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Here we document the occurrence of phyllosilicates and alteration phases in three martian meteorites, suggest formation conditions required for phyllosilicate formation and speculate on the extent of fluid:rock interactions during the past history of Mars.
A reexamination of a piece of the Orgueil meteorite revealed that its amino acid composition is strikingly different to two other carbonaceous chondrites, suggesting different parent bodies. A cometary origin for Orgueil would be one possibility.
Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 microns in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnets, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27/o of ALH84001 magnetite particles. also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates.
Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 nm in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnetites, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27% of ALH84001 magnetite particles, also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates. Additional information is contained in the original extended abstract.
We have studied the microdomain oxygen and carbon isotopic compositions by SIMS of complex carbonate rosettes from spinel therzolite xenoliths, hosted by nepheline basanite, from the island of Spitsbergen (Norway). The Quaternary volcanic rocks containing the xenoliths erupted into a high Arctic environment and through relatively thick continental crust containing carbonate rocks. We have attempted to constrain the sources of the carbonates in these rocks by combined O-18/O-16 and C-13/C-12 ratio measurements in 25 micron diameter spots of the carbonate and compare them to previous work based primarily on trace-element distributions. The origin of these carbonates can be interpreted in terms of either contamination by carbonate country rock during ascent of the xenoliths in the host basalt, or more probably by hydrothermal processes after emplacement. The isotopic composition of these carbonates from a combined delta.18O(sub SMOW) and delta.13C(sub PDB) standpoint precludes a primary origin of these minerals from the mantle. Here a description is given of the analysis procedure, standardization of the carbonates, major element compositions of the carbonates measured by electron microprobe, and their correlated C and O isotope compositions as measured by ion microprobe. Since these carbonate rosettes may represent a terrestrial analogue to the carbonate "globules" found in the martian meteorite ALH84001 interpretations for the origin of the features found in the Spitsbergen may be of interest in constraining the origin of these carbonate minerals on Mars.
This paper proposes tests for exobiological examination of samples prior to obtaining martian rocks of known provenance via future sample-return missions. If we assume that all of the secondary minerals in martian meteorite ET79001 were indeed cogenetic and originate from Mars, we list conclusions that can be drawn that are of exobiological interest. This work serves as a preamble for the subsequent work listed below.
Ion microprobe oxygen isotopic measurements of a chemically diverse suite of carbonates from Martian meteorite ALH84001 are reported. The delta(sup 18)O values are highly variable, ranging from +5.4 to + 25.3%, and are correlated with major element compositions of the carbonate. The earliest forming (Ca-rich) carbonates have the lowest delta(sup 18)O values and the late-forming (Mg-rich) carbonates have the highest delta(sup 18)O values. Two models are presented which can explain the isotopic variations. The carbonates could have formed in a water rich environment at relatively low, but highly variable temperatures. In this open-system case the lower limit to the temperature variation is approx. 125 C, with fluctuations of over 250 C possible within the constraints of the model. Alternatively, the data can be explained by a closed-system model in which the carbonates precipitated from a limited amount of CO2-rich fluid. This scenario can reproduce the isotopic variations observed at a range of temperatures, including relatively high temperatures (less than 500 C). Thus the oxygen isotopic compositions do not provide unequivocal evidence for formation of the carbonates at low temperature. Although more information is needed in order to distinguish between the models, neither of the implied environments is consistent with biological activity. Thus, we suggest that features associated with the carbonates which have been interpreted to be the result of biological activity were most probably formed by inorganic processes.
Olivine from Martian meteorite Allan Hills (ALH) 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass. The inclusions are irregular in shape and range in size from approx. 40 microns to submicrometer. Some of the inclusions are elongate and boudinage-like. The olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite The olivine exhibits a very limited range of composition from Fo(sub 65) to Fo(sub 66) (n = 25). The delta(sup 18)O values of the olivine and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3% and are indistinguishable from each other within analytical uncertainty. The mineral chemistries, O-isotopic data, and textural relationships indicate that the olivine inclusions were produced at a temperature greater than 800 C. It is unlikely that the olivines formed during the same event that gave rise to the carbonates in ALH 84001, which have more elevated and variable delta(sup 18)O values, and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine The reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel If the olivine was formed by either reaction during a postcarbonate beating event, the implications are profound with regards to the interpretations of McKay et al. Due to the low diffusion rates in carbonates, this rapid, high-temperature event would have resulted in the preservation of the fine-scale carbonate zoning' while partially devolatilizing select carbonate compositions on a submicrometer scale. This may have resulted in the formation of the minute magnetite grains that McKay et al attributed to biogenic activity.
The composition of the parent magma for the Nakhla (martian) meteorite has been estimated from mineral-melt partitioning and from magmatic inclusions in olivine and in augite. These independent lines of evidence have converged on small range of likely compositions. Additional information is contained in the original extended abstract.
We use high temperature TL data to evaluate perihelia of Antarctic meteorites. Perihelion has been constant for the ordinary chondrites over the last 40,000-100,000 years. Additional information is contained in the original extended abstract.
New I-Xe data obtained for magnetic separates from CV3 meteorites Kaba, Bali, Mokoia. Additional information is contained in the original extended abstract.
This document discusses Antarctic meteorite stranding surfaces and complex ice emergent mechanisms. Additional information is contained in the original extended abstract.
Two new HED meteorites are described. GRA98108 is an olivine-bearing diogenite at the Mg-rich end of the diogenite clan. GRA98030 is a howardite with 30% eucritic and 70% diogenitic clasts, and contains an MgO-rich and CaO- and Al2O3-poor glassy spherule. Additional information is contained in the original extended abstract.
Low-level doped solid metal/liquid metal experiments analyzed by laser ablation ICP-MS allow Henry's Law to be tested. The results indicate Henry's Law is obeyed and the experimental partition coefficients can be applied to iron meteorites. Additional information is contained in the original extended abstract.
New data from SNC meteorites suggests that organic material may be present in the martian upper crust. This adds to possibility that the Viking biology experiments may have plausible biological interpretations as well as inorganic chemical interpretations Additional information is contained in the original extended abstract..
Re-Os on metal and schreibersite in iron meteorites provides the potential for the determination of internal isochrons for irons. This is applied to Wallapai (IID) and other samples. Additional information is contained in the original extended abstract.
Cosmogenic Be-10, Al-26, Cl-36, Ca-41, and Ni-59 were measured in the Campo del Cielo iron meteorite. Our results led us to conclude that the pre-atmospheric radius might have been approximately 2 m. Comparisons with other big bodies are also presented. Additional information is contained in the original extended abstract.
We present concentrations of cosmogenic radionuclides in 15 ordinary chondrites with low He-3/Ne-31 ratios. We identified only one or two meteorites with a complex exposure history, whereas the others are consistent with single-stage exposures. Additional information is contained in the original extended abstract.