Cretaceous isochron ages from K–Ar and Ar / Ar dating of eclogitic rocks in the Tso Morari Complex, western Himalaya, India

The Tso Morari Complex, which is thought to be originally the margin of the Indian continent, is composed of pelitic gneisses and schists including mafic rock lenses (eclogites and basic schists). Eclogites studied here have the mineral assemblage Grt + Omp + Ca-Amp + Zo + Phn + Pg + Qtz + Rt. They also have coesite pseudomorph in garnet and quartz rods in omphacite, suggesting a record of ultrahigh-pressure metamorphism. They occur only in the cores of meter-scale mafic rock lenses intercalated with the pelitic schists. Small mafic lenses and the rim parts of large lenses have been strongly deformed to form the foliation parallel to that of the pelitic schists and show the mineral assemblages of upper greenschist to amphibolite facies metamorphism. The garnet–omphacite thermometry and the univariant reaction relations for jadeite formation give 13–21 kbar at 600 °C and 16–18 kbar at 750 °C for the eclogite formation using the jadeite content of clinopyroxene (X_Jd = 0.48).

Phengites in pelitic schists show variable Si / Al and Na / K ratios among grains as well as within single grains, and give K–Ar ages of 50–87 Ma. The pelitic schist with paragonite and phengite yielded K–Ar ages of 83.5 Ma (K = 4.9 wt.%) for paragonite–phengite mixture and 85.3 Ma (K = 7.8 wt.%) for phengite and an isochron age of 91 ± 13 Ma from the two dataset. The eclogite gives a plateau age of 132 Ma in Ar/Ar step-heating analyses using single phengite grain and an inverse isochron age of 130 ± 39 Ma with an initial ⁴⁰Ar / ³⁶Ar ratio of 434 ± 90 in Ar/Ar spot analyses of phengites and paragonites. The Cretaceous isochron ages are interpreted to represent the timing of early stage of exhumation of the eclogitic rocks assuming revised high closure temperature (500 °C) for phengite K–Ar system. The phengites in pelitic schists have experienced retrograde reaction which modified their chemistry during intense deformation associated with the exhumation of these rocks with the release of significant radiogenic ⁴⁰Ar from the crystals. The argon release took place in the schists that experienced the retrogression to upper greenschist facies metamorphisms from the eclogite facies conditions.     

Primary volcanic structures from a type section of Deccan Trap flows around Narsingpur-Harrai-Amarwara, central India: Implications for cooling history

Field investigations of the Deccan Trap lava sequence along a 70 km traverse in the Narsingpur-Harrai-Amarwara area of central India indicate twenty lava flows comprising a total thickness of around 480 m. Primary volcanic structures like vesicles and cooling joints are conspicuous in this volcanic succession and are used to divide individual flows into three well-defined zones namely the lower colonnade zone, entablature zone, and the upper colonnade zone. The variable nature of these structural zones is used for identification and correlation of lava flows in the field. For twenty lava flows, the thicknesses of upper colonnade zones of eight flows are ∼5 m while those of eight other flows are ∼8 m each. The thicknesses of upper colonnade zones of remaining four flows could not be measured in the field. Using the thicknesses of these upper colonnade zones and standard temperature-flow thickness-cooling time profiles for lava pile, the total cooling time of these sixteen Deccan Trap lava flows has been estimated at 12 to 15 years.     

Fission track evidence for the Mesozoic Cenozoic tectonic uplift of Mt. Bogda, Xinjiang, Northwest China

1 IntroductionThe Mesozoic-Cenozoic tectonic evolution and ki-netics mechanism of the intracontinental orogen are thekey subjects of continental dynamics (Ma Zongjin andGao Xianglin, 2004) and the key to understanding theregional geological tectonics (Qia…     

南海西南部曾母盆地早中新世以来沉降史分析

采用回剥法和局部均衡模式研究曾母盆地早中新世以来的沉降史，并探讨了该盆地构造演化特征。曾母盆地自早中新世以来经历了17．5-11．6Ma、11．6-5．5Ma、5．5-3．0Ma和3．0-0Ma的4次快速沉降作用，其构造演化受控于曾母地块与南沙地块及婆罗洲地块的碰撞和盆地两侧的万安-卢帕尔断裂与廷贾走滑断裂的综合作用，可划分为南北双向挤压（晚始新世-早中新世）、走滑改造（中中新世-晚中新世）和区域沉降（上新世-第四纪）3个演化阶段。     

明代军事地理研究概述

军事地理是谋兵布防的平台。明代被迫在南北两条战线作战：北部沿长城一线防御少数民族南下；东南沿海抗击倭寇入侵。因此，明代格外重视军事地理的研究，研究成果丰硕，著述很多。概述明代军事地理研究成果，不仅是回顾历史，而是借鉴经验。一些著作中提出的御敌方略至今有参考价值。     

Study on effects of damping in laminated rubber bearings on seismic responses for a ⅛ scale isolated test structure

The effects of damping in various laminated rubber bearings (LRB) on the seismic response of a ?‐scale isolated test structure are investigated by shaking table tests and seismic response analyses. A series of shaking table tests of the structure were performed for a fixed base design and for a base isolation design. Two different types of LRB were used: natural rubber bearings (NRB) and lead rubber bearings (LLRB). Three different designs for the LLRB were tested; each design had a different diameter of lead plug, and thus, different damping values. Artificial time histories of peak ground acceleration 0.4g were used in both the tests and the analyses. In both shaking table tests and analyses, as expected, the acceleration responses of the seismically isolated test structure were considerably reduced. However, the shear displacement at the isolators was increased. To reduce the shear displacement in the isolators, the diameter of the lead plug in the LLRB had to be enlarged to increase isolator damping by more than 24%. This caused the isolator stiffness to increase, and resulted in amplifying the floor acceleration response spectra of the isolated test structure in the higher frequency ranges with a monotonic reduction of isolator shear displacement. Copyright © 2002 John Wiley & Sons, Ltd.     

新疆伽师强震群区的横波分裂与应力场特征

利用在新疆伽师地区布设的流动台阵记录到的地方震波形数据,研究了伽师强震群附近各台站横波分裂现象,给出了相应的快波偏振方向的平面场分布. 发现在台阵的塔里木盆地一侧,波偏振方向为近SN向,与塔里木盆地的区域主压应力方向一致,但在塔里木盆地北部边缘的褶皱变形带内,快波偏振方向变为近EW向,特别是在柯坪断裂附近,快波偏振方向与阿图什地震的震源断层方向基本一致. 由于快波偏振方向平行于主压应力方向,给出的快波偏振方向反映了相应的主压应力场特征. 结果表明,伽师强震群的成因很可能是塔里木盆地北缘横向非均匀变形造成的局部张性剪切应变能的释放.     

Nonlinear earthquake response analysis and energy calculation for seismic slit shear wall structures

Based on the concept of structural passive control, a new type of slit shear wall, with improved seismic performance when compared to an ordinary solid shear wall, was proposed by the authors in 1996. The idea has been verified by a series of pseudo-static and dynamic tests. In this paper a macro numerical model is developed for the wall element and the energy dissipation device. Then, nonlinear time history analysis is carried out for a 10-story slit shear wall model tested on a shaking table. Furthermore, the seismic input energy and the individual energy dissipated by the components are calculated by a method based on Newmark-β assumptions for this shear wall model, and the advantages of this shear wall are further demonstrated by the calculation results from the viewpoint of energy. Finally, according to the seismic damage criterion on the basis of plastic accumulative energy and maximum response, the optimal analysis is carried out to select design parameters for the energy dissipation device.     

梅州市名城文化景观的保护与开发研究

从名城文化内涵出发，着眼于作为客家人文中心和名城文化景观的集中的梅州市区，全面分析了其中丰富多样的文化景观资源的特征及其文化内蕴。揭示了梅州名城文化景观保护与开发过程中的成绩与存在问题。并从文化地理学的视觉，结合旅游开发和城市规划，论证了科学保护与开发梅州名城文化景观的下述对策与途径的必要性与可行性：提升名城办的职能并与相关部门共营名城文化氛围；强化名城轴线与标志性文化景观；抢救与保护“老字号”等一批文化景观景区；适度利用，以积极的开发促其效的保护。