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DENIS-DIDIER ROUSSEAU NICOLE LIMONDIN FRÉDÉRIC MAGNIN JEAN-JACQUES PUISSEGUR 《Boreas: An International Journal of Quaternary Research》1994,23(1):66-73
Snail assemblages are used to estimate February and August temperatures during the past 10,000 years in western Europe. We find that a strong warming occurred after the Younger Dryas event, followed by several rapid cooling and warming events. These observations are in agreement with insect and pollen proxy data from the European continent and with estimates of sea-surface temperature from the North Atlantic Ocean as well as with fluctuations of glaciers in western Norway. This study also confirms that terrestrial molluscs can provide reliable climatic data in conjunction with other proxy data. 相似文献
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A new, detailed tectonic model is presented for the Acadianorogenic belt of central New England (Vermont and New Hampshire)that accounts for a wide range of petrological and structuralobservations. Three belts are considered: the Eastern Vermont,Merrimack, and intervening Bronson Hill belts. Specific observationsin eastern Vermont that are accounted for in the model includethe following. P–T paths are clockwise with maximum pressuresnear the Athens, Chester, and Strafford domes of 8–11kbar, but with maximum pressures decreasing to 3–5 kbarat the boundary with the Bronson Hill belt. Differential exhumationof the Vermont domes relative to the rocks in easternmost Vermontis required by the recorded differences in maximum pressure(5–6 kbar; 15–20 km) and the present-day geographicalseparation (7–10 km). Specific observations in New Hampshirethat are explained include the following. P–T paths inthe Merrimack belt are counter-clockwise with maximum pressuresof 4–5 kbar and are related to high regional heat flowand heat transfer by early Acadian plutons. P–T pathsin the Bronson Hill belt are intimately associated with structuralposition. An early contact metamorphism is evidenced in theSkitchewaug and Fall Mountain nappes near contacts with theearly Acadian Bethlehem gneiss ( 相似文献
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A model for garnet and plagioclase growth in pelitic schists: implications for thermobarometry and P-T path determinations 总被引：2，自引：1，他引：2
Numerical models of the progressive evolution of pelitic schists in the NCMnKFMASH system with the assemblage garnet + biotite + chlorite ± staurolite + plagioclase + muscovite + quartz + H2O are presented with the goal of predicting compositional changes in garnet and plagioclase along different P-T paths. The numerical models support several conclusions that should prove useful for interpreting the P-T paths of natural parageneses: (i) Garnet may grow along P-T vectors ranging from heating with decompression to cooling with compression. P-T paths deduced from garnet zoning that are inconsistent with these growth vectors are self-contradictory. (ii) There is a systematic relation between garnet and plagioclase composition and growth such that for most P-T paths, garnet growth requires plagioclase consumption. Furthermore, mass balance in a closed system requires that as plagioclase is consumed the remaining plagioclase becomes increasingly albitic. Inclusions of plagioclase in the core of garnet should be more anorthitic than those near the rim and zoned matrix plagioclase should have rims that are more albitic than the cores. Complex plagioclase textures may arise from the local variability of growth and precipitation kinetics. (iii) A decrease of Fe/(Fe + Mg) in a garnet zoning profile is a reliable indicator of increasing temperature for the assemblage modelled. However, there is no single reliable ΔP monitor and inferences about ΔP can only be made by considering plagioclase and garnet together. (iv) Consumption of garnet during the production of staurolite removes material from the outer shell of a garnet and may make recovery of peak metamorphic compositions and P-T conditions impossible. Low ‘peak’temperatures typically recorded by staurolite-bearing assemblages may reflect this phenomenon. (v) Diffusional homogenization of garnet affects the computed P-T path and results in a clockwise rotation of the computed P-T vector relative to the true P-T path. 相似文献
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PHILIP DELINE MARIE GARDENT FLORENCE MAGNIN LUDOVIC RAVANEL 《Geografiska Annaler: Series A, Physical Geography》2012,94(2):265-283
One of the most glacierized areas in the European Alps, the Mont Blanc massif, illustrates how fast changes affect the cryosphere and the related morphodynamics in high mountain environments, especially since the termination of the Little Ice Age. Contrasts between the north‐west side, gentle and heavily glaciated, and the south‐east side, steep and rocky, and between local faces with varying slope angle and aspect highlight the suitability of the study site for scientific investigations. Glacier shrinkage is pronounced at low elevation but weaker than in other Alpine massifs, and supraglacial debris covers have developed over most of the glaciers, often starting in the nineteenth century. Lowering of glacier surface also affects areas of the accumulation zone. While modern glaciology has been carried out in the massif for several decades, study of the permafrost has been under development for only a few years, especially in the rock walls. Many hazards are related to glacier dynamics. Outburst flood from englacial pockets, ice avalanche from warm‐based and cold‐based glaciers, and rock slope failure due to debuttressing are generally increasing with the current decrease or even the vanishing of glaciers. Permafrost degradation is likely involved in rockfall and rock avalanche, contributing to the chains of processes resulting from the high relief of the massif. The resulting hazards could increasingly endanger population and activities of the valleys surrounding the Mont Blanc massif. 相似文献
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KIEFFER BRUNO; ARNDT NICHOLAS; LAPIERRE HENRIETTE; BASTIEN FLORENCE; BOSCH DELPHINE; PECHER ARNAUD; YIRGU GEZAHEGN; AYALEW DEREJE; WEIS DOMINIQUE; JERRAM DOUGAL A.; KELLER FRANCINE; MEUGNIOT CLAUDINE 《Journal of Petrology》2004,45(4):793-834
The Ethiopian plateau is made up of several distinct volcaniccentres of different ages and magmatic affinities. In the NE,a thick sequence of 30 Ma flood basalts is overlain by the 30Ma Simien shield volcano. The flood basalts and most of thisshield volcano, except for a thin veneer of alkali basalt, aretholeiitic. In the centre of the province, a far thinner sequenceof flood basalt is overlain by the 22 Ma Choke and Guguftu shieldvolcanoes. Like the underlying flood basalts, these shieldsare composed of alkaline lavas. A third type of magma, whichalso erupted at 30 Ma, is more magnesian, alkaline and stronglyenriched in incompatible trace elements. Eruption of this magmawas confined to the NE of the province, a region where the lavaflows are steeply tilted as a result of deformation contemporaneouswith their emplacement. Younger shields (e.g. Mt Guna, 10·7Ma) are composed of Si-undersaturated lavas. The three maintypes of magma have very different major and trace element characteristicsranging from compositions low in incompatible elements in thetholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/Yb = 4·2],moderate in the alkali basalts (La7 = 24, La/Yb = 9·2),and very high in the magnesian alkaline magmas (La7 = 43, La/Yb= 17). Although their Nd and Sr isotope compositions are similar,Pb isotopic compositions vary considerably; 206Pb/204Pb variesin the range of 相似文献
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