地震活动性总体参量Rt在东南沿海地震带西段地震预测中的应用     

史水平  李细光  李柳英 《华南地震》2007,27(4):41-47

分析了1974年以来东南沿海地震带西段发生的MS≥4.9级地震前地震活动性总体状态参量Rt的变化特点,同时对Rt值在东南沿海地震带西段的地震预测效能进行了检验评估。结果表明,当Rt>0.82时,表明东南沿海地震带西段地震活动状态比较正常,发生4.9级以上地震的概率较低;反之,当Rt≤0.82时,则表明东南沿海地震带西段地震活动比较活跃,发生4.9级以上地震的概率较大。  相似文献   

利用非线性方法反演琉球-台湾-吕宋地区的岩石层P波速度结构   总被引：1，自引：1，他引：1       下载免费PDF全文

李志伟  胥颐  郝天珧  刘劲松 《地球物理学进展》2007,22(5):1345-1351

根据中国地震台网和ISC台站提供的P波走时资料,使用差异演化全局优化算法(DE算法)和移动窗方法反演了琉球-台湾-吕宋地区岩石层尺度的P波速度结构.在台站和地震分布较为密集的地区,反演窗口为2°×2°,移动步长为1°;在台站和地震较少的地区,反演窗口为4°×4°左右,移动步长为2°.反演结果揭示出琉球-台湾-吕宋地区壳幔结构的横向差异:琉球岛弧西侧受冲绳海槽地幔热扰动的地壳减薄,东侧由于菲律宾海板决的俯冲挤压地壳略有增厚;欧亚大陆与菲律宾海板块的相互碰撞导致台湾地区地壳及岩石层明显增厚;吕宋及菲律宾北部岩石层受岛弧火山下方热流影响较大.结果表明,非线性全局优化算法和移动窗方法能够用于反演较大尺度速度结构的横向变化.  相似文献   

Dating alluvial deposits with optically stimulated luminescence, AMS C and cosmogenic techniques, western Transverse Ranges, California, USA     

S.B. DeLong  L.J. Arnold 《Quaternary Geochronology》2007,2(1-4):129-136

In an effort to better understand chronology of alluvial episodes in Cuyama Valley in the western Transverse Ranges of California, USA, we employed optically stimulated luminescence, radiocarbon and cosmogenic radionuclide surface exposure dating methods. Twenty-one optical dates ranging from 0.01 to 27 ka were obtained from exposures of late-Holocene axial-fluvial deposits, Pleistocene–Holocene alluvial-fan deposits, and axial-fluvial sands interbedded within a late Pleistocene alluvial fan. These were cross-checked with 37 AMS radiocarbon dates from charcoal and wood from within a and five ¹⁰Be surface exposure dates from boulders on alluvial-fan surfaces. The OSL results show generally good stratigraphic consistency, logical comparison with the radiocarbon and cosmogenic data, and appear to be the best method for accurate dating within deposits of this nature because suitable material is fairly easy to find in these environments. The radiocarbon data contained numerous “detrital ages”, but well-bedded lenses of apparently in situ or minimally transported charcoal provide reliable age estimates for the associated alluvium. Radiocarbon dating of detrital charcoal in the older alluvial fan deposits was problematic. Our cosmogenic surface-exposure dating was consistent stratigraphically and with our other data, but we were unable to determine its accuracy due to the limited number of samples and the possibility of inherited radionuclides and post-depositional erosion. In light of our results, we suggest that OSL dating using the latest analytical techniques combined with rigorous methods for estimation of paleodase is reliable and of increasing utility in otherwise difficult-to-date coarse alluvial environments in the southwestern United States and elsewhere.  相似文献   

修正的莫尔-库仑理论的解析和验证     

石寒 《岩土力学》2007,28(7):1491-1494

根据主应力可分解为静水应力和偏应力,以及它们在应力莫尔圆和变形方面的相关性,推导出修正的莫尔-库仑理论的数学表达式。从理论上解决了库仑理论和莫尔理论存在的许多缺陷,特别是中间主应力对材料抗剪强度的影响。它的四参数准则的计算结果与一些混凝土的试验数据相当吻合。  相似文献   

青海同仁县隆务峡地区首次发现镁铁质——超镁铁质岩带   总被引：10，自引：4，他引：10  

张克信朱云海  林启祥寇晓虎樊光明  陈奋宁罗根明 《地质通报》2007,26(6):61-667

在青海省同仁县隆务峡南段的二叠纪地层中首次发现了北西—南东向分布的镁铁质—超镁铁质岩带,命名为隆务峡镁铁质—超镁铁质岩带。该岩带的岩石组合包括纯橄岩、辉石橄榄岩、辉长岩、辉绿岩、枕状玄武岩等。从超镁铁岩—下部堆晶岩—辉绿岩—上部堆晶岩,其稀土元素总量逐渐增加,稀土元素配分型式总体一致,从超镁铁岩的Eu正异常到上部辉长岩的Eu负异常,显示了各岩石间的同源性。根据对其两侧沉积岩中化石的研究,推测该镁铁质—超镁铁质岩带的形成时代为二叠纪。该岩带位于西秦岭造山带与祁连造山带的接舍部,对于揭示秦岭和祁连接合部的大地构造演化有重要意义。  相似文献   

西藏冈底斯尼木地区斑岩铜矿地质特征与找矿标志   总被引：1，自引：0，他引：1  

晏子贵  李作华 《四川地质学报》2007,27(2):99-103

西藏冈底斯斑岩铜矿带属全球特提斯—喜马拉雅构造—成矿域东延部分,位于冈底斯火山—岩浆弧中东段,为国土资源大调查以来确认的最重要的成矿区带之一。尼木西北部地区为冈底斯斑岩铜矿带的重要组成部分,现已确认为冈底斯成矿带上最重要的斑岩型铜(钼)矿化集中区之一。通过成矿地质背景、典型矿床地质特征、成矿控制因素的综合分析,对尼木地区斑岩铜矿的找矿标志进行了初步总结。  相似文献   

云南茶树林铅锌矿电磁波找矿效果     

李本茂  张学良  史家良  普建林 《云南地质》2007,26(2):257-263

茶树林铅锌矿，过去认为震旦系赋矿，钻探验证未见矿。本次利用物探方法实施深部探矿。依据物探异常，结合地质规律综合分析，认为是构造控矿。布置验证坑道，沿断裂破碎带发现新的厚大、品位高铅锌矿体，收到良好的找矿效果。  相似文献   

阿尔泰额尔齐斯带东段酸性岩墙群地球化学特征及其地质意义     

宫红良陈正乐  胡远清李丽赖新荣  马庆佑李玉英胡博  张文贵 《岩石学报》2007,23(5):889-899

野外地质调查发现在阿尔泰南缘额尔齐斯构造带东段、额尔齐斯活动断裂与富蕴-锡泊渡断裂之间发育了一套未变形的酸性岩墙群。岩墙群侵位于海西期片麻岩化花岗岩和上石炭统深变质的额尔齐斯组岩层中,薄片鉴定和岩石地球化学分析确定为具有细晶结构的流纹斑岩。岩石的SiO_2含量为70.9%～75.38%,K_2O Na_2O含量为7.55%～8.99%;大部分样品Na_2O>K_2O,里特曼指数值为1.8～2.5之间,Al_2O_3=12.80%～14.53%,A/CNK=0.9～1.1,NK/A=0.7～0.9,具有准铝质—弱过铝质、低镁、高钾钠、低钙和锶、高(Fe)_(mol)/(Mg)_(mol)特点,具A型花岗岩类特点,属于亚碱性脉岩。岩石轻稀土富集,大离子亲石元素相对富集,具有明显的中等负铕异常,壳源特征明显。锆石U-Pb二次粒子微探针测年显示岩墙群形成于277～286Ma。推断岩墙是阿尔泰海西期造山运动结束后,在拉张构造环境下的地壳局部熔融产物。  相似文献   

Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province)     

Payman Navabpour  Jacques Angelier  Eric Barrier   《Tectonophysics》2007,432(1-4):101-131

The Zagros fold-and-thrust belt of SW-Iran is among the youngest continental collision zones on Earth. Collision is thought to have occurred in the late Oligocene–early Miocene, followed by continental shortening. The High Zagros Belt (HZB) presents a Neogene imbricate structure that has affected the thick sedimentary cover of the former Arabian continental passive margin. The HZB of interior Fars marks the innermost part of SE-Zagros, trending NW–SE, that is characterised by higher elevation, lack of seismicity, and no evident active crustal shortening with respect to the outer (SW) parts. This study examines the brittle structures that developed during the mountain building process to decipher the history of polyphase deformation and variations in compressive tectonic fields since the onset of collision. Analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors. Various strike–slip, compressional, and tensional stress regimes are thus identified with different stress fields. Brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of corresponding stress fields, considering the folding process. Results indicate that in the studied area, the main fold and thrust structure developed in a general compressional stress regime with an average N032° direction of σ₁ stress axis during the Miocene. Strike–slip structures were generated under three successive strike–slip stress regimes with different σ₁ directions in the early Miocene (N053°), late Miocene–early Pliocene (N026°), and post-Pliocene (N002°), evolving from pre-fold to post-fold faulting. Tensional structures also developed as a function of the evolving stress regimes. Our reconstruction of stress fields suggests an anticlockwise reorientation of the horizontal σ₁ axis since the onset of collision and a significant change in vertical stress from σ₃ to σ₂ since the late stage of folding and thrusting. A late right-lateral reactivation was also observed on some pre-existing belt-parallel brittle structures, especially along the reverse fault systems, consistent with the recent N–S plate convergence. However, this feature was not reflected by large structures in the HZB of interior Fars. The results should not be extrapolated to the entire Zagros belt, where the deformation front has propagated from inner to outer zones during the younger events.  相似文献   

U–Pb SHRIMP monazite ages of the giant Morro Velho and Cuiabá gold deposits, Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Minas Gerais, Brazil     

L.M. Lobato  J.O.S. Santos  N.J. McNaughton  I.R. Fletcher  C.M. Noce 《Ore Geology Reviews》2007,32(3-4):674

U–Pb SHRIMP results of 2672 ± 14 Ma obtained on hydrothermal monazite crystals, from ore samples of the giant Morro Velho and Cuiabá Archean orogenic deposits, represent the first reliable and precise age of gold mineralization associated with the Rio das Velhas greenstone belt evolution, in the Quadrilátero Ferrífero, Brazil. In the basal Nova Lima Group, of the Rio das Velhas greenstone belt, felsic volcanic and volcaniclastic rocks have been dated between 2792 ± 11 and 2751 ± 9 Ma, coeval with the intrusion of syn-tectonic tonalite and granodiorite plutons, and also with the metamorphic overprint of older tonalite–trondhjemite–granodiorite crust. Since cratonization and stable-shelf sedimentation followed intrusion of Neoarchean granites at 2612 + 3/− 2 Ma, it is clear that like other granite–greenstone terranes in the world, gold mineralization is constrained to the latest stages of greenstone evolution.  相似文献