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31.
Anthony J. Crawford 《Contributions to Mineralogy and Petrology》1981,75(4):353-367
The Howqua Olivine Pyroxenite of eastern Victoria, Australia, intrudes a metamorphosed sequence of Cambrian high-Mg lavas. It crystallized an unusual mineral assemblage: Cr-rich magnesiochromite, olivine (Fo94), and protoenstatite (now inverted to polysynthetically-twinned clinoenstatite). Residual liquid crystallized strongly-zoned interstitial pyroxenes followed by pargasite. Pargasite, often showing quench habit, crystallized in interstitial glass which is now altered to serpentine.The extremely refractory nature of the cumulus phases indicates a very high temperature of crystallization for liquidus olivine and chromite from a high-MgO, low-Al2O3 parent liquid similar in some respects to Archaean peridotitic komatiites. The suggested origin by hydrous melting of depleted mantle peridotite, plus other compositional and mineralogical similarities (especially the olivine-liquid reaction producing protoenstatite) indicate that the parent magma of the Howqua Olivine Pyroxenite had many features in common with the high-SiO2, high-MgO clinoenstatite-bearing boninitic lavas of the Western Pacific. It is interpreted as a more extreme melt with affinities to boninite and it demonstrates that ultramafic magmas existed in the Cambrian. 相似文献
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An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples
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Louise Alexander Joshua F. Snape Katherine H. Joy Hilary Downes Ian A. Crawford 《Meteoritics & planetary science》2016,51(9):1654-1677
Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance. 相似文献
35.
Katherine H. Joy Ian A. Crawford Hilary Downes Sara S. Russell Anton T. Kearsley 《Meteoritics & planetary science》2006,41(7):1003-1025
Abstract— LaPaz Icefield (LAP) 02205, 02226, and 02224 are paired stones of a crystalline basaltic lunar meteorite with a low‐Ti (3.21–3.43% TiO2) low‐Al (9.93–10.45% Al2O3), and low‐K (0.11–0.12% K2O) composition. They consist mainly of zoned pyroxene and plagioclase grains, with minor ilmenite, spinel, and mesostasis regions. Large, possibly xenocrystic, forsteritic olivine grains (<3% by mode) contain small trapped multiphase melt inclusions. Accessory mineral and mesostasis composition shows that the samples have experienced residual melt crystallization with silica oversaturation and late‐stage liquid immiscibility. Our section of LAP 02224 has a vesicular fusion crust, implying that it was at one time located sufficiently close to the lunar surface environment to have accumulated solar‐wind‐implanted gases. The stones have a comparable major element composition and petrography to low‐Ti, low‐Al basalts collected at the Apollos 12 and 15 landing sites. However, the LAP stones also have an enriched REE bulk composition and are more ferroan (Mg numbers in the range of 31 to 35) than similar Apollo samples, suggesting that they represent members of a previously unsampled fractionated mare basalt suite that crystallized from a relatively evolved lunar melt. 相似文献
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Ian A. Crawford Sarah A. Fagents Katherine H. Joy M. Elise Rumpf 《Earth, Moon, and Planets》2010,107(1):75-85
One of the principal scientific reasons for wanting to resume in situ exploration of the lunar surface is to gain access to
the record it contains of early Solar System history. Part of this record will pertain to the galactic environment of the
Solar System, including variations in the cosmic ray flux, energetic galactic events (e.g., supernovae and/or gamma-ray bursts),
and passages of the Solar System through dense interstellar clouds. Much of this record is of astrobiological interest as
these processes may have affected the evolution of life on Earth, and perhaps other Solar System bodies. We argue that this
galactic record, as for that of more local Solar System processes also of astrobiological interest, will be best preserved
in ancient, buried regolith (‘palaeoregolith’) deposits in the lunar near sub-surface. Locating and sampling such deposits
will be an important objective of future lunar exploration activities. 相似文献
37.
Corey Lang 《Climatic change》2014,125(3-4):291-303
Learning about the causes and consequences of climate change can be an important avenue for supporting mitigation policy and efficient adaptation. This paper uses internet search activity data, a distinctly revealed preference approach, to examine if local weather fluctuations cause people to seek information about climate change. The results suggest that weather fluctuations do have an effect on climate change related search behavior, however not always in ways that are consistent with the projected impacts of climate change. While search activity increases with extreme heat in summer and extended periods of no rainfall and declines in extreme cold in winter, search activity also increases with colder winter and spring average temperatures. Some of the surprising results are magnified when heterogeneity by political ideology and educational attainment in responsiveness is modeled, which could suggest that different people have different perceptions about what types of weather define climate change or that climate science deniers seek information through Google. However, the results also indicate that for all groups in the political and educational spectrum, there exist weather events consistent with the predicted impacts of climate change that elicit increased information seeking. 相似文献
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David L. Crawford 《Experimental Astronomy》1994,5(1-2):187-188
Astronomy is faced with environmental threats to observational research, such as light pollution and space junk. Space billboards are the latest of these potential serious impacts. There are solutions to most of these issues, but we all have to work together to ensure a positive approach. The International Dark-Sky Association, a membership based non-profit organization offers a route for us all to participate. 1 Operated by AURA, Inc. under cooperative agreement with the National Science Foundation. 相似文献
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I. A. Crawford 《Earth, Moon, and Planets》2004,94(3-4):245-266
I will argue that an ambitious programme of human space exploration, involving a return to the Moon, and eventually human missions to Mars, will add greatly to human knowledge. Gathering such knowledge is the primary aim of science, but science’s compartmentalisation into isolated academic disciplines tends to obscure the overall strength of the scientific case. Any consideration of the scientific arguments for human space exploration must therefore take a holistic view, and integrate the potential benefits over the entire spectrum of human knowledge. Moreover, science is only one thread in a much larger overall case for human space exploration. Other threads include economic, industrial, educational, geopolitical and cultural benefits. Any responsibly formulated public space policy must weigh all of these factors before deciding whether or not an investment in human space activities is scientifically and socially desirable. 相似文献
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