First seismic record for intra-arc strike-slip tectonics along the Liquiñe-Ofqui fault zone at the obliquely convergent plate margin of the southern Andes     

D. Lange  J. Cembrano  A. Rietbrock  C. Haberland  T. Dahm  K. Bataille 《Tectonophysics》2008,455(1-4):14-24

A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to M_w 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent M_w 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region.  相似文献   

An experimental study of the grain-scale processes of peridotite melting: implications for major and trace element distribution during equilibrium and disequilibrium melting   总被引：1，自引：0，他引：1  

Mauro Lo Cascio  Yan Liang  Nobumichi Shimizu  Paul C. Hess 《Contributions to Mineralogy and Petrology》2008,156(1):87-102

The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free, olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements in residual minerals reequilibrate with their surrounding melt. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Food Preferences of Dominant Salt Marsh Herbivores and Detritivores     

Carol S.  Rietsma  Ivan  Valiela Ana  Sylvester-Serianni 《Marine Ecology》1982,3(2):179-189

Abstract. Food preferences of six dominant salt marsh invertebrates were studied to identify detritivores and to assess differences in their diets. Animals fed on agar suspensions of dead and live foods in petri dishes with four compartments. Only two foods were included in each dish. Relative palatability was assessed by measuring the amount of suspension removed or by counting the number of feeding marks left on the surface of the suspensions.
Feeding marks reflected differences in mouth parts and feeding mechanisms of the six invertebrates. Melampus bidentatus, Orchestia grillus , and Philoscia vittata preferred dead litter over live tissues of marsh graminoids, blue-green algae, and sulfur bacteria. No preference for detritus from different graminoids was shown by M. bidentatus. Orchestia grillus fed preferentially on Spartina patens detritus. Philoscia vittata preferred detritus from S. alterniflora and S. patens. Blue-green algae and sulfur bacteria were preferred over detritus by Littorina saxatalis , but detritus was preferred over live graminoids. Littorina saxatalis fed preferentially on Juncus gerardi detritus. Blue-green algae, sulfur bacteria, and live graminoids were preferred over detritus by L. littorea. Talorchestia longicornis also preferred blue-green algae.
On the basis of their food preferences, Littorina saxatalis, Melampus bidentatus, Orchestia grillus , and Philoscia vittata were classified as detritivores. Feeding on detritus from different plant species could result in a partitioning of this food resource in the detritus-based food chains of the salt marsh ecosystem.  相似文献   

基于分区的局域神经网络时空建模方法研究   总被引：1，自引：0，他引：1  

王海起  王劲峰 《遥感学报》2008,12(5)

区域数据表现为两种尺度的空间特性:反映全局特征的空间依赖性和反映局域特征的空间波动性.空间波动性表现为空间数据在局部地区的聚集或高低交错现象.在研究区域数据时空预测性建模时,从降低数据的空间波动和不平稳性对模型预测能力的影响角度出发,提出了一种基于分区的局域神经网络时空非线性建模的思路.分区过程由基于空间邻接关系的K-means聚类算法完成.不同的分区方案通过相关性、波动性、紧凑性等指标进行评价和优选.在确定最优分区方案的基础上,对各子区分别采用两层前馈网络进行建模,模型的输入不仅要考虑本区内单元的作用,而且要考虑相邻子区的边界效应.各神经网络模型的时空预测能力通过平均相均差和动态相似率等指标进行衡量.最后,通过对法国94个县每周流感报告病例的时空建模分析表明,与全局神经网络模型相比,基于分区的局域神经网络模型具有更好的预测能力.  相似文献   

山区煤田地震勘探中静校正存在的问题及其改进方法     

沈辉  ;李辉峰 《中国煤炭地质》2008,(8):54-59

在山区或地表复杂地区进行地震勘探,采用基于地表一致性假设的静校正将会严重影响勘探效果,该影响主要源于地表一致性假设存在着不合理因素。如较高的低速带、巨厚的低速带、基岩裸露、地形起伏较大等。为分析一致性假设静校正偏差产生的原因及大小．构建一地形起伏、基岩出露的复杂模型,通过正演其射线路径,对比其时距曲线与理论时距曲线的差异,以及二者静校正量误差大小。模型分析证实该差异与偏移距、地震波穿透深度及基准面高程之间存在直接的联系,据此提出了改进方法,如浮动基准面校正及分块静校正等。理论模型和实际地震资料试算表明,使用改进的方法可有效改善地震时间刮面同相轴聚焦效果及连续性。  相似文献   

Structural architecture of a highly oblique divergent plate boundary segment   总被引：1，自引：0，他引：1  

Amy E. Clifton  Simon A. Kattenhorn 《Tectonophysics》2006,419(1-4):27-40

The Reykjanes Peninsula in southwest Iceland is a highly oblique spreading segment of the Mid-Atlantic Ridge oriented about 30° from the direction of absolute plate motion. We present a complete and spatially accurate map of fractures for the Reykjanes Peninsula with a level of detail previously unattained. Our map reveals a variability in the pattern of normal, oblique- and strike-slip faults and open fractures which reflects both temporal and spatial strain partitioning within the plate boundary zone. Fracture density varies across the length and width of the peninsula, with density maxima at the ends and at the northern margin of the zone of volcanic activity. Fractures with similar strike cluster into distinct structural domains which can be related to patterns of faulting predicted for oblique extension and to their spatial distribution with respect to volcanic fissure swarms. Additional structural complexity on the Reykjanes Peninsula can be reconciled with magmatic periodicity and associated temporal strain partitioning implied by GPS data, as well as locally perturbed stress fields. Individual faults show variable slip histories, indicating that they may be active during both magmatic and amagmatic periods associated with different strain fields.  相似文献   

Strain partitioning and preservation of Ar/Ar ages during Variscan exhumation of a subducted crust (Malpica–Tui complex, NW Spain)     

J. Rodr&#x;&#x;guez  M.A. Cosca  J.I. Gil Ibarguchi  R.D. Dallmeyer 《Lithos》2003,70(3-4):111-139

The Malpica–Tui complex (NW Iberian Massif) consists of a Lower Continental Unit of variably deformed and recrystallized granitoids, metasediments and sparse metabasites, overridden by an upper unit with rocks of oceanic affinities. Metamorphic minerals dated by the ⁴⁰Ar/³⁹Ar method record a coherent temporal history of progressive deformation during Variscan metamorphism and exhumation. The earliest stages of deformation (D1) under high-pressure conditions are recorded in phengitic white micas from eclogite-facies rocks at 365–370 Ma. Following this eclogite-facies peak-metamorphism, the continental slab became attached to the overriding plate at deep-crustal levels at ca. 340–350 Ma (D2). Exhumation was accompanied by pervasive deformation (D3) within the continental slab at ca. 330 Ma and major deformation (D4) in the underlying para-autochthon at 315–325 Ma. Final tectonothermal evolution included late folding, localized shearing and granitic intrusions at 280–310 Ma.

Dating of high-pressure rocks by the ⁴⁰Ar/³⁹Ar method yields ages that are synchronous with published Rb–Sr and Sm–Nd ages obtained for both the Malpica–Tui complex and its correlative, the Champtoceaux complex in the French Armorican Massif. The results indicate that phengitic white mica retains its radiogenic argon despite been subjected to relatively high temperatures (500–600 °C) for a period of 20–30 My corresponding to the time-span from the static, eclogite-facies M1 peak-metamorphism through D1-M2 eclogite-facies deformation to amphibolite-facies D2-M3. Our study provides additional evidence that under certain geological conditions (i.e., strain partitioning, fluid deficiency) argon isotope mobility is limited at high temperatures, and that ⁴⁰Ar/³⁹Ar geochronology can be a reliable method for dating high pressure metamorphism.  相似文献   

Researches on Cartographic Database-Based Interactive Three-Dimensional Topographic Map     

JiangWenping XiDaping 《中国地质大学学报(英文版)》2003,14(4):374-380

With the development of computer graphics, the three-dimensional (3D) visualization brings new technological revolution to the traditional cartography. Therefore, the topographic 3D-map emerges to adapt to this technological revolution, and the applications of topographic 3D-map are spread rapidly to other relevant fields due to its incomparable advantage. The researches on digital map and the construction of map database offer strong technical support and abundant data source for this new technology, so the research and development of topographic 3D-map will receive greater concern. The basic data of the topographic 3D-map are rooted mainly in digital map and its basic model is derived from digital elevation model (DEM) and 3D-models of other DEM-based geographic features. In view of the potential enormous data and the complexity of geographic features, the dynamic representation of geographic information becomes the focus of the research of topographic 3D-map and also the prerequisite condition of 3D query and analysis. In addition to the equipment of hardware that are restraining, to a certain extent, the 3D representation, the data organization structure of geographic information will be the core problem of research on 3D-map. Level of detail (LOD). space partitioning, dynamic object loading (DOL) and object culling are core technologies of the dynamic 3D representation. The objectselection, attribute-query and model-editing are important functions and interaction tools for users with 3D-maps provided by topographic 3D-map system, all of which are based on the data structure of the 3D-model. This paper discusses the basic theories, concepts and cardinal principles of topographic 3I)-map,expounds the basic way to organize the scene hierarchy of topographic 3D-map based on the node mechanism and studies the dynamic representation technologies of topographic 3D-map based on LOD, space partitioning, DOL and object culling. Moreover. such interactive operation functions are explored, in this paper, as spatial query, scene editing and management of topographic 3D-map. Finally, this paper describes briefly the applications of topographic 3D-map in its related fields.  相似文献   

The separation of the influence of nutrients and climate on the varve time-series of baldeggersee, Switzerland   总被引：7，自引：2，他引：7  

A. F. Lotter  H. J. B. Birks 《Aquatic Sciences - Research Across Boundaries》1997,59(4):362-375

The varve data-set from a freeze-core taken in the deepest part of Baldeggersee was subjected to different multivariate statistical analyses in order to estimate the amount of variance in the varve thickness measures explicable by past climate and by the trophic state of the lake. A comparison of two different time-periods (1902 to1992 versus 1920 to 1980) revealed that the lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Results of the partitioning of the variance in the varve thickness measures showed that about two thirds of the variance are unexplained by a climate and trophic state model and that trophic state explains 6%, whereas climate accounts for about 28% of the variance before the effect of lake restoration had a strong impact on the varves. Among the climate parameters the amount of annual precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thickness, whereas summer precipitation is important for the thickness of the light layer.  相似文献   

陆源碎屑沉积作用对化学元素配分的制约——兼论五台地区前寒武纪碎屑沉积岩示踪源区陆壳成分的意义   总被引：1，自引：0，他引：1  

杨忠芳  陈岳龙 《地质论评》1997,43(6):593-600

为探讨粒度分选沉积作用对沉积物化学成分配分的影响,对比研究了五台群中石英岩、长石石英岩、粉砂岩和粘土岩等不同粒度沉积岩的化学成分特征,结果表明:不同粒度沉积岩的主元素及微量元素均具有较大的变化范围,SiO_2与Al_2O_3及TFe_2O_3之间呈线性负相关关系,这种负相关关系还表现在SiO_2与REE,Rb,Sr之间,这种特征可以用石英的稀释作用进行解释;铁族元素Cr,Ni,Co和REE,Rb,Sr等大离子亲石元素与Al_2O_3呈正相关关系,表明这些元素易在富铝的粘土岩中聚积。不同粒度成分沉积岩的稀土  相似文献