Slope transport processes and hydrology. A tribute to Jan Nieuwenhuis     

Th.W.J. Van Asch  E.F.J. de Mulder 《Engineering Geology》2007,91(1):1-3

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Depleted lithosphere from the mantle wedge beneath Tres Lagos, southern Patagonia, Argentina   总被引：1，自引：0，他引：1  

Th. Ntaflos  E.A. Bjerg  C.H. Labudia  G. Kurat 《Lithos》2007,94(1-4):46-65

Anhydrous spinel lherzolite and harzburgite xenoliths from Tres Lagos, situated inboard of the Volcanic Arc Gap (VAG) in southernmost Patagonia, are samples of a depleted lithospheric mantle and can be divided into two major groups: metasomatized and non-metasomatized. Metasomatized samples, which are the minority, are partly mylonitized and their metasomatism is related to this tectonic process. A group of non-metasomatized samples have enriched whole rock LREE-abundances that are not consistent with the depleted LREE-abundances in their clinopyroxenes. Intergranular host basalt infiltration could be responsible for the whole rock LREE enrichments. Their Sr- and Nd-isotopic ratios have also been affected by host basalt infiltration, whereas their high Sr-isotopic ratios point to subsequent contamination by ground-water and/or Ca-rich surface solutions. Similar contamination is thought to cause the decoupling of Sr- and Nd-isotopes (high Sr- and Nd-isotopic ratios) observed in the non-metasomatized samples with depleted whole rock LREE. A two-stage partial melting process could be responsible for the origin of the Tres Lagos xenoliths. Model calculations have shown that in the first stage, 2% of batch melting took place in the garnet peridotite field and subsequently the residue experienced 2–8% batch melting in the spinel peridotite field. The Tres Lagos peridotites have not been affected by subduction-related metasomatic processes and they could represent an old lithospheric mantle.  相似文献   

A Tsunami Risk Management Pilot Study in Heraklion,Crete     

Papadopoulos  Gerassimos A.  Dermentzopoulos  Th. 《Natural Hazards》1998,18(2):91-118

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Shallow gas in the muddy sediments of Eckernförde Bay, Germany     

Th. F. Wever  F. Abegg  H. M. Fiedler  G. Fechner  I. H. Stender 《Continental Shelf Research》1998,18(14-15)

The seafloor of central Eckernförde Bay is characterised by soft muddy sediments that contain free methane gas. Bubbles of free gas cause acoustic turbidity which is observed with acoustic remote sensing systems. Repeated surveys with subbottom profiler and side scan sonar revealed an annual period both of depth of the acoustic turbidity and backscatter strength. The effects are delayed by 3–4 months relative to the atmospheric temperature cycle. In addition, prominent pockmarks, partly related to gas seepage, were detected with the acoustic systems. In a direct approach gas concentrations were measured from cores using the gas chromatography technique. From different tests it is concluded that subsampling of a core should start at its base and should be completed as soon as possible, at least within 35 min after core recovery. Comparison of methane concentrations of summer and winter cores revealed no significant seasonal variation. Thus, it is concluded that the temperature and pressure influences upon solubility control the depth variability of acoustic turbidity which is observed with acoustic remote sensing systems. The delay relative to the atmospheric temperature cycle is caused by slow heat transfer through the water column. The atmospheric temperature cycle as ‘exiting function’ for variable gas solubility offers an opportunity for modelling and predicting the depth of the acoustic turbidity. In practice, however, small-scale variations of, e.g., salinity, or gas concentration profile in the sediment impose limits to predictions. In addition, oceanographic influences as mixing in the water column, variable water inflow, etc. are further complications that reduce the reliability of predictions.  相似文献   

A note on the feldspars in the granite xenoliths of the nyiragongo magma     

M. Lehtinen  Th. G. Sahama 《Bulletin of Volcanology》1981,44(3):451-454

The lavas of the Nyiragongo volcano in Eastern Zaire contain partially fused granite xenoliths. The relictic feldspars found in these xenoliths were studied by microprobe analysis and by X-ray diffraction methods. Some xenoliths represent originally two-feldspar granites, in others only alkali feldspars or those of an anorthoclase composition were detected. All feldspars are homogeneous without perthitic textures detectable under the microscope. In thebc-diagram of Stewart and Wright all feldspars plot on the analbite-high sanidine join. These feldspars have been perfectly disordered through heating in the melilite-nephelinite magma of the volcano.  相似文献   

On the thermal stability of Rb-Sr and K-Ar biotite systems: Evidence from coexisting Sveconorwegian (ca 870 Ma) and Caledonian (ca 400 Ma) biotites in SW Norway   总被引：3，自引：0，他引：3  

R. H. Verschure  P. A. M. Andriessen  N. A. I. M. Boelrijk  E. H. Hebeda  C. Maijer  H. N. A. Priem  E. A. Th. Verdurmen 《Contributions to Mineralogy and Petrology》1980,74(3):245-252

The Caledonian orogeny has imposed a zone of greenschist facies metamorphism on the high-grade Sveconorwegian basement along the front of the Caledonian nappe system in S.W. Norway. In this zone a Caledonian generation of green biotite (ca 400 Ma old) has developed, indicating a metamorphic temperature of about 400° C. This Caledonian biotite occurs side by side with relicts of a Sveconorwegian generation of brown biotite (ca 870 Ma old). The somewhat younger ages obtained from a number of brown biotites can be related to a partial transformation of the old biotite to titanite+green biotite during the Caledonian metamorphic recrystallization. Loss of radiogenic Ar and Sr from the biotite by volume diffusion apparently has not been operative, even at a temperature as high as 400° C. The Sveconorwegian biotite appears to have remained virtually closed to K-Ar and Rb-Sr up to the break-down due to metamorphic recrystallization.  相似文献   

Genesis of the Nyiragongo lavas     

Th. G. Sahama 《Bulletin of Volcanology》1964,27(1):195-195

Mt. Nyiragongo is one of the eight major volcanoes of the large Virunga volcanic field in the Lake Kivu area in the Eastern Congo. The lavas of Nyiragongo are rather unique. Starting from the top of the mountain, the rocks are nephelinites with some leucite and melilite. The molten material of the present-day lava lake belongs to this type of lava. Under the nephelinites, there is a thin series of leucite-rich lava beds. The main part of the volcano consists of bergalitic melitite lavas alternating with pyroclastics of similar composition. The nephelinitic material is considered to constitute the main portion of the pre-volcanic magma under the future volcano. It is pointed out that the Nyiragongo represents just the type of volcano with which the African volcanic carbonatites are associated. It is concluded that the Nyiragongo nephelinite must be interpreted in a way accepted for the Central African volcanic nephelinites in general. The bergalitic melilitite material is interpreted as a product of carbonation of the nephelinitic magma.  相似文献   

On the Elastic and Viscous Properties of Media Containing Strongly Interacting In-plane Cracks     

T. Dahm  Th. Becker 《Pure and Applied Geophysics》1998,151(1):1-16

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On the dynamics of the molecular temperature boundary layer above the sea     

Th. Foken  S. A. Kitajgorodskij  O. A. Kuznecov 《Boundary-Layer Meteorology》1978,15(3):289-300

Results of measurements carried out in the Caspian Sea in 1975 and 1976 have been used to study the thickness of the molecular temperature boundary layer and the difference of temperature in this layer as functions of hydrometeorological parameters. This thickness of the molecular temperature boundary layer was found to be dependent on both the friction velocity and wave phase. The same is also true for the temperature difference. On the other hand, it was not possible to observe a definite dependence upon the roughness of the surface of the sea and the stability.  相似文献   

The molecular temperature boundary layer of the atmosphere over various surfaces     

Dipl.-Met. Th. Foken 《Meteorology and Atmospheric Physics》1978,27(1):59-67

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