Oxygen isotope variation in stony-iron meteorites

Asteroidal material, delivered to Earth as meteorites, preserves a record of the earliest stages of planetary formation. High-precision oxygen isotope analyses for the two major groups of stony-iron meteorites (main-group pallasites and mesosiderites) demonstrate that each group is from a distinct asteroidal source. Mesosiderites are isotopically identical to the howardite-eucrite-diogenite clan and, like them, are probably derived from the asteroid 4 Vesta. Main-group pallasites represent intermixed core-mantle material from a single disrupted asteroid and have no known equivalents among the basaltic meteorites. The stony-iron meteorites demonstrate that intense asteroidal deformation accompanied planetary accretion in the early Solar System.     

Phosphide from metorites: barringerite, a new iron-nickel mineral

Schreibersite, (Fe,Ni)(3)P, and a higher phosphide, barringerite, occur in the Ollague pallasite. The composition of the higher phosphide, determined by electron probe microanalysis, is (Fe(0.58)Ni(0.42)Co(0.003))(1.95)P. It is hexagonal, with space group P62m and a = 5.87 +/- 0.07 angstroms and c = 3.44 +/- 0.04 angstroms. If we assume a primary origin, the new mineral indicates that troilite and schreibersite crystallized at high temperatures. The occurrence of a higher phosphide in a pallasite indicates local nonequilibria within a group of meteorites that are remarkable for their overall degree of equilibrium crystallization.     

Djerfisherite, alkali copper-iron sulfide: a new mineral from enstatite chondrites

A new mineral, essentially a potassium-copper-iron sulfide, occurs in accessory amounts in the enstatite chondrites Kota Kota (a find) and St. Marks (a fall), and has been identified visually in the enstatite achondrite Pena Blanca Springs (a fall). The x-ray diffraction pattern, electron-microprobe analysis, and its appearance in polished sections all serve to identify it.     

A new source of basaltic meteorites inferred from Northwest Africa 011

Eucrites are a class of basaltic meteorites that share common mineralogical, isotopic, and chemical properties and are thought to have been derived from the same parent body, possibly asteroid 4 Vesta. The texture, mineralogy, and noble gas data of the recently recovered meteorite, Northwest Africa (NWA) 011, are similar to those of basaltic eucrites. However, the oxygen isotopic composition of NWA011 is different from that of other eucrites, indicating that NWA011 may be derived from a different parent body. The presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies, perhaps similar to 4 Vesta, in the early solar system.     

Cliftonite in meteorites: a proposed origin

Cliftonite, a polycrystalline aggregate of graphite with cubic morphology, is known in ten meteorites. Some workers have considered it to be a pseudomorph after diamond, and have used the proposed diamond ancestry as evidence of a meteoritic parent body of at least lunar dimensions.We have synthesized cliftonite in Fe-Ni-C alloys in vacuumn, as a product of decomposition of cohenite [(Fe, Ni)(3)C]. We therefore suggest that a high pressure origin is unnecessary for meteorites which contain cliftonite, and that these meteorites were formed at low pressures. This concluision is in agreement with other recent evidence.     

Cohenite in meteorites: a proposed origin

Cohenite [(Fe, Ni)(3)C] is found almost exclusively in meteorites containing from 6 to 8 percent nickel (by weight). On the basis of iron-nickel-carbon phase diagrams at 1 atmosphere and of kinetic data, the occurrence of cohenite within this narrow composition range as a low-pressure metastable phase and the nonoccurrence of cohenite in meteorites outside the range 6 to 8 percent nickel can be explained. Cohenite formed in meteorites containing less than 6 to 8 percent nickel decomposed to metal and graphite during cooling; it cannot form in meteorites containing more than about 8 percent. The presence of cohenite in meteorites cannot be used as an indicator of pressure of formation. However, the absence of cohenite in meteorites containing the assemblage, metal plus graphite, requires low pressures during cooling.     

Catch a falling star: meteorites and old ice

A model for the process of meteorite concentration in blue ice regions of the Antarctic ice sheet is proposed based on data from near the Allan Hills and the assumptions that both meteorite influx and glacial flow have been constant. The meteorite influx is calculated to be 60 x 10(-6) kilogram per square kilometer per year, and the age of the exposed ice to be 0 to 600,000 years, varying with distance from the Allan Hills. These results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites, providing support for the assumption of steady flow and meteorite influx. This may be the oldest sequence of ice in stratigraphic order yet discovered, and the results imply that this part of the east Antarctic ice sheet has been approximately steady during this time interval.     

Martian surface paleotemperatures from thermochronology of meteorites

The temporal evolution of past martian surface temperatures is poorly known. We used thermochronology and published noble gas and petrographic data to constrain the temperature histories of the nakhlites and martian meteorite ALH84001. We found that the nakhlites have not been heated to more than 350 degrees C since they formed. Our calculations also suggest that for most of the past 4 billion years, ambient near-surface temperatures on Mars are unlikely to have been much higher than the present cold (<0 degrees C) state.     

一种新型磷酸钛的溶剂热法合成与表征

采用溶剂热合成方法，以乙二胺为模板剂，在正丁醇溶剂体系中合成出一种新型磷酸钛，并通过X-射线衍射分析，红外光潜分析，差热-热重分析对其进行了表征。     

Gas-rich meteorites: possible evidence for origin on a regolith

The asymmetry of irradiation features of grains in the Kapoeta and Fayetteville meteorites suggests irradiation on a regolith before meteorite formation. Chondrules and broken grains require approximately 10(4) years of irradiation time between formation or fracturing and compaction into the meteorite. Shock erasure of tracks from irradiated Kapoeta feldspars requires a severe shock event during or after meteorite formation.     

Hexagonal diamonds in meteorites: implications

A new polymorph of carbon, hexagonal diamond, has been discovered in the Canyon Diablo and Goalpara meteorites. This phase had been synthesized recently under specific high-pressure conditions in the laboratory. Our results: provide strong evidence that diamonds found in these meteorites were produced by intense shock pressures acting on crystalline graphite inclusions present within the meteorite before impact, rather than by disintegration of larger, statically grown diamonds, as some theories propose.     

Magnetic particles extracted from manganese nodules: suggested origin from stony and iron meteorites

On the basis of x-ray diffraction and electron microprobe data, spherical and ellipsoidal particles extracted from manganese nodules were divided into three groups. Group 1 particles are believed to be derived from iron meteorites, and Group 11 particles from stony meteorites. Group III particles are believed to be volcanic in origin.     

History of meteorites from the moon collected in antarctica

In large asteroidal or cometary impacts on the moon, lunar surface material can be ejected with escape velocities. A few of these rocks were captured by Earth and were recently collected on the Antarctic ice. The records of noble gas isotopes and of cosmic ray-produced radionuclides in five of these meteorites reveal that they originated from at least two different impact craters on the moon. The chemical composition indicates that the impact sites were probably far from the Apollo and Luna landing sites. The duration of the moon-Earth transfer for three meteorites, which belong to the same fall event on Earth, lasted 5 to 11 million years, in contrast to a duration of less than 300,000 years for the two other meteorites. From the activities of cosmic ray-produced radionuclides, the date of fall onto the Antarctic ice sheet is calculated as 70,000 to 170,000 years ago.     

X-ray diffraction study of minerals from shocked iron meteorites

Diffraction analysis of minerals from iron meteorites indicates a pronounced shock-induced alteration in the minerals' crystallographic character. The extent of alteration seems to be dependent on the degree of shock and can therefore serve as a measure of shock intensity. The changes appear to be due to the minerals' direct recrystallization during passage of the shock wave.     

Interstellar chemistry recorded in organic matter from primitive meteorites

Organic matter in extraterrestrial materials has isotopic anomalies in hydrogen and nitrogen that suggest an origin in the presolar molecular cloud or perhaps in the protoplanetary disk. Interplanetary dust particles are generally regarded as the most primitive solar system matter available, in part because until recently they exhibited the most extreme isotope anomalies. However, we show that hydrogen and nitrogen isotopic compositions in carbonaceous chondrite organic matter reach and even exceed those found in interplanetary dust particles. Hence, both meteorites (originating from the asteroid belt) and interplanetary dust particles (possibly from comets) preserve primitive organics that were a component of the original building blocks of the solar system.     

Potassium: argon dating of iron meteorites

The potassium:argon age of the metal phase of Weekeroo Station iron meteorite, determined by neutronactivation analysis, is about 10(10) years; it is similar to ages previously measured for other iron meteorites, but distinctly disagrees with a strontium: rubidium age of 4.7 X 10(9) years measured by other workers on silicate inclusions in this meteorite.