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1.
Abstract The Campo del Cielo meteorite crater field in Argentina contains at least 20 small meteorite craters, but a recent review of the field data and a remote sensing study suggest that there may be more. The fall occurred ~4000 years ago into a uniform loessy soil, and the craters are well enough preserved so that some of their parameters of impact can be determined after excavation. The craters were formed by multi-ton fragments of a type IA meteoroid with abundant silicate inclusions. Relative to the horizontal, the angle of infall was ~9°. Reflecting the low angle of infall, the crater field is elongated with apparent dimensions of 3 × 18.5 km. The largest craters are near the center of this ellipse. This suggests that when the parent meteoroid broke apart, the resulting fragments diverged from the original trajectory in inverse relation to their masses and did not undergo size sorting due to atmospheric deceleration. The major axis of the crater field as we know it extends along N63°E, but the azimuths of infall determined by excavation of Craters 9 and 10 are N83.5°E and N75.5°E, respectively. This suggests that the major axis of the crater field is not yet well determined. The three or four largest craters appear to have been formed by impacts that disrupted the projectiles, scattering fragments around the outsides of the craters and leaving no large masses within them; these are relatively symmetrical in shape. Other craters are elongated features with multi-ton masses preserved within them and no fragmentation products outside. There are two ways in which field research on the Campo del Cielo crater field is found to be useful. (1) Studies exist that have been used to interpret impact craters on planetary surfaces other than the Earth. This occurrence of a swarm of projectiles impacting at known angles and similar velocities into a uniform target material provides an excellent field site at which to test the applicability of those studies. (2) Individual craters at Campo del Cielo can yield the masses of the projectiles that formed them and their velocities, angles and azimuths of impact. From these data, there is a possibility to estimate parameters for the parent meteoroid at entry and, thus, learn enough about its orbit to judge whether or not it was compatible with an asteroidal origin. Preliminary indications are that it was. Campo del Cielo is a IA iron meteorite and Sikhote-Alin, an observed fall, is a IIB iron meteorite in Wasson's classification. The Sterlitamak iron, also an observed fall, is a medium octahedrite in the Prior-Hey classification. It would be interesting to compare their orbital parameters.  相似文献   

2.
The mineralogy and bulk chemical compositions of three iron meteorites (Zhaoping, Xifu and Hami) recently found in China are reported here and are classified on the basis of their bulk chemical compositions. Zhaoping contains 93.4 mg/g Ni, 85.9 μg/g Ga, 418 μg/g Ge, 5.24 mg/g Co, 1.94 μg/g Ir, 0.774 μg/g W, and 1.62 μg/g Au and belongs to the low-Ni, low-Au subgroup of IAB. It is a coarse octahedrite and consists of kamacite, taenite, troilite, schreibersite and cohenite. The cohenite has entirely decomposed to graphite and low-Ni kamacite in our samples. Zhaoping contains some inclusions of Mn-free sarcopside which were rarely reported in IAB iron meteorites. Xifu has 74.1 mg/g Ni, 58.8gμg/g Ga, 150 μg/g Ge, and 0.913 μg/g W. Xifu is a member of group IIICD iron meteorite. Like most of IIICD irons, Xifu is a coarsest octahedrite with kamacite bandwidth larger than 3mm, and contains kamacite, taenite and schreibersite. Carbides and graphite are not found in the sample because of its being heterogeneous. Hami has 106 mg/g Ni, 5.36 mg/g Co and 0.922 μg/g Ir. We did not obtain the Ga and Ge contents in Hami because of their low concentrations and the limited precision of the INAA technique. Hami is an unclassified iron meteorite on the basis of the contents of other trace elements, structure and mineralogy. On mineralogy and structure, Hami resembles Rafruti, another unclassified iron meteorite.  相似文献   

3.
A sample of Campo del Cielo with any other name would have the same composition. During the last three decades, our instrumental neutron activation analyses (INAA) of many supposedly new iron meteorites have shown an anomalously large fraction to have compositions within the compositional field of the IAB‐MG iron Campo del Cielo. A plot of Ir versus Au provides the best discrimination; only two independent‐fall irons found after 1980 with good recovery documentation fall within the 90% contour ellipse around the centroid of this Campo field, and one of these is from Antarctica. Now (early 2018) a total of 36 other irons attributed to other geographical locations have compositions that cannot be resolved from the Campo compositional field. Because it is possible that some of these are actually independent falls, the Meteoritical Society Nomenclature Committee has chosen to assign about half these meteorites Nova XXX names used for meteorites whose discovery localities are not adequately documented. However, for Campo‐like irons with too little information (e.g., total weight not known) or for which no adequately large type specimens are available, the decision is to call them Campos with the working name used during the UCLA analysis. In the UCLA Meteorite Collection, they are cataloged together with the documented Campos.  相似文献   

4.
The thermal conductivity of meteorites: New measurements and analysis   总被引:1,自引:0,他引:1  
C.P. Opeil  D.T. Britt 《Icarus》2010,208(1):449-6159
We have measured the thermal conductivity at low temperatures (5-300 K) of six meteorites representing a range of compositions, including the ordinary chondrites Cronstad (H5) and Lumpkin (L6), the enstatite chondrite Abee (E4), the carbonaceous chondrites NWA 5515 (CK4 find) and Cold Bokkeveld (CM2), and the iron meteorite Campo del Cielo (IAB find). All measurements were made using a Quantum Design Physical Properties Measurement System, Thermal Transport Option (TTO) on samples cut into regular parallelepipeds of ∼2-6 mm dimension. The iron meteorite conductivity increases roughly linearly from 15 W m−1 K−1 at 100 K to 27 W m−1 K−1 at 300 K, comparable to typical values for metallic iron. By contrast, the conductivities of all the stony samples except Abee appear to be controlled by the inhomogeneous nature of the meteorite fabric, resulting in values that are much lower than those of pure minerals and which vary only slightly with temperature above 100 K. The L and CK sample conductivities above 100 K are both about 1.5 W m−1 K−1, that of the H is 1.9 W m−1 K−1, and that of the CM sample is 0.5 W m−1 K−1; by contrast the literature value at 300 K for serpentine is 2.5 W m−1 K−1 and those of enstatite and olivine range from 4.5 to 5 W m−1 K−1 (which is comparable to the Abee value). These measurements are among the first direct measurements of thermal conductivity for meteorites. The results compare well with previous estimates for meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of a higher precision and cover a wider range of temperatures and meteorite types. If the rocky material that makes up asteroids and provides the dust to comets, Kuiper Belt objects, and icy satellites has the same low thermal conductivities as the ordinary and carbonaceous chondrites measured here, this would significantly change models of their thermal evolution. These values would also lower their thermal inertia, thus affecting the Yarkovsky and YORP evolution of orbits and spin for solid objects; however, in this case the effect would not be as great, as thermal inertia only varies as the square root of the conductivity and, for most asteroids, is controlled by the dusty nature of asteroidal surfaces rather than the conductivity of the material itself.  相似文献   

5.
Abstract— Long‐lived cosmogenic radioisotopes, 10Be, 26Al, 36Cl, 41Ca and 59Ni, have been measured in five samples from the Campo del Cielo iron meteorite by accelerator mass spectrometry (AMS). The 36Cl activities were significantly above the background. For the concentrations of the other four radioisotopes, only upper limits were obtained that were, however, consistent with the 36Cl result. The measured 36Cl activity allowed an estimate of the meteoroid's preatmospheric size: a radius larger than 300 cm and a mass of at least 840 000 kg. We conclude that this meteorite might be one of the largest meteorites to have been recovered.  相似文献   

6.
Abstract Melnikovo is a relatively unweathered 545.6-g LL6 chondrite that was found in 1983. Only a few poorly defined chondrules are discernable in the examined sections; two of these are enriched in chromite. The meteorite contains olivine (Fa27,8), low-Ca pyroxene (Fs24,4), plagioclase, rare clinopyroxene, chlorapatite, merrillite and opaque minerals, which have a modal abundance (in wt%) of troilite (3.9%), kamacite (0.4%), taenite plus tetrataenite (0.7%), chromite (0.8%), and trace amounts of ilmenite and Mn-ilmenite. The meteorite appears unbrecciated on a centimeter scale.  相似文献   

7.
The Campo del Cielo impact structure exhibits several penetration funnels and impact craters. Here, we model the formation of these funnels with pre-impact conditions consistent with the results of meteoroid entry models. We study vertical impacts to find the dependence of funnel geometry (depth, diameter) on impact velocity and target porosity. At velocities above 1 km s−1, we observe strong deformation of the projectile and transformation of funnels into regular impact craters. We also use 3-D impact models to study oblique impacts and find that in the case of impact angles <25° to the horizon, the projectile bounces off the target. Instead of a funnel, an elongated groove forms, while the fragmented projectile escapes and moves farther downrange. At steeper impact angles, funnels form with the projectile at its tip. Early interpretations of the Campo del Cielo impact angle at 9–10° were based on (i) an oversimplified atmospheric model allowing “correct” strewn field elongation and (ii) the results of excavation in which the sloping boundary between breccia-like materials and infilling loess was interpreted as a true crater floor and its slope was equated to the impact angle. As our models show, the projectile trajectory within the target is not a straight line, and the angle to horizon changes from a steep one at the impact point to zero and then to a negative value (the projectile is moving upward). We also model two impact craters (Hoyo de la Cañada and Laguna Negra) created by high-velocity fragments to demonstrate the projectile remnants ricochet in the downrange direction.  相似文献   

8.
Abstract— The mineralogy and composition of six Mongolian meteorites were studied in some detail. Previously, only limited information existed about these rocks, and some were still unclassified. The six meteorites include three ordinary chondrites and three irons. The ordinary chondrite Adzhi-Bogdo (stone) is a regolith breccia (LL3–6) containing various types of clasts (some of foreign origin) embedded within a fine-grained clastic matrix. Tugalin Bulen (H6) and Noyan Bogdo (L6) meteorites are typical, well-metamorphosed ordinary chondrites. Adzhi-Bogdo (iron) has to be regarded as an IA iron meteorite like Campo del Cielo or Canyon Diablo; although the sample studied had been heated to about 900 °C–950 °C some time in the past, thus eradicating all original structural elements. Manlai is structurally closely related to the IIC iron meteorites; but based on its chemistry, which does not fit into this group, it is suggested that Manlai is an anomalous iron meteorite. The third iron, Sargiin Gobi, is certainly a normal member of the IA iron meteorites. The concentrations and isotopic compositions of He, Ne, and Ar were measured for all meteorites and their gas retention ages and exposure ages are discussed.  相似文献   

9.
Fossil iron meteorites are extremely rare in the geological sedimentary record. The paleometeorite described here is the first such finding at the Cretaceous‐Paleogene (K‐Pg) boundary. In the boundary clay from the outcrop at the Lechówka quarry (Poland), fragments of the paleometeorite were found in the bottom part of the host layer. The fragments of meteorite (2–6 mm in size) and meteoritic dust are metallic‐gray in color and have a total weight of 1.8181 g. Geochemical and petrographic analyses of the meteorite from Lechówka reveal the presence of Ni‐rich minerals with a total Ni amount of 2–3 wt%. The identified minerals are taenite, kamacite, schreibersite, Ni‐rich magnetite, and Ni‐rich goethite. No relicts of silicates or chromites were found. The investigated paleometeorite apparently represents an independent fall and does not seem to be derived from the K‐Pg impactor. The high degree of weathering did not permit the chemical classification of the meteorite fragments. However, the recognized mineral inventory, lack of silicates, and their pseudomorphs and texture may indicate that the meteorite remains were an iron meteorite.  相似文献   

10.
Abstract— The Leedey, Oklahoma, meteorite shower fell on 1943 November 25, following a fireball which was visible across much of southwestern Oklahoma and northcentral Texas. The shower produced 24 stones with a total mass of ~51.5 kg. The stones formed a strewnfield ~18 km in length in the same direction as the observed path of the meteor (N50°W). Leedey is classified as an L6(S3) ordinary chondrite. We report bulk major element chemical analyses from four separate laboratories. Leedey contains an unusual 6 by 8 mm composite Fe,Ni-FeS grain, which is composed of a 3 mm kamacite grain adjacent to a 5 mm troilite grain. A 50–100 μm rim of high-Ni (45–55 wt%) taenite (tetrataenite) occurs at the boundary between kamacite and troilite. A single, zoned pyrophanite grain is observed at the boundary between the inclusion troilite and host silicates. An origin as a foreign particle incorporated after metamorphism or during impact melting appears unlikely. This particle likely formed by a complex set of processes, including melting in the nebula, parent body metamorphism and reheating by later shock, mirroring the history of the host chondrite.  相似文献   

11.
On August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15o ± 0.05. The data identified the body as an Apollo object, an Earth-crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5-6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well-defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr−1.  相似文献   

12.
Abstract— MÖssbauer spectroscopy, x-ray diffraction (XRD) measurements, and electron microprobe analysis (EMPA) have been carried out for the investigation of a newly fallen Sudanese meteorite named New Haifa. The room temperature MÖssbauer spectrum is fitted with three sextets and two doublets. The sextets are assigned to Fe in troilite, kamacite, and taenite, and the two doublets are assigned to Fe2+in olivine and pyroxene (no Fe3+was found). The microprobe trace of Ni concentration across a kamacite-taenite-kamacite area shows a high-Ni concentration at the interfaces between kamacite and taenite. From the microprobe analysis, olivine appears to have a constant composition, whereas pyroxene has a varying composition. The mole fractions of the Fe end members of olivine (fayalite) and pyroxene (ferrosilite) are found to be 23.5% and 23.2%, respectively. Accordingly, the New Haifa meteorite is classified as an ordinary L-type chondrite.  相似文献   

13.
We present predictions for the radio pulses emitted by extensive air showers using ZHAireS, an AIRES-based Monte Carlo code that takes into account the full complexity of ultra-high energy cosmic-ray induced shower development in the atmosphere, and allows the calculation of the electric field in both the time and frequency domains. We do not presuppose any emission mechanism and our results are compatible with a superposition of geomagnetic and charge excess radio emission effects. We investigate the polarization of the electric field as well as the effects of the refractive index n and shower geometry on the radio pulses. We show that geometry, coupled to the relativistic effects that appear when using a realistic refractive index n > 1, play a prominent role on the radio emission of air showers.  相似文献   

14.
On February 24, 1979, a deeply oxidized mass of iron meteorite was excavated from bauxite at an open cut mine on the Gove Peninsula, Northern Territory, Australia. The meteorite, measuring 0.75–1 m in diameter and of unknown total weight, was found at coordinates 12°15.8′S, 136°50.3′E. On removal from the ground, the meteorite is reported to have disintegrated rapidly. A preliminary analysis at the mine laboratory reportedly gave 8.5 wt% Ni. A modern analysis of oxidized material gave Ni = 32.9, Co = 3.67 (both mg g?1), Cr = 168, Cu = 195, Ga = 22.5, Ge = <70, As = 4.16, W = 1.35, Ir = 10.5, Pt = 21.2, Au = 0.672 (all μg g?1), Sb = <150, and Re = 844 (both ng g?1). Competent fragments of oxidized material retain a fine to medium Widmanstätten pattern with an apparent average bandwidth of 0.5 mm (range 0.2–0.9 mm in plane section). Primary mineralogy includes rare γ–taenite and daubréelite, and secondary minerals produced by weathering include awaruite (with up to 78.5 wt% Ni) and an, as yet, unnamed Cu‐Cr‐bearing sulfide with the ideal formula CuCrS2 that is hitherto unknown in nature. Deep weathering has masked many of the features of the meteorite; however, the analysis normalized to the analyses of fresh iron meteorites favors chemical group IIIAB. The terrestrial age of the meteorite is unknown, although it is likely to be in the Neogene (2.5–23 Ma), which is widely accepted as the major period of bauxite formation in the Northern Territory of Australia. Gove is the second authenticated relict meteorite found in Australia.  相似文献   

15.
Abstract– In the context of the MEMIN project, a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite Campo del Cielo as projectile accelerated to 4.56 km s?1, and a block of Seeberger sandstone as target material. The ejecta, collected in a newly designed catcher, are represented by (1) weakly deformed, (2) highly deformed, and (3) highly shocked material. The latter shows shock‐metamorphic features such as planar deformation features (PDF) in quartz, formation of diaplectic quartz glass, partial melting of the sandstone, and partially molten projectile, mixed mechanically and chemically with target melt. During mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co yielding a Fe/Ni that is generally higher than Fe/Ni in the projectile. This fractionation results from the differing siderophile properties, specifically from differences in reactivity of Fe, Ni, and Co with oxygen during projectile‐target interaction. Projectile matter was also detected in shocked quartz grains. The average Fe/Ni of quartz with PDF (about 20) and of silica glasses (about 24) are in contrast to the average sandstone ratio (about 422), but resembles the Fe/Ni‐ratio of the projectile (about 14). We briefly discuss possible reasons of projectile melting and vaporization in the experiment, in which the calculated maximum shock pressure does not exceed 55 GPa.  相似文献   

16.
Abstract— The Ulasitai iron was recently found about 130 km southeast to the find site of the Armanty (Xinjiang, IIIE) meteorite. It is a coarse octahedrite with a kamacite bandwidth of 1.2 ± 0.2 (0.9–1.8) mm. Plessite is abundant, as is taenite, kamacite, cohenite, and schreibersite with various microstructures. Schreibersite is Ni‐rich (30.5–55.5 wt%) in plessite or coexisting with troilite and daubreelite, in comparison with the coarse laths (20.6–21.2 wt%) between the Widmanstätten pattern plates. The correlation between the center Ni content and the half bandwidth of taenite suggest a cooling rate of ?20 °C/Myr based on simulations. The petrography and mineral chemistry of Ulasitai are similar to Armanty. The bulk samples of Ulasitai were measured, together with Armanty, Nandan (IIICD), and Mundrabilla (IIICD), by inductively coupled plasma atomic emission spectrometry (ICP‐AES) and mass spectrometry (ICP‐MS). The results agree with literature data of the same meteorites, and our analyses of four samples of Armanty (L1, L12, L16, L17) confirm a homogeneous composition (Wasson et al. 1988). The bulk composition of Ulasitai is identical to that of Armanty, both plotting within the IIIE field. We classify Ulasitai as a new IIIE iron and suggest that it pairs with Armanty.  相似文献   

17.
K.L. Rasmussen 《Icarus》1981,45(3):564-576
Measurements of Ni concentration profiles of a large number of neighboring kamacite and taenite lamellae in the iron meteorite Cape York (IIIA) have revealed that the kamacite plates have nucleated in a taenite of varying Ni concentration, equal to or above the bulk Ni concentration of the meteorite. This variation indicates that the kamacite plates nucleated stepwise (i.e., independently) during cooling through a certain temperature interval, rather than simultaneously after more or less undercooling of the meteorite. The latter is assumed in most previous cooling rate determinations (e.g., Moren and Goldstein, 1978). In this paper the measured local bulk Ni concentrations are used in the computer simulation of the evolution of the Widmannstaetten pattern in order to calculate the cooling rate of the meteorite. The cooling rate obtained for Cape York is 1.3°K/my. In most previous work, a correlation is seen between the resulting taenite width and the cooling rate in one and the same meteorite. No such correlation is seen using the present method.  相似文献   

18.
Measurements of the bulk density, grain density, porosity, and magnetic susceptibility of 19 Gao-Guenie H5 chondrite meteorite samples are presented. We find average values of bulk density 〈ρbulk〉=3.46±0.07 g/cm3, grain density 〈ρgrain〉=3.53±0.08 g/cm3, porosity 〈P(%)〉=2.46±1.39, and bulk mass magnetic susceptibility 〈log χ〉=5.23±0.11. Measurements of the specific heat capacity for a 3.01-g Gao-Guenie sample, a 61.37-g Gao-Guenie sample, a 62.35-g Jilin H5 chondrite meteorite sample, and a 51.37-g Sikhote-Alin IIAB Iron meteorite sample are also presented. Temperature interpolation formula are further provided for the specific heat capacity, thermal conductivity, and thermal diffusivity of the 3.01-g Gao-Guenie sample in the temperature range 300<T (K)<800. We briefly review the possible effects of the newly deduced specific heat and thermal conductivity values on the ablation of meteoroids within the Earth's atmosphere, the modeling of asteroid interiors and the orbital evolution of meteoroids through the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect.  相似文献   

19.
The Ko?ice meteorite was observed to fall on 28 February 2010 at 23:25 UT near the city of Ko?ice in eastern Slovakia and its mineralogy, petrology, and geochemistry are described. The characteristic features of the meteorite fragments are fan‐like, mosaic, lamellar, and granular chondrules, which were up to 1.2 mm in diameter. The fusion crust has a black‐gray color with a thickness up to 0.6 mm. The matrix of the meteorite is formed mainly by forsterite (Fo80.6); diopside; enstatite (Fs16.7); albite; troilite; Fe‐Ni metals such as iron and taenite; and some augite, chlorapatite, merrillite, chromite, and tetrataenite. Plagioclase‐like glass was also identified. Relative uniform chemical composition of basic silicates, partially brecciated textures, as well as skeletal taenite crystals into troilite veinlets suggest monomict breccia formed at conditions of rapid cooling. The Ko?ice meteorite is classified as ordinary chondrite of the H5 type which has been slightly weathered, and only short veinlets of Fe hydroxides are present. The textural relationships indicate an S3 degree of shock metamorphism and W0 weathering grade. Some fragments of the meteorite Ko?ice are formed by monomict breccia of the petrological type H5. On the basis of REE content, we suggest the Ko?ice chondrite is probably from the same parent body as H5 chondrite Morávka from Czech Republic. Electron‐microprobe analysis (EMPA) with focused and defocused electron beam, whole‐rock analysis (WRA), inductively coupled plasma mass and optical emission spectroscopy (ICP MS, ICP OES), and calibration‐free laser induced breakdown spectroscopy (CF‐LIBS) were used to characterize the Ko?ice fragments. The results provide further evidence that whole‐rock analysis gives the most accurate analyses, but this method is completely destructive. Two other proposed methods are partially destructive (EMPA) or nondestructive (CF‐LIBS), but only major and minor elements can be evaluated due to the significantly lower sample consumption.  相似文献   

20.
Tube‐shaped beads excavated from grave pits at the prehistoric Gerzeh cemetery, approximately 3300 BCE, represent the earliest known use of iron in Egypt. Using a combination of scanning electron microscopy and micro X‐ray microcomputer tomography, we show that microstructural and chemical analysis of a Gerzeh iron bead is consistent with a cold‐worked iron meteorite. Thin fragments of parallel bands of taenite within a meteoritic Widmanstätten pattern are present, with structural distortion caused by cold‐working. The metal fragments retain their original chemistry of approximately 30 wt% nickel. The bulk of the bead is highly oxidized, with only approximately 2.4% of the total bead volume remaining as metal. Our results show that the first known example of the use of iron in Egypt was produced from a meteorite, its celestial origin having implications for both the perception of meteorite iron by ancient Egyptians and the development of metallurgical knowledge in the Nile Valley.  相似文献   

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