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911.
912.
913.
Deformation-related microstructures in magmatic zircon and implications for diffusion 总被引:1,自引:1,他引:0
Steven Michael Reddy Nicholas E. Timms Patrick Joseph Hamilton Helen R. Smyth 《Contributions to Mineralogy and Petrology》2009,157(2):231-244
An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole
glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation.
A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous
zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron
backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of
up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic
bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations
are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD
maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations
are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with
the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts
and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon
grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior
to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic
stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain
deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal
plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic
microstructures in zircon is not restricted to high-strain rocks. Such microstructures have previously been shown to enhance
bulk diffusion of trace elements (U, Th and REE) in zircon. The development of deformation microstructures, and therefore
multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of
geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion
and dissolution rates. 相似文献
914.
915.
916.
软土e-p曲线确定的简化方法及在非线性沉降计算中的应用 总被引:1,自引:0,他引:1
首先假设软土的压缩曲线符合双曲线方程,并通过某工程一系列的数据进行验证,验证结果表明双曲线假定比较符合软土压缩曲线;由于双曲线方程参数相对较少,数据拟合确定比较简单易行,可对实际工程软土地基沉降进行简化计算并能满足工程的精度要求;同时还针对目前地质报告一般不提供详细的孔隙比-压缩应力(简称e-p)试验数据的情况,对e-p双曲线方程提出了一个只采用初始孔隙比e0、压缩模量Es来确定其参数的简化方法。在此基础上,基于e-p曲线确定邓肯-张模型的切线模量Et,采用分层总和法应用于软土地基的非线性沉降计算。对计算结果与实测数据进行比较分析表明,所提出的方法是切实可行的。 相似文献
917.
小波分析和RBF神经网络在地基沉降预测中的应用研究 总被引:4,自引:2,他引:2
地基沉降是一种危害很大的环境灾害。地基沉降的监测数据经常受降雨及工程施工等诸多外界因素的干扰,故而在沉降曲线中存在许多数据突变点。为此,提出基于小波分析与RBF神经网络相结合的新的地基沉降预测方法,首先采用小波分析对对原始监测数据进行数据去噪处理,进而得到反映实际变化的地基沉降曲线,然后采用径向基函数(RBF)神经网络方法对其进行预测,为工程设计提供依据。最后结合工程实例分析,通过多种小波去噪与预测结果的对比研究,表明3次B样条小波的去噪及预测效果最好,与实测值能较好地吻合,具有较好的工程应用前景。 相似文献
918.
垃圾土一维压缩修正公式及有机物降解验证试验研究 总被引:2,自引:1,他引:1
针对垃圾填埋场沉降计算问题,考虑垃圾土中有机物降解及对降解过程中重度变化,在张振营压缩量计算方法的基础上推导了垃圾土一维压缩计算的修正公式;通过垃圾土有机物降解试验和计算分析,研究了有机物的降解规律;以相同配比的垃圾土进行了垃圾土柱的沉降和计算参数试验,对推导的垃圾土一维压缩计算修正公式进行了验证。研究表明,修正的计算公式能考虑更多的影响因素,有机物的降解规律可以用Richards生物生长规律来模拟,修正的计算公式能够合理地计算出垃圾土沉降的过程。 相似文献
919.
沉陷区域埋地管线数值模拟分析 总被引:4,自引:0,他引:4
场地的不均匀沉陷是导致埋地管线破坏的重要原因之一。本文考虑了材料非线性、几何非线性以及管土接触非线性,将管线计算分析模型模拟为四节点薄壳单元结构,周围填覆土体采用八节点六面体单元划分。管土相互作用模拟为三维刚性与柔性的面面接触单元结构,并采用线性位移加载来模拟土体的沉陷作用,对三维薄壳有限元模型进行数值计算分析。通过比较不同参数,如沉陷长度、沉陷深度、埋深、管径、径厚比、土特性等对管线的反应影响,得出管线在沉陷情况下的应力和应变的关系,通过算例分析,说明了该方法能更好地模拟管线的破坏过程,该方法将为沉陷区域埋地管线数值模拟提供理论分析依据。 相似文献
920.
YuQun Xue JiChun Wu Yun Zhang ShuJun Ye XiaoQing Shi ZiXin Wei QinFen Li Jun Yu 《中国科学D辑(英文版)》2008,51(6):808-825
Investigation of the deformation characteristics of individual hydrostratigraphic units is the key to construct a regional land subsidence model. All of 12 hydrostratigraphic units in the study area were discussed throughout. On the basis of the measured data of groundwater level, five kinds of changing patterns of groundwater level were deduced and the relationship between the deformation characteris-tics of aquifer units and the corresponding changing patterns of groundwater level was discussed. The study area is 1.7×104 km2, where the geological condition is complex. The changing patterns of groundwater level the hydrostratigraphic units have experienced vary from site to site and from time to time. Consequently, the deformation characteristics of units are sophisticated. An identical hydros-tratigraphic unit may exhibit different deformation characteristics, such as elasticity, elasto-plasticity, visco-elasticity, and visco-elasto-plasticity, at different sites or during different periods, not to mention the different units. The existing models are difficult to describe the complex visco-elasto-plastic con-stitutive law under the condition of land subsidence. So the Merchant’s model was modified to depict the visco-elasto-plastic behavior of units. Then a three-dimensional flow model with variable parame-ters and a vertical one-dimensional subsidence model were constructed and coupled. The coupled model was applied in simulating land subsidence in the southern Yangtze Delta and a satisfactory re-sult was obtained. The simulation results show that the new coupled model can depict the complex geological conditions and describe the developing process of land subsidence very well in the south-ern Yangtze Delta. The new model can surely be used to predict land subsidence in the future, which is very helpful to taking measurements to control land subsidence. 相似文献