藏北双湖地区海西期和印支期火山岩地球化学特征及其构造意义     

李延平  林振宏  张宗雁  伊三泉  王岫岩  姜耀俭 《世界地质》2005,24(3):230-235,281

藏北双湖地区海西期和印支期火山岩均以夹层形式产于海相沉积岩层中.海西期火山岩高度富集轻稀土元素和明显富集Rb、Ba、K等大离子亲石元素与Nb、Ta、Ti、P等高场强元素,无Nb、Ta、Ti亏损等特点,表明其具有大陆裂谷碱性玄武岩和洋岛碱性玄武岩的特征;以其不相容元素比值,相当于Gough岛EMⅠ OIB型洋岛玄武岩,其构造环境判别图进一步印证了海西期火山岩形成于洋岛碱性玄武岩环境.印支期火山岩贫轻稀土元素和Rb、Ba、K等大离子亲石元素,相对贫Nb、Ta、Ti、P等高场强元素;但Nb、Ta并不亏损以及稀土配分曲线较平缓等特点,表明其具有大陆裂谷拉斑玄武岩特征;其微量元素、稀土元素的丰度及曲线特征可以与确定环境的红海88GTV岩样、东非大裂谷B10C岩样的丰度及曲线特征相类比,且构造环境判别图也共同印证了印支期火山岩形成于类似红海-东非裂谷型的大陆裂谷,初始洋盆的环境.  相似文献   

琼中古-中元古代变基性火山岩地球化学特征及其地质意义   总被引：3，自引：1，他引：2  

徐德明  谢才富  张业明  付太安  李志宏 《地球学报》2006,27(3):227-234

琼中古—中元古代抱板岩群斜长角闪(片麻)岩为高钾变基性-中基性火山岩。化学成分上具有富钾(K2O/Na2O值大于0.6)、高铝(Al2O3含量高于15%)和低钛(TiO2含量低于1.3%)等特点。岩石的K、Rb、Ba、Th等大离子亲石元素和轻稀土元素明显富集,LREE/HREE值较高,并具有显著的Ta、Nb、Ti负异常。微量元素和Sm、Nd同位素特征表明,琼中变基性火山岩岩浆源区偏离原始地幔,并且未受成熟地壳物质的明显污染,它们是俯冲消减带上部陆弧区地幔楔受俯冲洋壳析出的流体和硅酸盐融体交代作用后部分熔融的产物。古—中元古代时期,海南地块可能经历了由拉张到挤压的地球动力学转变,早期拉张阶段形成琼西洋脊型和过渡型拉斑玄武岩,中晚期则形成与洋壳俯冲作用相关的琼中岛弧型高钾钙碱性玄武岩,这一过程可能与华南大陆的裂解及随后洋壳向华夏古陆的深俯冲作用有关。  相似文献   

On Blind Tests and Spatial Prediction Models   总被引：3，自引：0，他引：3  

Andrea G. Fabbri  Chang-Jo Chung 《Natural Resources Research》2008,17(2):107-118

This contribution discusses the usage of blind tests, BT, to cross-validate and interpret the results of predictions by statistical models applied to spatial databases. Models such as Bayesian probability, empirical likelihood ratio, fuzzy sets, or neural networks were and are being applied to identify areas likely to contain events such as undiscovered mineral resources, zones of high natural hazard, or sites with high potential environmental impact. By processing the information in a spatial database, the models establish the relationships between the distribution of known events and their contextual settings, described by both thematic and continuous data layers. The relationships are to locate situations where similar events are likely to occur. Maps of predicted relative resource potential or of relative hazard/impact levels are generated. They consist of relative values that need careful quantitative scrutiny to be interpreted for taking decisions on further action in exploration or on hazard/impact mitigation and avoidance. The only meaning of such relative values is their rank. Obviously, to assess the reliability of the predicted ranks, tests are indispensable. This is also a consequence of the impracticality of waiting for the future to reveal the goodness of our prediction. During the past decade only a few attempts have been made by some researchers to cross-validate the results of spatial predictions. Furthermore, assumptions and applications of cross-validations differ considerably in a number of recent case studies. A perspective for all such experiments is provided using two specific examples, one in mineral exploration and the other in landslide hazard, to answer the fundamental question: how good is my prediction?  相似文献   

Petrogenesis and geodynamic significance of the Ganhe Formation lavas,eastern Great Xing'an Range,China: Evidence from geochemistry and geochronology          下载免费PDF全文

A‐lei Gu  Jing‐gui Sun  Ling‐an Bai  Yong Zhang  Pei‐long Cui  Peng Chai  Ke‐qiang Zhao  Qing‐long Sun  Liang Ren  Yan‐jun Chen  Jun‐quan Zhu 《Island Arc》2016,25(2):87-110

Mesozoic volcanic rocks are widespread throughout the Great Xing'an Range of northeastern China. However, there has been limited investigation into the age and petrogenesis of the Mesozoic volcanics in the eastern Great Xing'an Range. According to our research, the volcanic rocks of the Dayangshu Basin, eastern Great Xing'an Range are composed mainly of trachybasalt, basaltic andesite, and basaltic trachyandesite, with minor intermediate–basic pyroclastic rocks. In this study, the geochemistry and geochronology of the Mesozoic volcanic rocks are presented in order to discuss the petrogenesis and tectonic setting of the Ganhe Formation in the Dayangshu Basin. Zircon U–Pb dating by laser ablation inductively coupled plasma–mass spectrometry indicates that the Mesozoic lavas formed during the late Early Cretaceous (114.3–108.8 Ma). This suite of rocks exhibits a range of geochemical signatures indicating subduction‐related genesis, including: (i) calc‐alkaline to high‐K calc‐alkaline major element compositions; (ii) enrichment of large ion lithophile elements (e.g. Rb, Ba, K) and light rare earth elements (LREEs/HREEs =7.33–9.85); and (iii) weak depletion in high field strength elements (e.g. Nb, Ta, Ti). Furthermore, Sr–Nd–Pb isotopic data yield initial ⁸⁷Sr/⁸⁶Sr values of 0.70450–0.70463, positive ε_Nd(t) values of +1.8 to +3.3, and a mantle‐derived lead isotope composition. Combined with the regional tectonic evolution, the results of this study suggest that the Ganhe Group lavas are derived from decompression melting of a metasomatized (enriched) lithospheric mantle, related to asthenospheric upwelling, which resulted from lithospheric mantle delamination and produced extension of the continental margin following the subduction of the Paleo‐Pacific Plate.  相似文献   

准噶尔盆地中拐凸起东斜坡带火山岩储层岩相特征及主控因素   总被引：1，自引：0，他引：1  

邓西里  宋新民  李顺明  孔垂显  何辉  蒋庆平 《现代地质》2015,29(6):1387-1397

综合岩石薄片、岩心观察、各类测井资料以及三维地震资料,对准 噶尔盆地西北缘中拐凸起东斜坡带佳木河组火山岩的岩石学特征、测井响应特征、地震响应特征进行研究,总结出该区的火山岩岩性岩相识别模板及分布规律。采用不同曲线交会图对火山岩大类进行识 别,采用FMI成像测井“结构特征+构造特征”模板识别成分相近的火山岩亚类,共识别出3大类8种火山岩岩性,结合地震相特征,识别出4种火山岩岩相。研究区北部以爆发相火山角砾岩为主,在JIN215 、JIN218井及其以北地区存在多个复杂叠置的火山机构;南部则以喷溢相的熔结角砾岩和中性熔岩为主,局部发育火山沉积相。在此基础上,结合试油资料及裂缝预测分析,认为该区火山岩储层受到岩 性岩相、构造裂缝和风化淋滤作用的共同控制,靠近佳木河组顶部风化淋滤带裂缝发育区的爆发相火山角砾岩是最为有利的储集层类型。  相似文献   

南海北部新生代火山岩微量元素与同位素体系特征研究   总被引：2，自引：0，他引：2  

涂湘林  邹和平 《地球学报》1997,18(Z1):34-36

南海北部新生代火山岩由早期的钙碱性双峰式向晚期的碱性玄武岩和拉斑玄武岩演化，微量元素与同位素体系特征研究表明这种趋势与该地区边缘海的扩张过程相对应，在拉伸作用早期，岩浆来源于富集型岩石圈地幔，而在晚期则来源于亏损的软流圈地幔。  相似文献   

阿尔泰麦兹地区海相火山岩及其与成矿作用的关系   总被引：2，自引：0，他引：2  

张进红  王京彬  丁汝福 《地质论评》1999,45(7):1116-1125

阿尔泰麦兹地区下泥盆统康布铁堡组火山岩,下亚组为偏碱性的富钠流纹岩夹少量的拉斑—碱性玄武岩和粗安岩;上亚组为钙碱性流纹岩类。其构造环境为大陆边缘活化带。下亚组基性火山岩来源于过渡—富集型地幔,酸性火山岩为壳幔混合源,岩浆经历了结晶分异、岩浆混合和岩浆不混熔作用;上亚组酸性火山岩来源于地壳,岩浆演化主要为与上地壳和海水的同化混染作用。本文还探讨了火山岩与铁和铅锌成矿作用的关系。  相似文献   

A Mechanism for the Building of the Qinghai-Tibet Plateau     

BAI Wenji  YANG Jingsui  SHI Rendeng 《Continental Dynamics》1999,(2)

l.IntroductionSinceArgand's(l924)recognitionthattheCenozoictectonicsoftheHighAsiaareprincipallytheresultoftheconvergenceofGondwanancontinentalfragmentswithLaurisic,therehasbeenageneralacceptanceoftheviewthattheHimalayasandQinghai-TibetPlateauhavebeenformedbyacollisionbetweentheIndianandTibetcontinentsalongtheIndus-Zangbosuture(MolnarandTapponnief,l975,Sengor,l979;ChenBingwei,l982;DengWanming,l978,HuangJiqing,l954;LoZhongshu,l982;PanGuitangetal.,l984,WangQianshenetal.,l982,Besseetal.…  相似文献   

山东牟平辽上金矿床地质特征     

罗忠明 《山东国土资源》2000,(3)

山东省烟台市牟平区辽上金矿床位于郭城断裂带东侧 ,赋存于荆山群野头组大理岩与震旦期花岗岩之接触带附近 ,矿体受NE向次级构造裂隙控制 ,呈盲矿体产出。  相似文献   

The role of pre-existing discontinuities in the development of extensional faults: An analog modeling perspective     

《Journal of Structural Geology》2015

Several mountainous regions are currently affected by syn- or post-orogenic active extension. We investigate how a newly-formed normal fault interacts with structures inherited from a previous contractional phase. To this end, we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer; this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane. We carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment. All other conditions are identical for all seven realizations. Fault evolution is monitored by taking closely-spaced snapshots analyzed through the Digital Image Correlation method. We find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation. Such precuts can also promote or inhibit the formation of bending-moment faults. These interactions between master fault and precut also affect the shape of the fault-related syncline–anticline pair.  相似文献