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1.
Seven trace elements (Ag, Co, Cs, Ga, In, Te, Tl) are either completely retained or are lost to the same extent in Abee samples heated at 700 °C for one week at 10?5-10?3 atm Ne or in 10?5 atm H2. Bi and Se are lost significantly more easily and Zn is better retained in samples heated in Ne than in H2. Zn retention varies inversely with ambient Ne pressure. Mobile element transport seems unaffected by physical interactions in the gas phase but may reflect solid-state surface effects. During week-long heating at low pressures (initially ～ 10?5 atm H2) S is mobilized only at 1000 °C while C contents decrease progressively from 600–1000 °C. Apparent activation energies for C are 60 kcal/mole below 700 °C and 16 kcal/mole above this temperature suggesting diffusive loss from different hosts and/or processes over different temperature intervals. In E4–6 chondrites C and S contents largely reflect nebular fractionation and condensation processes.  相似文献   

2.
Based on the example of Abernathy (L6 chondrite), this study shows how petrographic investigation can be used to unravel the nature, chronology and conditions of superposed metamorphic events in chondrites. Features considered include the texture of the rock, optical characteristics of olivine, pyroxene and plagioclase, refractive index of plagioclase, metallographical characteristics and microhardness of Fe-Ni alloys. From these data it is deduced that Abernathy has been involved in at least six metamorphic events since the formation of the chondrite. Four distinct shock events and two separate reheating events have been identified. The chronology of these events is established. The conditions for the last four events are reasonably well constrained. These include successively, i) severe reheating (T > 1200°C), ii) severe shock causing complete melting of plagioclase and local melting of the rock (90 < P < 110 GPa, 1250°GC < T < 1350°C), iii) mild shock (10 < P < 25 GPa, T<500°C), and iv) reheating below 800°C.  相似文献   

3.
Some eucrites contain up to 10 vol% silica minerals; however, silica minerals have not been studied in detail so far. We performed a mineralogical study of silica minerals in three cumulate eucrites (Moore County, Moama, and Yamato [Y] 980433). Monoclinic tridymite was common in all three samples. Moama contained orthorhombic tridymite as lamellae within monoclinic tridymite grains. Y 980433 included quartz around an impact melt vein. The presence of orthorhombic tridymite in Moama indicates that Moama cooled more rapidly than the other two samples at low temperatures (<400 °C). This result is different from the slower cooling rates of Moama (?0.0004 °C yr?1) than that of Moore County (>0.3 °C yr?1, after the shock event) at high temperatures (>500 °C) estimated from compositional profiles of pyroxene exsolution lamellae. The difference of the cooling rates may reflect their geological settings. Y 980433 cooled slowly at low temperature, as did Moore County. Quartz in Y 980433 could be a local product transformed from monoclinic tridymite by a shock event. We suggest that silica minerals in meteorites record thermal histories at low temperatures and shock events.  相似文献   

4.
Abstract— The microstructure of Fe‐rich clinopyroxene from synthetic analogues of chondrules was studied by transmission electron microscopy. The samples were cooled at various rates from 1455 °C to the quench temperature of 1000 °C. Slow cooling at rates below approximately 50–60 °C/h leads to the development of coherent pigeonite/augite exsolution lamallae on (001). A final wavelength of 19.6 ± 1.1 nm was obtained at a cooling rate of 10 °C/h, and 17.4 ± 2.4 ran at a cooling rate of 50 °C/h. Faster cooling at rates between approximately 50 and 450 °C/h yields only modulated structures with a wavelength on the order of 17–19 nm for the (001) orientation. Coherent exsolution lamellae on (001) in clinopyroxene occur in chondrules of H, L, LL, and CV chondrites, indicating that slow cooling of chondrules at subsolidus temperatures is a widespread phenomenon. The variation of the lamellar wavelength observed in natural chondrules corresponds to a variation of the subsolidus cooling rates between ～0.1 and 50 °C/h. The low cooling rates at subsolidus temperatures deduced from the microstructure of Fe‐rich clinopyroxene point to nonlinear cooling, with cooling rates decreasing with decreasing temperature.  相似文献   

5.
《Icarus》1987,69(1):1-13
If chondritic meteorites were internally heated after accretion had ended, then the hottest material would have been buried the deepest and should have cooled the slowest. If this is correct, there ought to be a correlation between cooling rate and petrographic type, a measure of the extent to which chondrites were metamorphosed (i.e., heated). Published and new cooling rates derived from the compositions of metallic iron-nickel grains do not display this correlation, implying either that chondrite parent asteroids never had onion-shell structures or that bodies with onion-shell structures were broken up and reassembled prior to cooling to below 500°C, the temperature at which cooling-rate information is recorded in metallic iron-nickel. Chondritic regolith breccias formed from materials that resided on the surfaces of their parent asteroids. Metallic iron-nickel grains in H- and L-chondrite regolith breccias indicate that the breccia constituents cooled at rates ranging from 1 to > 1000°K/myr. Based on thermal calculations, these cooling rates suggest that the materials spread out on the surfaces of H- and L-chondrite parent asteroids originated at depths ranging from about one kilometer to several tens of kilometers. Craters deep enough to excavate tens of kilometers cannot form on typical asteroidal bodies only 100 to 300 km in diameter without disrupting them. Therefore, it appears that at least some asteroids, namely, the parent bodies of H and L chondrites, were disrupted after cooling to below 300°C, and then reassembled to create surfaces containing rocks that originated at a wide range of depths. These results support theoretical calculations suggesting that many asteroids were broken up and subsequently reassembled into gravitationally bound rubble piles.  相似文献   

6.
Abstract— Sixteen texturally different (porphyritic, barred, radial, cryptocrystalline) FeO‐rich chondrules from the unequilibrated ordinary chondrites Brownfield, Frontier Mountain (FRO) 90003 and FRO 90032 were characterized by optical and scanning electron microscopy and then thoroughly studied by transmission and analytical electron microscopy. Nanotextural and nanochemical data indicate similar thermal evolution for chondrules of the same textural groups; minor, yet meaningful differences occur among the different groups. Olivine is the earliest phase formed and crystallizes between 1500 and 1400 °C. Protoenstatite crystallizes at temperatures higher than 1350–1200 °C; it later inverts to clinoenstatite in the 1250–1200 °C range. Enstatite is surrounded by pigeonitic or (less frequently) augitic rims; the minimal crystallization temperature for the rims is 1000 °C; high pigeonite later inverts to low pigeonite, between 935 and 845 °C. The outer pigeonitic or augitic rims are constantly exsolved, producing sigmoidal augite or enstatite precipitates; sigmoidal precipitates record exsolution temperatures between 1000 and 640 °C. Cooling rate (determined using the speedometer based upon ortho‐clinoenstatite intergrowth) was in the order of 50–3000 °C/h at the clinoenstatite‐orthoenstatite transition temperature (close to 1250–1200 °C), but decreased to 5–10 °C/h or slower at the exsolution temperature (between 1000 and 650 °C), thus revealing nonlinear cooling paths. Nanoscale observations indicate that the individual chondrules formed and cooled separately from 1500 °C down to at least 650 °C. Accretion into chondritic parent body occurred at temperatures lower than 650 °C.  相似文献   

7.
Abstract— Due to the discoveries in Antarctica, the number of known enstatite chondrites has doubled in the last few years, and many rare or previously unknown types have been collected, most notably many EL3 and EH3 chondrites. We have applied the five major enstatite chondrite thermometers to the new and previously known enstatite chondrites, the thermometers being: (1) kamacite-quartz-enstatite-oldhamite-troilite (KQEOT), (2) oldhamite, (3) alabandite-niningerite, (4) sphalerite, and (5) phosphide-metal. Measured temperatures based on the KQEOT and oldhamite systems are 800 °C-1000 °C with the type 3 enstatite chondrites having values similar to those of type 4–6. It seems likely that these temperatures relate to events prior to parent body metamorphism, such as nebula condensation or chondrule formation, and were not significantly reset by later events. Measured temperatures for alabandite-niningerite, metal-phosphide and sphalerite in EH chondrites increase from 300 °C-400 °C to 600 °C-800 °C with petrographic indications of increasing metamorphism. In contrast, measured temperatures for all EL chondrites, including the most heavily metamorphosed, are generally <400 °C. Apparently EL chondrites cooled more slowly than the EH chondrites regardless of metamorphism experienced. Measured temperatures for the alabandite-niningerite, metal-phosphide and sphalerite are actually closure temperatures for the last thermal event suffered by the meteorite, and the fast cooling rates indicated are most consistent with processes occurring in thick regoliths.  相似文献   

8.
Abstract— iron-magnesium ordering was determined in orthopyroxenes from two suites of unshocked (shock stage S1, S2), equilibrated L- and LL-chondrites (10 grains from 5 meteorites and 7 grains from 4 meteorites, respectively) by means of single crystal x-ray diffraction (SCXRD). This study, together with a previous investigation of H-chondrites (13 grains from 8 meteorites), produces an internally consistent data set about the thermal record in equilibrated ordinary chondrites (EOCs). The major feature outlined by cation ordering in EOC orthopyroxenes is that H-, L- and LL-chondrites share a common low-temperature record, that is, a common range of similar cooling rates in the 340–480 °C interval for the petrographic types 4 to 6. As a consequence, the thermal evolution of EOCs consists of at least two subsolidus stages; the first stage occurred at temperatures >480 °C where petrographic types were established in distinct environments; the second stage occurred when EOCs, irrespective of chemical class and type, cooled through 340–480 °C in environments characterized by close temperature-time conditions. Quantitative estimates of minimal cooling rates for EOCs range from a few °C/ka to ～102°C/ka in the 340–480 °C interval. Possibly, final ordering was attained in environments where moderate radiative heat-loss was possible and, thus indicating shallow burial depths in the parent body.  相似文献   

9.
Abstract— We studied the texture, mineralogy, and bulk chemical composition of Dhofar 007, a basaltic achondrite. Dhofar 007 is a polymict breccia that is mostly composed of coarse‐grained granular (CG) clasts with a minor amount of xenolithic components, such as a fragment of Mg‐rich pyroxene. The coarse‐grained, relict gabbroic texture, mineral chemistry, and bulk chemical data of the coarse‐grained clast indicate that the CG clasts were originally a cumulate rock crystallized in a crust of the parent body. However, in contrast to monomict eucrites, the siderophile elements are highly enriched and could have been introduced by impact events. Dhofar 007 appears to have experienced a two‐stage postcrystallization thermal history: rapid cooling at high temperatures and slow cooling at lower temperatures. The presence of pigeonite with closely spaced, fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures (>0.5 °C/yr at ˜1000 °C) than typical cumulate eucrites. However, the presence of the cloudy zone in taenite and the Ni profile across the kamacite‐taenite boundaries indicates that the cooling rate was very slow at lower temperatures (˜1–10 °C/Myr at <600–700 °C). The slow cooling rate is comparable to those in mesosiderites and pallasites. The two‐stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that Dhofar 007 is a large inclusion of mesosiderite. However, we cannot rule out a possibility that Dhofar 007 is an anomalous eucrite.  相似文献   

10.
Zinner and Göpel ( 1992 , 2002 ) found clear evidence for the former presence of 26Al in the H4 chondrites Ste. Marguerite and Forest Vale. They assumed that the 26Al‐26Mg systematics of these chondrites date “metamorphic cooling of the H4 parent body.” Plagioclase in these chondrites can have very high Al/Mg ratios and low Mg concentrations, making these ion probe analyses susceptible to ratio bias, which is inversely proportional to the number of counts of the denominator isotope (Ogliore et al. 2011 ). Zinner and Göpel ( 2002 ) used the mean of the ratios to calculate the isotope ratios, which exacerbates this problem. We analyzed the Al/Mg ratios and Mg isotopic compositions of plagioclase grains in thin sections of Ste. Marguerite, Forest Vale, Beaver Creek, and Sena to evaluate the possible influence of ratio bias on the published initial 26Al/27Al ratios for these meteorites. We calculated the isotope ratios using total counts, a less biased method of calculating isotope ratios. The results from our analyses are consistent with those from Zinner and Göpel ( 2002 ), indicating that ratio bias does not significantly affect 26Al‐26Mg results for plagioclase in these chondrites. Ste. Marguerite has a clear isochron with an initial 26Al/27Al ratio indicating that it cooled to below 450 °C 5.2 ± 0.2 Myr after CAIs. The isochrons for Forest Vale and Beaver Creek also show clear evidence that 26Al was alive when they cooled, but the initial 26Al/27Al ratios are not well constrained. Sena does not show evidence that 26Al was alive when it cooled to below the Al‐Mg closure temperature. Given that metallographic cooling rates for Ste. Marguerite, Forest Vale, and Beaver Creek are atypical (>5000 °C/Myr at 500 °C) compared with most H4s, including Sena, which have cooling rates of 10–50 °C/Myr at 500 °C (Scott et al. 2014 ), we conclude that the Al‐Mg systematics for Ste. Marguerite, Forest Vale, and Beaver Creek are the result of impact excavation of these chondrites and cooling at the surface of the parent body, instead of undisturbed cooling at depth in the H chondrite parent body, like many have assumed.  相似文献   

11.
Abstract— Dynamic crystallization experiments performed with different container materials (Fe crucible, pure Pt wire loop, presaturated Pt wire loop) demonstrate the strong influence of Fe loss on texture, mineralogy and chemical zoning in olivine. The use of pure Pt wire loops results in severe Fe loss and prevents the development of strong Fe/Mg zoning in olivine in slower cooled runs (≤ 100 °C/h). Presaturated Pt wire loops reduce Fe loss to some extent but not completely. If severe Fe loss from the melt is avoided by the use of Fe crucibles, then cooling rates between 2000 and 1.2 °C/h yield textures, modal mineral abundances and Fe/Mg zoning in olivine comparable to natural porphyritic olivine chondrules. However, Fe gain from the crucible may possibly enhance Fe/Mg zoning in olivine for cooling rates < 10 °C/h. Therefore, it is concluded that the lower limit of cooling rates of porphyritic olivine chondrules derived from dynamic crystallization experiments is 10 °C/h, perhaps it is even lower, on the order of a few degrees Celsius per hour. This value is not significantly different from estimates for subsolidus temperatures based on the microstructure of chondrule minerals (Weinbruch and Müller, 1995). The lower limit of chondrule cooling rates of 100 °C/h advocated by Hewins (1988) and Radomsky and Hewins (1990) seems to be an artifact of the experimental technique, as their samples were crystallized in pure Pt wire loops.  相似文献   

12.
A culture of E. coli was initially subjected to brief exposures to heat for durations of 30–60 s, starting with a temperature of 270 °C. A stepwise increase of this temperature from 270 °C–750 °C and a sequential culturing led to the emergence of a strain of this bacterium with a much higher resistance to flash heating than the original culture possessed. This behaviour would have an important relevance to the survival of micro-organisms upon entering a planetary atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
Abstract— Crystallization of parent melts for nakhlites was experimentally studied under QFM ± 2 at one bar. Isothermal experiments suggest that melts having parent magma composition for nakhlites crystallize both augites and titanomagnetites at liquidus temperatures of 1144–1154 °C. Compositions of the augites are identical to those of phenocrystic core augites (En36–38Fs22–25Wo39–40) in nakhlites. No olivines crystallize from the isothermal runs, and solidus temperature is about 1000 °C. Linear‐cooling experiments were carried out at various cooling rates (1–17 °C/h) ranging from liquidus to solidus temperatures under similar pressure conditions to the isothermal runs. Augites, titanomagnetites, and fayalites crystallized in the cooling runs, but magnesian olivines never crystallized there. Magnesian core augite in the cooling runs has the same composition as those of nakhlites. Rims of augite crystals from the cooling runs of 1–4 °C/h consist of two layers, ferroan augite inner rim and hedenbergite outer rim, which are very similar to those in the Miller Range (MIL) 03346 nakhlite. Small amounts of pyroxferroite crystallized in mesostasis and augite rims from two cooling runs. Titanomagnetites from cooling runs never accompany ilmenite lamellae as seen in nakhlites, suggesting that the subsolidus cooling rate of the cooling runs was much more rapid than those of nakhlite intercumulus melts. The cooling experiments reproduce the crystallization processes of pyroxenes and the compositional change of residual melt for a rapidly cooled magma such as MIL 03346.  相似文献   

14.
Abstract— Olivine in the angritic meteorite Lewis Cliff (LEW) 86010 contains abundant exsolution lamellae of kirschsteinite. Compositional gradients adjacent to the interface in both host and lamellae were formed by diffusion of chemical components into and out of the lamellae during cooling and growth. We have compared these gradients with compositional profiles calculated from diffusion and heat flow equations to estimate the cooling rate and burial depth of the sample. The resulting values for cooling rate and burial depth depend on which values are used for the diffusion rate of Ca in olivine, and how measured diffusivities are extrapolated to the lower temperatures at which the lamellae grew. If the highest diffusion coefficients are used, the cooling rates obtained from seven different lamellae range from 30 to 52 °C/year, with an average of 42 °C/year, and burial depths (assuming an overburden with a thermal diffusivity typical of solid rock) range from 14 to 17 m, with an average of 15 m. If the lowest reasonable diffusion coefficients are used, the cooling rates range from 1.4 to 2.2 °C/year, with an average of 1.7 °C/year, and the depths range from 68 to 83 m, with an average of 75 m. For the highest Ca diffusivities, details of the compositional profiles near the olivine/kirschsteinite interface suggest that continuous cooling was greatly accelerated at a temperature near 600–700 °C. The simplest physical explanation for such an acceleration is excavation of the sample from its original burial depth by an impact event. If Ca diffusivities are lower, a two-stage cooling history is not required.  相似文献   

15.
Abstract— An important and poorly understood group of rocks found in the ancient lunar highlands is called “feldspathic granulitic impactites.” Rocks of the granulite suite occur at most of the Apollo highlands sites as hand samples, rake samples, clasts in breccias, and soil fragments. Most lunar granulites contain 70–80% modal plagioclase, but they can range from anorthosite to troctolite and norite. Previous studies have led to different interpretations for the thermal history of these rocks, including formation as igneous plutons, long-duration metamorphism at high temperatures, and short-duration metamorphism at low temperatures. This paper reports on a study of 24 polished thin sections of lunar granulites from the Apollo 15, 16, and 17 missions. We identify three different textural types of granulitic breccias: poikilitic, granoblastic, and poikilitic-granoblastic breccias. These breccias have similar equilibration temperatures (1100 ± 50 °C), as well as common compositions. Crystal size distributions in two granoblastic breccias reveal that Ostwald ripening took place during metamorphism. Solid-state grain growth and diffusion calculations indicate relatively rapid cooling during metamorphism (0.5 to 50 °C/year), and thermal modeling shows that they cooled at relatively shallow depths (<200 m). In contrast, we conclude that the poikilitic rocks formed by impact melting, whereas the poikilitic-granoblastic rocks were metamorphosed and may have partially melted. These results indicate formation of lunar granulites in relatively small craters (30–90 km in diameter), physically associated with the impact-melt breccia pile, and possibly from fine-grained fragmental precursor lithologies.  相似文献   

16.
Abstract— The distribution and petrography of surficial suevite breccias of the Ries impact crater in Southern Germany are reviewed, and the morphology, petrography and chemical composition of impact glasses in suevite breccias and their postdepositional devitrification is synthesized. Origin and thermal history of suevite breccia and suevite glasses are inferred from these data and from recent results of cooling and crystallization experiments with suevite glass melts under controlled conditions. In a montmorillonitic groundmass, the suevite breccia contains pieces of glass, up to some decimeters in size, and crystalline rock clasts of all stages of shock metamorphism. The glass particles originated in impact melt of basement gneisses and cooled by adiabatic pressure release from ～80 GPa to atmospheric pressure during ejection from the crater. They were deposited on the ground together with the other suevite components at a temperature of ～750 °C. Fractured glass pieces in the breccia show that during deposition of the suevite the temperature was below the temperature at which undercooled melt transforms to rigid glass. The suevite cooled after deposition mainly by convection of heat by emanating gases and vapors. In chilled layers at the base and at the top of suevite deposits, the glasses are preserved in vitreous state. Between these zones, the glasses were devitrified, yet crystallization of pyroxene, plagioclase and magnetite took place below the glass-transformation temperature. Annealing experiments show that this unusual devitrification below the transformation temperature can be explained by the impact origin of suevite glasses. Due to rapid adiabatic cooling on decompression, the glasses were oversaturated with water and internally strained. Under these conditions, devitrification, especially the formation of plagioclase, was possible at temperatures below the transformation range. The origin from adiabatically cooled impact melt of deep-seated rocks distinguishes water-bearing suevite glasses from the Ries-derived, water-free moldavite tektites, which are interpreted as condensates of vaporized, surficial sediments (Engelhardt et al., 1987).  相似文献   

17.
L. Wallace 《Icarus》1983,54(1):110-132
A series of time-dependent radiative/convective models are presented for the atmosphere of Uranus. The effects of atmospheric dynamics have been omitted from the models. The inclination of the pole of rotation to the pole of the orbit, approximately 90°, produces large seasonal changes in the insolation. Because of the relatively small flow of heat from the interior, these seasonal changes cause the effective temperature, which is about 60°K, to vary through the 84-year orbital period by ～5°K at the poles, ～4°K at ±60° latitude, ～2°K at ±30° latitude, and ～0.5°K at the equator. For a particular latitude, the minimum effective temperature and the maximum convective flow of heat from the interior occur near the end of the period when the sun remains below the horizon during the Uranian day. If the methane mixing ratio is not limited by its saturated vapor pressure (SVP) in the convective region, the maximum convective flow would be a few times the orbital average convective flow and persist for an interval of several years. On the other hand, if the methane mixing ratio is limited by its SVP in the convective regions, the maximum convective flow could be orders of magnitude greater than the orbital average and could persist for less than an hour. If the orbital mean internal heat flow is negligible, the difference in effective temperatures between 30 and 60° latitude would be in the range 2 to 4°K. If the internal heat is taken to be about the maximum allowable and is assumed to be redistributed in the interior in a manner to compensate for the minimum in insolation at low latitudes, the corresponding temperature difference would be in the range 12 to 2°K. In either case, the existing theory of atmospheric dynamics for the outer planets indicates that such large temperature differences will drive large-scale motions which would in turn reduce these temperature differences.  相似文献   

18.
Poorly-graphitised carbon particles are formed during manufacture of sample substrates (holey carbon films) for Analytical Electron Microscopy studies of small particles. The particles form during heat treatment of cellulose acetobutyrate at about 975 °C and 1050 °C. In AEM studies of fine-grained carbonaceous extraterrestrial materials, these particles are easily recognised.  相似文献   

19.
Abstract— Studies of lunar meteorite Dhofar 026, and comparison to Apollo sample 15418, indicate that Dhofar 026 is a strongly shocked granulitic breccia (or a fragmental breccia consisting almost entirely of granulitic breccia clasts) that experienced considerable post‐shock heating, probably as a result of diffusion of heat into the rock from an external, hotter source. The shock converted plagioclase to maskelynite, indicating that the shock pressure was between 30 and 45 GPa. The post‐shock heating raised the rock's temperature to about 1200 °C; as a result, the maskelynite devitrified, and extensive partial melting took place. The melting was concentrated in pyroxene‐rich areas; all pyroxene melted. As the rock cooled, the partial melts crystallized with fine‐grained, subophitic‐poikilitic textures. Sample 15418 is a strongly shocked granulitic breccia that had a similar history, but evidence for this history is better preserved than in Dhofar 026. The fact that Dhofar 026 was previously interpreted as an impact melt breccia underscores the importance of detailed petrographic study in interpretation of lunar rocks that have complex textures. The name “impact melt” has, in past studies, been applied only to rocks in which the melt fraction formed by shock‐induced total fusion. Recently, however, this name has also been applied to rocks containing melt formed by heating of the rocks by conductive heat transfer, assuming that impact is the ultimate source of the heat. We urge that the name “impact melt” be restricted to rocks in which the bulk of the melt formed by shock‐induced fusion to avoid confusion engendered by applying the same name to rocks melted by different processes.  相似文献   

20.
We report the first combined atom‐probe tomography (APT) and transmission electron microscopy (TEM) study of a kamacite–tetrataenite (K–T) interface region within an iron meteorite, Bristol (IVA). Ten APT nanotips were prepared from the K–T interface with focused ion beam scanning electron microscopy (FIB‐SEM) and then studied using TEM followed by APT. Near the K‐T interface, we found 3.8 ± 0.5 wt% Ni in kamacite and 53.4 ± 0.5 wt% Ni in tetrataenite. High‐Ni precipitate regions of the cloudy zone (CZ) have 50.4 ± 0.8 wt% Ni. A region near the CZ and martensite interface has <10 nm sized Ni‐rich precipitates with 38.4 ± 0.7 wt% Ni present within a low‐Ni matrix having 25.5 ± 0.6 wt% Ni. We found that Cu is predominantly concentrated in tetrataenite, whereas Co, P, and Cr are concentrated in kamacite. Phosphorus is preferentially concentrated along the K‐T interface. This study is the first precise measurement of the phase composition at high spatial resolution and in 3‐D of the K‐T interface region in a IVA iron meteorite and furthers our knowledge of the phase composition changes in a fast‐cooled iron meteorite below 400 °C. We demonstrate that APT in conjunction with TEM is a useful approach to study the major, minor, and trace elemental composition of nanoscale features within fast‐cooled iron meteorites.  相似文献   

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