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SARA S. RUSSELL TIMOTHY J. McCOY EUGENE JAROSEWICH RICHARD D. ASH 《Meteoritics & planetary science》1998,33(4):853-856
Abstract— The Burnwell, Kentucky, meteorite fell as a single stone on 1990 September 4. The Burnwell meteorite has lower Fa in olivine (15.8 mol%), Fs in orthopyroxene (13.4 mol%), Co in kamacite (0.36 wt%), FeO from bulk chemical analysis (9.43 wt%), and Δ17O (0.51 ± 0.02%), and higher Fe, Ni, Co metal (19.75 wt% from bulk wet chemical analysis) than observed in H chondrites. The Burnwell meteorite plots on extensions of H-L-LL chondrite trends for each of these properties towards more reducing compositions than in H chondrites. Extensions of this trend have been previously suggested in the case of other low-FeO chondrites or silicate inclusions in the HE iron Netschaëvo, but interpretation of the evidence in these meteorites is complicated by terrestrial weathering, chemical disequilibrium or reduction. In contrast, the Burn-well meteorite is an equilibrated fall that exhibits no evidence for reduction. As such, it provides the first definitive evidence for extension of the H-L-LL ordinary chondrite trend beyond typical H values towards more reducing compositions. 相似文献
3.
ANDREW RUSSELL GERAINT VAUGHAN EMILY G. NORTON HUGO M. A. RICKETTS CYRIL J. MORCRETTE TIM J. HEWISON KEITH. A. BROWNING ALAN M. BLYTH 《地球,A辑:动力气象学与海洋学》2009,61(2):250-263
A narrow line of convective showers was observed over southern England on 18 July 2005 during the Convective Storm Initiation Project (CSIP). The showers formed behind a cold front (CF), beneath two apparently descending dry layers (i.e. sloping so that they descended relative to the instruments observing them). The lowermost dry layer was associated with a tropopause fold from a depression, which formed 2 d earlier from a breaking Rossby wave, located northwest of the UK. The uppermost dry layer had fragmented from the original streamer due to rotation around the depression (This rotation was also responsible for the observations of apparent descent—ascent would otherwise be seen behind a CF). The lowermost dry layer descended over the UK and overran higher θ w air beneath it, resulting in potential instability. Combined with a surface convergence line (which triggered the convection but had less impact on the convective available potential energy than the potential instability), convection was forced up to 5.5 km where the uppermost dry layer capped it. The period when convection was possible was very short, thus explaining the narrowness of the shower band. Convective Storm Initiation Project observations and model data are presented to illustrate the unique processes in this case. 相似文献
4.
PETER JENNISKENS PAUL WERCINSKI JOE OLEJNICZAK GARY ALLEN PRASUN N. DESAI GEORGE RAICHE DEAN KONTINOS DOUG REVELLE JASON HATTON RICHARD L. BAKER RAY W. RUSSELL MIKE TAYLOR FRANS RIETMEIJER 《Earth, Moon, and Planets》2004,95(1-4):339-360
The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents
the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape
speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than
escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing
campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission
spectrum consists mostly of blackbody emission from the SRC surface (T∼
∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution,
shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N2+, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as
the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material,
calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also
permit the sampling of products of ablation. 相似文献
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Primitive Magma From the Jericho Pipe, N.W.T., Canada: Constraints on Primary Kimberlite Melt Chemistry 总被引:12,自引:7,他引:5
We report the first estimates of primary kimberlite melt compositionfrom the Slave craton, based on samples of aphanitic kimberlitefrom the Jericho kimberlite pipe, N.W.T., Canada. Three samplesderive from the margins of dykes where kimberlite chilled againstwall rock (JD51, JD69 and JD82) and are shown to be texturallyconsistent with crystallization from a melt. Samples JD69 andJD82 have geochemical characteristics of primitive melts: theyhave high MgO (2025 wt %), high mg-numbers (8688),and high Cr (13001900 ppm) and Ni (8001400 ppm)contents. They also have high contents of CO2 (1017 wt%). Relative to bulk macrocrystal kimberlite, they have lowermg-numbers and lower MgO but are enriched in incompatible elements(e.g. Zr, Nb and Y), because the bulk kimberlite compositionsare strongly controlled by accumulation of mantle olivine andother macrocrysts. The compositions of aphanitic kimberlitefrom Jericho are similar to melts produced experimentally bypartial melting of a carbonate-bearing garnet lherzolite. Onthe basis of these experimental data, we show that the primarymagmas from the Jericho kimberlite could represent 0·70·9%melting of a carbonated lherzolitic mantle source at pressuresand temperatures found in the uppermost asthenosphere to theSlave craton. The measured CO2 contents for samples JD69 andJD82 are only slightly lower than the CO2 contents of the correspondingexperimental melts; this suggests that the earliest hypabyssalphase of the Jericho kimberlite retained most of its originalvolatile content. As such these samples provide a minimum CO2content for the primary kimberlite magmas from the Slave craton. KEY WORDS: kimberlite; melt; primitive; primary magma; Slave craton 相似文献
7.
ANDREW J. RUSSELL PHILIP M. MARREN 《Boreas: An International Journal of Quaternary Research》1998,27(4):231-242
This study provides an insight into the impact of probably the largest flood ever to have been identified in mainland Britain by examining new sedimentary evidence from the Auchteraw terrace, Fort Augustus, Scotland. Study of three sections reveals a succession consisting of: (1) sheet gravels; (2) large trough-shaped depressions infilled with cross-stratified sands and gravels; (3) smaller-scale, finer-grained cross-strata; and (4) sheet-like, occasionally channelized, bimodal sand and gravel beds. This study shows that both the sedimentology and morphology of the Auchteraw terrace are consistent with jökulhlaup deposition and reveal a greater variety of lithofacies types than identified in previous studies of jökulhlaups from ice-dammed lakes. The fine-grained nature of the sediment discussed in this study emphasizes the importance of sediment supply for the formation of distinctive jökulhlaup successions. The sedimentary evidence recorded here provides a valuable tool for the interpretation of the magnitude and frequency of proglacial meltwater flows associated with Pleistocene ice sheets worldwide. 相似文献
8.
B. S. PALIWAL R. R. MAHAJAN S. V. S. MURTY A. D. SHUKLA P. N. SHUKLA N. BHANDARI R. NATARAJAN R. HUTCHISON S. RUSSELL I. A. FRANCHI 《Meteoritics & planetary science》2001,36(9):1249-1256
Abstract— The mineralogical and chemical characteristics of the Didwana‐Rajod chondrite are described. The mean mineral composition is found to be olivine (Fo83.2) and pyroxene (En83.5Wo0.7Fs15.8), and feldspar is mainly oligoclase. Oxygen isotopic analysis shows δ18O = +3.8%0 and δ17O = +2.59%0. The nitrogen content of Didwana‐Rajod is ~2 ppm with δ15N ? 3.4%0. Based on microscopic, chemical, isotopic and electron probe microanalysis, the meteorite is classified as an H5 chondrite. Cosmogenic tracks, radionuclides and the isotopic composition of rare gases were also measured in this meteorite. The track density in olivines varies in a narrow range with an average value of (6.5 ± 0.5) × 105/cm2 for four spot samples taken at the four corners of the stone. The cosmic‐ray exposure age based on neon and argon is 9.8 Ma. 22Na/26Al ? 0.94 is lower than the solar‐cycle average value of ~1.5 and is consistent with irradiation of the meteoroid to lower galactic cosmic‐ray fluxes as expected at the solar maximum. The track density, rare gas isotopic ratios, 60Co activity and other radionuclide data are consistent with a preatmospheric radius of ~15 cm, corresponding to a mass of ~50 kg. The cosmogenic properties are consistent with a simple exposure history in interplanetary space. 相似文献
9.
RUSSELL J. WHITE GLENN A. SPINELLI PETER S. MOZLEY NELIA W. DUNBAR 《Sedimentology》2011,58(5):1138-1154
A minor amount (ca 1 wt%) of amorphous silica cement sourced from volcanic glass inhibits consolidation of hemipelagic sediment approaching the Nankai Trough subduction zone throughout the Shikoku Basin. The distribution and nature of the cement were examined via secondary and backscattered electron imaging. The amorphous silica occurs as altered material in contact with volcanic glass, coating grains (including grain contacts) and filling pores. Based on chemical and petrographic evidence, the cement is probably sourced from volcanic glass; this is in contrast to a previous suggestion that this silica cement is sourced dominantly from biogenic silica. Amorphous silica sourced from disseminated volcanic glass shards has the ability to form a thin coating on clay‐dominated sediment throughout the Shikoku Basin. Measured amorphous silica content in hemipelagic sediments suggests that the cementing process is active throughout the Shikoku Basin (at sites separated by >500 km). The cementation process may occur in other locations where sediment containing hydrated disseminated volcanic glass is buried sufficiently for heat to facilitate alteration (i.e. Central America, Cascadia and the Gulf of Alaska). 相似文献
10.
Mineralogy, Chemistry, and Genesis of the Boninite Series Volcanics, Chichijima, Bonin Islands, Japan 总被引:11,自引:1,他引:11
TAYLOR REX. N.; NESBITT ROBERT W.; VIDAL PHILLIPE; HARMON RUSSELL S.; AUVRAY BERNARD; CROUDACE IAN W. 《Journal of Petrology》1994,35(3):577-617
The Bonin archipelago represents an uplifted fore-arc terrainwhich exposes the products of Eocene supra-subduction zone magmatism.Chichijima, at the centre of the chain, represents the typelocality for the high-Mg andesitic lava termed boninite. Therange of extrusives which constitute the boninite series volcanicsare present on Chichijima, and are disposed in the sequenceboninite-andesite-dacite with increasing height in the volcano-stratigraphy.Progression to evolved compositions within the Chichijima boniniteseries is controlled by crystal fractionation from a boniniteparental magma containing 15% MgO. Olivine and clinoenstatiteare the initial liquidus phases, but extraction of enstatiticorthopyroxene, followed by clinopyroxene and plagioclase, isresponsible for the general evolution from boninite, throughandesite, to dacite. Some andesites within the overlying MikazukiyamaFormation are petrographically distinct from the main boniniteseries in containing magnetite phenocrysts and a high proportionof plagioclase. As such, these andesites have affinities withthe calc-alkaline series. Major and trace element data for 74 boninitic series rocks fromChichijima are presented. Although major element variation isdominantly controlled by high-level crystal fractionation, thelarge variations in incompatiable trace element concentrationsat high MgO compositions cannot be explained by this mechanism.Nd, Pb, and Sr isotopic data indicate the following: (1) a strongoverprint on 87Sr/86Sr by seawater alteration; (2) Pb isotopeslie above the northern hemisphere reference line (NHRL) andare thus similar to the <30-Ma are and basin lavas of theIzuBonin system, and (3) Nd(40 Ma) ranges between 2.8and 6.8 within the boninite series volcanics. Differences inrare-earth elements (REE), Zr, Ti, and 143Nd/144Nd at similardegrees of fractionation can be explained by the addition ofa component of fixed composition from the down-going oceaniccrustal slab to a variably depleted source region within theoverlying wedge. Data presented for Sm/Zr and Ti/Zr indicatethat boninite series volcanics are characterized by low valuesfor both of these ratios. In particular, boninites appear tohave uniquely low Sm/Zr ratios. These characteristics may bethe result of slab melting in the presence of residual amphibole;the resultant melt could combine with typical slab dehydrationfluids and infiltrate the overlying mantle wedge. Such a fluidmeltcomponent could mix either with shallow mantle or directly withprimitive melts from depleted mantle. Trace elements, REE, andisotope data thus point to a model for boninite genesis whichrequires tightly constrained pressuretemperature conditionsin the slab combined with melting of a variably depleted sourcein the overlying wedge. Such constraints are rarely met exceptduring the subduction of juvenile oceanic crust beneath a young,hot overriding plate. 相似文献