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71.
The chlorine isotope composition of Martian meteorites 2. Implications for the early solar system and the formation of Mars
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Zachary Sharp Jeffrey Williams Charles Shearer Carl Agee Kevin McKeegan 《Meteoritics & planetary science》2016,51(11):2111-2126
We determined the chlorine isotope composition of 16 Martian meteorites using gas source mass spectrometry on bulk samples and in situ secondary ion microprobe analysis on apatite grains. Measured δ37Cl values range from ?3.8 to +8.6‰. The olivine‐phyric shergottites are the isotopically lightest samples, with δ37Cl mostly ranging from ?4 to ?2‰. Samples with evidence for a crustal component have positive δ37Cl values, with an extreme value of 8.6‰. Most of the basaltic shergottites have intermediate δ37Cl values of ?1 to 0‰, except for Shergotty, which is similar to the olivine‐phyric shergottites. We interpret these data as due to mixing of a two‐component system. The first component is the mantle value of ?4 to ?3‰. This most likely represents the original bulk Martian Cl isotope value. The other endmember is a 37Cl‐enriched crustal component. We speculate that preferential loss of 35Cl to space has resulted in a high δ37Cl value for the Martian surface, similar to what is seen in other volatile systems. The basaltic shergottites are a mixture of the other two endmembers. The low δ37Cl value of primitive Mars is different from Earth and most chondrites, both of which are close to 0‰. We are not aware of any parent‐body process that could lower the δ37Cl value of the Martian mantle to ?4 to ?3‰. Instead, we propose that this low δ37Cl value represents the primordial bulk composition of Mars inherited during accretion. The higher δ37Cl values seen in many chondrites are explained by later incorporation of 37Cl‐enriched HCl‐hydrate. 相似文献
72.
Zoning of phosphorus in igneous olivine 总被引:2,自引:2,他引:0
Margaret S. Milman-Barris John R. Beckett Michael B. Baker Amy E. Hofmann Zachary Morgan Meghan R. Crowley Daniel Vielzeuf Edward Stolper 《Contributions to Mineralogy and Petrology》2008,155(6):739-765
We describe P zoning in olivines from terrestrial basalts, andesites, dacites, and komatiites and from a martian meteorite.
P2O5 contents of olivines vary from below the detection limit (≤0.01 wt%) to 0.2–0.4 wt% over a few microns, with no correlated
variations in Fo content. Zoning patterns include P-rich crystal cores with skeletal, hopper, or euhedral shapes; oscillatory
zoning; structures suggesting replacement of P-rich zones by P-poor olivine; and sector zoning. Melt inclusions in olivines
are usually located near P-rich regions but in direct contact with low-P olivine. Crystallization experiments on basaltic
compositions at constant cooling rates (15–30°C/h) reproduce many of these features. We infer that P-rich zones in experimental
and natural olivines reflect incorporation of P in excess of equilibrium partitioning during rapid growth, and zoning patterns
primarily record crystal-growth-rate variations. Occurrences of high-P phenocryst cores may reflect pulses of rapid crystal
growth following delayed nucleation due to undercooling. Most cases of oscillatory zoning in P likely reflect internal factors
whereby oscillating growth rates occur without external forcings, but some P zoning in natural olivines may reflect external
forcings (e.g., magma mixing events, eruption) that result in variable crystal growth rates and/or P contents in the magma.
In experimental and some natural olivines, Al, Cr, and P concentrations are roughly linearly and positively correlated, suggesting
coupled substitutions, but in natural phenocrysts, Cr zoning is usually less intense than P zoning, and Al zoning weak to
absent. We propose that olivines grow from basic and ultrabasic magmas with correlated zoning in P, Cr, and Al superimposed
on normal zoning in Fe/Mg; rapidly diffusing divalent cations homogenize during residence in hot magma; Al and Cr only partially
homogenize; and delicate P zoning is preserved because P diffuses very slowly. This interpretation is consistent with the
fact that zoning is largely preserved not only in P but also in Al, Cr, and divalent cations in olivines with short residence
times at high temperature (e.g., experimentally grown olivines, komatiitic olivines, groundmass olivines, and the rims of
olivine phenocrysts grown during eruption). P zoning is widespread in magmatic olivine, revealing details of crystal growth
and intra-crystal stratigraphy in what otherwise appear to be relatively featureless crystals. Since it is preserved in early-formed
olivines with prolonged residence times in magmas at high temperatures, P zoning has promise as an archive of information
about an otherwise largely inaccessible stage of a magma’s history. Study of such features should be a valuable supplement
to routine petrographic investigations of basic and ultrabasic rocks, especially because these features can be observed with
standard electron microprobe techniques. 相似文献
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Zachary M. Easton M. Todd Walter Daniel R. Fuka Eric D. White Tammo S. Steenhuis 《水文研究》2011,25(20):3131-3143
Most semi‐distributed watershed water quality models divide the watershed into hydrologic response units (HRU) with no flow among them. This is problematic when watersheds are delineated to include variable source areas (VSAs) because it is the lateral flows from upslope areas to downslope areas that generate VSAs. Although hydrologic modellers have often successfully calibrated these types of models, there can still be considerable uncertainty in model results. In this paper, a topographic‐index‐based method is described and tested to distribute effective soil water holding capacity among HRUs, which can be subsequently adjusted using the watershed baseflow coefficient. The method is tested using a version of the Soil and Water Assessment Tool (SWAT) model that simulates VSA runoff and is applied to two watersheds: a New York State (NYS) watershed, and one in the head waters of the Blue Nile Basin (BNB) in Ethiopia. Daily streamflow predicted using effective soil water storage capacities based only on the topographic index were reassuringly accurate in both the NYS watershed (daily Nash Sutcliffe (E) = 0·73) and in the BNB (E = 0·70). Using the baseflow coefficient to adjust the effective soil water storage capacity only slightly improved streamflow predictions in NYS (E = 0·75) but substantially improved the BNB predictions (E = 0·80). By comparison, the standard SWAT model, which uses the traditional look‐up tables to determine a runoff curve number, performed considerably less accurately in un‐calibrated form (E = 0·51 for NYS and E = 0·45 for BNB), but improved substantially when explicitly calibrated to streamflow measurements (E = 0·76 for NYS and E = 0·67 for the BNB). The calibration method presented here provides a parsimonious, systematic approach to using established models in VSA watersheds that reduces the ambiguity inherent in model calibration. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
76.
Utku Solpuker Zachary Cotter Yongje Kim Franklin W. Schwartz 《Ground Water Monitoring & Remediation》2014,34(4):93-101
This study investigates the use of KMnO4 doped geopolymers as controlled‐release materials for remedial applications. The geopolymers were prepared by mixing alkali activated Na‐silicate solutions, metakaolin, and various amounts of granular KMnO4. Samples were heat treated at 75 °C for 48 h. Concentrations of KMnO4 in samples 1, 2, and 3 were 1.40 × 10?1, 4.63 × 10?1, and 6.07 × 10?1 g/cm3, respectively. 1D column experiments showed that a high MnO4? release rate lasted for the first few hours, followed by a gradual decrease of MnO4? release. Neither cracks nor surface erosion of the geopolymers were observed throughout the experiments. Sample 1 approached exhaustion at the end of the Day 7. It took about 18 d for exhaustion of KMnO4 releases in samples 2 and 3. Modeling of the observed KMnO4 releases suggested diffusion and dissolution‐related fast transport as the most important mechanisms. This latter mechanism involves the creation of a connected secondary porosity in the geopolymers by dissolution of KMnO4 granules. The contribution of Fickian diffusion to the total release decreased as the KMnO4 content of the samples increased, and the dissolution mechanism became increasingly important. 相似文献
77.
Eric C. Merten Zachary R. Snobl Todd A. Wellnitz 《Aquatic Sciences - Research Across Boundaries》2014,76(2):165-172
Understanding the factors controlling insect emergence from streams has applications to ecological theory regarding cross-boundary flux, along with practical value for monitoring stream function after restoration projects. We hypothesized that stream microhabitat would have effects on emergence that were independent of those mediated by the local stock of benthic macroinvertebrates. We set 50 emergence traps in a third-order stream in northern Minnesota, USA, during two study periods and used structural equation modeling to examine direct and indirect effects of benthic stock and microhabitat features on emergence. Emergence by biomass showed direct positive relationships to substrates of fines and detritus in the first sampling period, and to shallow depth and wood area in the second period. Emergence by abundance had direct positive relationships with benthic stock, CPOM, and fewer macrophytes in the first period, and with benthic stock and periphyton in the second period. Fine substrates may act to concentrate burrowing larvae, whereas CPOM and particularly wood may intercept drifting pre-emergent insects and provide exiting surfaces. Shallow depths may reduce the extent to which resident insects drift downstream (and leave the sample area) while emerging. Periphyton may be an indicator for patches with greater illumination, which itself attracts emergers. Our results suggest emergence is sensitive to environmental conditions at the microhabitat scale, and that stream restoration activities should consider habitat for emerging insects when designing projects. 相似文献
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Amira is a powerful three-dimensional visualization package that has been employed recently by the science and engineering communities to gain insight into their data. We discuss a new paradigm for the use of Amira in the Earth sciences that relies on the client-server paradigm. We have developed a module called WEB-IS2, which provides web-based access to Amira. This tool allows Earth scientists to manipulate Amira controls remotely and to analyze, render and view large datasets through the Internet without regard for time or location. This could have important ramifications for GRID computing.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10069-003-0013-y 相似文献
79.
George B. Perkins Zachary D. Sharp Jane Selverstone 《Contributions to Mineralogy and Petrology》2006,151(6):633-650
Spinel lherzolite and pyroxenite xenoliths from the Rio Puerco Volcanic Field, New Mexico, were analyzed for oxygen isotope ratios by laser fluorination. In lherzolites, olivine δ18O values are high (+5.5‰), whereas δ18O values for pyroxenes are low (cpx=+5.1‰; opx=+5.4‰) compared to average mantle values. Pyroxenite δ18O values (cpx=+5.0‰; opx=+5.3‰) are similar to those of the lherzolites and are also lower than typical mantle oxygen isotope compositions. Texturally and chemically primary calcite in pyroxenite xenoliths is far from isotopic equilibrium with other phases, with δ18O values of +21‰. The isotopic characteristics of the pyroxenite xenoliths are consistent with a petrogenetic origin from mixing of lherzolitic mantle with slab-derived silicate and carbonatite melts. The anomalously low δ18O in the pyroxenes reflects metasomatism by a silicate melt from subducted altered oceanic crust, and high δ18O calcite is interpreted to have crystallized from a high δ18O carbonatitic melt derived from subducted ophicarbonate. Similar isotopic signatures of metasomatism are seen throughout the Rio Puerco xenolith suite and at Kilbourne Hole in the southern Rio Grande rift. The discrete metasomatic components likely originated from the subducted Farallon slab but were not mobilized until heating associated with Rio Grande rifting occurred. Oxygen diffusion modeling requires that metasomatism leading to the isotopic disequilibrium between calcite and pyroxene in the pyroxenites occurred immediately prior to entrainment. Melt infiltration into spinel-facies mantle (xenoliths) prior to eruption was thus likely connected to garnet-facies melting that resulted in eruption of the host alkali basalt. 相似文献
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