岩石受压破裂的ULF和LF电磁前兆信号   总被引：15，自引：1，他引：15  

钱书清  郝锦绮  周建国  高金田 《中国地震》2003,19(2):109-116

实验观测到了4类岩性、18块样品在单轴压力下直至破裂发生全过程中的ULF和LF电磁前兆信号。这些不同频率的信号是零散出现的，其形态为一组组脉冲，宽度为4ms～16ms，幅度为0．1mV～1．4mV。实验发现具同一谐振频率的天线收到的信号频次与其相对于裂缝的位置和方位有关。结果还表明，电磁前兆信号的频度与岩样强度有关，抗压强度高的岩样电磁前兆信号多。微破裂可能产生了偶电层，在破裂过程中向外辐射，产生了LF频段的磁信号，ULF磁信号则主要由压磁效应产生。  相似文献   

Petrogenesis of the Ulsan carbonate rocks from the south-eastern Kyongsang Basin, South Korea   总被引：1，自引：0，他引：1  

Kyounghee Yang  Jin-Yeon Hwang  Sung-Hyo Yun 《Island Arc》2003,12(4):411-422

Abstract The petrogenesis of the Ulsan carbonate rocks in the Mesozoic Kyongsang Basin of South Korea, which have previously been interpreted as limestone of Paleozoic age, is reconsidered in the present study. Within the Kyongsang Basin, a small volume of carbonate rocks, containing a magnetite deposit and spatially associated ultramafic rocks, is surrounded by sedimentary, volcanic and granitic rocks of the Mesozoic age. The simple cross‐cutting relationships and other outcrop features of the area indicate that the carbonate rocks are an intrusive phase and younger than the other surrounding Mesozoic rocks. The Ulsan carbonates have low concentrations of rare earth elements (REE) and trace elements with the carbon and oxygen isotope values in the range of δ¹³C_PDB = 2.4 to 4.0‰ and δ¹⁸O_SMOW = 17.0 to 19.5‰. Outcrop evidence and geochemical signatures indicate that the Ulsan carbonates were formed from crustal carbonate melts, which were generated by the melting/fluxing of crustal carbonate materials, caused by the emplacement‐related processes of alkaline A‐type granitic rocks. Compared to typical mantle‐derived carbonatites associated with silica‐undersaturated, strongly peralkaline systems, the relatively small size and geochemical characteristics of the Ulsan carbonates reflect carbonatite genesis in a silica‐saturated, weakly alkali intrusive system. Major deep‐seated tectonic fractures formed by the collapse of the cauldron or the rift system associated with the opening of the East Sea (Japan Sea) might have facilitated the ascent of the crustal carbonate melts.  相似文献   

渤海—鲁西地区白垩-早第三纪裂谷活动——火山岩的地球化学证据   总被引：9，自引：3，他引：9  

侯贵廷  钱祥麟  蔡东升 《地质科学》2003,38(1):13-21

渤海—鲁西地区的白垩早第三纪火山岩在渤海东部主要沿郯庐断裂带呈北北东向分布,在渤海西部和鲁西地区主要沿北西向断裂带分布。白垩纪火山岩以安山岩类为主,早第三纪以玄武岩类为主,玄武岩浆源于富集型地幔,即富集轻稀土和大离子亲石元素,但明显亏损Yb、Ni和Cr等元素。火山岩的Sr和Nd同位素初始比值结果表明白垩纪的火山岩来源于Ⅱ型富集地幔,而早第三纪火山岩来源于接近原始地幔的略富集型地幔。这可能由于早第三纪岩石圈大规模伸展减薄,致使上地幔深部的亏损型物质上涌参与岩浆活动,与富集型地幔混染的结果。  相似文献   

试论碳酸盐岩上覆红土的形成模式及演化趋势   总被引：14，自引：1，他引：14  

符必昌  黄英 《地质科学》2003,38(1):128-136

据长期对岩溶及红土化作用等的研究成果,本文全面系统地分析了碳酸盐岩上覆红土的形成及演化规律,提出了一个新的碳酸盐岩上覆红土的形成模式,进而深入阐明了碳酸盐岩上覆红土的演化规律及其在现代气候条件下的演化趋势等,在解决岩溶及红土学术界存在的碳酸盐岩上覆红土的形成、碳酸盐岩与上覆红土之间的相互关系及其发展演化规律等一系列重大疑难问题上向前迈进了一步,对相关学科的发展将产生积极的推动作用.  相似文献   

羌塘岩带碰撞后超钾质火山岩地球化学特征及成因探讨   总被引：1，自引：0，他引：1  

刘燊  胡瑞忠  迟效国  李才  冯彩霞  王天武 《大地构造与成矿学》2003,27(2):167-175

羌塘超钾质火山岩为板块碰撞后的产物,地球化学特征表明,其同时具有板内火山岩和俯冲带岛弧火山岩的双重地球化学特性。化学组成上富含轻稀土和大离子亲石元素而亏损Cr、Ni等相容元素。在成因上受分离结晶作用和源区混合作用共同制约。源区为受古俯冲上地壳物质和下地幔上升流体交代混合的EMII型富集地幔端元,可能富含角闪石和金云母等矿物。  相似文献   

Paléoenvironnements et caractérisation des roches mères pétrolières des séries pré-salifères du bassin intérieur du Gabon     

Michel Mbina Mounguengui  François Baudin  Jacques Lang  Olivier Jocktane 《Comptes Rendus Geoscience》2003,335(3):327-334

The Interior Basin of Gabon, created during the break-up between South America and Africa, displays thick Neoproterozoic to Aptian p.p. fluvio-lacustrine deposits overlain by Aptian to Albian marine facies. Rock–Eval analyses from outcrop and drillhole samples show high content in organic matter (up to 25%) related to types I and II. These intervals are encountered within Permian, Neocomian–Barremian as well as Aptian siliciclastic succession. They constitute fairly good to excellent potential petroleum source rocks, which are most probably at the origin of oil indices recognized both in drillholes and in surface.  相似文献   

A Linear Programming Approach to Determine the Normative Composition of Sedimentary Rocks     

V. N. Podkovyrov  O. V. Graunov  R. L. Cullers 《Mathematical Geology》2003,35(4):459-476

The analysis of modal and normative composition of sedimentary rocks is widely used for studying their sources and tectonic settings. The normative calculation of the mineral composition of rocks in this study is formulated as a linear programming problem and is solved by means of the simplex method. This enables both simultaneous and successive subtraction of a set of basic minerals from a rock sample represented by its chemical composition {SiO₂...LOI}. Such an approach provides a more exact calculation of the contribution of basic minerals in the rock. This mathematical approach is used to study two representative sets of sandstones and fine-grained rocks from a Meso- to Neoproterozoic marginal basin of southeastern Siberia (Uchur–Maya region, Yakutia) and a Pennsylvanian-Lower Permian uplifted continental block in Colorado, USA. The calculated normative mineral compositions of the Siberian sandstones are consistent with the observed modal compositions. These sandstones vary from K- Feldspar rich arkoses at the base of the sequence (the Uchur Group, lower Riphean) to quartz arenites or lithic sandstones and wacke in transgressive successions of the middle-upper Riphean. Arkoses and quartz arenites are dominant in Meso- to Neoproterozoic Siberia. These samples represent craton interior uplifted basement and quartzose, recycled orogen provenance of a stable craton in Rodinia. There are higher but consistent discrepancies between the calculated and observed compositions for the Pennsylvanian to Lower-Permian arkoses and quartz arenites (Sangre de Cristo, Belden, and Maroon Formations). The differences between the predicted and observed mineralogy may be due to uncertainties in the modes in the matrix and cement of the sandstones. This normative program should supplement modal calculations and provide better genetic constructions, especially in case of matrix-rich sandstones.  相似文献   

Cosmic-ray Exposure Ages of Meteorites and Lunar Rocks and Their Significance   总被引：1，自引：0，他引：1  

O. Eugster 《Chemie der Erde / Geochemistry》2003,63(1):3-30

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达拉布特镁铁质岩的Sr-Nd同位素及微量元素地球化学   总被引：1，自引：0，他引：1  

杨瑞瑛  刘丛强  高桥和也  增田彰正 《地球学报》1997,18(Z1):92-94

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硅岩的Rb-Sr同位素组成特点及其地质意义   总被引：2，自引：0，他引：2  

王东安  陈瑞君 《地球学报》1997,18(Z1):108-110

通过对扬子地台和东昆仑山地区的不同时代、不同成因、成分上差异较大的硅岩Rb-Sr同位素组成的对比研究，探讨其物源和形成环境，利用所测Rb-Sr等时线年龄，有效的解决硅岩的地层年代，开创硅岩测年的应用前景。  相似文献