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91.
92.
CHRISTOPHER S. ROMANEK EUGENE C. PERRY ALLAN H. TREIMAN RICHARD A. SOCKI JOHN H. JONES EVERETT K. GIBSON 《Meteoritics & planetary science》1998,33(4):775-784
Abstract— Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and 18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette. Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ~90% separate. Based on these measurements, end-member iddingsite has a δ18O of 15.6%, which places it among other 18O-enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (~11%) is typical of low-temperature alteration products. A range of crustal fluid δ18O values can be interpreted from the δ18O for end-member iddingsite, assuming isotopic equilibrium was achieved during low-temperature hydrous alteration (<100 °C; Treiman et al., 1993). The calculated range of values, ?15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O-bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO2-carbonate-iddingsite-H2O system at low temperature. The SNC meteorite samples in this study have Δ17O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ17O of ~1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ17O is similar in direction to Δ17O reported for waters extracted from bulk samples of Lafayette (Karlsson et al., 1992). If the Δ17O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago. 相似文献
93.
RICHARD SYMANSKI 《Geographical review》1998,88(4):571-579
ABSTRACT. Hurricane Mitch, the most deadly hurricane to strike the Western Hemisphere in two centuries, killed at least 10,000 people in Honduras, Nicaragua, and El Salvador and left tens of thousands homeless. Some needed food; others, medical attention. Americans, Europeans, Mexicans, and others almost immediately responded to the widespread devastation by sending large donations of food, clothing, and medicine. Six weeks after Mitch struck the Honduran mainland, the author traveled to Honduras with the aim of photographing the physical damage and its effect on humans. In San Pedro Sula he was sidetracked by the issue of where the refugees were being housed and whether they were receiving the donations that had been sent on their behalf. This essay narrates that search and what he found. 相似文献
94.
KATHRYN B. BICKNELL RICHARD J. BALL ROSS CULLEN HUGH R. BIGSBY 《New Zealand geographer》1998,54(2):4-11
Sustainability has become a primary goal for much of the legislation which governs resource management in New Zealand. A major difficulty associated with sustainable development objectives, however, is the absence of reliable indicators to measure progress towards the goal of sustainability. The ‘ecological footprint’ provides an estimate of the amount of ecologically productive land required on a continuous basis to sustain current levels of resource consumption and waste assimilation for a given population. By comparing the ecological footprint of a community with the amount of land available, we can more clearly determine whether our current consumption patterns are likely to be sustainable. This paper explores the use of ecological footprint analysis within a New Zealand context. Modifications to the existing procedure for calculating an ecological footprint are proposed, and estimates based on the modified procedures are presented for New Zealand. 相似文献
95.
The zonation pattern of rocky shores on north-west Spitsbergen is described. Intertidal communities on protected sites have features remarkably similar to temperate areas. Black lichens dominate the littoral fringe, fucoids and gastropods the eulittoral zone, whereas upper sublittoral zone is occupied by kelp. The species composition seems to be typical for the Atlantic arctic areas. 相似文献
96.
97.
THORSTEN HOFFMANN JAY R. ODUM FRANK BOWMAN DONALD COLLINS DIETER KLOCKOW RICHARD C. FLAGAN JOHN H. SEINFELD 《Journal of Atmospheric Chemistry》1997,26(2):189-222
Measurements of aerosol formation during thephotooxidation of -pinene, -pinene,d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, andtrans-caryophyllene were conducted in anoutdoor smog chamber. Daylight experiments in thepresence of
and dark experiments withelevated ozone concentrations were performed. Theevolution of the aerosol was simulated by theapplication of a gas/particle absorption model inconnection with a chemical reaction mechanism. Thefractional aerosol yield is shown to be a function ofthe organic aerosol mass concentration andtemperature. Ozone and, for selected hydrocarbons, theNO3 reaction of the compounds were found torepresent efficient routes to the formation ofcondensable products. For initial hydrocarbon mixingratios of about 100 ppb, the fractional aerosol yieldsfrom daylight runs have been estimated to be 5%for open-chain hydrocarbons, such as ocimene andlinalool, 5–25% for monounsaturated cyclicmonoterpenes, such as -pinene, d-3-carene, orterpinene-4-ol, and 40% for a cyclic monoterpenewith two double bonds like d-limonene. For the onlysesquiterpene investigated, trans-caryophyllene, afractional aerosol yield of close to 100% wasobserved. The majority of the compounds studied showedan even higher aerosol yield during dark experimentsin the presence of ozone. 相似文献
98.
Mineral Chemistry, and major and trace element variations ofthe basalts from Klyuchevskoy, the world's most active islandare volcano, are most consistently explained by the persistenceof a non-steady state, erupting, recharging, and fractionatingmagma chamber in which fractionation of a parental high-MgObasalt melt produces high-Al2O3 basalt. Although fractionalcrystallization is the dominant controlling mechanism, periodicrecharge with a more primitive high-MgO basalt is also an importantprocess contributing to the chemical evolution of the magmas.Hybrid basalts are the mixed product of high-Al2O3 basalt rechargedwith high-MgO basalt. The lavas range in composition from high-MgO, low-Al2O3 ( 12wt. % MgO, 14 wt. % Al2O3) to high-Al2O3, low-MgO ( 18 wt. %Al2O3, 4 wt. % MgO). The high-MgO lavas are characterized byphenocrysts of olivine (cores FO9080 and rims FO8575)with chromite inclusions [Cr/(Cr + Al)0.7], clinopyroxene (Wo4642En4842Fs157),and the rare occurrence of orthopyroxene (En7270). Allthe phenocrysts are normally zoned and set in a groundmass ofplagioclase, pigeonite, clinopyroxene, magnetite, orthopyroxene.The high-Al2O3 basalts contain plagioclase (An8555),olivine (Fo8065), clinopyroxene (Wo4530En5038Fs2311), orthopyroxene (En7270) phenocrysts, that preserve bothnormal and reverse zoning in a groundmass of plagioclase, pigeonite,olivine, clinopyroxene, magnetite, orthopyroxene. Hybrid basaltshave characteristics of both high-MgO basalts and high-Al2O3basalts and preserve complicated normal-to-reverse, reverse-to-normal,and normally zoned phenocrysts. No hydrous minerals are presentin any of the lavas. The varied basaltic magmas erupted from Klyuchevskoy are derivedfrom a magma chamber(s) located near the base of the Kamchatkacrust (pressures 0.50.9 GPa) and characterized by relativelyhigh crystallization temperatures, some in excess of 1150C.Under these conditions, the fractionation of a parental high-MgOmagma, produced principally from the melting of a fluid-fluxed,peridotitic mantle wedge, results in the production of a chemicallydiverse spectrum of basalts ranging from high-MgO, low-Al2O3to high-Al2O3, low-MgO basalt, traversing the relatively primitiveend of both the calc-alkalic and tholeiitic differentiationtrends. 相似文献
99.
100.
Historical first‐generation frontier roads in America's trans‐Appalachian West often evolved from buffalo and Indian trails into pioneer routeways such as Daniel Boone's Trace and, eventually, into twentieth‐century hard‐surface highways. Period cartographers found these routes difficult to document accurately, and present‐day scholars often depict them only on small‐scale maps, which simply illustrate connections between origin and destination points. Accurately mapping Kentucky's first‐generation roads at large scale requires detailed site and contextual topographic information over long distances, but historical maps, diaries, surveyors' reports, and other period documents often lack sufficient detail for route‐related sites to support mapping. Use of gis software enables positioning historical routes onto U.S. Geological Survey contour‐ and hill‐shaded base maps by mapping verifiable locations and linking them through interpretation of best‐choice routes that consider frontier migrants' transportation priorities, such as direction, distance, gradient, and land‐surface character. 相似文献