The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3     

Jean-Paul Cadet  Kazuo Kobayashi  Jean Aubouin  Jacques Boulgue  Christine Deplus  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kinichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km² and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary?  相似文献   

Dating of sediments from Lake Zurich (Switzerland) with210Pb and137Cs     

H. N. Erten  H. R. von Gunten  E. Rössler  M. Sturm 《Aquatic Sciences - Research Across Boundaries》1985,47(1):5-11

²¹⁰Pb- and¹³⁷Cs-measurements, and varve counting have been used to date sediment cores from Lake Zurich (Switzerland). Two cores from different water depths were dated with²¹⁰Pb/²¹⁰Po and revealed sediment accumulation rates of (0.055±0.015) g·cm^?2·y^?1 and (0.09±0.03) g·cm^?2·y^?1, respectively. A comparable rate of (0.07±0.01) g·cm^?2·y^?1 has been obtained from¹³⁷Cs measurements. These rates were confirmed by annual layer (varve)-counts which lead to rates of 0.07 g·cm^?2·y^?1. Constant²¹⁰Pb activities were observed in the top 6 cm of the sediment cores. This constancy is generally explained in the literature by mixing processes caused by bioturbation and by distortion during coring operations of the uppermost water-rich fluffy sediments. However the distinct¹³⁷Cs-maxima and the regular and undisturbed varve lamination of the top sediment observed in the cores of Lake Zurich contradict this assumption. In addition, measurements of⁷Be at the water/sediment interaces proved complete sediment core recovery and mechanically undisturbed sediments. Remobilization processes are assumed to cause the observed constant²¹⁰Pb activities. Remobilization may also be the reason for an incomplete²¹⁰Pb inventory in the sediments which contain only about 50% of the fallout from atmosphere. The results of the²¹⁰Pb dating should therefore be considered with some care. If existent, varve counting represents the easiest and most reliable means for dating lake sediments.  相似文献   

Drop shape and erosivity part II: Splash detachment,transport and erosivity indices     

Hans Th. Riezebos  Gerrit F. Epema 《地球表面变化过程与地形》1985,10(1):69-74

The relevance of drop shape for erosivity was tested for different combinations of drop sizes and fall heights. For all test combinations together the introduction of the observed drop shape in erosivity parameters only produces minor improvements in the relation between erosivity and detachment and transport by splash. This result is attributed to the dominance of oblate shapes in high velocity conditions. Using small fall heights and low fall velocities as in many rainfall simulators and drop tests it is shown that prolate drops produce a splash detachment which is 2 to 3 times higher than that produced by drops with an oblate shape at impact. As drop production in rainulators or for aggregate stability drop tests may result in more or less uncontrolled variations of drop shape, it is concluded that in addition to other test conditions drop shape should be specified. Moreover it is noted that the erosive capability of prolate drops can explain partly the high splash erosion amounts below vegetation.  相似文献   

Origin of the Tertiary basaltic volcanism in the northern Hessian Depression   总被引：2，自引：0，他引：2  

K. Hans Wedepohl 《Contributions to Mineralogy and Petrology》1985,89(2-3):122-143

Volcanic activity started about 20 Ma before present with quartz tholeiites (QTh), had a climax with alkali olivine basalts (AOB) 13 to 14 Ma ago and ended 7 Ma ago with nepheline basanites (NB) and olivine nephelinites (ON). AOB covers 73% of the volcanic area. About 250 basalts and peridotite xenoliths were sampled for investigation. An upper mantle layer ranging from about 90 to 60 km depth has been conditioned for a preferential alkali basalt production by advection of H₂O-CO₂-fluids containing Si, Al, Ca, K, Na, P as major constituents beside numerous incompatible minor elements. At the onset of the geodynamically triggered mantle conditioning locally restricted diapirism into shallow depth has caused formation of olivine tholeiite magmas (OTh) at about 1,300° C by partial melting. All of these OTh primary melts intruded due to a favourable compressibility into granulites of the lower crust. The rare QTh basalts are their derivative magmas which have been slightly contaminated in the crust. Magmas of the subsequent alkali basaltic volcanism (AOB, bAOB, NB, ON, MON) formed by in-situ partial melting at about 75 to 90 km depth after depression of the peridotite solidi by fluids to temperatures 1,200° C. Except many AOB these magmas are primary melts as characterized by olivine/melt distribution coefficients of Mg/Fe²⁺ (K _D=0.29 to 0.34), by Ni concentrations (260 to 330 ppm) and the occurrence of peridotite xenoliths. Rapid rise of gas charged melts due to saturation in CO₂ prevented separation of olivine etc. and of xenoliths. The sequence of magmas from OTh to ON (or MON) is formed from decreasing proportions of orthopyroxene (opx) and increasing contributions of clinopyroxene (cpx) and phlogopite (ph) at almost equal proportions of spinel (sp). Incongruent melting of opx (and cpx) for OTh, AOB, NB and ON is correlated with precipitation of olivine. The average xenolith composition (73% ol, 18% opx, 7% cpx, 1.1% sp and 1.3/0.5% ph) was used to model the sources of the investigated melts by 9 incompatible elements and to calculate degrees of partial melting. The occurrence of garnet cannot be reliably excluded by modelling on the basis of HREE distribution coefficients. The average xenolith composition was used for modelling because of its resemblance with worldwide sampled depleted mantle inclusions. For avoiding to exhaust at least one mineral of the model mantle in the support of the norm composition of OTh, AOB, NB and MON magmas the degrees of partial melting cannot exceed 12.5%, 6%, 6% and 4% respectively. Mantle containing about 500 ppm K (and the correlated incompatible elements), like the average of 36 xenoliths, allows to explain the formation of OTh magmas. AOB, NB and ON melts require peridotite with slightly less than 1,500 ppm K, 670 ppm P and proportions of the correlated elements LREE, Sr, Ba, Zr, Rb, Cs, Ta, Th, Hf, U, which are higher than their abundance in primitive mantle rocks. About 20% of the xenoliths have this composition. Metasomatism of fluids with these elements must have been an immediate precursor of the alkali basaltic volcanism. Otherwise the preservation of a local disequilibrium in ⁸⁷Sr/⁸⁶Sr ratios between cpx cores and total rock at upper mantle temperatures cannot be explained.  相似文献   

U/Pb- und K/Ar-Datierungen des Uranvorkommens Höhenstein/Oberpfalz     

Dr. Claudia Carl  Dr. Harald Dill  Hans Kreuzer  Prof. Dr. Immo Wendt 《International Journal of Earth Sciences》1985,74(3):483-504

K/Ar dating of micas from rocks of Fichtelgebirge and the northern Oberpfalz (NE-Bavaria) covers the rather wide range from 330 to 300 Ma. In combination with Rb/Sr wholerock isochron ages of post-tektonic granites four Variscian events can be traced:

1. Regional metamorphism ～ 330 Ma,
2. Intrusion of the older post-deformative granite G1 about 320 Ma (Falkenberger Granit) followed by rapid cooling.
3. About 300 Ma ago the older mineral ages were more or less reset by the intrusion of younger granites (G2 to G4, Flossenbürger Granit) again followed by a rapid cooling.
4. Local influences later than 290 Ma are recorded by some white micas in fault gauges at least up to the middle Jurassic (< 150 Ma).

The different U-black ore types yielded strongly discordant U/Pb dates. Applying the three dimensional U/Pb-discordia plane method the following results have been obtained: the older pitchblende generation with an upper concordia intersection of 336±17 Ma can be correlated with the regional metamorphism as well as with the intrusion of the older post-deformative granites. The younger generation with 298±4 Ma is of equal age as the intrusion of the younger granites. The brannerite mineralisation which according to thin section evaluation must be still younger could be only roughly dated to 288±78 Ma. The low precision is due to low uranium concentration and high common lead contents of the samples. The lower concordia intersection ages are 0 to 7 Ma. They were obtained more precisely by dating of secondary U-minerals: 10 torbernite samples with extremely high²³⁸U/²⁰⁶Pb-ratios of 30 000 to 50 000 yielded a positive slope of the discordia which points to an age of (137±12)×10³a. The²³⁰Th/²³⁸U-activity ratio of 0.68 determined byα-spectrometry indicates an age of (130.4±5.0)×10³ a. Pyrite and chalcopyrite samples which had U-concentration of some 100 ppm and which according to thin section evaluation are younger than the brannerite showed a positive slope of the²⁰⁷Pb/²⁰⁶Pb vs.²³⁸U/²⁰⁶Pb discordia, too. They could not be dated because the²⁰⁷Pb/²⁰⁶Pb-ratios corrected for common lead contribution are lower than 0.046 (radiogenic lead of zero age). This may be explained by an addition of²⁰⁶Pb due to²²²Rn migration from the pitchblende in only a few cm distance.  相似文献   

The role of gravitophotophoresis for stratospheric and mesospheric particulates     

Hans rohatschek 《Journal of Atmospheric Chemistry》1984,1(4):377-389

Gravitophotophoresis, a type of photophoresis related to the direction of gravity, is examined in view of its possible importance to some aerosols in stratosphere and mesosphere. particles of various materials from about 1 to 100 m in size show levitation by photophoretic forces under laboratory simulation of irradiation by the sun at air densities of the middle atmosphere. Minimum air densities for levitation are about 2–3 g m^–3 with mineral and metallic powders, about 0.08 g m^–3 with carbonaceous powders. The fraction of rising particles can be about 0.01 to 1%. Velocities of ascent are in the range of 0.001 to 0.01 m s^–1 at a pressure of several mbar. The magnitude and the mechanical character of the force of gravitophotophoresis can be explained if it is identified with a radiometer force caused by a difference of the accommodation coefficient on the surface. It is suggested that gravitophotophoresis can be important to the residence time and the maximum altitude of carbonaceous and mineral particles, such as volcanic ash or products of meteorite impact, and to the presence of microorgnisms in the middle atmosphere.  相似文献   

Mercury pollution in the waters around Harboøre Tange and Limfjord,Denmark     

Hans Ulrik Riisgård 《Marine pollution bulletin》1984,15(4):129-133

High concentrations of mercury have been measured in mussels (Mytilus edulis) collected in two ‘hot spot’ areas: (1) near a closed-down chemical factory on the west coast of the Limfjord, and (2) on groynes in the immediate vicinity of a chemical deposit in the dunes on the Danish west coast. By collecting comparable samples of mussels from chains of buoys, the mercury pollution in the western Limfjord could be traced 50–100 km into the central and innermost parts of the Limfjord as a gradual decreasing mercury concentration gradient. By collecting mussels from groynes north and south of the chemical deposit, it was possible to monitor the relative extent of the mercury leakage to the North Sea before and after the excavation of the deposit. The investigations have demonstrated the applicability of M. edulis as a monitoring organism for mercury when importance is attached to concentration gradients and distribution patterns in well defined and homogeneous samples of mussels collected from natural populations.  相似文献   

Nature and classification of waterlain glaciogenic sediments,exemplified by Pleistocene,Late Paleozoic and Late Precambrian deposits   总被引：1，自引：0，他引：1  

C.P. Gravenor  V. von Brunn  A. Dreimanis 《Earth》1984,20(2):105-166

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The significance of discrete baltic nutrient samples discussed on the basis of continuous measurements     

Dr. Hans Peter Hansen 《Ocean Dynamics》1984,37(6):245-258

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Dependence of velocity variance on sampling time     

Gabriele C. Wollenweber  Hans A. Panofsky 《Boundary-Layer Meteorology》1989,47(1-4):205-215

The dependence of the lateral and vertical velocity variances on sampling time have been investigated, based on recent spectral models. The results have been compared with observations at Vandenberg Air Force Base and at the Boulder Atmospheric Observatory.For sampling times of l s to 1 hr, the variation of lateral variances is much smaller in neutral than in unstable conditions. In a stable atmosphere, the variances show a stronger increase with sampling time than predicted by the model. The vertical velocity variances do not increase significantly between 1 and 60 min. Again in stable conditions, the measurements show a more pronounced increase of variances as compared to the calculations, indicating significant energy between periods of a few to 20 min. This additional energy may be ascribed to gravity waves.The models cannot be applied in cases with trends in the data. The model tends to underestimate the dependence of variances on sampling time in cases when systems, such as longitudinal vortices or gravity waves exist.This work was undertaken while the authors were associated with the Scripps Institution of Oceanography, La Jolla, California.Deceased 28 February 1988  相似文献