实验流水地貌学研究的回顾与展望

本文简述了地貌实验研究的概况,罗列了我国主要的地貌实验室、站,叙述了我国30多年来,河型造床试验、边界条件及构造运动对河型发育影响实验,应用河流地貌实验、试验理论和技术方面的进展情况,指出实验研究中存在的问题,在回顾基础上,展望了流水地貌实验研究的未来发展趋势。     

Development of composite planar fabric in mylonites along the Median Tectonic Line, southwest Japan

Abstract Mylonites along the Median Tectonic Line, southwest Japan commonly contain shear bands comprising S(-C)-Ss fabrics. This paper stresses the lithologic control on the orientation, dimension and development of shear bands by comparing the microstructure of the shear bands in different rock types (P mylonites, F mylonites, micaceous phyllonite and quartzose phyllonite). There is no significant change of the α angles (average 21–24°) between Ss and S toward the centre of the shear zone (viz. increasing the intensity of mylonitization) and it is different from the S-C relationship in a narrow sense.
The generation of the composite planar fabric can be classified into four different strain partitioning models: S only type without any slip surface (model A); S-C type (model B); S-Ss type with Ss-slip precedence (model C), and S-Ss type with S-slip precedence (model D). Model C is proposed in this paper and is similar to the model for the generation of Riedel shears in brittle shear zones. An unstable slip between porphyroclasts and the matrix during ductile flow can easily initiate shear bands. Formation of a composite planar fabric is initiated according to model A, followed by model C in conditions of increasing strain, and then model D when the angle between S and the shear zone boundary becomes small enough (α/2 = 10°) to produce S-slip. Thus the generation of the shear bands probably begins in the early stages of shear deformation and continues until the latest stages.     

如何正确使用玄武岩判别图

为了正确使用玄武岩判别图,在投图之前要对样品加以筛选并对数据作出估计。还要将样品适当分组,投图时应遵循一定的程序。文中讨论了可能出现的几种判别结果及可能的解释方案,指出了判别图的局限性,认为玄武岩判别图所标定的各种构造环境的分区,实际上代表的是各种不同的岩浆类型。作者认为,投在洋中脊玄武岩区域的玄武岩绝大多数并非来自大洋中脊环境。     

新疆博罗霍洛山地区上志留统博罗霍洛山组沉积构造背景分析

新疆中天山西段的博罗霍洛山地区,在早古生代具有裂陷带性质。上志留统博罗霍洛山组形成于该裂陷带的最后闭合阶段,具有其特殊的形成时间和沉积特征。通过对该组地层的沉积学、岩石学及地球化学等方面的分析,本文较深入地讨论了其沉积环境及其沉积构造背景。认为该组岩石为浊流沉积物,其形成与活动性较强的大陆边缘区有着密切的关系,其陆源物质来源以当时存在于裂陷带以南的具有一定陆壳厚度和中等成熟度的“伊宁古陆”区为主。     

南岭地区万洋山岩体锆石LA-ICP-MS U-Pb年龄和地球化学特征及其构造意义

万洋山岩体位于湘赣两省交界地带,为加里东期多阶段岩浆活动的复式岩体,花岗岩主要岩石类型有黑云母二长花岗岩、黑云母花岗闪长岩和二云母二长花岗岩,以黑云母二长花岗岩分布面积最广。对岩体中黑云母二长花岗岩中的锆石样品进行激光剥蚀—多接收器电感耦合等离子体质谱(LA-ICP-MS)U-Pb定年,锆石的16个测点206Pb/238U的加权平均年龄为(446.0±3.4)Ma(n=16,MSWD=0.15)(95%置信度),反映该岩体形成于晚奥陶世至早志留世。岩石地球化学表明岩体中Si O2的含量为65.91%~73.35%,K2O的平均含量为4.20%,Na2O+K2O为5.90%~7.88%,K2O/Na2O平均值为1.64,Al2O3平均值为13.81%,ASI平均值为1.09%,总体属于高钾钙碱性过铝质花岗岩。微量元素组成中Ba、K、Sr、P、Ti表现出明显的亏损,Rb、Th、U、Nb、Zr、Hf等则相对富集,稀土元素总量中等(159.71×10-6~262.78×10-6),轻稀土富集LREE/HREE=6.16~10.01,(La/Yb)N=6.37~12.17,具明显的负Eu异常(δEu=0.30~0.59)。岩体的[n(87Sr)/n(86Sr)]i值为0.71223~0.72509,εSr(t)值为117.5~299.9Ma,εNd(t)值为-9.39~-7.30,两阶段Nd模式年龄(TDM2)为1.77~1.94 Ga。根据上述岩石地球化学特征表明万洋山岩体为来源于地壳的S型花岗岩,花岗岩氧化物和微量元素构造环境判别图解指示岩体形成于后碰撞构造环境。结合前人对华南加里东期岩体的研究成果,推断华南加里东期花岗岩岩体的具体形成机制为:在全球板块构造的影响,华夏板块与扬子板块拼接后,板块间的强烈挤压应力相对松弛、压力降低的后碰撞构造环境下,因地壳增厚而升温的中上地壳岩石减压熔融并向上侵位。     

关于辽西北票组地质时代及区域对比的再讨论

北票组是辽西侏罗纪主要含煤地层,大部分学者从植物化石角度论述其时代为早侏罗世,区域上与窑坡组、永定庄组、富县组、三工河组对比。本文从地层层序、岩性、构造演化、古气候演化等角度对北票组的地质时代和区域对比进行了讨论,认为该组为印支期后地壳伸展阶段早侏罗世早—中期兴隆沟组火山喷发之后和中侏罗世中晚期海房沟组、蓝旗组燕山期火山活动之前的含煤盆地沉积产物。前者火山活动在冀北、京西形成南大岭组,在北疆三工河组局部形成火山岩夹层;后者火山活动在冀北、京西形成九龙山组、髫髻山组,晋北形成云岗组、天池河组,北疆形成头屯河组。北票组底部杂色地层化石稀少,有机质含量低,气候应相对干热,北票组(杂色地层以上部分)、海房沟组、蓝旗组植物化石和孢粉证明古气候由温湿向干热逐渐演化,而该特征和中国北方以至全球早侏罗世晚期干热、中侏罗世从早期到晚期由温湿向干热的演化规律—致。从而,北票组底部杂色地层属于早侏罗世晚期并和三工河组、富县组、永定庄组、阳眷组、窑坡组底部对比;北票组杂色地层以上部分属于中侏罗世早期,与西山窑组、延安组、大同组、下花园组、窑坡组(K1砂岩以上部分)对比。     

基于ALOS-PALSAR卫星数据对青藏高原东缘龙日坝断裂带地表构造伸展的研究及其大地构造指示意义

龙日坝断裂带位于青藏高原最东缘,呈北东-南西向延伸,平行于其东侧的龙门山断裂带,二者大约相距150 km。与龙门山断裂带不同的是,龙日坝断裂带在青藏高原东缘相关GPS测量中表现为一明显的速度梯度带,说明龙日坝断裂带可能具有很重要的构造属性。然而有关龙日坝断裂带的地表结构构造延伸问题一直悬而未决,目前还存在许多的争议,这在一定程度上也阻碍了我们对青藏高原东缘相对于印度-欧亚板块碰撞地球动力学响应的了解。在本次研究中,我们将首次采用ALOS-PALSAR卫星数据,并结合地表地质和前人的地球物理学研究成果,来监测与龙日坝断裂带的构造活动相关的细微地表形变,并由此控制龙日坝断裂带的延伸范围。研究结果表明,龙日坝断裂带与其西南侧的抚边河断裂带相交且近乎垂直,而非前人研究所认为的龙日坝断裂带延伸至其西缘的鲜水河断裂带。综合研究结果也为了解龙日坝断裂带的大地构造属性提供了数据支持。     

安阳上第三系化学矿物指标显示物源区大地构造

南水北调（中线）安阳主干渠段施工过程中开挖出大量成熟度低且受近源构造影响较大的河湖相沉积岩。对现场采集的上第三系岩石样品开展了化学成分、 岩石骨架成分测试。利用Dickinson法和化学指标法, 研究得到安阳主干渠段西部物源区属于被动陆缘, 在上新世晚期向活动陆缘变化的认识。同期构造活动强烈的克什米尔N—J引水隧洞段的沉积岩, 属于岛弧和活动陆缘的大地构造背景。本文结果丰富了构造稳定和活跃区新近纪沉积构造背景认识, 可为喜马拉雅运动以来不同构造活动背景下的岩石组分和化学指标特征提供参考。     

Simulation of three-dimensional tectonic stress fields and quantitative prediction of tectonic fracture within the Damintun Depression,Liaohe Basin,northeast China

Tectonic fractures are important factors that influence oil and natural gas migration and accumulation within “buried hill” reservoirs. To obtain a quantitative forecast of the development and distribution of reservoir fractures in the Damintun Depression, we analyzed the characteristics of regional structural evolution and paleotectonic stress field setting. A reasonable geological model of the research area was built based on an interpretation of the geological structure, a test for rock mechanics, and experiment on acoustic emission. Thereafter, a three-dimensional paleotectonic stress field during the Yanshan movement was simulated by the finite element method. Rock failure criterion and comprehensive evaluation coefficient of fractures were used to determine the quantitative development of fractures and predict zones that are prone to fracture development. Under an intense Yanshan movement, high stress strength is distributed in the south and northeast parts of the study area, where stress is extremely high. The fracture development zones are mainly controlled by the tectonic stress field and typically located in the same areas as those of high maximum principal and shear stresses. The predicted areas with developed fractures are consistent with the wells with high fracture linear density and in locations with high-producing oil and gas wells.     

Active normal faulting during the 1997 seismic sequence in Colfiorito,Umbria: Did slip propagate to the surface?

In order to determine whether slip during an earthquake on the 26th September 1997 propagated to the surface, structural data have been collected along a bedrock fault scarp in Umbria, Italy. These collected data are used to investigate the relationship between the throw associated with a debated surface rupture (observed as a pale unweathered stripe at the base of the bedrock fault scarp) and the strike, dip and slip-vector. Previous studies have suggested that the surface rupture was produced either by primary surface slip or secondary compaction of hangingwall sediments. Some authors favour the latter because sparse surface fault dip measurements do not match nodal plane dips at depth. It is demonstrated herein that the strike, dip and height of the surface rupture, represented by a pale unweathered stripe at the base of the bedrock scarp, shows a systematic relationship with respect to the geometry and kinematics of faulting in the bedrock. The strike and dip co-vary and the throw is greatest where the strike is oblique to the slip-vector azimuth where the highest dip values are recorded. This implies that the throw values vary to accommodate spatial variation in the strike and dip of the fault across fault plane corrugations, a feature that is predicted by theory describing conservation of strain along faults, but not by compaction. Furthermore, published earthquake locations and reported fault dips are consistent with the analysed surface scarps when natural variation for surface dips and uncertainty for nodal plane dips at depth are taken into account. This implies that the fresh stripe is indeed a primary coseismic surface rupture whose slip is connected to the seismogenic fault at depth. We discuss how this knowledge of the locations and geometry of the active faults can be used as an input for seismic hazard assessment.