K-Ar ages of the Brandberg and Okenyenya igneous complexes,north-western Namibia

K-Ar mineral ages from intrusive units of the Brandberg and Okenyenya igneous complexes, north-western Namibia, confirm the Early Cretaceous age of the subvolcanic centres. The two centres are contemporaneous, although the range of ages from Brandberg, 135.2 ± 1.5 to 125.4 ± 1.3 Ma, suggests a rather longer period of intrusion than is represented by the rocks of Okenyenya, 133.3 ± 1.4 to 129.2 ± 0.7 Ma. The mean K-Ar age of the Okenyenya complex is essentially equivalent to previously determined Rb-Sr ages for the Messum and Paresis complexes on the same igneous lineament, but is a little greater than that suggested recently from Rb-Sr dating of this complex (129.1–123.4Ma). K-Ar chronology for the Brandberg complex is in conflict with the order of emplacement of granite units previously inferred from field evidence. In particular, the Amis peralkaline layered intrusion yields the oldest age from the complex, 135.2 ± 1.4 Ma. The concordancy of age measurements of amphibole and biotite, having very different potassium contents, from single rock samples is compelling evidence that neither inherited radiogenic argon, nor argon loss, presents a significant problem in the dated rocks. If the K - Ar age of 135 Ma for the Amis intrusion is correct, it constrains the minimum age for the onset of Etendeka flood volcanism, associated with continental break-up, as Etendeka lavas exhibit contact metamorphism and metasomatism around the rim of the Brandberg complex.     

Structural studies in the Pre-Vindhyan rocks of Rajasthan: A summary of work of the last three decades

Multiple deformation in all the Precambrian metamorphic-migmatitic rocks has been reported from Rajasthan during the last three decades. But, whereas the Aravalli Group and the Banded Gneissic Complex show similarity in the style and sequence of structures in all their details, the rocks of the Delhi Group trace a partly independent trend. Isoclinal folds of the first generation (AF₁) in the rocks of the Aravalli Group had gentle westerly plunge prior to later deformations. These folds show reclined, inclined, and upright attitude as a result of coaxial upright folding (AF_la). Superposition of upright folds (AF₂) of varying tightness, with axial plane striking N to NNE, has resulted in interference patterns of diverse types in the scale of maps, and deformation of earlier planar and linear structures in the scale of hand specimens. The structures of the third generation (AF₃) are either open recumbent folds or reclined conjugate folds with axial planes dipping gently towards NE or SW. Structures of the last phase are upright conjugate folds (AF₄) with axial planes striking NNE-SSW and E-W. The Banded Gneissic Complex (BGC) underlies the Aravalli Group with a conglomerate horizon at the contact, especially in southern Rajasthan. But, for a major part of central and southern Rajasthan, migmatites representing BGC show a structural style and sequence identical with those in the Aravalli Group. Migmatization, broadly synkinematic with the AF₁ folding, suggests extensive remobilization of the basement. Very rare relict fabric athwart to and overprinted by structures of AF, generation provide tangible evidence for a basement. Although the structures of later phases in the rocks of the Delhi Group (DF₃ and DF₄) match with the late-phase structures in the Aravalli Group (AF₃ and AF₄), there is a contrast in the structural history of the early stages in the rocks of the two groups. The folds of the first generation in the Delhi Group (DF₁) were recumbent to reclined with gentle plunge towards N to NNE or S to SSW. These were followed by coaxial upright folds of varying tightness (DF₂). Absence of westerly trending AF₁ folds in the Delhi Group, and extreme variation in plunge of the AF₂ folds in contrast with the fairly constant plunge of the DF₂ folds, provide evidence for an angular unconformity between the Aravalli and the Delhi Groups. Depending on the importance of flattening attendant with and following buckling during AF₂ deformation, the lineations of AF₁ generation show different patterns. Where the AF₁ lineations are distributed in circular cones around AF₂ axes because of flexural-slip folding in layered rocks with high viscosity contrast, loci of early lineations indicate that the initial orientation of the AF₁ axes were subhorizontal, trending towards N280°. The orientation of the axial planes of the earlier folds has controlled the development of the later folds. In sectors where the AF, axial planes had N-S strike and gentle dips, or E-W strike with gentle to steep dips, nearly E-W horizontal compression during AF₂ deformation resulted in well-developed AF₂ folds. By contrast, where the AF, axial planes were striking nearly N-S with steep dips, E-W horizontal compression resulted in tightening (flattening) of the already isoclinal AF₁ folds, and probably boudinage structures in some instances, without the development of any AF₂ folds. A similar situation obtains when DF₄ deformation is superposed on earlier structures. Where the dominant S-planes were subhorizontal, N-S compression during DF₄ deformation resulted in either chevron folds with E-W striking axial plane or conjugate folds with axial plane striking NE and NW. In zones with S-planes striking E-W and dipping steeply, the N-S compression resulted in flattening of the earlier folds without development of DF₄ folds.     

Silurian granites of northern Kazakhstan: U-Pb age and tectonic position

The isotopic-geochronological studies of zircons from granites of the Borovoe, Makinsk, and Zhukei massifs located in the eastern part of the Precambrian Kokchetav median massif revealed that they were formed during the relatively brief period from 431 to 423 Ma ago, which allowed them to be united into the Early Silurian Borovoe Complex.     

利用单频双程波动方程计算初至走时及其振幅

通过在频率域双程波动方程模拟算法中加入一个复数频率（实部表示频率,虚部表示衰减因子）压制地震波初至走时之后的能量,从而把初至走时及其振幅的计算问题转换为单一频率波场中最大能量走时和振幅的拾取问题,然后利用单一频率域波场的相位项和振幅项分别计算初至走时及其振幅.本文还提出利用参数分析方法求取最优的复数频率,并给出数值计算例子,将本方法的计算结果与有限差分程函方程初至走时和最大能量走时振幅进行比较,结果表明,该方法具有适应于任意复杂介质和多炮多接收点走时和振幅的计算.     

狼山地区叠布斯格岩群变形研究及其构造意义

阿拉善东北缘狼山地区的叠布斯格岩群（杂岩）作为阿拉善地块前寒武纪基底之一,主要出露有条痕状黑云斜长片麻岩、斜长角闪片麻岩及透镜状斜长角闪岩,夹透辉石大理岩和磁铁石英岩等。本次研究通过构造解析与填图,系统分析了狼山地区叠布斯格岩群构造变形样式、变形期次与时限。研究显示,古元古代变质杂岩叠布斯格岩群至少记录了四期变形,第一期变形主要表现为片麻岩早期面理的枢纽近E- W向褶皱变形（D1）,轴面倾向NNW,应与华北克拉通统一化过程有关;第二期为近N- S向褶皱变形（D2）,褶皱枢纽向NNE倾伏,古生代时期阿拉善地块与华北板块增生拼合,在阿拉善地块东缘产生近东西向挤压,在狼山地区形成枢纽近N- S向的褶皱;第三期变形为NE向巴彦乌拉山- 狼山断裂带的左行韧性走滑剪切作用（D3）,中-晚三叠世扬子板块与华北板块碰撞造成的阿拉善地块相对华北板块沿巴彦乌拉山- 狼山断裂发生左行剪切运动,使早期构造发生逆时针旋转,是狼山地区一期重要的变形事件;第四期为NE- SW向紧闭褶皱（D4）,褶皱轴面多倾向NW,晚侏罗世来自古太平洋的俯冲和鄂霍茨克洋的闭合产生的NW- SE向挤压,使叠布斯格岩群片麻岩及后期糜棱岩化花岗岩再次发生枢纽NE- SW向褶皱变形。     

黑龙江跃进山杂岩中砾岩的碎屑锆石年代学及其大地构造意义

黑龙江省饶河县石场一带分布的跃进山杂岩为一套富含晚三叠世化石的海陆交互相沉积地层.砾岩样品中的LA-ICP-MS锆石U-Pb测年结果显示,样品中的碎屑锆石年龄谱具有4组年龄,分别为800 Ma以上、500 Ma、251~284 Ma和219~222 Ma.前三者与佳木斯地块中的热事件年龄完全一致,表明其沉积物源主要来自佳木斯地块;后者为砾岩最小年龄组,大致可将这组最小年龄视为这套砾岩的沉积时代下限,与西侧松辽地块东缘的张广才岭地区广泛分布的210~228 Ma的晚三叠世早期花岗岩基本一致,说明具有最小年龄组的碎屑锆石可能来自松辽地块东部.碎屑锆石年龄及其源区特征表明,在晚三叠世之前,跃进山增生杂岩已经就位在佳木斯地块东缘,并成为佳木斯地块东部大陆边缘的一部分.     

基于主组分分析的概率神经网络损伤定位研究

概率神经网络(PNN)以贝叶斯概率的方法描述测量数据,因而PNN在有噪声条件下的结构损伤检测方面具有巨大潜力。与此同时,PNN的网络规模随着训练样本的增加而增大,这极大地降低了网络运行速度。基于此,本文提出了基于主组分分析(PCA)的PNN损伤定位方法,分别用传统PNN(TPNN)、主组分分析PNN(PCAPNN)和自适应PNN(APNN)三种模型进行了悬索桥的损伤定位研究。研究发现,APNN的识别精度最好,PCAPNN次之,TPNN最差。但APNN需要很长的训练时间,网络规模较大;其他两个网络几乎不需要训练时间,且PCAPNN网络规模较其他两个网络减少了1／3～1／4。在低噪声情况下,PCAPNN的识别效果基本上等同于APNN。     

藏南吉隆地区早古生代大喜马拉雅片麻岩锆石SHRIMP U-Pb年龄、Hf同位素特征及其地质意义

藏南吉隆地区眼球状片麻岩是大喜马拉雅结晶岩系的一部分,其矿物组成为石英、斜长石、钾长石、黑云母和少量的白云母。片麻岩中的锆石具有核边结构,由继承碎屑锆石核和具有同心环带结构的岩浆锆石边组成,SHRIMP U Pb测年显示,边部岩浆锆石加权平均年龄为（4989±44） Ma,表明片麻岩的原岩为早古生代的花岗岩,εHf加权平均值为-83±095,暗示片麻岩原岩为壳源,可能是印度大陆北部地壳部分熔融的产物。文中和现有的地质年代学数据表明,喜马拉雅造山带是一个复合造山带,经历了早古生代的造山作用,早古生代的喜马拉雅造山带是原特提斯洋向冈瓦纳大陆北缘俯冲的结果,是冈瓦纳大陆拼合之后在其边缘形成的安第斯型造山带,而不属于冈瓦纳超大陆聚合过程中陆陆碰撞形成的泛非造山带的一部分。     

Geological relationship between Anyui Metamorphic Complex and Samarka terrane,Far East Russia

The Anyui Metamorphic Complex (AMC) of Cretaceous age is composed of metachert, schist, gneiss, migmatite and ultramafic rocks, and forms a dome structure within the northernmost part of the Jurassic accretionary complex of the Samarka terrane. The two adjacent geological units are bounded by a fault, but the gradual changes of grain size and crystallinity index of quartz in chert and metachert of the Samarka terrane and the AMC, together with the gradual lithological change, indicate that at least parts of the AMC are metamorphic equivalents of the Samarka rocks. Radiolarian fossils from siliceous mudstone of the Samarka terrane indicates Tithonian age (uppermost Jurassic), and hence, form a slightly later accretion. This signifies that the accretionary complex in the study area is one of the youngest tectonostratigraphic units of the Samarka terrane. The relationship between the Samarka terrane and AMC, as well as their ages and lithologies, are similar to those of the Tamba–Mino–Ashio terrane and Ryoke Metamorphic Complex in southwest Japan. In both areas the lower (younger) part of the Jurassic accretionary complexes were intruded and metamorphosed by Late Cretaceous granitic magma. Crustal development of the Pacific‐type orogen has been achieved by the cycle of: (i) accretion of oceanic materials and turbidites derived from the continent; and (ii) granitic intrusion by the next subduction and accretion events, accompanied by formation of high T/P metamorphic complexes.     

复杂地表条件下基于线性插值和窄带技术的地震波走时计算

为了在复杂地表条件下实现地震波走时计算,提出了一种基于线性插值和窄带技术的走时计算新方法.其中,线性插值用于局部走时计算,窄带技术用于局部波前捕获和追踪.为了逼近起伏地表,采用三角网和矩形网相结合的方法对速度模型进行剖分.为了得到局部走时计算公式,利用费马（Fermat）原理和关于入射点位置的限定条件.有关编程实践和数值试验表明：新方法不仅可以有效、灵活地处理地表高程的剧烈变化,而且还具有很好的适应性和稳定性,得到的计算结果满足波前传播规律.