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61.
南极罗斯岛及泰勒谷地区火山岩的地球化学特征及成因讨论 总被引:2,自引:0,他引:2
利用微量元素和Sr,Nd,Pb同位素资料,得出了南极罗斯岛及泰勒谷地区火山岩来自于上地幔,五个地区火山岩具有相同的源区。岩石具有大洋岛屿玄武岩(OIB)的特征。来自地幔的火山喷发的岩浆未遭受地壳物质的混染作用。地幔源区是具有高μ(=206Pb/204Pb)比值的地幔组分HIMU与亏损地幔组分DMM混合作用的结果,其中以HIMU组分为主,原生岩浆由具HIMU组分特征的深部地幔柱与浅部的DMM混合而成。 相似文献
62.
大长沙火山岩盆地铀成矿条件分析 总被引:7,自引:0,他引:7
文章分析了盆地的火山活动、火山岩的地球化学特点和铀矿化特征。认为盆地是塌陷式的,岩浆活动分为两个旋迥,并且不同族迥的岩浆来源深度不同。盆地发育有多期次的矿化蚀变,铀源有地幔铀、基底铀及盖层蚀变而迁移出的活化铀。盆地断裂构造发育,有较好的矿质沉淀场所,又处在有利的铀成矿区域背景之下,因此具有较大的铀成矿远景。 相似文献
63.
Johannes Bruining Diederik van Batenburg Larry W. Lake An Ping Yang 《Mathematical Geology》1997,29(6):823-848
Random field generators serve as a tool to model heterogeneous media for applications in hydrocarbon recovery and groundwater
flow. Random fields with a power-law variogram structure, also termed fractional Brownian motion (fBm) fields, are of interest
to study scale dependent heterogeneity effects on one-phase and two-phase flow. We show that such fields generated by the
spectral method and the Inverse Fast Fourier Transform (IFFT) have an incorrect variogram structure and variance. To illustrate
this we derive the prefactor of the fBm spectral density function, which is required to generate the fBm fields. We propose
a new method to generate fBm fields that introduces weighting functions into the spectral method. It leads to a flexible and
efficient algorithm. The flexibility permits an optimal choice of summation points (that is points in frequency space at which
the weighting function is calculated) specific for the autocovariance structure of the field. As an illustration of the method,
comparisons between estimated and expected statistics of fields with an exponential variogram and of fBm fields are presented.
For power-law semivariograms, the proposed spectral method with a cylindrical distribution of the summation points gives optimal
results. 相似文献
64.
Nils-Otto Kitterrød Lars Gottschalk 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(6):459-482
Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function.
This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients
from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance
model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns
out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of
eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the
2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance
function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields
with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial
interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the
predefined covariance functions are evaluated. 相似文献
65.
Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function.
This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients
from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance
model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns
out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of
eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the
2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance
function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields
with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial
interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the
predefined covariance functions are evaluated. 相似文献
66.
67.
In order to clarify the relationship between microscopic and macroscopic magnetic features of a rock, we applied magnetic force microscopy (MFM) as a local probe on a sample with an intense natural remanent magnetisation, a norite from Heskestad, Norway. We studied in detail seven magnetite (Fe3O4) exsolution lamellae, five of them were about 30 μm long and a few micrometers wide, two were significantly shorter; all were located in their natural host, a grain of clinopyroxene. By combining MFM images of surface magnetisation with information about shape observed with optical microscopy (OM), the internal domain structure was determined for individual grains. In general, the lamellae were pseudo-single-domain grains with open-flux domain magnetisations parallel to their long axes. The domain sizes were, in cross-section, on the order of a micrometer for the longer lamellae and about 300 nm for the short lamellae. By increasing the separation between the MFM probe and the exposed end of the lamellae, information could be obtained about the decrease in stray fields for the individual grains. Close to the lamellae, stray fields were significant even for grains with multiple domains. The largest fields were found above the largest domains. A separation of approximately one domain width was found to be a characteristic distance, where stray fields from adjacent domains begin to cancel one another. 相似文献
68.
主要介绍了近 2 0年来稻田甲烷排放的模式研究和排放量的估算以及减少稻田甲烷排放的措施。数值模式是估算稻田甲烷排放量的一条有效途径 ,模式的研究现在正处于发展阶段。介绍了几个主要的模型 ,既有物理过程模型也有经验模型。年排放量的估算范围为 6 79~ 4 1 4Tg ,随着技术的发展和大量实验的进行估算值的精度正得到不断的提高。减排措施是减少稻田甲烷排放的必要手段 ,但是目前的减排技术均处于研究阶段 ,应用还不成熟 相似文献
69.
议京西大台地区的燕山运动 总被引:3,自引:1,他引:3
作者研究了京西大台地区的燕山运动,初步研究表明:这里不存在强烈的挤压变形迹象和显著的角度不整合.缺乏磨拉石建造。龙门组是厚度有限的河流相沉积,九龙山组是具有弱火山活动的湖相一滨湖相沉积。在隆起带和沉降带之间侏罗系地层显著的厚度变化率、大安山一斋堂滑覆构造及其派生的髫髻山断陷盆和大量高角度滑动面理,都显示了伸展构造背景下基底断块的差异升降。髫髻山组与壳幔相互作用有关的一套火山岩显示了上述运动的深部背景。 相似文献
70.
北京延庆北部地区后城组火山岩岩石化学特征与成因探讨 总被引:3,自引:0,他引:3
根据TAS图解 ,北京延庆北部地区后城组火山属于玄武粗安岩 流纹岩 (和粗面岩 )的双峰式组合。该套火山岩不属于典型的钾玄岩系列 ,在基性岩和中性岩中总体上以碱性系列和向碱性系列过渡的高钾钙碱性系列、钾玄岩系列为主 ,流纹岩类属于富钾质的拉斑系列。该套火山岩轻稀土元素明显富集。玄武粗安岩类岩石没有负铕异常或负铕异常不明显 ,而流纹岩存在明显的负铕异常。延庆北部地区后城组火山岩形成于燕山运动早期或中期阶段的造山变形事件趋于结束时的后碰撞构造环境中。 相似文献