Melting of Amphibole-bearing Wehrlites: an Experimental Study on the Origin of Ultra-calcic Nepheline-normative Melts   总被引：2，自引：0，他引：2  

MEDARD  ETIENNE; SCHMIDT  MAX W.; SCHIANO  PIERRE; OTTOLINI  LUISA 《Journal of Petrology》2006,47(3):481-504

Olivine + clinopyroxene ± amphibole cumulates have beenwidely documented in island arc settings and may constitutea significant portion of the lowermost arc crust. Because ofthe low melting temperature of amphibole (1100°C), suchcumulates could melt during intrusion of primary mantle magmas.We have experimentally (piston-cylinder, 0·5–1·0GPa, 1200–1350°C, Pt–graphite capsules) investigatedthe melting behaviour of a model amphibole–olivine–clinopyroxenerock, to assess the possible role of such cumulates in islandarc magma genesis. Initial melts are controlled by pargasiticamphibole breakdown, are strongly nepheline-normative and areAl₂O₃-rich. With increasing melt fraction (T > 1190°Cat 1·0 GPa), the melts become ultra-calcic while remainingstrongly nepheline-normative, and are saturated with olivineand clinopyroxene. The experimental melts have strong compositionalsimilarities to natural nepheline-normative ultra-calcic meltinclusions and lavas exclusively found in arc settings. Theexperimentally derived phase relations show that such naturalmelt compositions originate by melting according to the reactionamphibole + clinopyroxene = melt + olivine in the arc crust.Pargasitic amphibole is the key phase in this process, as itlowers melting temperatures and imposes the nepheline-normativesignature. Ultra-calcic nepheline-normative melt inclusionsare tracers of magma–rock interaction (assimilative recycling)in the arc crust. KEY WORDS: experimental melting; subduction zone; ultra-calcic melts; wehrlite  相似文献   

Grain-size information from the statistical properties of digital images of sediment     

DANIEL BUSCOMBE  GERHARD MASSELINK 《Sedimentology》2009,56(2):421-438

The autocorrelation technique for estimating grain-size from digital images of sand beds has been extended and validated for use on coarse sand (0·7 mm) and gravel (up to ∼20 mm). A number of aspects of the technique have been explored and some potential improvements suggested. Autocorrelation is just one suitable statistical method sensitive to the grain-size of sediment in digital images; four additional techniques are presented and their relative merits discussed. A collective suite of techniques applicable to the general problem of grain-size estimation from digital images of sediment might broaden the applicability to more sedimentary environments, as well as improve its accuracy. These techniques are compared using a large data set from a gravel barrier beach in southern England. Based on over 180 samples, mean grain-size of sieved and imaged sediments correspond to within between 8% and 16%. Some theoretical aspects of the spatial arrangement of image intensity in digital images of natural sediments are addressed, including the fractal nature of sediments in images, which has potential implications for derivation of grain-size distributions from images of sand-sized material through segmentation and thresholding. The methods outlined in this contribution may also find application in further uncovering the geometric structure of sediment beds, as well as in the simulation of sedimentation processes.  相似文献   

Chironomids as indicators of the Holocene climatic and environmental history of two lakes in Northeast Greenland     

STEFFI SCHMIDT  BERND WAGNER  OLIVER HEIRI  MARTIN KLUG  OLE BENNIKE  MARTIN MELLES 《Boreas: An International Journal of Quaternary Research》2011,40(1):116-130

Schmidt, S., Wagner, B., Heiri, O., Klug, M., Bennike, O. & Melles, M. 2010: Chironomids as indicators of the Holocene climatic and environmental history of two lakes in Northeast Greenland. Boreas, 10.1111/j.1502‐3885.2010.00173.x. ISSN 0300‐9483. Two Holocene sediment sequences from arctic lakes on Store Koldewey, an island in Northeast Greenland, were investigated for fossil chironomid assemblages. A total of 18 and 21 chironomid taxa were identified in 290‐ and 252‐cm‐long sediment sequences from Duck Lake and Hjort Lake, respectively. The chironomid assemblages were very similar in the two lakes. Canonical correspondence analysis (CCA) was used to compare fossil chironomid assemblages from Store Koldewey with chironomid assemblages and environmental conditions presently found in Canadian Arctic lakes and, hence, to infer environmental changes for Northeast Greenland. The first chironomids appeared at c. 9500 cal. a BP in Hjort Lake, and 500 years later in Duck Lake. Taxa typical for cold and nutrient‐poor arctic lakes dominated the earliest assemblages. Chironomid assemblages with taxa typical of higher summer air temperatures and lakes with higher nutrient availability occur between 8000 and 5000 cal. a BP. This period probably marks the regional Holocene thermal maximum, which is relatively late compared with some palaeoenvironmental records from East Greenland. One possible reason could be the location of Store Koldewey at the very outer coast, with local climatic conditions strongly influenced by the cold East Greenland Current. From around 5000 cal. a BP, chironomid assemblages in Duck Lake and Hjort Lake again became more typical of those presently found in Northeast Greenland, indicating relatively cold and nutrient‐poor conditions. This shift coincides with an increase of ice‐rafting debris off East Greenland and an intensification of the East Greenland Current.  相似文献   

Size-dependent aerosol activation at the high-alpine site Jungfraujoch (3580 m asl)     

S. HENNING  E. WEINGARTNER  S. SCHMIDT  M. WENDISCH  H. W. GÄGGELER  U. BALTENSPERGER 《Tellus. Series B, Chemical and physical meteorology》2002,54(1):82-95

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The stability of a zonally averaged thermohaline circulation model     

G. A. SCHMIDT  L. A. MYSAK 《地球，A辑:动力气象学与海洋学》1996,48(1):158-178

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The Western Baltic sea ice season in terms of a mass-related severity index 1879–1992     

PETER LOEWE  GERHARD KOSLOWSKI 《地球，A辑:动力气象学与海洋学》1998,50(2):219-241

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有机组分土-水分配系数的确定(英文)     

Erping BI　 Torsten SCHMIDT 《地学前缘》2005,12(Z1):199-208

有机组分的土水分配系数(Kd)是描述有机组分在地下系统中吸附特征的重要参数。同时,它也是物质运移模拟和环境评价中的主要参数之一。影响Kd的因素可概括为三个方面:土壤性质、有机组分本身特征及水相的物理化学性质。一般而言,对于非极性和弱极性有机组分,土壤中的有机质含量(foc )是影响Kd的最主要因素。但是,对于极性有机组分(POCs), 特别是在土壤有机质含量较低的情况下,土壤中矿物的种类和含量、水化学组分特征(pH、离子力等)经常在吸附过程中起重要作用。实验室内测定Kd的方法包括批实验和柱实验方法。批实验法适用于研究Kd较高情况下的吸附。在Kd较低的情况下,如低有机质土壤对极性有机污染物的吸附,土柱色谱法(SCC)是更适宜的选择。另外,可用土柱色谱法快速了解各种因素对吸附过程的影响,并获取详细的吸附和解吸信息。应用土柱色谱法时应当注意非平衡吸附和可能的柱堵塞问题。很多文献中提到结合柱实验和已有的吸附数据来预测土壤有机碳标准化的分配系数Koc(=Kd/foc)。但是,如果没有考虑吸附中特定的作用过程(如矿物吸附),对极性有机组分Koc的预测将会产生很大的误差。在环境评价中,将从一种土壤测定的Koc 应用到不同性质的土壤中,可能会导致错误的认识。在进行室内实验时,应把标准土(如Eurosoi  相似文献   

Six-year record of atmospheric carbon dioxide and methane at a high-altitude mountain site in Poland   总被引：2，自引：0，他引：2  

JAROSLAW NECKI  MARTINA SCHMIDT  KAZIMIERZ ROZANSKI  MIROSLAW ZIMNOCH  ADAM KORUS  JAN LASA  ROLF GRAUL  INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):94-104

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Partial Melting and Assimilation of Dolomitic Xenoliths by Mafic Magma: the Ioko-Dovyren Intrusion (North Baikal Region, Russia)   总被引：5，自引：0，他引：5  

WENZEL  THOMAS; BAUMGARTNER  LUKAS P.; BRUGMANN  GERHARD E.; KONNIKOV  EDUARD G.; KISLOV  EVGENIY V. 《Journal of Petrology》2002,43(11):2049-2074

A petrological study was carried out on Mg-skarn-bearing dunitecumulates that are part of the Neo-Proterozoic Ioko-Dovyrenintrusion (North Baikal region, Russia). Skarn xenoliths containbrucite pseudomorphs after periclase, forsterite and Cr-poorspinel. Fine-grained forsterite–spinel skarns occur withthe brucite skarns or as isolated schlieren. Field relationshipsreveal that the Mg-skarns formed from silica-poor dolomiticxenoliths by interaction with the mafic magma of the Ioko-Dovyrenintrusion. Rapid heating of dolomitic xenoliths by the maficmagma caused the decomposition of dolomite into calcite + periclase,releasing much CO₂. Further heating quantitatively melted thecalcite. A periclase-rich restite was left behind after extractionof the low-density, low-viscosity calcite melt. The extractedcalcite melt mixed with the surrounding mafic melt. This resultedin crystallization of olivine with CaO contents up to 1·67wt %. A local decrease in the silica concentration stabilizedCaAl₂SiO₆-rich clinopyroxene. Brucite/periclase-free forsterite–spinelskarns probably originated by crystallization from the maficmelt close to the xenoliths at elevated fO₂. The high fO₂ wascaused by CO₂-rich fluids released during the decompositionof the xenoliths. The above case study provides the first evidencefor partial melting of dolomite xenoliths during incorporationby a mafic magma. KEY WORDS: dunite; dolomite assimilation; partial melting  相似文献   

High-Pressure Metamorphism in the SW Tauern Window, Austria: P-T Paths from Hornblende-Kyanite-Staurolite Schists     

SELVERSTONE  JANE; SPEAR  FRANK S.; FRANZ  GERHARD; MORTEANI  GIULIO 《Journal of Petrology》1984,25(2):501-531

The hornblende garbenschist horizon of the Lower Schieferhulleseries (LSH) in the SW Tauern Window, Austria, contains theassemblage hornblende + kyanite + staurolite + garnet + biotite+ epidote + plagioclase + ankerite + quartz + rutile + ilmenite,with either chlorite or paragonite present in all samples. Theseassemblages are divariant in the system SiO₂-Al₂O₃-TiO₂-Fe₂O₃-MgO-FeO-MnO-CaO-Na₂O-K₂O-H₂O-CO₂.Garnet-biotite geothermometry yields temperatures of final equilibrationof {small tilde}550 °C, and garnet-plagioclase-kyanite-quartzgeobarometry indicates pressures of 6–8 kb for the matrixassemblage and 9–10 kb for plagioclase inclusions in garnet.Quantitative modelling of zoned garnet, hornblende, and plagioclaseindicates growth and equilibration along a decompression pathfrom {small tilde}530 °C, 10 kb to {small tilde}550 °C,7 kb. Fluid inclusion data constrain the uplift path to havepassed through a point at {small tilde} 375 °C, 1.5 kb. These data permit the construction of a relatively completeP-T loop for metamorphism associated with the Alpine orogeniccycle in the LSH of the SW Tauern Window. The maximum pressureconditions ({small tilde}10 kb at 530 °C) recorded alongthis loop are considerably higher than previous estimates of5–7 kb for the region. Simple overthrust models developedfor the Tauern Window cannot account for pressures of this magnitude;a more likely scenario involves partial subduction of the rocksto a depth of {small tilde}35 km, followed by prolonged heatingin response to decay of the subduction isotherms. Initial upliftappears to have been rapid and occurred along a nearly isothermalpath. Significant cooling did not occur until the rocks werewithin {small tilde}5 km of the surface. Detailed tectonic modelsfor the evolution of the Tauern Window must be able to accountfor the quantitative features of the P-T loop.  相似文献