Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific)     

Roger Hekinian  Peter Stoffers  Dietrich Akermand  Nicolas Binard  Jean Francheteau  Colin Devey  Dieter Garbe-Schönberg 《Marine Geophysical Researches》1995,17(4):375-397

The Easter microplate-Crough Seamount region located between 25° S–116° W and 25° S–122° W consists of a chain of seamounts forming isolated volcanoes and elongated (100–200 km in length) en echelon volcanic ridges oriented obliquely NE (N 065°), to the present day general spreading direction (N 100°) of the Pacific-Nazca plates. The extension of this seamount chain into the southwestern edge of the Easter microplate near 26°30 S–115° W was surveyed and sampled. The southern boundary including the Orongo fracture zone and other shallow ridges (< 2000 m high) bounding the Southwest Rift of the microplate consists of fault scarps where pillow lava, dolerite, and metabasalts are exposed. The degree of rock alternation inferred from palagonitization of glassy margins suggests that the volcanic ridges are as old as the shallow ridges bounding the Southwest Rift of the microplate. The volcanics found on the various structures west of the microplate consist of depleted (K/Ti < 0.1), transitional (K/Ti = 0.11–0.25) and enriched (K/Ti > 0.25) MORBs which are similar in composition to other more recent basalts from the Southwest and East Rifts spreading axes of the Easter microplate. Incompatible element ratios normalized to chondrite values [(Ce/Yb)_N = 1–2.5}, {(La/Sm)_N = 0.4–1.2} and {(Zr/Y)_N = 0.7–2.5} of the basalts are also similar to present day volcanism found in the Easter microplate. The volcanics from the Easter microplate-Crough region are unrelated to other known South Pacific intraplate magmatism (i.e. Society, Pitcairn, and Salas y Gomez Islands). Instead their range in incompatible element ratios is comparable to the submarine basalts from the recently investigated Ahu and Umu volcanic field (Easter hotspot) (Scientific Party SO80, 1993) and centered at about 80 km west of Easter Island. The oblique ridges and their associated seamounts are likely to represent ancient leaky transform faults created during the initial stage of the Easter microplate formation ( 5 Ma). It appears that volcanic activity on seamounts overlying the oblique volcanic ridges has continued during their westward drift from the microplate as shown by the presence of relatively fresh lava observed on one of these structures, namely the first Oblique Volcanic Ridge near 25° S–118° W at about 160 km west of the Easter microplate West Rift. Based on a reconstruction of the Easter microplate, it is suggested that the Crough seamount (< 800 m depth) was formed by earlier (7–10 Ma) hotspot magmatic activity which also created Easter Island.  相似文献   

Characterizing hydraulic conductivity with the direct-push permeameter   总被引：2，自引：0，他引：2  

Butler JJ  Dietrich P  Wittig V  Christy T 《Ground water》2007,45(4):409-419

The direct-push permeameter (DPP) is a promising approach for obtaining high-resolution information about vertical variations in hydraulic conductivity (K) in shallow unconsolidated settings. This small-diameter tool, which consists of a short screened section with a pair of transducers inset in the tool near the screen, is pushed into the subsurface to a depth at which a K estimate is desired. A short hydraulic test is then performed by injecting water through the screen at a constant rate (less than 4 L/min) while pressure changes are monitored at the transducer locations. Hydraulic conductivity is calculated using the injection rate and the pressure changes in simple expressions based on Darcy's Law. In units of moderate or higher hydraulic conductivity (more than 1 m/d), testing at a single level can be completed within 10 to 15 min. Two major advantages of the method are its speed and the insensitivity of the K estimates to the zone of compaction created by tool advancement. The potential of the approach has been assessed at two extensively studied sites in the United States and Germany over a K range commonly faced in practical field investigations (0.02 to 500 m/d). The results of this assessment demonstrate that the DPP can provide high-resolution K estimates that are in good agreement with estimates obtained through other means.  相似文献   

Stochastic processes of soil production and transport: erosion rates,topographic variation and cosmogenic nuclides in the Oregon Coast Range     

Arjun M. Heimsath  William E. Dietrich  Kunihiko Nishiizumi  Robert C. Finkel 《地球表面变化过程与地形》2001,26(5):531-552

Landscapes in areas of active uplift and erosion can only remain soil‐mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma^?1 occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large‐scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment‐averaged erosion rate of 117 m Ma^?1 is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Cyclops glacialis n. sp. (Copepoda: Cyclopoida) from a high mountain lake in Northwestern Mongolia     

Dietrich Flßner 《Limnologica》2001,31(4):303-306

A new species of Cyclops s. str. (strenuus subgroup) from a high mountain lake in Northwestern Mongolia is described. As no cytological investigations were possible, the species diagnosis and taxonomic relationships were made on the basis of morphological and morphometrical data. It is most similar to Cyclops abyssorum, but there are clear distinguishing features.  相似文献   

Der Laurier Belt,Eine Rotationszone Zwischen Kern-Orogen und Saumsenke (Kanadische Rocky Mountains)     

Dr. Dietrich Röder 《International Journal of Earth Sciences》1962,52(1):189-201

Between Lat. 56° N and 57° 30′ N, the Central Ranges of the Canadian Rocky Mountains contain a belt of slaty-cleaved vertical or overturned east-dipping beds which is considered as the west edge of the thrust-faulted area. Its antithetic rotation is accompanied by small-scale folding parallel to the plane of greatest shear stress, by synthetic and later antithetic movements along the plane of slaty cleavage. Reversal of movement on older reverse faults and a discordant, post-Laramide phase of synthetic normal faulting terminate the movements. Folding and rotation are contemporaneous with the thrusting to the east, and the synthetic normal faulting belongs to the grabening of the Rocky Mountain Trench adjacent to the east. Since rotation and thrusting above the uninvolved basement are contemporaneous, the rotation cannot be powered by differential movement along a stationary lineament within the basement. Its cause is suspected in the west-dipping clinoforms of the Palaeozoic sediments whose inclination placed them within the antithetic quadrant of the Laramide stress field, forcing them to continue rotation and to develop compressional folding instead of bedding-parallel elongated thrust sheets. One of two structurally analogous cases, the Swiss Massif Zone with the Helvetic nappes, shows an antithetically inclined gneissic foliation which might be a mechanical equivalent of the clinoforms in the Rocky Mountains. In the other example, from the north flank of the Hercynian Mosel syncline, a remarkably similar tectonic history and a close geographic coincidence between clinoformic sedimentation and development of an antithetic rotation zone is known.  相似文献   

Die ozeanographischen Verhandlungen auf der 11. Generalversammlung der Internationalen Union für Geodäsie und Geophysik in Toronto vom 3. bis 14. September 1957     

G. Dietrich 《Ocean Dynamics》1958,11(1):31-35

Ohne Zusammenfassung  相似文献   

Zwölfstündige Wasserstandsvorhersage in der Deutschen Bucht—Untersuchungen zur Online-Vorhersagequalität     

Dietrich Lange  Prof. Dr. Hans-Joachim Kümpel 《Ocean Dynamics》1993,45(6):433-448

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I.A.G. newsletter. International association of geomorphologists newsletter no. 11(2/1994)     

Denys Brunsden  Dietrich Barsch 《地球表面变化过程与地形》1994,19(8):763-766

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Neuere Veröffentlichungen     

Günter Weichart  Dietrich Voppel 《Ocean Dynamics》1977,30(4):137-138

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Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter     

Matthias Radke  Dietrich H. Welte  Helmut Willsch 《Geochimica et cosmochimica acta》1982,46(1):1-10

Thirty-one rock samples from a Western Canada Basin well have been analysed for aromatics, using glass capillary gas chromatography with simultaneous flame ionization and sulfur-selective flame photometric detection. A uniform aromatic distribution pattern with a marked predominance of di- and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising Cretaceous and Jurassic sediments. The very high relative abundance of sulfur aromatics at two narrow intervals in the Triassic and Mississippian is attributed to a major change in facies. Gradual changes with increasing depth have been observed for a series of compound ratios, which had been calculated from the isomers of methyl- and dimethylphenanthrene, and their parent compounds. These changes reflect the increasing thermal maturation of the sedimentary organic matter. A Methylphenanthrene Index (MPI) has been introduced, which exhibited a very good correlation with vitrinite reflectance data. The MPI is the first maturity parameter which is based on a series of aromatic hydrocarbons. This hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity (e.g. vitrinite reflectance) of source rocks.  相似文献