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541.
Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis 总被引:1,自引:1,他引:1
P. HASALOVÁ K. SCHULMANN O. LEXA P. TÍPSKÁ F. HROUDA S. ULRICH J. HALODA P. TÝCOVÁ 《Journal of Metamorphic Geology》2008,26(1):29-53
A detailed field study reveals a gradual transition from high‐grade solid‐state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation‐parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well‐equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high‐energy like–like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole‐rock volume and changes completely its macro‐ and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt‐enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains. 相似文献
542.
543.
关于侵入岩和火山岩二者之间的联系,已有上百年的争论。该争论主要集中于中—酸性岩,对于长英质火山岩的岩浆来源目前主要有2种观点:(1)由花岗质岩浆的“晶粥”中的熔体抽离而来;(2)与同期侵入岩无关,具有独立的岩浆形成过程。近些年来,随着高精度定年测试方法的进步和地球物理等研究方式的介入,对长英质火山岩和侵入岩二者的成因联系有了新的认知,“晶粥”模型和“穿地壳岩浆系统”受到较多关注,但同时也带来了新的矛盾和问题。文章系统总结了火山岩与侵入岩联系的不同观点、历史沿革、以及不同研究方法引起的争议,展望了该领域未来研究前景;提出大数据总体上展现出的长英质火山岩和侵入岩之间强烈的地球化学相似性,但这种总体上的相似性并不排除特定区域某个火山—侵入杂岩中的火山岩和侵入岩之间存在地球化学的差异,并在成因上符合“晶粥”模型。文章指出,深部探测、原位精细分析和实验模拟是火山岩—侵入岩成因联系研究方面有望取得突破的重要研究方向,而将火山岩—侵入岩形成机制与大陆演化和环境变迁等问题的研究有机结合可能是未来的重要研究领域。 相似文献
544.
545.
确定岩石中矿物成核速度,成核密度,晶体生长速度和结晶时间的CSD理论及应用 总被引:1,自引:0,他引:1
结晶岩类的热力学研究是岩石学研究的重要内容之一。本文介绍了结晶岩石中矿物
结晶过程,包括矿物成核密度、成核速度、晶体生长速度、结晶时间与晶体大小分布的关系即CSD理论以及岩浆冷却、喷发、混合,接触变质、区域变质等过程各自具有的CSD特征;并对CSD理
论、方法及其地质应用进行了评价:指出复杂的自然过程对CSD的影响,在定向构造发育较好的
岩石巾由二维晶体测定转向三维计算的改进方法以及GSD所具有的重要的年代学意义。 相似文献
546.
西藏阿里地区火山岩的岩石系列及特征 总被引:2,自引:0,他引:2
西藏阿里地区冈底斯构造带分布有早白垩世的玄武岩-安山岩-英安岩系列及晚白垩—第三纪的玄武岩-安山岩-流纹岩系列,它们分别属于拉斑玄武及钙碱性系列。前者主要由地幔导源的玄武岩浆经分离结晶作用形成,而钙碱性系列主要由混合作用及同化作用形成。此外其岩浆房的fO_2与fH_2O高,液相线温度偏低并与地壳导源的岩基活动有密切的关系. 相似文献
547.
对于离子型或以离子键为主的晶体,其光学和磁学性质可用晶体场理论解释。通过晶场微扰矩阵元的计算,可定量地确定晶场光谱谱带位置。以往资料无矩阵元的计算过程,只是给出了部分积分结果,这不利于在任何对称情况下晶场微扰矩阵元的计算。推导了中心对称矿物的晶场势能算符,计算了积分值,得出了矩阵元以系数Aλx,r^2和r^4的表达式。并以绿松石的结构数据为基础,计算了Cu^2+的晶场微扰矩阵元表达式中的系数Aλx,从而计算了各矩阵元,通过对称矩阵的对角化,最终求得绿松石中Cu^2+d轨道能量和晶体场谱带位置计算值。与实验资料对比,符合较好。因此,用晶体场理论和实验资料相结合可定量地阐明具离子键晶体的呈色机制。 相似文献
548.
针对PO7D频标比对器存在独占性和程控性差的特点,结合晶体技术指标的检测方法和PO7D自身的优点设计了一个晶体频率自动测量系统,解决PO7D的独占性,增强其程控功能.具体实现是通过调整测量命令的执行方式,控制PO7D对被检晶体的信号和参考信号的比对,将测量所得的频率差值数据,再根据规范计算出晶振的相关技术指标. 相似文献
549.
O. LEXA P. TÍPSKÁ K. SCHULMANN L. BARATOUX A. KRÖNER 《Journal of Metamorphic Geology》2005,23(8):649-666
A structural, metamorphic and geochronological study of the Staré Město belt implies the existence of two distinct metamorphic events of similar peak P–T conditions (700–800 °C, 8–10 kbar) during the Cambro‐Ordovician and the Carboniferous tectonometamorphic events. The hypothesis of two distinct periods of metamorphism was suggested on the basis of structural discordance between an undoubtedly Carboniferous granodiorite sill intrusion and earlier Cambro‐Ordovician fabrics of a banded amphibolite complex. The analysis of crystal size distribution (CSD) shows high nucleation density (N0) and low average growth rate (Gt) for Carboniferous mylonitic metagabbros and mylonitic granodiorites. The parameter N0 decreases whereas the quantity Gt increases towards higher temperatures progressively approaching the values obtained from the Cambro‐Ordovician banded amphibolite complex. The spatial distribution of amphibole and plagioclase shows intense mechanical mixing for lower‐temperature mylonitic metagabbros. In high‐temperature mylonites a strong aggregate distribution is developed. Cambro‐Ordovician amphibolites unaffected by Carboniferous deformation show a regular to anticlustered spatial distribution resulting from heterogeneous nucleation of individual phases. This pattern, together with CSD, was subsequently modified by the grain growth and textural equilibration controlled by diffusive mass transfer during Carboniferous metamorphism. The differences between the observed textures of the amphibolites are interpreted to be a consequence of the different durations of the Carboniferous and Cambro‐Ordovician thermal events. 相似文献
550.
Yujie Liu Wenqiang Yang Chao Zhang Zhian Bao Shitou Wu Renat R. Almeev Filippo Ridolfi Roberta Oberti 《Geostandards and Geoanalytical Research》2023,47(3):595-608
The amphiboles from Kakanui and Arenal are two natural minerals that have been used worldwide as microanalytical reference materials, but their compositions and crystal structures are still poorly constrained. In this paper, we report new data on H2O and trace element mass fractions and single-crystal structural refinement of these two amphiboles. H2O mass fractions of the Kakanui and Arenal amphiboles determined via Karl-Fischer titration are 0.92 ± 0.18 (2s) and 1.56 ± 0.22% m/m (2s), respectively; these values estimated based on crystal-structure refinement are 0.86 and 1.46% m/m, respectively. Trace element mass fractions measured via LA-ICP-MS in two laboratories are in good agreement, and spots from five fragments for both Kakanui and Arenal amphiboles are generally consistent within reproducibility precision (2s). Our measurements indicate a better homogeneity for the amphiboles from Kakanui than that from Arenal. According to the latest scheme for amphibole classification and nomenclature (Hawthorne et al. 2012), the sample from Arenal is a (partially dehydrogenated) pargasite, and that from Kakanui is a kaersutite. The significant amount of oxo-component and that CTi4+ content is strongly ordered at the M(1) site for both amphiboles indicate crystallisation under high fO2 conditions. 相似文献