲击凿入深度越来越浅,冻土的硬度越来越大,钻进程度越来越难。通过回归分析,凿碎比能随着冲击韧度的增加而增大,且在冲击韧度一定的情况下,随着凿入次数的增加,凿碎比能增加的值越来越小,凿碎比能与冲击韧度的相关性较好,表明用冻土的冲击韧度来反映凿碎比能是可行的。 相似文献
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Ali El-Naqa 《Environmental Geology》2005,47(5):632-639
An environmental impact assessment (EIA) study for the solid waste landfill was prepared for the Russeifa area, northeast Jordan. As landfill was not subjected to sophisticated EIA, serious environmental problems are still occurring, such as groundwater contamination and air pollution. Three alternatives were proposed to rehabilitate the landfill: upgrading the existing landfill, construction of a biogas plant and its relocation. The EIA for the three options was carried out using the rapid impact assessment matrix (RIAM), it applies a consistent and recordable assessment of the importance of the different components. The scoping components included in the RIAM were: physical/chemical, biological/ecological, social/cultural and economic/operational components. The RIAM analysis showed that the least negative impacts would be to relocate to a better-managed sanitary landfill. The most serious negative impacts were the contamination of groundwater, air pollution and public health. These impacts can be mitigated through a comprehensive environmental management plan for the Russeifa landfill to address the deterioration of environmental components in the vicinity of landfill. 相似文献
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Hairong LI Qinbin LIU Wuyi WANG Xuehui LIU Hailong LI Shuhai LI Xiaoyu ZHAO Lizhen WANG 《中国地球化学学报》2006,25(B08):73-74
Tea bush is one of the plants cultivated in acidic soil, and is a typical hyper-accumulator of F and Al. Brick tea is a kind of brick-formed tea compressed using the older and coarse leaves and branches of tea trees. Brick tea mixed with milk is drunk as a daily indispensable beverage for Mongols, Ewenki, and other minority nationalities in the pastoral and semi-pastoral areas of Northwest China. It is reported that drinking brick tea can result in dental and skeletal fluorosis due to the high F content in it. Because Alzheimer＇s disease （AD） is related with Al in human brain, and Al has potential toxicities for skeletal and neural systems, 相似文献
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CSDP core Yaxcopoil-1 was drilled to a depth of 1,511 m within the Chicxulub crater. An organic-rich marly limestone near the base of the hole (1,495 to 1,452 m) was deposited in an open marine shelf environment during the latest Cenomanian (uppermost Rotalipora cushmani zone). The overlying sequence of limestones, dolomites and anhydrites (1,495 to 894 m) indicates deposition in various carbonate platform environments (e.g., sabkhas, lagoons). A 100-m-thick suevite breccia (894–794 m) identifies the Chicxulub impact event. Above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of Plummerita hantkeninoides zone CF1, which spans the last 300 ky of the Maastrichtian. An erosional surface 50 cm above the breccia/dolomite contact marks the K/T boundary and a hiatus. Limestones above this contact contain the first Tertiary planktic foraminifera indicative of an upper P. eugubina zone P1a(2) age. Another hiatus 7 cm upsection separates zone P1a(2) and hemipelagic limestones of planktic foraminiferal Zone P1c. Planktic foraminiferal assemblages of Zone Plc to P3b age are present from a depth of 794.04 up to 775 m. The Cretaceous carbonate sequence appears to be autochthonous, with a stratigraphic sequence comparable to late Cretaceous sediments known from outside the Chicxulub crater in northern and southern Yucatan, including the late Cenomanian organic-rich marly limestone. There is no evidence that these sediments represent crater infill due to megablocks sliding into the crater, such as major disruption of sediments, chaotic changes in lithology, overturned or deep dipping megablocks, major mechanical fragmentation, shock or thermal alteration, or ductile deformation. Breccia units that are intercalated in the carbonate platform sequence are intraformational in origin (e.g., dissolution of evaporites) and dykes are rare. Major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center. Yaxcopoil-1 may be located outside the collapsed transient crater cavity, either on the upper end of an elevated and tilted horst of the terrace zone, or even outside the annular crater cavity. The Chicxulub site thus records a large impact that predates the K/T boundary impact and mass extinction. 相似文献
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Bhuiyan Tariqur Rahman Er Ah Choy Muhamad Nurfashareena Pereira Joy Jacqueline 《Natural Hazards》2021,109(2):1509-1538
Small-scale flash flood events are climate-related disasters which can put multiple aspects of the system at risk. The consequences of flash floods in densely populated cities are increasingly becoming problematic around the globe. However, they are largely ignored in disaster impact assessment studies, especially in assessing socioeconomic loss and damage, which can provide a significant insight for disaster risk reduction measures. Using a structured questionnaire survey, this study applied a statistical approach and developed a structural equation model (SEM) for assessing several socioeconomic dimensions including physical impacts, mobility disruption, lifeline facilities, health and income-related impacts. The study reveals that respondents have experienced a stronger impact on direct tangible elements such as household contents and buildings as well as direct intangible elements with β coefficients 0.703, 0.576 and 0.635, respectively, at p?<?0:001 level. The direct intangible impacts affect mobility disruption with β coefficients equal to 0.701 at p?<?0:001 level which then further cause adversity to income-generating activities with β 0.316 at significant p?<?0:001 as well. The overall model fit indices show highly acceptable scores of SRMR 0.068, RMSEA 0.055 and PClose 0.092. Thus, the SEM has successfully incorporated the socioeconomic dimensions of disaster impact and explained the impact phenomena reliably. This modeling approach will allow inclusion of various variables from different disciplines to assess hazard impact, vulnerability and resilience.
相似文献15.
滚石冲击力测试研究 总被引：4，自引：0，他引：4
以国内外代表性滚石冲击力计算方法为基础,针对冲击力的影响因素,设计了一套滚石冲击力测试装置。通过试验设计,选取不同的滚石质量、冲击速度、入射角度、缓冲材料性质及厚度等影响因素,获得冲击力变化规律。结果表明：最大冲击力随滚石重量的减小或冲击速度的降低而逐渐减小,2 cm厚度缓冲层比直接冲击时减小了90%左右,缓冲效果明显。同时最大冲击力随着入射角度的变小而降低,但入射角度越小,冲击力值降低的幅度越小。结合冲击试验结果,通过冲击力计算方法对比分析,建立了可用于各影响因素的最大冲击力计算方法,验算表明误差很小。研究结果可为滚石灾害的防治设计提供参考依据。 相似文献
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William R. Stanley Prof. Dr. 《GeoJournal》1990,22(1):67-79
Taxes and royalties from the oil industry in Nigeria have made possible massive infrastructural and social development throughout the country; this single industry continues to be the most important contributor to the national treasury. Along with oil, however, have come environmental and social problems, some severe and, in the social sector, possibly of long duration. Questionnaires were employed to solicit environmental and socioeconomic information from residents in the oil-impacted area as well as to ascertain the views of the oil companies with respect to their Nigerian operations, in particular to their socio-economic responsibilities to the local residents. Responses point to serious discontent on the part of the impacted population, especially in the most important southern (Niger Delta) oil producing region. These negative attitudes in part are based upon the impacted population’s inability to secure for itself a sufficiently large number of oil industry jobs and in part to the presence in the local community of ethnic strangers who do have such employment. There is evidence of serious environmental damage, but its biological dimension has been overshadowed by claims for monetary compensation at the local level. Data derived from these investigations might well be applicable in the wider field of trans-national mining and petroleum extraction operations in developing countries, especially to the unwritten social obligations of the expatriate firm to local residents. 相似文献
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《地学前缘(英文版)》2022,13(5):101410
This work presents isotopic data for the non-traditional isotope systems Fe, Cu, and Zn on a set of Chicxulub impactites and target lithologies with the aim of better documenting the dynamic processes taking place during hypervelocity impact events, as well as those affecting impact structures during the post-impact phase. The focus lies on material from the recent IODP-ICDP Expedition 364 Hole M0077A drill core obtained from the offshore Chicxulub peak ring. Two ejecta blanket samples from the UNAM 5 and 7 cores were used to compare the crater lithologies with those outside of the impact structure. The datasets of bulk Fe, Cu, and Zn isotope ratios are coupled with petrographic observations and bulk major and trace element compositions to disentangle equilibrium isotope fractionation effects from kinetic processes. The observed Fe and Cu isotopic signatures, with δ56/54Fe ranging from ?0.95‰ to 0.58‰ and δ65/63Cu from ?0.73‰ to 0.14‰, mostly reflect felsic, mafic, and carbonate target lithology mixing and secondary sulfide mineral formation, the latter associated to the extensive and long-lived (>105 years) hydrothermal system within Chicxulub structure. On the other hand, the stable Zn isotope ratios provide evidence for volatility-governed isotopic fractionation. The heavier Zn isotopic compositions observed for the uppermost part of the impactite sequence and a metamorphic clast (δ66/64Zn of up to 0.80‰ and 0.87‰, respectively) relative to most basement lithologies and impact melt rock units indicate partial vaporization of Zn, comparable to what has been observed for Cretaceous-Paleogene boundary layer sediments around the world, as well as for tektites from various strewn fields. In contrast to previous work, our data indicate that an isotopically light Zn reservoir (δ66/64Zn down to ?0.49‰), of which the existence has previously been suggested based on mass balance considerations, may reside within the upper impact melt rock (UIM) unit. This observation is restricted to a few UIM samples only and cannot be extended to other target or impact melt rock units. Light isotopic signatures of moderately volatile elements in tektites and microtektites have previously been linked to (back-)condensation under distinct kinetic regimes. Although some of the signatures observed may have been partially overprinted during post-impact processes, our bulk data confirm impact volatilization and condensation of Zn, which may be even more pronounced at the microscale, with variable degrees of mixing between isotopically distinct reservoirs, not only at proximal to distal ejecta sites, but also within the lithologies associated with the Chicxulub impact crater. 相似文献