New paleomagnetic data from Upper Oligocene–Lower Miocene rocks of the Northern Argentine Puna–Southern Bolivian Altiplano: Constraining the age of vertical axis rotations

Along the Central Andes a pattern of vertical axis rotations has been paleomagnetically identified. Such rotations are counterclockwise north of Arica Deflection (∼19° S) and clockwise to the south. Different hypothesis and models have been proposed to explain the Central Andean Rotation Pattern (CARP). However, the origin of the CARP is a subject of ongoing debate. Recently, different authors have proposed the possible existence of a close correlation between the time–space distribution of deformation and the amount of registered vertical axis rotations in the Southern Central Andes. In order to further investigate such relationship, new paleomagnetic studies were carried out in Upper Oligocene–Lower Miocene rocks of the Northern Argentine Puna and the Southern Bolivian Altiplano. Our results indicate that while one of the sampled localities did not undergo significant vertical axis rotations, the other two recorded clockwise vertical axis rotations larger than 30°. These results suggest the occurrence of small-block rotations in the Southern Bolivian Altiplano–Northern Argentine Puna prior to 15 Ma, which would correspond to the local accommodation of the regional deformation field.     

陕西临潼骊山地区的地质构造演化

本文依据最新资料对骊山地区太华群地层进行划分对比,并且从变形、变质等方面,应用板块构造、韧性剪切断裂等理论对骊山构造演化进行了论述。     

Record of deformation by secondary magnetic remanences and magnetic anisotropy in the Nar/Phu valley (central Himalaya)

Secondary magnetic remanences residing in pyrrhotite and anisotropy of magnetic susceptibility (AMS) were studied in low-grade metamorphic carbonates of the Tethyan Himalaya in Nar/Phu valley (central Nepal) and used for interpretation of tectonic deformations. The characteristic remanence (ChRM) is likely of thermomagnetic origin related to post-peak metamorphic cooling occurring after the Eohimalayan phase (35–32 Ma). The ChRM postdates small-scale folding (main Himalayan folding F1 and F2) as shown by a negative fold test of site mean directions at 99% confidence level, and has been probably acquired between 32 and 25 Ma. Late-orogenic long-wavelength folding associated with the Chako antiform (CA) is recorded by the spatial dispersion of ChRM directions and the distribution of the main axes of the AMS tensor. The mean tilting of the ChRM direction since remanence acquisition (≈20–30°) approximately coincides with the tilting of the CA (31°) at the study area indicating that the pyrrhotite remanence predates the CA (CA formed at <18 Ma according to preliminary U/Pb dating). However, comparison of tilt angles of remanence directions and AMS tensor axes suggests that remanence acquisition was not completed before the onset of the CA formation. This could imply a younger age (Early Miocene or even younger) of the ChRM. Using the distribution of remanence directions along a small-circle as well as the distribution of AMS tensor axes, a clockwise mean rotation of 16° is obtained for a remanence age of ≈30 Ma. An Early Miocene remanence age would not change this result substantially. Compilation of rotations in the Tethyan Himalaya deduced from secondary pyrrhotite remanences reveals an increasing clockwise rotation from the Hidden valley in the W to the Shiar valley in the E (≈150 km distance), incompatible with an oroclinal bending model.     

On the Effect of Planetary Rotation on Shear and Density Layers in Stratified Flows

The effect of the Coriolis forces on the dynamicsof shear and density layers instratified flows is investigated, an effectthat has not been taken into account inmost previous studies of turbulence-meanfield or wave-mean field interactions.For instance, recent studies have shownthat shear and density layers can grow inthe presence of turbulence in a stronglystratified fluid but the effect of planetaryrotation was not taken into account. Toaddress this problem, wave-mean flowinteraction in a stratified fluid is hereinvestigated in the presence of rotation usingdirect numerical simulation. The results showthat the wave-mean flow interactionand the formation of layers is less intensewhen rotation is present because thehorizontal mean motions are deviated by theCoriolis forces, which tends to reducethe distortion of the wave field, and thusthe wave-induced fluxes of buoyancy andmomentum. This effect appears even when therotation rate is weak.     

Prediction of Earth orientation parameters by artificial neural networks

 Earth orientation parameters (EOPs) [polar motion and length of day (LOD), or UT1–UTC] were predicted by artificial neural networks. EOP series from various sources, e.g. the C04 series from the International Earth Rotation Service and the re-analysis optical astrometry series based on the HIPPARCOS frame, served for training the neural network for both short-term and long-term predictions. At first, all effects which can be described by functional models, e.g. effects of the solid Earth tides and the ocean tides or seasonal atmospheric variations of the EOPs, were removed. Only the differences between the modeled and the observed EOPs, i.e. the quasi-periodic and irregular variations, were used for training and prediction. The Stuttgart neural network simulator, which is a very powerful software tool developed at the University of Stuttgart, was applied to construct and to validate different types of neural networks in order to find the optimal topology of the net, the most economical learning algorithm and the best procedure to feed the net with data patterns. The results of the prediction were analyzed and compared with those obtained by other methods. The accuracy of the prediction is equal to or even better than that by other prediction methods. Received: 6 February 2001 / Accepted: 23 October 2001     

Φ108旋转式孔口封闭循环灌浆栓塞的设计和应用

摘水库大坝基础防渗帷幕灌浆方法及其不同灌浆栓塞的使用，直接影响工程施工的进度、质量和成本。本文介绍全强风化岩体中灌浆时应用的新型灌浆栓塞。     

东太平洋Juan de Fuca板块的大地电磁研究

本研究做为电磁感应国际合作研究项目—EMSLAB计划的一部分,主要目的在于确定东太平洋年轻的海洋板块——Juan de Fuca板块及其周围地区岩石圈和软流圈的电性结构。 在对海底观测的大地电磁资料定性和定量分析的基础上,进行了二维数学模拟。在二维模型中,海洋地形和已知的表层构造被确定。通过改变模型的重要参数,评价响应函数和观测资料之间偏差的增加,检验模型的可靠性。结果表明,Juan de Fuca板块深部存在两个导电层,一个在40km,另一个在200km左右。这里岩石圈比其它较老板块的岩石圈薄     

西伯利亚板块旋转漂移运动刍议

西伯利亚板块是世界上古老的地质构造单元之一。根据板块构造理论，该板块当今的地表形态和地理位置，是其经过不断迁移，与其它板块不断发生碰撞的结果。本文试从展现板块的水平运动特点出发，着重揭示西伯利亚板块在各地质时期的运动状态，从而阐述该板块自寒武纪以来的旋转漂移的全过程。     

Paleomagnetic evidence for large en-bloc rotations in the Eastern Alps during Neogene orogeny

We present new paleomagnetic data from the Northern Calcareous Alps and the Central Alps of Austria. All new data are overprint magnetizations and can be subdivided into two groups: In rocks older than earliest Rupelian, two remagnetizations reflecting both clockwise and counter-clockwise rotation were detected. In rocks of late Rupelian and younger ages, only a counter-clockwise rotated remagnetization was found. Our results together with results from previous paleomagnetic studies from the Eastern and Southern Alps suggest two main phases of vertical axis rotation. The first, clockwise rotation affecting the Northern Calcareous Alps was active between earliest to Late Rupelian. We propose a model where the Northern Calcareous Alps are segmented into individual blocks. Within a dextral shear corridor these blocks rotated clockwise due to the counter-clockwise rotation of the Southern Alps and Central Alps. The second, counter-clockwise rotation occurred in the Late Oligocene to Middle Miocene, affecting Eastern and Southern Alps. In this stage of orogeny, the internal massifs of the Western Alps were already accreted to the upper plate and therefore included in counter-clockwise rotation. This rotation is contemporaneous with counter-clockwise rotation in the Apennines and opening of the Balearic basin, and a genetic relationship is suggested. A second step of counter-clockwise rotation, reconstructed from published data, is observed in the sedimentary basins at the southeastern margin of the Eastern Alps, where counter-clockwise rotated Miocene and Pliocene sedimentary rocks are present. This rotation is seen in connection to a young counter-clockwise rotation of the Adriatic plate.     

1996～1998年逐月地震地温场与降水场演变分析

利用最近３ａ逐月的地温、地球自转和地震资料,分析了地热涡的演变与我国降水场的关系。发现在地转加快月有利于地热涡族的加强,降水增多;地转减慢月则反之。还发现地震是地热涡发展增强的一个强信号。