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161.
Cecilia Johansson Barbara Hennemuth Jens Bösenberg Holger Linné Ann-sofi Smedman 《Boundary-Layer Meteorology》2005,114(2):389-412
Double-layered structures found over the Baltic Sea are investigated using radiosoundings and lidar measurements. Situations with double-layer structures are also simulated with the regional model REMO in a realistic manner. The double layer consists of two adjacent well-mixed layers, with a sharp inversion in between.Results from radiosoundings show that the double-layer structure over the Baltic Sea mainly occurs during the autumn with thermally unstable stratification near the surface. The structure is present in about 50 % of the radiosoundings performed during autumn. The presence of the double-layer structure cannot be related to any specific wind direction, wind speed or sea surface temperature.The lidar measurements give a more continuous picture of the time evolution of the double-layer structure, and show that the top of the lower layer is not a rigid lid for vertical transport. Two possible explanations of the double-layer structure are given, (i) the structure is caused by `advection' of land boundary-layer air over the convective marine boundary layer or, (ii) by development of Sc clouds in weak frontal zones connected to low pressure systems. Also the forming of Cu clouds is found to be important for the development of a double-layer structure. 相似文献
162.
Werner Skrotzki Roland Tamm Carl-Georg Oertel Jens Rseberg Heinz-Günter Brokmeier 《Journal of Structural Geology》2000,22(11-12)
Lead sulfide (galena) of different purity and grain size was extruded through a round and rectangular die at temperatures between 773 and 923 K. Global and local lattice preferred orientations (here referred to as textures) were measured by neutron and electron back-scattering diffraction. Tension leads to a <100> <111> double fibre texture. Pure shear deformation yields texture components near the ideal face-centered cubic metal brass, copper, Goss and cube positions. The intensity of the components depends on the purity and/or grain size. The microstructure is partially recrystallized. Electron back-scattering diffraction indicates that in tension the <100> and in pure shear the Goss and cube components are associated with dynamic recrystallization. The deformation texture can be qualitatively explained by the full and relaxed constraints Taylor model using slip on {100}<110>, {110}<110> and {111}<110> systems. The texture formation in lead sulfide compares well with that observed for other ionic crystals with the NaCl-structure as well as for face-centered cubic metals with a high stacking fault energy. 相似文献
163.
164.
Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling 总被引:32,自引:1,他引:31
Yilin Xiao Jochen Hoefs Alfons M. van den Kerkhof Jens Fiebig Yongfei Zheng 《Contributions to Mineralogy and Petrology》2000,139(1):1-16
This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive
H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater
and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding
episodes of mafic magmatism (from 10,600 to ∼3000 14C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine
Lake system have not always been low H2O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous
mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites
contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence
of H2O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined
to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization
of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to
the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted
granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by
hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes.
Received: 4 January 1999 / Accepted: 30 August 1999 相似文献
165.
Hermann D. Bermúdez Jenny García Wolfgang Stinnesbeck Gerta Keller José Vicente Rodríguez Michael Hanel Jens Hopp Winfried H. Schwarz Mario Trieloff Liliana Bolívar Francisco J. Vega 《地学学报》2016,28(1):83-90
The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit. 相似文献
166.
167.
In 2005, a German research project was started to develop a novel approach to prove safety for a HLW repository in a salt formation, to refine the safety concept, to identify open scientific issues and to define necessary R&D work. This project aimed at identifying the key information for a HLW repository in salt. One important question is how this information may be best fulfilled by natural analogue studies. This question is answered by starting a review of the required key information needs of the safety case (post-closure phase) in order to assess whether or not these requirements can be supported by natural analogues information. In order to structure the review and to address the key elements of the safety concepts, three types of natural analogues are distinguished: (i) natural analogues for the integrity of the geological barrier, (ii) natural analogues for the integrity of the geotechnical barriers and (iii) natural analogues for release scenarios. For the safety case in salt type (i) and (ii) are of highest importance and are treated in this paper. The assessment documented in this paper on the one hand indicates the high potential benefit of natural analogues for a safety case in salt and on the other hand helps to focus the available human and financial resources for the safety case on the most safety-relevant aspects. 相似文献
168.
Donald Lewis Bowden John C. Bridges Agnes Cousin William Rapin Julia Semprich Olivier Gasnault Olivier Forni Patrick Gasda Debarati Das Valerie Payré Violaine Sautter Candice C. Bedford Roger C. Wiens Patrick Pinet Jens Frydenvang 《Meteoritics & planetary science》2023,58(1):41-62
Askival is a light-toned, coarsely crystalline float rock, which was identified near the base of Vera Rubin Ridge in Gale crater. We have studied Askival, principally with the ChemCam instrument but also using APXS compositional data and MAHLI images. Askival and an earlier identified sample, Bindi, represent two rare examples of feldspathic cumulate float rocks in Gale crater with >65% relict plagioclase. Bindi appears unaltered whereas Askival shows textural and compositional signatures of silicification, along with alkali remobilization and hydration. Askival likely experienced multiple stages of alteration, occurring first through acidic hydrolysis of metal cations, followed by deposition of silica and possible phyllosilicates at low T and neutral-alkaline pH. Through laser-induced breakdown spectroscopy compositional analyses and normative calculations, we suggest that an assemblage of Fe-Mg silicates including amphibole and pyroxene, Fe phases, and possibly Mg-rich phyllosilicate are present. Thermodynamic modeling of the more pristine Bindi composition predicts that amphibole and feldspar are stable within an upper crustal setting. This is consistent with the presence of amphibole in the parent igneous rocks of Askival and suggests that the paucity of amphiboles in other known Martian samples reflects the lack of representative samples of the Martian crust rather than their absence on Mars. 相似文献
169.
Sebastián Tomás Sánchez Gómez Jens Ormö Carl Alwmark Sanna Holm-Alwmark Gabriel Zachén Robert Lilljequist Juan Antonio Sánchez Garrido 《Meteoritics & planetary science》2023,58(10):1512-1539
The Tabernas–Alhabia Basin is a structural depression situated in the province of Almería, southeastern Spain. The basin is filled with Neogene, Pliocene, and Pleistocene sediments resting discordantly on a Paleozoic metamorphic basement. During the marine Tortonian sedimentation, a bed of breccia (Gordo megabed) was formed. It consists of rotated sedimentary megablocks commonly capped and/or surrounded by a polymict breccia composed mainly of up to dm-sized clasts of the crystalline (schist) basement. Previous work has suggested the bed to be a seismite corresponding to events induced by earthquakes. Here, we link the formation of the Gordo megabed with an ∼5 km wide, rimmed depression with exposed breccias on the northern flank of the Sierra de Gádor mountain. This semicircular structure, developed in mainly schists and dolostone of the basement, is delimited to the W, S, and E by an up to 350 m high escarpment with overturned stratigraphy. Toward the north, this crater-like structure opens toward the Gordo megabed of the Tabernas Basin. In the southern sector, the overturned strata transform outward for into a blocky allochthonous breccia with decreasing thickness and clast size. In the interior of the structure, there are occurrences of graded breccia and arenite superposed on a blocky, autochthonous breccia. Based on the presence of mineralogical shock metamorphic evidence, potential shatter cones, and a high Ir anomaly (∼500 ppb) as well as the position of the structure near the town of Alhama de Almería, we propose to call it the Alhama de Almería impact structure. 相似文献
170.
Lucia Villar-Muñoz Jan H. Behrmann Juan Diaz-Naveas Dirk Klaeschen Jens Karstens 《Geo-Marine Letters》2014,34(2-3):185-198
Between 33°S and 47°S, the southern Chile forearc is affected by the subduction of the aseismic Juan Fernandez Ridge, several major oceanic fracture zones on the subducting Nazca Plate, the active Chile Ridge spreading centre, and the underthrusting Antarctic Plate. The heat flow through the forearc was estimated using the depth of the bottom simulating reflector obtained from a comprehensive database of reflection seismic profiles. On the upper and middle continental slope along the whole forearc, heat flow is about 30–60 mW m–2, a range of values common for the continental basement and overlying slope sediments. The actively deforming accretionary wedge on the lower slope, however, in places shows heat flow reaching about 90 mW m–2. This indicates that advecting pore fluids from deeper in the subduction zone may transport a substantial part of the heat there. The large size of the anomalies suggests that fluid advection and outflow at the seafloor is overall diffuse, rather than being restricted to individual fault structures or mud volcanoes and mud mounds. One large area with very high heat flow is associated with a major tectonic feature. Thus, above the subducting Chile Ridge at 46°S, values of up to 280 mW m–2 indicate that the overriding South American Plate is effectively heated by subjacent zero-age oceanic plate material. 相似文献