Magnetic susceptibility variations of the Edicaran cap carbonates in the Yangtze platform and their implications for paleoclimate     

吴怀春  张世红  蒋干清  李海燕 《中国海洋湖沼学报》2005,(3)

1 INTRODUCTION One of the most intriguing phenomena in the late Neoproterozoic (~750 to 543 Ma) is the globa occurrence of thin carbonates that directly overlie glacial deposits in almost every continent (Kennedy 1996; Hoffman et al., 1998; Hoffman and Schrag 2002; Brasier and Shields, 2000; James et al., 2001 Jiang et al., 2003; Nogueira et al., 2003). These “cap carbonates”, commonly several to tens of meters thick, have attracted enormous interests because o their unusually negati…  相似文献   

可移动中继节点在传感器网络中的节能应用     

唐帙  罗惠琼 《成都信息工程学院学报》2005,20(2):147-150

介绍了一种新颖的静态传感器网络实现方法，它利用可移动的中继节点来收集静态传感器网络的数据，有效的节约各传感器节点的能源，延长整个传感器网络的有效工作时间。也可以对该方法进行适当的改进，应用到某些实时性要求较高的场合中去。然后介绍了应用该原理实现的一个通讯协议。  相似文献   

首都圈地区现今断层活动的数学模拟及地震危险性讨论     

李群芳  张云柱  高忠宁 《大地测量与地球动力学》1995,(1)

以首都圈地区现今活动断层上近２０年的位移测量资料为依据，用二维线弹性有限元对该区断层的活动特征进行了拟合，并结合有关资料讨论了该区的地震危险性。结果表明：１９７７－１９８６年间该区主压应力优势方位与华北较一致，约为Ｎ４５°－８０°Ｅ；１９８６－１９９０年其主压应力方向向北偏转，约为Ｎ５°－６０°Ｅ；１９９０年至现在其主压应力又向东偏转，角度大于第一阶段，约为Ｎ８０°－９５°Ｅ。该区的张家口－延庆一带近期有发生中强震的可能；丰镇－阳高－大同地区和凉城－古营盘地区应力较高，也应引起注意。  相似文献   

大气垂直折射与时序垂直角值的谱分析     

王泽民  张学廉 《大地测量与地球动力学》1995,(2)

本文介绍了对时序垂直角观测值进行谱分析的方法和所得到的结论。使以往对于大气折射影响及其变化规律的定性认识得以定量化。  相似文献   

Flow directions in ash-flow tuffs: a comparison of geological and magnetic susceptibility measurements, Tshirege member (upper Bandelier Tuff), Valles caldera, New Mexico, USA     

W D MacDonadl  H C Palmer 《Bulletin of Volcanology》1991,53(1):45-59

This study concludes that the elongation axis (K ₁) of the ellipsoid of anisotropic magnetic susceptibility (AMS) is a suitable proxy for flow axis in ashflow tuffs. 153 oriented samples (176 specimens) were studied from 18 sites in the 1.1 Ma Tshirege member of the Bandelier Tuff. These sites are distributed around the Valles caldera at distances of 5–25 km outside of the rim.K ₁ axes correlate well with postulated radial flow axes at 13 sites.K ₁ also agrees with measured geological flow indicators, mainly imbricated larger clasts, at 7 sites. At 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredK ₁ axes, theK ₁ axes correspond well with geological flow indicators, indicating that the divergence of flow from the predicted radial flow pattern is real. Two major topographic buttresses are suggested as the cause of flow divergence for the Tshirege ash flows: the San Pedro buttress northwest of the caldera, and the San Miguel buttress in the southeast. In situK ₁ axes plunge about 7° toward the source at two-thirds of the sites; therefore the plunge ofK ₁ is a plausible in situ indicator for thedirection of flow. Multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash-flow emplacement. These observations raisre the question of how best to represent mean flow directions in ash-flow sheets: by eigenvector methods, by vector-sum methods, or by modes. A method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined. Imbrication, determined in this way at one-third of the sites, dips toward the source, i.e., up-flow. The minimum (K ₃) axis of the AMS ellipsoid correlates with the flow foliation rather than with the larger clast imbrication. The flow axes of ash flows correspond with theK ₁ axes, not with the declination ofK ₃ axes as suggested by some authors. Initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction, which is reversed with a mean ofD=173.5°,I=-38.4°, ₉₅=3.4°N=18. This mean is not different at the 95% confidence level from that of earlier workers. The mean pole, at 098.0°E, 74.8°N,A ₉₅=3.3°,N=18, is about 15° far-sided relative to the expected time-averaged geomagnetic pole, suggesting a history of emplacement too short to adequately average secular variation.  相似文献   

On the practice of estimating fractal dimension   总被引：11，自引：0，他引：11  

James R. Carr  William B. Benzer 《Mathematical Geology》1991,23(7):945-958

Coastlines epitomize deterministic fractals and fractal (Hausdorff-Besicovitch) dimensions; a divider [compass] method can be used to calculate fractal dimensions for these features. Noise models are used to develop another notion of fractals, a stochastic one. Spectral and variogram methods are used to estimate fractal dimensions for stochastic fractals. When estimating fractal dimension, the objective of the analysis must be consistent with the method chosen for fractal dimension calculation. Spectal and variogram methods yield fractal dimensions which indicate the similarity of the feature under study to noise (e.g., Brownian noise). A divider measurement method yields a fractal dimension which is a measure of complexity of shape.  相似文献   

    

Guocheng Pan  D. P. Harris 《Mathematical Geology》1991,23(6):861-886

A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional factor plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations  相似文献   

Commission health and development     

M. Erdtmann-Vourliotis  M. Klein  K. Hohgardt 《GeoJournal》1991,25(1):125-126

IGU-Reports

Commission health and development  相似文献   

Littoral '92     

H. Flanquart  C. Meur-Férec  Ph. Deboudt  V. Morel  A.-P. Hellequin  et al. 《GeoJournal》1991,24(2):223-223

Reports

Littoral '92  相似文献   

造山带中富集型上地幔的成因——以萨尔托海蛇绿岩块为例   总被引：1，自引：0，他引：1  

郝梓国  王希斌  鲍佩声 《地球学报》1991,12(1):159-166

发育于造山带中的蛇绿岩,其剖面下部的地幔橄榄岩部分是造山带地区富集型上地幔的直接标本。其地球化学特点是:主要元素Al_2O_3、TiO_2、CaO、Na_2O、K_2O强烈亏损,而REE,痕量元素和87Sr/86Sr则强烈富集;同时,143Nd/144Nd<0.511836,亦表明它们属于一个富集型的源区。 形成富集型上地幔的主要机制是地幔交代作用,富含不相容元素的低熔岩浆和富Ca-LREE流体与已亏损的地幔橄榄岩发生脉状交代和渗透交代反应,从而造成上地幔中不相容元素的富集。造山带富集型上地幔形成的构造环境是:洋壳从扩张脊向两侧运移并最终拼入造山带这段时间内。富集型上地幔不但存在于大陆区,而且亦存在于造山带地区,它可能是一种全球性的地球内部的化学作用。  相似文献