Deformation temperatures and flow vorticities near the base of the Greater Himalayan Series,Sutlej Valley and Shimla Klippe,NW India     

《Journal of Structural Geology》2013

We report new deformation temperature and flow vorticity data from the base of the Greater Himalayan Series (GHS) exposed in the Sutlej Valley and Shimla Klippe of NW India. We focus on three groups of transects across the hanging wall of the Main Central Thrust (MCT). In order of relative foreland – hinterland positions, they are the Shimla Klippe, Western and Eastern Sutlej transects. Deformation temperatures indicated by quartz c-axis fabric opening-angles increase both from foreland to hinterland at a given structural distance above the MCT and up structural section from the MCT within individual transects. Deformation temperatures in the immediate hanging wall to the MCT are estimated at ∼510–535, 535–550 and 610 °C on the Shimla, Western Sutlej and Eastern Sutlej transects, respectively. The steepest inferred field gradients in deformation temperatures are recorded adjacent to the MCT and progressively decrease up structural section following a power law relationship. Comparison with temperature estimates based on multi-mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions. Vorticity analyses indicate that shearing along the base of the GHS occurred under sub-simple shear conditions (Wm values of 0.9–1.0) with a minor component of pure shear.  相似文献   

透镜体油气成藏机理研究现状与发展趋势   总被引：16，自引：1，他引：16  

陈冬霞  庞雄奇  姜振学 《地球科学进展》2002,17(6):871-876

随着石油勘探研究的不断深入,砂岩透镜体油藏日益受到重视。国内外学者提出了多种成藏机制,包括未知重力运动机制作用下,少数流体分子的个别特性控制透镜状砂岩油藏聚集;毛细管力作用下油气替换透镜体中的孔隙水;烃浓度差是油气向砂体运移的主要动力;流体压力差使油气首先沿着裂隙向砂岩透镜体中运移、聚集而成藏;差异突破作用使砂岩透镜体成藏等。成藏动力学、成藏模式及主控因素、定量研究、物理模拟实验、数值模拟及分布预测等将是今后发展的方向。  相似文献   

Role of southeastern Sanandaj–Sirjan Zone in the tectonic evolution of Zagros Orogenic Belt,Iran     

Ramin Arfania  Sohrab Shahriari 《Island Arc》2009,18(4):555-576

Geological studies indicate that the southeastern Sanandaj–Sirjan Zone, located in the southeastern Zagros Orogenic Belt, is subdivided transversally into the Esfahan–Sirjan Block with typical Central Iranian stratigraphic features and the Shahrekord–Dehsard Terrane consisting of Paleozoic and Lower Mesozoic metamorphic rocks. The Main Deep Fault (Abadeh Fault) is a major lithospheric fault separating the two parts. The purpose of this paper is to clarify the role of the southeastern Sanandaj–Sirjan Zone in the tectonic evolution of the southeastern Zagros Orogenic Belt on the basis of geological evidence. The new model implies that Neo‐Tethys 1 came into being when the Central Iran Microcontinent split from the northeastern margin of Gondwana during the Late Carboniferous to Early Permian. During the Late Triassic a new spreading ridge, Neo‐Tethys 2, was created to separate the Shahrekord–Dehsard Terrane from Afro–Arabian Plate. The Zagros sedimentary basin was formed on a continental passive margin, southwest of Neo‐Tethys 2. The two ophiolitic belts of Naien–Shahrebabak–Baft and Neyriz were developed to the northeast of Neo‐Tethys 1 and southwest of Neo‐Tethys 2 respectively, related to the sinking of the lithosphere of the Neo‐Tethys 1 in the Late Cretaceous. It can be concluded that deposition of the Paleocene conglomerate on the Central Iran Microcontinent and Pliocene conglomerate in the Zagros Sedimentary Basin is directly linked to the uplift generated by collision.  相似文献   

Emplacement of the Ardara pluton (Ireland): new constraints from magnetic fabrics, rock fabrics and age dating     

S. Siegesmund  J. K. Becker 《International Journal of Earth Sciences》2000,89(2):307-327

The Ardara pluton as part of the Donegal batholith was intruded into Neoproterozoic metasediments and metadolerites at mid-crustal levels. The emplacement mechanism of the Ardara granite is very controversial, and mechanisms ranging from diapirism, ballooning and stoping followed by nested diapirism have been proposed. Magnetic fabrics, rock fabrics and K/Ar dating of micas are used here to constrain the emplacement history. The compositional zoning of the Ardara pluton is clearly reflected in the different bulk magnetic susceptibilities between the outer quartz monzodiorite and the central granodiorite, whereas the intervening tonalite is of intermediate nature. The magnetic carriers are characterized by the anisotropy of the magnetic susceptibility (AMS), thermomagnetic measurements and through high field analyses (HFA). The separation of the ferrimagnetic and paramagnetic contributions revealed that biotite and magnetite control the AMS in the quartz monzodiorite. Both minerals are oriented in such a way that their summed contribution is constructive and originates from the shape fabric of magnetite and the texture of biotite. Biotite is responsible mainly for the AMS in the tonalite and granodiorite. The magnetic foliation can be directly related to the macroscopic foliation and also to the D4 structures in the country rocks. The foliation is consistent with the geometry of the roughly circular shape and has a mostly steep to vertical dip. Towards the central granodiorite the magnetic foliation dies out, although plagioclase texture measurements indicate a weak magmatic shape fabric. With the exception of the tail, the K_max axes (magnetic lineation) vary from steeply to gently plunging. The so-called lineation factor is approximately 1.01 and therefore points to a less significant axial symmetry. These observations coincide with strain estimates on mafic enclaves that show a very consistent pattern of K ∼0 flattening strain. Texture analyses of biotite and quartz additionally support the observations made by the strain analyses and the magnetic fabric data. Microstructural investigations give evidence that the fabrics are associated with the emplacement over a range of temperatures from truly magmatic to high-temperature solid-state conditions. The age of the intrusion is still under discussion, but a new cooling age was determined by K/Ar dating of biotite at 403.7±8 Ma corresponding to a temperature range between 450 and 300°C. For a mylonite along the southern contact between the Ardara pluton and the country rock a K/Ar muscovite age of 378.8±7 Ma indicates a minimum age for the shear zone when the Ardara pluton must have already been cooled down below 350±50°C. Received: 28 January 1999 / Accepted: 28 December 1999  相似文献   

聂拉木地区高喜马拉雅岩石磁组构及其构造含义   总被引：5，自引：2，他引：3       下载免费PDF全文

李建忠  潘忠习  冯心涛  庄忠海  朱同兴  邹光富 《地球物理学报》2006,49(2):496-503

利用岩石磁化率量值椭球体与岩石构造应变椭球体的共轴性,在缺乏岩性标志层的高喜马拉雅结晶基底（聂拉木地区）进行岩石磁组构研究,进而研究喜马拉雅造山带的变形期次和过程.磁组构特征表明：磁化率各向异性度P在樟木镇北1km处的片岩最高为172,在康山桥南1km处最低,为113;百分率各向异性度H在1182%～4507%之间;磁性线理L在102～109之间,磁性面理F在106～160之间,磁性面理F比磁性线理L发育;磁化率椭球体的形状因子T在019～076之间,磁化率椭球的扁率E在104～149之间,磁化率椭球体的形状为一压扁椭球;樟木镇北1km到肉切村,平均最小磁化率主轴方向D3为S－N（除聂拉木北1km的MA9外）,大多数样品最小磁化率主轴方向倾角I3＞51°,最高达726°,局部发育有拉长形磁化率量值椭球体.本文研究结果表明,聂拉木地区早期经历强烈的韧性变形,推测可能是一条巨大的右旋逆冲韧性变形带,晚期构造掀斜.  相似文献   

A comparative study of the main factors controlling geohazards induced by 10 strong earthquakes in Western China since the Wenchuan earthquake in 2008     

Chao Peng  Zhi-qiang Yin  Xu-jiao Zhang  Hai Shao  Ming-fei Pang 《China Geology》2023,6(1):70-84

Determining the main controlling factors of earthquake-triggered geohazards is a prerequisite for studying earthquake geohazards and post-disaster emergency response. By studying these factors, the geomorphic and geological factors controlling the nature, condition, and distribution of earthquake-induced geohazards can be analyzed. Such insights facilitate earthquake disaster prediction and emergency response planning.The authors combined field investigations and spatial data analysis to examine...  相似文献   

Effects of wave directionality on extreme response for a long end-anchored floating bridge     

《Applied Ocean Research》2019

Reliable design codes are of great importance when constructing new civil engineering concepts such as floating bridges. Previously only a scarce number of floating bridges have been built in rough wave conditions and only limited knowledge of the extreme environmental conditions and the associated extreme response exists. To form a better design basis an increased understanding of the sensitivity in the structural response towards changes in short-crested sea parameters is needed. Furthermore, acquiring the necessary accuracy in simulated extreme response is often a computationally expensive endeavour and the number of simulations needed is often based on experience. The present study investigates the wave-induced short-term extreme response of a simplified end-anchored floating bridge concept for several wave environments with a return period of 100 years. The study includes convergence of the coefficient of variation for the extreme response for different realization lengths as well as number of realizations. The sensitivity in the structural response towards different main wave directions and spreading exponents is investigated and includes both transverse and vertical displacement response spectra and extreme Von Mises stress in the bridge girder cross-section. The extreme response is based on an accuracy of 2% in the coefficient of variation equivalent to 40 3-h realizations and a low sensitivity in the response is found for natural occurring spreading exponents and for main wave directions within 15° from beam sea.  相似文献   

地球非偶极磁场对虚地磁极计算的影响          下载免费PDF全文

徐文耀  杜爱民  陈耿雄 《地球物理学报》2007,50(5):1298-1303

古地磁学使用的虚地磁极（VGP）是在地心偶极磁场假设下计算的,由于地球非偶极磁场的存在,VGP一般不同于真地磁极（RGP）.为了定量检验非偶极磁场对VGP的影响,本文利用国际参考地磁场模型IGRF 1900～2000,在全球5°×5°的“虚拟测点”网格上计算了VGP和RGP的位置,并求出两种磁极的经纬度偏差和二者的角距离.结果表明,南极地区VGP与GP的角距离最大,可达26°,南大西洋和欧亚大陆北部最大达到24°和18°,其余地区一般小于15°.VGP对RGP的偏差与地磁场分布有关：在非偶极磁场较弱的地区（如太平洋半球）,纬度偏差一般不大（≤10°）,但是在主要地磁异常区（如南大西洋和南极地区）,VGP对RGP的纬度偏差可达25°.VGP对RGP的经度偏差要比纬度偏差大得多,例如在欧亚大陆北部地区,经度偏差分布在-180°到180°的大范围内.  相似文献   

贺兰山群层序及主变形期褶皱构造探讨     

冯鸿儒 《地球科学与环境学报》1995,(1)

本文对贺兰山群由下到上划分为阿楞呼都格变粒岩组、柳树沟片麻岩组和秃鲁根钙硅酸粒岩－大理岩组。主变形期的构造事件为在南倾的北东东向倒转复式褶皱上发育着与其平行的区域性轴面面理、线理和逆冲型同变质韧性剪切带，其中又以塔什沟－柳树沟复背形和秃鲁根向形最具代表性。  相似文献   

持续光照下光强对北极海域芬迪亚历山大藻生长及产毒的影响          下载免费PDF全文

吕意华熊小飞  吴加欣杨振雄杨熙  董燕红 《极地研究》2017,29(1):74-81

以格陵兰岛西部、冰岛沿海和楚科奇海的芬迪亚历山大藻为受试对象,并以缅因湾的芬迪亚历山大藻藻株做为参照,从沉积物或海水中的休眠孢囊或营养细胞中分离到12株目标藻种,并在实验室建立纯培养系。然后对这些地域的藻种在不同光照下生长特性的比较、对毒素含量进行研究,发现芬迪亚历山大藻在持续光照条件下最适的生长光强范围是38—91μmol×m~(–2)×s~(–1)。另外,在所有分离到的12株藻细胞中均未检测到脱氨甲酰基膝沟藻毒素2(dc GTX2),大部分藻细胞都在光强较强时,即生长速率低时表现出更高的细胞毒素含量和毒性。  相似文献