Noble gas systematics of deep rift zone glasses from Loihi Seamount, Hawaii   总被引：3，自引：0，他引：3  

Peter J. Valbracht  Thomas Staudacher  Alex Malahoff  Claude J. Allgre 《Earth and Planetary Science Letters》1997,150(3-4):399-411

We report new noble gas fusion and crushing data for six pillow rim glasses, recovered between 3 and 5 km water depth on the south rift zone of Loihi Seamount, Hawaii. Helium abundances of the glasses vary from 0.3 to 2.3 μcc/g, with ⁴He/³He ratios between 30000 and 27000 (24–27 R_A), similar to previously reported values. The neon data form a correlation line which is similar to the Loihi-Kilauea line reported by Honda et al. [1], but extends to much higher ratios, up to 12.9 and 0.0382 for the ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios, respectively. This provides conclusive evidence for the suggestion that the Hawaiian plume, thought to originate in the lower mantle, has a solar-like ²⁰Ne/²²Ne composition [1], but a slightly higher ²¹Ne/²²Ne ratio. ⁴⁰Ar/³⁶Ar ratios of the deep rift-zone glasses are as high as 2600, and show a positive correlation with neon isotopic ratios. In contrast to neon and argon, all xenon isotopic compositions are isotopically indistinguishable from air, which either suggests preferential atmospheric contamination of xenon, or could indicate an atmospheric xenon isotopic composition for the lower mantle.  相似文献   

The location of deep salinity sources in the Israeli Coastal aquifer     

Uri Shavit  Alex Furman 《Journal of Hydrology》2001,250(1-4):63-77

The salinization process of the Israeli Coastal aquifer has led to an average concentration of about 200 mgCl/l with a significant number of discrete salinity plumes in the middle and southern regions. The salinity of these plumes is high (500–1000 mgCl/l) and is increasing rapidly. Geochemical evidence has suggested that the salinity source in the Be'er Tuvia plume (in the south part of the aquifer) is at the bottom of the aquifer. This paper describes a solution of the source inverse problem and its application in the Be'er Tuvia plume. A transient two-dimensional finite element model was solved and the source terms were computed at each node in a 14×14 km² area. An error analysis has shown that when no errors are introduced in the input data the reconstruction is perfect. The results of a sensitivity analysis are presented and the actual reconstruction errors are estimated. Applying the model in the Be'er Tuvia region indicates that a salinity source exists about 1 km to the west and 1.5 km to the north of the center of the salinity plume. This source is believed to be the plume source.  相似文献   

Toward a physical undenstanding of earthquake scaling relations     

Z. -M. Yin  G. C. Rogers 《Pure and Applied Geophysics》1996,146(3-4):661-675

In seismological literature, there exist two competing theories (the so-calledW model andL model) treating earthquake scaling relations between mean slip and rupture dimension and between seismic moment and rupture dimension. The core of arguments differentiating the two theories is whether the mean slip should scale with the rupture width or with the rupture length for large earthquakes. In this paper, we apply the elastic theory of dislocation to clarify the controversy. Several static dislocation models are used to simulate strike-slip earthquakes. Our results show that the mean slip scales linearly with the rupture width for small earthquakes with a rupture length smaller than the thickness of the seismogenic layer. However, for large earthquakes with a rupture length larger than the thickness of the seismogenic layer, our models show a more complicated scaling relation between mean slip and rupture dimension. When the rupture length is smaller than a cross-over length, the mean slip scales nearly linearly with the rupture length. When the rupture length is larger than a cross-over length, the mean slip approaches asymptotically a constant value and scales approximately with the rupture width. The cross-over length is a function of the rupture width and is about 75 km for earthquakes with a saturated rupture width of 15 km. We compare our theoretical predictions with observed source parameters of some large strike-slip earthquakes, and they match up well. Our results also suggest that when large earthquakes have a fixed aspect ratio of rupture length to rupture width (which seems to be the case for most subduction earthquakes) the mean slip scales with the rupture dimension in the same way as small earthquakes.  相似文献   

Sr-Nd isotopic constraints on the petrogenesis of the Central Bohemian Pluton,Czech Republic     

Vojtěch Janoušek  Graeme Rogers  D. R. Bowes 《International Journal of Earth Sciences》1995,84(3):520-534

The Sr-Nd isotopic data for selected granitoids of the Central Bohemian Pluton show a broad negative correlation with the total range of (⁸⁷Sr/⁸⁶Sr)₃₃₀ = 0.7051–0.7129 and _Nd ³³⁰ = +0.2 to –8.9. The older intrusions have more depleted Sr-Nd compositions and calc-alkaline geochemistry (Sázava suite), whereas the younger intrusions shift towards K-rich calc-alkaline (Blatná suite) and shoshonitic rocks (íany and ertovo bemeno suites) with more evolved isotopic signatures. The distribution of the data is interpreted as reflecting a diversity of sources and processes, rather than a single progressive crustal contamination trend. The Sázava suite could have originated by partial melting of metabasites, or of a mantle source with an isotopic composition close to bulk earth, or by hybridization of crustally-derived tonalitic and mantle-derived magmas. Variation within the Blatná suite is modelled by mixing between a moderately enriched [(⁸⁷Sr/⁸⁶Sr)₃₃₀ 0.708, _Nd ³³⁰ –3] mantle component with either an isotopically evolved metasedimentary component, or with more evolved magmas of the suite. The íany suite was most probably produced by partial melting of peraluminous lithologies, possibly of the adjacent Moldanubian unit. The ertovo bemeno suite evolved from strongly enriched mantle-derived magmas [(⁸⁷Sr/⁸⁶Sr)₃₃₀0.7128, _Nd ³³⁰ –7], either through closed-system fractional crystallization or interaction with magma corresponding to leucogranites of the Central Bohemian Pluton.  相似文献   

Human activities in UK offshore waters: an assessment of direct, physical pressure on the seabed   总被引：1，自引：0，他引：1  

Eastwood  P. D.; Mills  C. M.; Aldridge  J. N.; Houghton  C. A.; Rogers  S. I. 《ICES Journal of Marine Science》2007,64(3):453-463

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The geological significance of kelp-rafted rock along the west coast of South Africa     

M. W. Woodborne  J. Rogers  N. Jarman 《Geo-Marine Letters》1989,9(2):109-118

Angular to well-rounded pebbles and cobbles have been observed along the southwest coast of South Africa, attached to holdfasts of three species of kelp:Ecklonia maxima, Laminaria pallida, andLaminaria schinzii. A kelp-rafted clast has been dredged from the outer shelf and other clasts have been observedin situ in up to 5 m of water near Cape Town. The clasts have been found on both rocky and sandy shores as well as in a large backshore lagoon on the exposed Atlantic coast of the Cape Peninsula. Isolated clasts in a mid-Holocene lagoon were probably rafted ashore during winter storms in the mid-Holocene.  相似文献   

Diffusion reduction in an arbitrary scale third generation wind wave model   总被引：1，自引：0，他引：1  

W. E. Rogers  J. M. Kaihatu  H. A. H. Petit  N. Booij  L. H. Holthuijsen 《Ocean Engineering》2002,29(11):1357-1390

The numerical schemes for the geographic propagation of random, short-crested, wind-generated waves in third-generation wave models are either unconditionally stable or only conditionally stable. Having an unconditionally stable scheme gives greater freedom in choosing the time step (for given space steps). The third-generation wave model SWAN (“Simulated WAves Nearshore”, Booij et al., 1999) has been implemented with this type of scheme. This model uses a first order, upwind, implicit numerical scheme for geographic propagation. The scheme can be employed for both stationary (typically small scale) and nonstationary (i.e. time-stepping) computations. Though robust, this first order scheme is very diffusive. This degrades the accuracy of the model in a number of situations, including most model applications at larger scales. The authors reduce the diffusiveness of the model by replacing the existing numerical scheme with two alternative higher order schemes, a scheme that is intended for stationary, small-scale computations, and a scheme that is most appropriate for nonstationary computations. Examples representative of both large-scale and small-scale applications are presented. The alternative schemes are shown to be much less diffusive than the original scheme while retaining the implicit character of the particular SWAN set-up. The additional computational burden of the stationary alternative scheme is negligible, and the expense of the nonstationary alternative scheme is comparable to those used by other third generation wave models. To further accommodate large-scale applications of SWAN, the model is reformulated in terms of spherical coordinates rather than the original Cartesian coordinates. Thus the modified model can calculate wave energy propagation accurately and efficiently at any scale varying from laboratory dimensions (spatial scale O(10 m) with resolution O(0.1 m)), to near-shore coastal dimension (spatial scale O(10 km) with resolution O(100 m)) to oceanic dimensions (spatial scale O(10 000 km) with resolution O(100 km).  相似文献   

Factors affecting the annual abundance and regional distribution of English inshore demersal fish populations: 1973 to 1995   总被引：2，自引：0，他引：2  

Rogers  S. I.; Millner  R. S. 《ICES Journal of Marine Science》1996,53(6):1094-1112

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晚泥盆世海岸平原的沼泽沉积——沉积特征和碳酸盐层序地层学意义     

Alex J MacNeil  郭了萍  李登伟  于百江  曲凡华  殷畅 《海洋地质前沿》2007,23(6):19-22

沼泽碳酸盐是盐水从淡到浓的沉积物,具有成土作用的证据,是环海或湖的典型沉积物(Freytet,1973; Freytet 和Plaziat,1982; Alonso-Zarza,2003).如果气候允许,它们能形成在位于海岸平原和潮坪的浅水、富碳、由淡到浓的盐水沼泽中 (Monty和Hardie,1976;Shinn,1983; Platt和Wright,1992).在这些边缘海环境中,沼泽沉积能覆盖数千平方千米,可能伴随发生喀斯特和钙质结壳岩现象(Platt和Wright,1992).  相似文献   

Implications of bedform dimensions for the prediction of local scour in tidal inlets: a case study from the southern North Sea     

Riko Noormets  Verner B. Ernstsen  Alex Bartholomä  Burg W. Flemming  Dierk Hebbeln 《Geo-Marine Letters》2006,26(3):165-176

The bedforms and the local scour at the base of a cylindrical pile were studied in a tidal inlet in the Wadden Sea, southern North Sea, using high-resolution multibeam bathymetry data from four surveys. The observed changes in scour and bedform dimensions were interpreted in terms of hydraulic forcings varying periodically at different time scales. It appears that bedform orientation reacts to changing flow conditions on a semidiurnal basis, whereas bedform height and steepness reflect the spring-neap cycle as well as seasonal signals. The scour depth carries a strong overprint of the semidiurnal tidal cycle, which is at a maximum during the strongest tidal flow. Subtler variations in scour depth can possibly be attributed to the spring-neap tidal cycle. Based on these data on bedform and scour dimensions, correlation functions were established between scour depth and dune height as well as dune length. In measuring the scour depth under mobile bed conditions, establishing the seabed level based on the trough level of the bedforms nearest to the scour proved useful. These findings suggest that the dimensions of bedforms in dynamic equilibrium with prevailing hydraulic flow conditions can be used to estimate scouring in tidal environments.  相似文献