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141.
Replacement of olivine by orthopyroxene is a frequently observed phenomenon in mantle metasomatism. In order to study element redistribution in SiO2 metasomatism we synthesised orthopyroxene reaction rims at the contacts between forsterite-rich olivine and quartz. The orthopyroxene rims grew from the original quartz-olivine interface into both directions implying counterdiffusion of iron/magnesium and silicon. Following local equilibrium partitioning the XFe is lower in the orthopyroxene than in the reactant olivine at the olivine-orthopyroxene replacement front. The resulting local iron excess is compensated by formation of orthopyroxene with a higher XFe at the quartz-orthopyroxene interface, which is out of equilibrium with the reactant olivine. This is facilitated through short circuit diffusion along grain boundaries within the orthopyroxene rim. Due to the low capacity of orthopyroxene to accommodate Ni, this component is forced to diffuse back into the olivine producing a Ni enriched zone ahead of the replacement front. This leads to Ni contents in the orthopyroxene rim, which are higher than what is expected in equilibrium with the unaltered olivine. Taking quartz as a proxy for a silica rich fluid or liquid metasomatising agent, we conclude that the overall element fractionation between olivine and the silica rich phase may deviate from equilibrium partitioning so that the Fe and Ni concentrations in the orthopyroxene which is in contact with quartz are higher than in equilibrium with the reactant olivine. This indicates that kinetic fractionation is important for the chemical evolution of both the mantle rocks and the metasomatising agents. 相似文献
142.
143.
The Aleutian island arc collides with the Kuril–Kamchatka arc in the area of the Cape Kamchatka peninsula. Field studies of neotectonic structures and apatite fission track analysis provide evidence for crustal plate shortening onshore the Cape Kamchatka peninsula. Tectonic blocks show differential mean exhumation rates varying from 0.18 ± 0.04 mm yr−1 in the north up to 1.2 ± 0.18 mm yr−1 in the south of the peninsula. A few of the fission track length data point to an unsteady exhumation rate. The blocks are separated by major dextral fault zones splaying off from Aleutian island arc fault zones. Across the western segment of the North American–Pacific Plate boundary the strain is partitioned along the fault zones and increases from north to south. Results from this study suggest that indentation and accretion of island arc fragments has recently occurred in the southeastern part of the Cape Kamchatka peninsula. 相似文献
144.
145.
Tibor Guzmics Roger H. Mitchell Csaba Szabó Márta Berkesi Ralf Milke Rainer Abart 《Contributions to Mineralogy and Petrology》2011,161(2):177-196
Kerimasi calciocarbonatite consists principally of calcite together with lesser apatite, magnetite, and monticellite. Calcite
hosts fluid and S-bearing Na–K–Ca-carbonate inclusions. Carbonatite melt and fluid inclusions occur in apatite and magnetite,
and silicate melt inclusions in magnetite. This study presents statistically significant compositional data for quenched S-
and P-bearing, Ca-alkali-rich carbonatite melt inclusions in magnetite and apatite. Magnetite-hosted silicate melts are peralkaline
with normative sodium-metasilicate. On the basis of our microthermometric results on apatite-hosted melt inclusions and forsterite–monticellite
phase relationships, temperatures of the early stage of magma evolution are estimated to be 900–1,000°C. At this time three
immiscible liquid phases coexisted: (1) a Ca-rich, P-, S- and alkali-bearing carbonatite melt, (2) a Mg- and Fe-rich, peralkaline
silicate melt, and (3) a C–O–H–S-alkali fluid. During the development of coexisting carbonatite and silicate melts, the Si/Al
and Mg/Fe ratio of the silicate melt decreased with contemporaneous increase in alkalis due to olivine fractionation, whereas
the alkali content of the carbonatite melt increased with concomitant decrease in CaO resulting from calcite fractionation.
Overall the peralkalinity of the bulk composition of the immiscible melts increased, resulting in a decrease in the size of
the miscibility gap in the pseudoquaternary system studied. Inclusion data indicate the formation of a carbonatite magma that
is extremely enriched in alkalis with a composition similar to that of Oldoinyo Lengai natrocarbonatite. In contrast to the
bulk compositions of calciocarbonatite rocks, the melt inclusions investigated contain significant amount of alkalis (Na2O + K2O) that is at least 5–10 wt%. The compositions of carbonatite melt inclusions are considered as being better representatives
of parental magma composition than those of any bulk rock. 相似文献
146.
Victoria F. Sachse Ralf Littke Sabine Heim Oliver Kluth Jürgen Schober Lahcen Boutib Haddou Jabour Ferdinand Perssen Sven Sindern 《Organic Geochemistry》2011,42(3):209-227
This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstruct its geochemical history. Outcrop samples covering different stratigraphic intervals, plus the northwestern part of the Zag/Tindouf Basin (Bas Draa area), were analyzed for total organic carbon (Corg) and total inorganic carbon contents and total sulfur content. Rock-Eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis Corg content. A set of 45 samples were extracted and non-aromatic hydrocarbons were analyzed by way of gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (GC-MS). Non-isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks.High quality petroleum source rocks with high Corg content and hydrogen index (HI) values were found for samples of Eocene, Coniacian, Turonian and Cenomanian age. Most samples were carbonate rich and organic/sulfur values were high to moderate. Various maturity parameters indicated immature or possibly early mature organic matter. Based on organic geochemical and petrological data, the organic matter is of marine/aquatic origin (Cenomanian) or a mixture of aquatic and terrigenous material (Eocene). The Early Cretaceous interval did not contain high quality source rocks, but indications of petroleum impregnation were found. 相似文献
147.
Andi Walther Marc Schröder Jürgen Fischer Ralf Bennartz 《Theoretical and Applied Climatology》2014,118(4):627-640
Observational data and simulations of the regional climate system Baltic integrated model system (BALTIMOS) were used to study precipitation in the Baltic Sea and its drainage basin with a special focus on the diurnal cycle. The study includes a general evaluation of BALTIMOS precipitation, showing that BALTIMOS has too many light rain events causing an overestimation of the total annual precipitation amount. The diurnal cycle as well as its spatial distribution was analysed. BALTIMOS captures the broad characteristics: a significant diurnal variability with an afternoon peak above land and weak variability with a nocturnal peak above sea. An algorithm to distinguish between frontal and convective precipitation was applied to examine the diurnal cycle more thoroughly. The local solar time of maximum rain in summer is about 1 to 2 h earlier in BALTIMOS than in radar observations of precipitation. 相似文献
148.
A regional groundwater management system has been elaborated, integrating Relational Database Management System (RDBMS) and various web services. It consists of web geospatial application so-called HydrIS (Hydrogeological Information System) based on Open Source components and technologies, leading to a feasible and low-cost solution. Therefore, HydrIS permits delivery of data from a number of heterogeneous sources to standards supported by the Open Geospatial Consortium (OGC). The protocols used for exchanging data are also derived from OGC standards, i.e., WMS (Web Mapping Service), WFS (Web Feature Service), and WCS (Web Coverage Service). Finally, a geoportal was developed, which consists of client-applications that communicate with different Web Services (WMS, WCS, and WFS) through http-requests. 相似文献
149.
Pavel SPURNÝ Philip A. BLAND Lukáš SHRBENÝ Jiří BOROVIČKA Zdeněk CEPLECHA Andrew SINGELTON Alex W. R. BEVAN David VAUGHAN Martin C. TOWNER Terence P. McCLAFFERTY Ralf TOUMI Geoff DEACON 《Meteoritics & planetary science》2012,47(2):163-185
Abstract– We report an analysis of the first instrumentally observed meteorite fall in Australia, which was recorded photographically and photoelectrically by two eastern stations of the Desert Fireball Network (DFN) on July 20, 2007. The meteoroid with an initial mass of 22 kg entered the atmosphere with a low speed of 13.36 km s?1 and began a luminous trajectory at an altitude of 62.83 km. In maximum, it reached ?9.6 absolute magnitude and terminated after a 5.7 s and 64.7 km long flight at an altitude of 29.59 km with a speed of 5.8 km s?1. The angle of the atmospheric trajectory to the Earth’s surface was 30.9°. The first organized search took place in October 2008 and the first meteorite (150 g) was found 97 m southward from the predicted central line at the end of the first day of searching (October 3, 2008). The second stone (174 g) was recovered 39 m northward from the central line, both exactly in the predicted mass limits. During the second expedition in February 2009, a third fragment of 14.9 g was found again very close (~100 m) from the predicted position. Total recovered mass is 339 g. The meteorite was designated Bunburra Rockhole (BR) after a nearby landscape structure. This first DFN sample is an igneous achondrite. Initial petrography indicated that BR was a brecciated eucrite but detailed analyses proved that BR is not a typical eucrite, but an anomalous basaltic meteorite ( Bland et al. 2009 ). BR was delivered from an unusual, Aten type orbit (a < 1 AU) where virtually the entire orbit was contained within Earth’s orbit. BR is the first achondrite fall with a known orbit and it is one of the most precise orbits ever calculated for a meteorite dropping fireball. 相似文献
150.
Ralf C.M. VerdonschotPiet F.M. Verdonschot 《Limnologica》2012,42(1):31-42
Variation in habitat structure provided by macrophytes is regarded as one of the determinants of macroinvertebrate species composition in lentic ecosystems, but mechanisms underlying this relationship appear to be confounded with site-specific factors, such as physicochemical factors, epiphyton and composition of the vegetation. To better understand the relationship between structural complexity of a macrophyte stand and its macroinvertebrate assemblage composition, it is essential to determine the ecological role of different components of habitat structure for the phytomacrofauna. Using artificial structures as macrophyte mimics, representing three growth forms (stems, broad-leaved, finely dissected) and three structure surface areas (0.1, 0.2, 0.3 m2), a full factorial field experiment was conducted in a series of drainage ditches. We investigated if macroinvertebrate assemblages colonizing the structures were affected by an increase in macrophyte structure surface area, structural complexity, or by a combination of both, and if the observed patterns were consistent among sites differing in physicochemical and habitat characteristics. Assemblages were characterized both in terms of taxonomic and functional composition, because we expected that non-taxonomic aggregation of species into functional categories would give a different insight in habitat complexity-macroinvertebrate relationships in comparison to approaches based on the taxonomic assemblage composition. Ditch intrinsic factors, in part reflected in the periphyton on the structures, explained the major proportion of the variance in both the taxonomical macroinvertebrate assemblages and functional groups among structures. Contrary to our expectation, patterns in the taxon-based and functional dataset resembled each other. Only a minor contribution of growth form to the explained variance was observed in the taxonomical dataset, whilst differences in functional composition were unrelated to habitat structure. In conclusion, processes operating on larger spatial scales overrode the micro-scale effects of habitat structural complexity and surface area on macroinvertebrates. 相似文献