The new polymict eucrite Dar al Gani 983: Petrography,chemical composition,noble gas record,and evolution     

Andrea PATZER  Jochen SCHLÜTER  Ludolf SCHULTZ  Dolores H. HILL  William V. BOYNTON 《Meteoritics & planetary science》2005,40(6):869-879

Abstract— Mineralogical and chemical studies of Dar al Gani 983 show that this meteorite is a eucrite. Its texture is that of an impact breccia. It contains cumulate pyroxene and feldspar megacrysts, a variety of recrystallized melt clasts, clasts of subophitic basalt, and mesostasis. These components are embedded in a matrix of fragmental pyroxene and plagioclase. In addition, the entire rock is penetrated by glassy melt veins and patches, and displays features of strong shock. The mineralogical and chemical evidence obtained for DaG 983 indicates that this meteorite experienced a complex evolutionary history. The presence of cumulate silicate crystals implies substantial, large scale cratering events on the HED asteroid. As a result of these impacts, rocks from different intrusive bodies to extrusive surface layers were laterally and vertically transported to form a thoroughly mixed megaregolith. DaG 983 represents a sample of this megabreccia.  相似文献   

The shedding of mesoscale anticyclonic eddies from the Alaskan Stream and westward transport of warm water   总被引：1，自引：0，他引：1  

Konstantin Rogachev  Natalya Shlyk  Eddy Carmack 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2643

The south-flowing waters of the Kamchatka and Oyashio Currents and west-flowing waters of the Alaskan Stream are key components of the western sub-Arctic Pacific circulation. We use CTD data, Argo buoys, WOCE surface drifters, and satellite-derived sea-level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow. Variability in the temperature of the upstream Oyashio and Kamchatka Currents is evident by warming in mesothermal layer in 1994–2005 compared to 1990–1991. A major fraction of the water in these currents is derived directly from the Alaskan Stream. The stream also sheds large anticyclonic (Aleutian) eddies, averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the Kamchatka Current itself. These eddies enclose pools of relatively warm and saline water whose temperature is typically 4 °C warmer and salinity is 0.4 greater than that of cold-core Kamchatka eddies in the same density range. Aleutian eddies drift at approximately 1.2 km d⁻¹ and retain their distinctive warm and salty characteristics for at least 2 years. Selected westward pathways during 1990–2004 are identified. If the shorter northern route is followed, Aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the Kamchatka Current. This was observed during 1994–1997 with substantial warming of the waters in the Kamchatka Current and upstream Oyashio. If the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream Oyashio, as in 2004–2005. However, the eddies following this southern route may dissipate before reaching the western boundary current region.  相似文献   

Crystal-Mush Compaction and the Origin of Pegmatitic Segregation Sheets in a Thick Flood-Basalt Flow in the Mesozoic Hartford Basin, Connecticut   总被引：9，自引：4，他引：5  

PHILPOTTS  ANTHONY R.; CARROLL  MAUREEN; HILL  JAMES M. 《Journal of Petrology》1996,37(4):811-836

Where the Holyoke flood-basalt flow in the Mesozoic HartfordBasin in Connecticut is thick and contains coarse-grained, horizontalsegregation sheets in its central part, the lower part of theflow is strongly depleted in incompatible elements; where theflow is thin and contains no segregation sheets it is homogeneousthroughout. This chemical variation can be explained only throughcompaction of the partly crystallized basalt. The compositionof the segregation sheets shows that they separated from thebasalt following only 33% crystallization. The segregation sheets,however, are clearly intrusive into the basalt, which must thereforehave already formed a crystal mush with finite strength at thislow degree of crystallinity. The incompatible element concentrationsindicate that the partly crystallized basalt underwent as muchas 28% compaction in the lowest 60 m of the flow. Between 60and 130 m above the base of the flow, the crystal mush becamedilated, and eventually ruptured with formation of the segregationsheets. No segregation sheet has a composition indicating separationafter more than 33% crystallization of the basalt. This is interpretedto indicate that compaction ceased at this stage because ofthe increasing strength of the mush and the increasing densityof the fractionating interstitial liquid KEY WORDS: crystal-mush compaction; segregation shtets; flood basalt; tholeiitie; Connecticut ^*e-mail: philpotts{at}geol.uconn.edu  相似文献   

Improved Petrological Modal Analyses from X-ray Powder Diffraction Data by use of the Rietveld Method I. Selected Igneous, Volcanic, and Metamorphic Rocks     

HILL  R. J.; TSAMBOURAKIS  G.; MADSEN  I. C. 《Journal of Petrology》1993,34(5):867-900

Mineral modes have been determined for specimens of eight rocktypes from CuK X-ray powder diffraction data using the Rietveldmethod. The samples include two granites, a granodiorite, adamellite,gabbro, basalt, trachyte, and two granulite-facies metamorphicrocks. Up to eight individual mineral components have been measuredin each sample (no glassy phases were observed), with a detectionlimit of {small tilde}1 wt.%, depending on the mineral assemblage.Marked variations in grain size (i.e., granite vs. trachyte)provide no difficulties for the X-ray method. The X-ray resultscompare very favourably with (1) optical modes determined forthe medium–coarse-grained samples by point counting, (2)normative calculations obtained using locally enhanced catanormand mesonorm software, and (3) corresponding Rietveld modesdetermined, for two samples, from neutron powder data. Wheredifferences occur, these are discussed in relation to the limitationsof each of the methods. The improved accuracy of the X-ray method is due primarily tothe incorporation of the full diffraction profile in the Rietveldanalysis calculations, and the elimination of preferred orientationby collecting the data from samples packed in glass capillaries(i.e., Debye–Scherrer mode). The good agreement of theX-ray and neutron modes shows that the usual problems encounteredwith microabsorption, extinction, and sampling are of littleconcern in these rocks. The results highlight one of the majoradvantages provided by Rietveld modal analysis over the moretraditional ‘reference intensity’ X-ray methods,namely, that the crystal chemistry (and thus the calibrationconstants) of the individual phases can be adjusted dynamicallyduring each individual analysis. This not only provides moreaccurate phase abundances, but also gives important supplementaryinformation about the mineralogy of the major components.  相似文献   

The effect of thermal treatment on the 57Fe Mössbauer spectrum of beryl     

Geraldo Magela da Costa  Gabriel de Oliveira Polli  Márcio A. Kahwage  Eddy de Grave  Antônio Claret Soares Sabioni  Júlio Cesar Mendes 《Physics and Chemistry of Minerals》2006,33(3):161-166

Mössbauer spectra (MS) of blue, green and yellow beryl (ideally Be₃Al₂Si₆O₁₈) containing approximately 1% of iron were obtained at 295 and 500 K. Room temperature (RT) spectra of both blue and green samples showed the presence of an asymmetric Fe²⁺ doublet (ΔE _Q~2.7 mm/s, δ~1.1 mm/s), with a very broad low-velocity peak. There is no clear evidence for the presence of a ferric component. The MS of the yellow sample at RT consists of an intense central absorption with parameters typical for Fe³⁺ (ΔE _Q~0.4 mm/s, δ~0.29 mm/s), plus an apparently symmetrical Fe²⁺ doublet. This sample acquires a light-blue shade upon heating in air at about 620 K. Thermal treatments at high temperatures caused no significant changes in the MS, but the green and yellow beryl acquire a blue colour. All these results are interpreted in relation to the existence of channel water and the distribution of iron among the available crystallographic sites.  相似文献   

Effect of heat treatment on tourmaline from Brazil   总被引：4，自引：0，他引：4  

Cristiane Castañeda  Sigrid G. Eeckhout  Geraldo Magela da Costa  Nilson F. Botelho  Eddy De Grave 《Physics and Chemistry of Minerals》2006,33(3):207-216

The crystal-chemical behaviour of tourmaline from Araçuaí, Minas Gerais state, Brazil, when subjected to heating in air atmosphere has been studied by several techniques, including EMPA, UV–Vis, TGA, and Mössbauer spectroscopy. The tourmaline samples are typically intermediate members of the elbaite-schorl series. The origin of colour and of its change after treatment has been discussed in terms of local disorder, presence of metal transition elements, oxidation of ferrous iron at the octahedral site, and simultaneous trap of the excess electron. These findings may be used to enhance the colour in tourmaline crystals or generate wanted colour changes.  相似文献   

Identification of Greigite in the Pliocene Sediments of Qinghai Lake and Its Geological Significance     

FU Chaofeng  Jan BLOEMENDAL  QIANG Xiaoke  Mimi J. HILL  AN Zhisheng 《《地质学报》英文版》2016,90(6):2261-2262

正Objective The Qinghai Lake in North China is the largest interior plateau lake in Central Asia,and is sensitive to climate change and the environmental effects of Tibetan Plateau uplift.An almost continuous 626 m long sediment core was drilled in an in-filled part of the southern lake basin in the Scientific Drilling at Qinghai Lake.Previous  相似文献   

The Perseverance Ultramafic Complex, Western Australia: The Product of a Komatiite Lava River   总被引：3，自引：0，他引：3  

BARNES  STEPHEN J.; HILL  ROBIN E. T.; GOLE  MARTIN J. 《Journal of Petrology》1988,29(2):305-331

The Perseverance ultramafic complex is a body of olivine-richkomatiitic rocks spatially associated with the Agnew nickeldeposit, in the Agnew-Wiluna greenstone belt of the ArchaeanYilgarn Block in Western Australia. The complex consists ofa central lenticular body, up to 700 m thick, of olivine adcumulates,flanked by laterally extensive sheet-like bodies of olivineorthocumulates and spinifextextured komatiite flows. Rocks progressivelyfurther away from the central lens have chemical compositionsreflecting higher original proportions of komatiite liquid tocumulus olivine. Parent liquids had MgO contents between 25and 32% MgO, approximately chondritic Al/Ti ratios and HREEpatterns, and moderate depletion in LREE. Olivines within the adcumulate lens show a progressive increasein forsterite content from Fo₉₃ at the bottom to Fo_94?5, atthe top. Calculated original olivine compositions in the flankingrocks are similar to those at the base of the central lens.Original olivine nickel contents show a symmetrical variationfrom maximum values of 3500 ppm at the top of the central lens,through minimum values of 1000 ppm at the base and margins ofthe central lens to intermediate values in the distal rocks.The complex as a whole shows evidence for nickel depletion relativeto other komatiite suites. These observations are explained in terms of prolonged eruptionand flow of komatiitic lava down a major flow channel or lavariver. Adcumulates crystallized on the floor and sides of thecentral channel, which was formed at an early stage by thermalerosion of floor rocks. Episodic overflow of the central channelproduced distal ‘flood plain’ rocks consisting ofolivine orthocumulates and layered flows. Lavas became moremagnesian and nickel-rich with time, giving rise to the observedspatial variation in primary olivine composition. Nickel depletionof the earliest lavas is attributed to pre-eruption segregationof large volumes of immiscible Fe-Ni-sulfide, which were concentratedto form the underlying Agnew nickel deposit.  相似文献   

The agricultural utility of lithic-mulch gardens: Past and present     

Dale R. Lightfoot  Frank W. Eddy 《GeoJournal》1994,34(4):425-437

The mulching of agricultural fields and gardens with stones, pebbles, volcanic ash and similar lithic materials is a variant agricultural strategy uniquely suited to the constraints of a dryland environment. While the agricultural literature contains reports on limited experiments with stone or gravel mulch, data regarding the employment of lithic mulch are lacking. This paper works to bridge this gap by comparing empirical data collected from prehistoric pebble-mulch gardens in the Galisteo Basin (New Mexico) to contemporary agricultural experiments with lithic mulch. Such past-present and experimental-real world comparisons allow us to more fully address the effectiveness of lithic mulching as an agricultural strategy. It is affirmed that lithic mulch is applied to garden plots, especially during periods of drought, in order to reduce soil erosion from wind and water, increase soil temperature to extend the growing season, increase water infiltration, and reduce the evaporative loss of water from wind and sun. The cumulative effect of this soil and water conserving technique is an increase in crop biomass and crop yield.  相似文献   

An early observation of λ8542 of the Ca II infrared triplet     

John A. Eddy 《Solar physics》1973,29(1):23-24

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