Geochemistry and Crustal Evolution of Volcano-sedimentary Successions and Orthogneisses in the São Gabriel Block, Southernmost Brazil — Relics of Neoproterozoic Magmatic Arcs

Precambrian metaplutonic rocks of the São Gabriel block in southernmost Brazil comprise juvenile Neoproterozoic calc-alkaline gneisses (Cambaí Complex). The connection with associated (ultra-)mafic metavolcanic and metasedimentary rocks (Palma Group) is not well established. The whole complex was deformed during the Brasiliano orogenic cycle. Both metasedimentary and metavolcanic rocks as well as metaplutonic rocks of the Cambaí Complex have been sampled for geochemical analyses in order to get constraints on the tectonic setting of these rocks and to establish a tectonic model for the São Gabriel block and its role during the assembly of West-Gondwana. The major element compositions of the igneous rocks (Palma Group and Cambaí Complex) indicate a subalkaline character; most orthogneisses have a calc-alkaline chemistry; many metavolcanic rocks of the Palma Group show signatures of low-K tholeiitic volcanic arc basalts. Trace element data, especially Ti, Zr, Y, Nb, of most igneous samples from both the lower Palma Group and the Cambaí Complex indicate origin at plate margins, i.e., in a subduction zone environment. This is corroborated by relative enrichment in LREE, low contents of Nb and other high field strength elements and enrichment in LILE like Rb, Ba, and Th. The data indicate the possible existence of two suites, an oceanic island arc and a continental arc or active continental margin. However, some ultramafic samples of the lower Palma Group in the western São Gabriel block indicate the existence of another volcanic suite with intra-plate character which possibly represents relics of oceanic island basalts (OIB). Trace element data indicate contributions from andesitic to mixed felsic and basic arc sources for the metasedimentary rocks. The patterns of chondrite- and N-MORB-normalized spider diagrams resemble the patterns of the igneous rocks, i.e., LILE and LREE enrichment and HFS depletion. The geochemical signatures of most igneous and metasedimentary samples and their low (⁸⁷Sr/⁸⁶Sr)_t ratios suggest only minor contribution of old continental crust.A geotectonic model for the São Gabriel block comprises east-ward subduction and following accretion of an intra-oceanic island arc to the eastern border of the Rio de la Plata Craton at ca. 880 Ma, and westward subduction beneath the newly formed active continental margin between ca. 750 and 700 Ma. The São Gabriel block represents relics of an early Brasiliano oceanic basin between the Rio de la Plata and Kalahari Cratons. This ocean to the east of the Rio de la Plata Craton might be traced to the north and could possibly be linked with Neoproterozoic juvenile oceanic crust in the western Brasília belt (Goiás magmatic arc).     

拉萨地体内低速异常成因的探讨--壳内局部熔融的地震层析证据

青藏高原南部天然地震体波的层析反演图像描绘出拉萨地体内在15～90km深度内低速异常的分布特征。在研究速度结构的基础上，根据熔融程度与纵波波速呈倒数衰减的特性，论证了拉萨地体中低速体的出现与壳内的局部熔融有关。壳内局部熔融则来源于板块俯冲、地壳增厚产生的热而非幔源侵入所造成。同时，也发现了在拉萨以东中下地壳低速体有向东发展的趋势。大面积部分熔融层分布的深度范围约在15～35km处。另外，据藏南地区的SKS波分裂时间延迟很小的特点，推测藏南地幔中可能不存在各向异性，也就是没有足够的热源使各向异性矿物的品格重新定位。这从另一方面佐证了部分熔融仅存在于地壳内而不是地幔中。     

Modélisation géométrique 3D des granites stéphaniens du massif du Pelvoux (Alpes,France)

The structural analysis and the 3D modelling of Stephanian granites of the Pelvoux Massif characterize an emplacement along sinistral NW–SE- and dextral NE–SW-trending shear zones in the Pelvoux and in the Aiguilles Rouges–Mont Blanc Massifs, respectively. This Carboniferous shear system is consistent with a north–south extension direction known in the whole Variscan belt at this time. To cite this article: P. Strzerzynski et al., C. R. Geoscience 337 (2005).     

Intraplate deformation and 3D rheological structure of the Rhine Rift System and adjacent areas of the northern Alpine foreland

The lithosphere of the Northern Alpine foreland has undergone a polyphase evolution during which interacting stress-induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere. In this paper we address relationships among deeper lithospheric processes, neotectonics and surface processes in the Northern Alpine foreland with special emphasis on tectonically induced topography. We focus on lithosphere memory and neotectonics, paying special attention to the thermo-mechanical structure of the Rhine Graben System and adjacent areas of the northern Alpine foreland lithosphere. We discuss implications for mechanisms of large-scale intraplate deformation and links with surface processes and topography evolution.     

Clustering and visualization of earthquake data in a grid environment

We present a web client-server service WEB-IS, which we have developed for remote analysis and visualization of seismic data consisting of both small magnitude events and large earthquakes. We show that the problem-solving environment (PSE) intended for prediction of large magnitude earthquakes can be based on this WEB-IS idea. The clustering schemes, feature generation, feature extraction techniques and rendering algorithms form a computational framework of this environment. On the other hand, easy and fast access both to the seismic data distributed among distant computing resources and to computational and visualization resources can be realized in a GRID framework. We discuss the usefulness of NaradaBrokering (iNtegrated Asynchronous Real-time Adaptive Distributed Architecture) as a middleware, allowing for flexibility and high throughput for remote visualization of geophysical data. The WEB-IS functionality was tested both on synthetic and the actual earthquake catalogs. We consider the application of similar methodology for tsunami alerts.     

Environmental significance of C/C and O/O ratios of modern land-snail shells from the southern great plains of North America

¹³C/¹²C and ¹⁸O/¹⁶O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for samples from twelve localities in a narrow east-west corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of the Sangre de Cristo Mountains in Northern New Mexico, USA. Across the study area, shell δ¹⁸O values (PDB scale) ranged from −4.1‰ to 1.2‰, while δ¹³C values ranged from −13.2‰ to 0.0‰. δ¹⁸O values of the shell aragonite were predicted with a published, steady state, evaporative flux balance model. The predicted values differed (with one exception) by less than 1‰ from locality averages of measured δ¹⁸O values. This similarity suggests that relative humidity at the time of snail activity is an important control on the δ¹⁸O values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells. Correlated δ¹³C values of coexisting Vallonia and Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant ecology. Although there is considerable scatter, multispecies, transect average δ¹³C values of the modern aragonite shells are related to variations in the type of photosynthesis (i.e., C₃, C₄) in the local plant communities. The results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals, species, etc., and thus better represent the “neighborhood” scale temporal and/or spatial environmental variations of interest in studies of modern and ancient systems.     

数字社区数据标准研究

当前数字社区建设缺乏统一的智能化综合管理平台以及相应的各项数据标准，使得数字社区难以真正实现统一的数字化管理。该文参考国内外相应数据标准，研究数字社区的标准体系结构。针对现有标准体系缺乏相关数据标准的现状，提出数字社区系列数据标准，包括数据接口层标准、数据分类编码标准、数据模型、数据字典和元数据标准。阐述系列标准中各标准间的相互关系以及各标准所包含的具体内容。     

空间运动对象与时空数据类型研究

当前时空数据模型多以描述空间实体的离散变化为主。该文中对空间运动对象在抽象层次的无限连续空间、离散层次的有限离散空间上的数据类型进行分析和定义，将其分别划分为时间类型、空间类型和时态类型来研究，并提出支持空间运动对象的表示方法和操作方式。该方法既能表示空间实体的连续运动，也能表示其离散变化，为空间运动对象时空数据模型的建立奠定了基础。