Nd isotopic composition of Paleoproterozoic volcanic and granitoid rocks of Vila Riozinho: implications for the crustal evolution of the Tapajós gold province, Amazon craton     

Claudio Nery Lamaro  Roberto Dall'Agnol  Marcio Martins Pimentel 《Journal of South American Earth Sciences》2005,18(3-4):277-292

Nd data from the Paleoproterozoic magmatic rocks of Vila Riozinho and Jamanxim (Tapajós gold province) indicate that original magmas were not produced exclusively by the remelting of Archean sialic crust and point to dominant Paleoproterozoic sources. ε_Nd(T) values preclude derivation from mantle sources for the ca. 2.0 Ga Vila Riozinho volcanics and older São Jorge granite. They may represent a subduction-related magmatic arc with magmas modified by interaction with crust or a post- to late-orogenic remelting of an older Paleoproterozoic juvenile arc with minimal contribution from the Archean crust. The origin of the 1.88 Ga Parauari, Maloquinha, Iriri, and Moraes Almeida igneous associations and the Jamanxim rhyolites has been attributed to large-scale taphrogenesis that marked the breakup of a large Paleoproterozoic continent. Derivation of the original magmas from the remelting of crustal sources older than ca. 1.9 Ga is consistent with geochemical and Nd isotopic data. Archean remnants probably occur between the Paleoproterozoic terrains of the Ventuari-Tapajós province. Archean terrains of the Amazon craton extend from the Xingu to the Itaituba region but have not been identified in the southern Guyana shield. Thus, data reveal that the boundaries between the central Amazon and Ventuari-Tapajós provinces need better definition and more detailed field and geochronological work.  相似文献   

An Interactive Sampling Strategy Based on Information Analysis and Ordinary Kriging for Locating Hot Spot Regions     

Shyan-Shu Shieh  Ji-Zheng Chu  Shi-Shang Jang 《Mathematical Geology》2005,37(1):29-48

This study proposes an interactive sampling strategy for locating the hot spot or maximum regions of a concerned attribute in a given area of survey. In the proposed strategy, information analysis is performed based on the ordinary kriging from the existing sample data to suggest a new batch of samples under the criterion of the highest information free energy. The information free energy (F) is a function of information energy (U) and information entropy (S) through F = U - TS, where T is information temperature and is used to coordinate the contribution of U and S to F. Information energy is the value of the concerned attribute, and information entropy is the transformed error variance of kriging and therefore measures the evenness and density of coverage of samples over the area under survey. At early sampling batches, information temperature is high and information entropy dominates the information free energy, and samples are suggested to give an even and dense enough coverage of the whole area under investigation. As samples accumulate, information temperature decreases to enlarge the contribution of information energy, and future samples are taken toward the locations with high attribute values. Two examples demonstrate the efficiency and effectiveness of the proposed sampling strategy in locating the hot spot regions of various fields: (1) a heavy metal contaminated site reproduced by modeling on 55 real field data; (2) a simulated two-dimensional field by the random phase volume (RPV) model. The results show that the proposed strategy, a robust interactive sampling procedure, is able to locate hot spot regions without compromising with the overall profile of an under-survey area.  相似文献   

吉林省夹皮沟金矿成因研究   总被引：1，自引：0，他引：1  

李碧乐  金巍 《世界地质》1998,17(1):22-25

吉林省夹皮沟金矿区金矿赋存在夹皮沟北西向韧性带内,控矿构造为叠加在韧性剪切带之上的脆性构造。中生代中酸性脉岩为成矿期脉岩,且与黄泥河花岗岩岩基有着密切的成因联系。成矿物质主要来自岩浆分异,金丰度值高的暗色岩类提供部分矿质。  相似文献   

湖南宜章瑶岗仙黑钨矿石英脉成矿流体性质的探讨   总被引：17，自引：0，他引：17  

Lin Xinduo Zhang Dehui Zhang Chuanling 《地球科学》1986,(2)

对于黑钨矿石英脉的成因,历来都认为是高中温热液充填而成。本文根据石英脉与细晶岩、伟晶岩过渡;围岩蚀变种类及强度的变化;石英脉中晶洞特征的研究;矿物包裹体研究及测温资料;金属矿物局部大量集中的不规律性;石英脉中黑钨矿的产出特点;产在角岩中的石英脉内出现花岗岩角砾;黑钨矿中MnO/FeO比值变化特征:含钨石英脉中矿物组合和化学成分变化特征,认为形成黑钨矿石英脉的成矿流体是一种粘稠的、密度较大、成分以SiO_2为主的熔浆—热液过渡性流体,它具有上部偏液、下部偏浆的特点。  相似文献   

底层框架砌体建筑隔震控制研究     

关罡  李和平  叶萍 《世界地震工程》2003,19(2):79-81

基于系统的振动微分方程，计算分析了底层框架砖砌体结构滑动隔震的有效性。结果表明，基底隔震控制使上部结构的最大振动响应尤其是底层框架的层间位移显著降低。  相似文献   

祁连党河南山北坡中-基性火山岩地质特征及时代   总被引：3，自引：0，他引：3  

李厚民  王崇礼  刘继庆  刘志武  沈远超 《矿物岩石》2003,23(1):1-4

根据地质研究、区域对比，结合首次获得的Rb-Sr等时线年龄数据，从祁连党河南山(又称乌兰达坂山）北坡原中奥陶统地层中厘定出晚震旦纪中－基性火山岩系。根据这一新成果，认为该区中基性火山岩，斜长角闪岩基底以及侵入其中的扎子沟等花岗闪长岩岩基在大地构造分区上应划归中祁连地块；晚震旦纪该区无疑有过扩张、地壳减薄的地质事件，震旦纪晚期有过挤压闭合事件。  相似文献   

隐爆角砾岩型金矿研究述评   总被引：22，自引：1，他引：22  

卿敏  韩先菊 《黄金地质》2002,8(2):1-7

隐爆角砾岩型金矿是国内外一种具有重要经济价值的矿床类型。不同类型隐爆角砾岩是该类金矿最主要的容矿围岩。造成隐爆作用发生最直接的因素是受热的多源流体或气体，岩浆隐蔽爆破主要作用方式是气爆和浆爆，其次是热液注入。通常气爆发生于早期，浆爆较晚，而热液注入最晚。浅成－超浅成中酸性斑岩体是隐爆角砾岩形成的决定性因素，气液的隐蔽爆破作用是隐爆角砾岩有角砾岩型金－多金属矿床形成的原因，成岩与成矿是同一地质过程不同阶段产物。不同级别的构造对该类型金矿档的产出空间、矿化类型和矿体形态等具有分级控制作用，矿化、蚀变存在明显的垂向分带及其空间套叠。该类型金矿可划分为Au-Ag和Au-Cu系列，矿床系列、矿床规模有富矿部位可通过一系列指标进行判别。  相似文献   

Optimal placement of sensors on buildings subjected to intermediate‐storey excitation according to QN control method     

Liping Xing  Eizaburo Tachibana  Yutaka Inoue 《地震工程与结构动力学》2002,31(1):1-13

An algorithm to calculate direct velocity feedback gain with limited number of sensors is developed in a simple way such that a certain performance index is minimized according to QN control method. If a limited number of velocity outputs can be measured, full velocity responses of the whole structure can be interpolated based on the mode shapes. By defining the performance index function as a combination of the structure's velocity responses and control forces only, feedback gain can be determined according to QN control method with the external excitation being taken into account throughout the entire algorithm. Control forces are then regulated by the time‐invariant feedback gain matrix. The effective location of the active control devices for a building structure subjected to intermediate‐storey excitation has been determined to be in the three floors adjacent to the vibration source. Hence for the purpose of this paper, only the optimal placement of sensors is verified. It is shown in this paper that if the dynamic behaviour of the structure is well described by a mathematical model, sufficient response reduction effect can be achieved according to the new DVFC algorithm, and the degradation of control performance due to time delay can also be verified. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Improved ENSO forecasts by assimilating sea surface temperature observations into an intermediate coupled model   总被引：2，自引：0，他引：2  

郑飞  朱江  周广庆 《大气科学进展》2006,23(4):615-624

A simple method for initializing intermediate coupled models (ICMs) using only sea surface temperature (SST) anomaly data is comprehensively tested in two sets of hindcasts with a new ICM. In the initialization scheme, both the magnitude of the nudging parameter and the duration of the assimilation are considered, and initial conditions for both atmosphere and ocean are generated by running the coupled model with SST anomalies nudged to the observations. A comparison with the observations indicates that the scheme can generate realistic thermal fields and surface dynamic fields in the equatorial Pacific through hindcast experiments. An ideal experiment is performed to get the optimal nudging parameters which include the nudging intensity and nudging time length. Twelve-month-long hindcast experiments are performed with the model over the period 1984–2003 and the period 1997–2003. Compared with the original prediction results, the model prediction skills are significantly improved by the nudging method especially beyond a 6-month lead time during the two different periods. Potential problems and further improvements are discussed regarding the new coupled assimilation system.  相似文献   

甘肃南祁连党河南山奥陶纪火山岩的岩石地球化学特征          下载免费PDF全文

冯备战 《甘肃地质》2006,15(2):15-19

甘肃南祁连褶皱带党河南山早奥陶纪火山岩主要赋存于吾力沟群中。地球化学研究结果表明,本区火山岩由基性火山岩和中性火山岩组成,基性火山岩分属拉斑玄武岩和钙碱性玄武岩,而中性火山岩则属钙碱性安山岩。它们均具有低TiO2、MgO,选择性富集大离子亲石元素(Rb、Th、Ba、Sr)和轻稀土元素(La、Ce、Sm),具有较高的高价大阳离子比值和Nb的强烈亏损,岩石学和地球化学特征表明本区火山岩形成于岛弧环境。  相似文献