Ernst Florens Friedrich Chladni (1756–1827) and the origins of modern meteorite research

Abstract— In 1794, Ernst F. F. Chladni published a 63-page book Über den Ursprung der von Pallas gefundenen und anderer ihr änlicher Eisenmassen und über einige damit in Verbindung stehende Naturerscheinungen in which he proposed that meteor-stones and iron masses enter the atmosphere from cosmic space and form fireballs as they plunge to Earth. These ideas violated two strongly held contemporary beliefs: (1) fragments of rock and metal do not fall from the sky, and (2) no small bodies exist in space beyond the Moon. From the beginning, Chladni was severely criticised for basing his hypotheses on historical eyewitness reports of falls which others regarded as folk tales and for taking gross liberties with the laws of physics. Eight years later, the study of fallen stones and irons was established as a valid field of investigation. Today, some scholars credit Chladni with founding meteoritics as a science; others regard his contributions as scarcely worthy of mention. Writings by his contemporaries suggest that Chladni's book alone would not have led to changes of prevailing theories; thus, he narrowly escaped the fate of those scientists who propose valid hypotheses prematurely. However between 1794 and 1798, four falls of stones were witnessed and widely publicized. There followed a series of epoch-making analyses of fallen stones and “native irons” by the chemist Edward C. Howard and the mineralogist Jacques-Louis de Bournon. They showed that all the stones were much alike in texture and composition but significantly different from the Earth's known crustal rocks. Of primary importance was Howard's discovery of nickel in the irons and the metal grains of the stones. This linked the two as belonging to the same natural phenomenon. The chemical results, published in 1802 February, persuaded leading scientists in England, France, and Germany that bodies fall from the sky. Within a few months, chemists in France reported similar results and a new field of study was inaugurated internationally—although opposition lingered on until 1803 April, when nearly 3,000 stones fell at L'Aigle in Normandy and transformed the last skeptics into believers. Chladni immediately received full credit for his hypothesis of falls, but decades passed before his linking of falling bodies with fireballs received general acceptance. His hypothesis of their origin met with strong resistance from those who argued that stones formed within the Earth's atmosphere or were ejected by lunar volcanoes. After 1860, when both of these hypotheses were abandoned, there followed a century of debate between proponents of an interstellar vs. a planetary origin. Not until the 1950s did conclusive evidence of their elliptical orbits establish meteorite parent bodies as members of the solar system. Thus, nearly 200 years passed before the questions of origin that Chladni raised finally were resolved.     

Shock features in iron-nickel metal and troilite of L-group ordinary chondrites

Abstract— Shock metamorphic features in opaque minerals (FeNi metal and troilite) of 22 L chondrites have been studied petrographically and geochemically in an attempt to establish a connection between the present silicate-based shock classification scheme (Stöffler et al., 1991) and the peak-shock and postshock thermal history recorded in these minerals. Unshocked to weakly shocked (S1–S3) L chondrites contain FeNi metal and troilite that display textures related to normal, slow cooling. They may also contain rare disequilibrium shock features, which suggest localized departures from equilibrium shock conditions. Above shock stage S3, selected melting of FeNi metal and troilite produces melt droplets whose composition and abundance correspond to the maximum equilibrium shock state achieved by the sample. At these higher shock levels, the abundance of other shock-induced features, such as polycrystalline kamacite, sheared and fizzed troilite, coarse-grained pearlitic plessite, polycrystalline troilite, and polymineralic melt veins serve as textural criteria that can be used to establish peak-shock conditions. Minimum postshock temperatures obtained from analyses of plessite components show a systematic increase in temperature with an increase in shock stage, thereby providing additional information about the postshock thermal histories of L chondrites. At the highest shock levels recorded in L chondrites (S6 and above), melting and chemical homogenization of FeNi metal produces flattened Ni profiles that may partially to completely obscure any evidence for an earlier, slow-cooling history. All of these features serve as aids for shock classifying L chondrites as well as for quantifying minimum peak temperatures that resulted during shock metamorphism.     

THE METEORITICAL SOCIETY: 1933 to 1993

Abstract— In August, 1933, at the Field Museum of Natural History in Chicago, The Society for Research on Meteorites was founded with an enrollment of 57 charter members and Frederick C. Leonard and Harvey H. Nininger as the first President and Secretary-Treasurer, respectively. Within five years, the Society had doubled in size, with members from the U.S.A. and ten other nations. Annual meetings were suspended during World War II (1942 through 1945) and when it reconvened in 1946 the members adopted the name “The Meteoritical Society”. By that time personal and professional antagonisms had arisen that threatened to fragment the Society and led, in 1949, to the resignation of Nininger and his wife. Throughout the 1950s the Society was widely regarded as a small, disorganized and essentially moribund organization. Revitalization of the Society began in the early 1960s after the advent of the Space Age when the Society steadily gained members with expertise in mineralogy, petrology, isotope geochemistry, electron microprobe and neutron activation analysis, and impact dynamics. When Nininger was persuaded rejoin in 1963, he found a renewed Society. In the election year of 1966 a group of youthful insurgents nominated an alternate slate to that proposed by the Council and won every contested seat on the Council except that of the Editor. The Society's first publication Contributions of the Society for Research on Meteorites was published as a section of Popular Astronomy and from 1935 to 1946 reprints of the items (articles, reviews, and notices) were bound and distributed separately each year. When the Society changed its name in 1946, its journal became Contributions of the Meteoritical Society, which continued publication until Popular Astronomy ceased publication in 1952. A new journal, Meteoritics, was instituted in 1953. After 1956, its publication lapsed for six years but began again in 1963 and has continued under the leadership of four successive editors becoming one of the most frequently cited geoscience journals. In 1970, the Society also became a co-sponsor with The Geochemical Society of Geochimica et Cosmochimica Acta, but the future of this arrangement remains in doubt. In 1938, the Society had gained considerable prestige by its acceptance as a full Affiliate of the American Association for the Advancement of Science, but in view of its increasingly international membership and activities the Society terminated its affiliation with the AAAS in 1976. Again in response to its international status, in 1992 The Meteoritical Society affiliated with the International Union of Geological Sciences. The Society held its first annual meeting outside North America at the Universität Tübingen in West Germany in 1971. Subsequently, it met in Europe every second year until 1990, when it met at Perth in Western Australia. During the 1980s, the membership of the Society grew to more than 900 and the annual meetings attracted between 300 and 450 participants. As meteoritical research continues to probe the borderlands with astrophysics, planetary science, and terrestrial geology, and as younger members assume leadership roles, a productive future seems assured for both meteoritical science and The Meteoritical Society.     

Vibroseis productivity: shake and go

We use both model and field data to compare three methods for increasing vibroseis productivity and decreasing acquisition costs. The first method, HFVS (high-fidelity vibratory seismic), allows us to separate the responses from individual vibrators when multiple vibrators are operating simultaneously. The data quality of the separated records is superior to that of conventional correlated data because they are processed with measured ground-force signals, but the number of sweeps must be greater than or equal to the number of vibrators. The second method, cascaded sweep, eliminates the listening time between multiple sweeps and partially mitigates harmonic noise observed at later times on near-offset traces. Finally, a combined method, continuous-HFVS (C-HFVS), allows source separation with a single, long, segmented sweep. Separation is as good as with HFVS and interference noise is limited to times near the end of a sweep-segment length. All three methods produce acceptable seismic images for post-stack and prestack amplitude interpretation.
The choice of which option to use depends upon the area being investigated. HFVS has numerous benefits, especially when fine sampling is required to mitigate static problems and elevation changes. Due to the ability to separate individual responses, fine sampling can be achieved without sacrificing productivity. For deeper targets, cascaded sweep can be more efficient but data quality suffers from harmonic noise. C-HFVS, which combines features of HFVS and cascaded sweep, has the potential to result in the highest productivity, without sacrificing either fine sampling or data quality.     

Geochemistry, strontium isotope data, and potassium-argon ages of the andesite-rhyolite association in the Padang area, West Sumatra

Quaternary volcanoes in the Padang area on the west coast of Sumatra have produced two-pyroxene, calc-alkaline andesite and volumetrically subordinate rhyolitic and andesitic ash-flow tuffs. A sequence of andesite (pre-caldera), rhyolitic tuff and andesitic tuff, in decreasing order of age, is related to Maninjau caldera. Andesite compositions range from 55.0 to 61.2% SiO₂ and from 1.13 to 2.05% K₂O. Six K-Ar whole-rock age determinations on andesites show a range of 0.27 ± 0.12 to 0.83 ± 0.42 m.y.; a single determination on the rhyolitic ashflow tuff gave 0.28 ± 0.12 m.y.Eight ⁵⁷Sr/²⁶Sr ratios on andesites and rhyolite tuff west of the Semangko fault zone are in the range 0.7056 – 0.7066. These ratios are higher than those elsewhere in the Sunda arc but are comparable to the Taupo volcanic zone of New Zealand and calc-alkaline volcanics of continental margins. An ⁸⁷Sr/⁸⁶Sr ratio of 0.7048 on G. Sirabungan east of the Semangko fault is similar to an earlier determination on nearby G. Marapi (0.7047), and agrees with ⁸⁷Sr/⁸⁶Sr ratios in the rest of the Sunda arc. The reason for this distribution of ⁸⁷Sr/⁸⁶Sr ratios is unknown.The high ⁸⁷Sr/⁸⁶Sr ratios are tentatively regarded to reflect a crustal source for the andesites, while moderately fractionated REE patterns with pronounced negative Eu anomalies suggest a residue enriched in plagioclase with hornblende and/or pyroxenes. Generation of associated andesite and rhyolite could have been caused by hydrous fractional melting of andesite or volcanogenic sediments under adiabatic decompression.     

Geochemical modelling of basalts from DSDP Leg 65, East Pacific Rise,Gulf of California

Major and rare earth element (REE) data for basalts from Holes 483, 483B, and 485A of DSDP Leg 65, East Pacific Rise, mouth of the Gulf of California, support a simple fractional crystallization model for the genesis of rocks from this suite. The petrography and mineral chemistry (presented in detail elsewhere) provide no evidence for magma mixing, but rather a simple multistage cooling process. Based on its lowest TiO₂ content (0.88%), $\text{FeO}{}^1\text{MgO}$ ratio (0.95 with total Fe as FeO), and Mg# (100 $\text{Mg}\text{Mg + Fe}\text{″ = 70}$), sample 483-17-2-(78–83) has been selected as the most primitive primary magma of the samples analyzed. This is supported by the REE data which show this sample has the lowest total REE content, a $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (chondrite-normalized) = 0.36, and $\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ = 1.05. Because other samples analyzed have higher SiO₂, lower Mg#, and a negative Eu anomaly ($\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ as low as 0.89), they are most likely derivative magmas. Wright-Doherty and trace element modelling support fractional crystallization of 14.1% plagioclase (An₈₈), 6.7% olivine (Fo₈₆), and 4.7% clinopyroxene (Wo₄₁En₄₉Fs₁₀) from 483-17-2-(78–83) to form the least differentiated sample with Mg# = 63. The $\text{La}\text{Sm}{}_{\mathrm{cn}}$ of this derivative magma is almost identical to the parent magma (0.35 to 0.36), but the other samples have higher $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (0.45 to 0.51), more total REE, and lower Mg# (60 to 56). Both Wright-Doherty and trace element modelling indicate that the primary magma chosen cannot produce these more evolved samples. For the major elements, the TiO₂ and P₂O₅ are too low in the calculated versus the observed (1.38 to 1.90; 0.11 to 0.17, respectively, for example). Rayleigh fractionation calculates a lower $\text{La}\text{Sm}{}_{\mathrm{cn}}$ and requires about 60% crystal removal versus 40% for the Wright-Doherty. These more evolved samples must be derived from a parent magma different from the one selected here and, unfortunately, not sampled in this study. A magma formed by a smaller degree of partial melting with slightly more residual clinopyroxene left in the mantle than for sample 483-17-2-(78–83) is required.     

40Ar/39Ar age spectra of some undisturbed terrestrial samples

⁴⁰Ar/³⁹Ar age spectra and ⁴⁰Ar/³⁶Ar vs ³⁹Ar/³⁶Ar isochrons were determined by incremental heating for 11 terrestrial rocks and minerals whose geology indicates that they represent essentially undisturbed systems. The samples include muscovite, biotite, hornblende, sanidine, plagioclase, dacite, diabase and basalt and range in age from 40 to 1700 m.y. For each sample, the ⁴⁰Ar/³⁹Ar ratios, corrected for atmospheric and neutron-generated argon isotopes, are the same for most of the gas fractions released and the age spectra, which show pronounced plateaus, thus are consistent with models previously proposed for undisturbed samples. Plateau ages and isochron ages calculated using plateau age fractions are concordant and appear to be meaningful estimates of the crystallization and cooling ages of these samples. Seemingly anomalous age spectrum points can be attributed entirely to small amounts of previously unrecognized argon loss and to gas fractions that contain too small (less than 2 per cent) a proportion of the ³⁹Ar released to be geologically significant. The use of a quantitative abscissa for age spectrum diagrams is recommended so that the size of each gas fraction is readily apparent. Increments containing less than about 4–5 per cent of the total ³⁹Ar released should be interpreted cautiously. Both the age spectrum and isochron methods of data reduction for incremental heating experiments are worthwhile, as each gives slightly different but complementary information about the sample from the same basic data. Use of a least-squares fit that allows for correlated errors is recommended for ⁴⁰Ar/³⁶Ar vs ³⁹Ar/³⁶Ar isochrons. The results indicate that the ⁴⁰Ar/³⁹Ar incremental heating technique can be used to distinguish disturbed from undisturbed rock and mineral systems and will be a valuable geochronological tool in geologically complex terranes.     

PETROLOGICAL CHARACTER OF THE LUNA 16 SAMPLE FROM MARE FECUNDITATIS

We have classified 1858 lithic and vitreous fragments from the Luna 16 core-tube sample. They were taken from the soil fractions ranging in size from 150 to 425 μ, at levels A and G (γ). No important differences are observed between the proportions of particle types in levels A and G, nor between the soils of Luna 16 and those from the Apollo 11 landing site in the nearby Mare Tranquillitatis. Luna 16 basalts are texturally and mineralogically similar to Apollo 11 basalts, though the former are characterized by more Fe-rich olivines and pyroxenes and by lower ilmenite contents than are Apollo 11 basalts. The atomic ratio Al/Ti in Luna 16 basalt pyroxenes in about 1.5; Apollo 11 basalt pyroxenes have Al/Ti = 2.0, indicating the possibility of a lower mean valence for Ti in the Luna 16 material than in the Apollo 11 material. Most light-colored lithic fragments are anorthositic rather than noritic in character and are comparable to Apollo 11 anorthosites in mineral chemistry. We believe they are samples of terra regions to the north of the Luna 16 landing site. Triangular diagrams plotting normative plagioclase, normative mafics plus oxides, and normative orthoclase plus apatite neatly separate the three major types of lunar materials — mare basalts, anorthosites, and noritic rocks — and reveal that the Luna 16 regolith is composed of mare basalt and anorthosite, with very little norite component. Colorless-to-greenish glass occurs in the Luna 16 sample, which has high Fe and low Ti; it may represent gabbroic rock related to the anorthosites