A new interpretation of Stephanian deformation in the Decazeville basin (Massif Central, France): consequences on late Variscan tectonism

Five stages of faulting were observed in and around the Stephanian Decazeville basin, in the SW French Massif Central, at the southern edge of the Sillon houiller fault. The older stage ends during middle Stephanian time, and corresponds to a strike-slip regime with N–S shortening and E–W extension. Before the end of the middle Stephanian, three other stages were recorded: two strike-slip regimes with NW–SE, then E–W compression and NE–SW, then N–S extension; and finally a NNE–SSW extensional regime during the main subsidence of the basin from the end of the middle Stephanian to late Stephanian. Based on mining documents, a new interpretation of the N–S striking folds of the Decazeville basin is proposed. Folding may not be associated with E–W compression but with diapirism of coal seams along syn-sedimentary normal faults during the extensional phase. A last strike-slip regime with N–S compression and E–W extension may be related to Cainozoic Pyrenean orogeny. At a regional scale, it is suggested that from the end of the middle Stephanian to the late Stephanian, the main faults in the Decazeville basin may represent a horsetail splay structure at the southern termination of the Sillon houiller fault.     

浅谈活断层及其研究方法

介绍了活断层的基础理论知识,包括活断层性质及地震的概念及特性。从理论上探讨了地震与活断层的关系,认为地震的产生往往伴随断层位移且可常见于地表。以已有的科研成果为例,总结了近年专家、学者研究活断层的几种方法及其应用,提出了综合应用活断层研究方法及相互论证是预测地震更为有效的技术。阐述了对地震产生的动力机制的认识,并认为活断层往往是地震孕育场所,但不一定所有地震都在活断层的基础上发生。     

Trenching studies of active faults in Kamchatka, eastern Russia: Palaeoseismic, tectonic and hazard implications

The central part of the Kamchatka Peninsula is characterized by a well defined depression associated with active volcanism, aligned NE–SW. On the east, the depression is bounded by a prominent system of active faults known as the East Kamchatka Fault Zone (EKFZ). In order to improve understanding of the behaviour and kinematic role of this fault zone a fieldwork programme, including study of trenches, was conducted in the north-central part of this system. Aerial photograph analysis, ground-truthed, indicates a westward fault dip with predominantly normal slip, while lateral offsets of river terraces and stream channels demonstrate a combined dextral component. Over 20 excavated pits and natural exposures were examined to confirm a detailed tephra succession extending from the early Holocene to recent historic eruptions. This chronological framework then provided age control on five past faulting events recognised in three trenches. These events took place at about 10.5, 6.0, 4.5 and, in a two-event succession within a short time span, at 3.3–3.2 ka BP. Event clustering may be characteristic and fault length–displacement values suggest earthquakes of M6.5, thus representing a significant new element in regional seismic hazard evaluations; additional to events generated at the subduction interface. The relatively long gap in faulting since the two most recent events may also be significant for hazard scenarios and there is a possible link between the faulting and volcanic activity in the depression. Overall, the EKFZ, together with the Nachiki Transverse Zone farther south, is thought to define a regional-scale block that is extending eastwards independently from the rest of Kamchatka.     

断层研究在地震安全性评价和石油勘探工作中的对比分析

对比分析了地震安全性评价和石油勘探中,断层研究的内容和方法。两者研究内容都包括断层活动时代、位置、规模、产状、性质等,但地震安全性评价更关注断层在地表和浅层的状况,活动时代等;石油勘探更关注较深处断层的状况,能否形成断块圈闭是主要研究内容。研究方法都包括地质露头调查、重力、地磁、地震勘探、钻井等。     

阿尔泰—萨彦山的新构造运动和区域控震断裂的再活化

阿尔泰—萨彦山系和新构造结构的形成被认为是印度-欧亚板块碰撞带来的远程陆内变形的结果。在本次构造模型中,我们对地质、地震活动数据和地形资料进行了联合分析,认为中亚山带北部地形和地震活动的最大变化仅限于晚古生代区域断层的交叉地带。断层的交叉和接合处应被视为增加基底破碎程度、影响局部应力场变化和预先定位M≥5级的地震震源的最重要的构造因素之一。由此,结合Charysh Terekta和Kurai区域断层交叉带出现的氦和钙华,本次研究获得了发震前兆的一些判断规律。     

鲁西地块NW走向断层的活动特征及裂变径迹证据

不同于华北克拉通东部普遍存在的NE走向断层,鲁西地块广泛发育一组特征明显的NW走向断层,包括非控盆断层和控盆断层两类。前者位于鲁西地块最南部,倾角相对较陡,错开了古生界及以下地层,下盘太古宇中发育韧性剪切带,断层碎裂岩指示断层存在多期活动;后者位于非控盆断层以北,除蒙山断层外韧性剪切带不发育,倾角相对较缓,控制了中生代以来的沉积。磷灰石/锆石裂变径迹证据分析得出NW走向断层的活动存在差异。断层上、下盘样品磷灰石裂变径迹表观年龄在在67±5~35±2Ma之间,径迹直方图表明样品在冷却过程中没有受到热扰动。通过平均径迹长度-年龄(或香蕉图)图、单颗粒峰值年龄、径迹年龄谱模式以及热史反演模拟综合分析来约束断层的活动时间,结果表明非控盆断层可能在早侏罗世约184Ma开始活动,之后在晚白垩世80~75Ma以及新生代~61Ma和51~43Ma活动,43Ma之后不再活动。控盆断层活动时间稍晚,于早白垩世约141Ma、晚白垩世80~75Ma活动,新生代活动时间为约61Ma、49~42Ma以及36~32Ma。总体上,NW走向断层由早到晚由南向北发育,非控盆断层活动时间早、结束早;控盆断层活动晚、结束晚,并控制了凹陷的向北发育。中生代以来区域构造应力场的变化和郯庐断裂带的走滑作用是导致两类NW走向断层差异演化的根本原因,在深部则受控于晚三叠世以来华北、扬子板块陆陆碰撞和古太平洋板块俯冲方向和速度的改变。印支期后挤压到伸展的转变,加上郯庐断裂带的左行走滑,使靠近华北克拉通南缘的前端NW走向断层首先发育,因倾角较大故不控制盆地发育;向北的后端相对伸展,成为控盆断层,后经早白垩世约141Ma期间的伸展、晚白垩世末80~75Ma和新生代的发育断层最终成型。NW走向断层的这种大致向北迁移的规律,隐示华北克拉通破坏可能始于早侏罗世或晚侏罗世,且由南向北逐渐拆沉。     

洋中脊拆离断层与洋底核杂岩的发育对扩张中心迁移的影响研究

洋中脊拆离断层和洋底核杂岩（OCC）发育于慢速-超慢速扩张洋中脊中央裂谷边界,常伴随不对称的洋底扩张方式,其形成与演化起源于洋中脊中央裂谷间歇性的岩浆作用循环。拆离断层的规模和位置会随其自身演化而变化,并影响到洋中脊扩张中心的位置变化。依据洋中脊扩张中心位置的离轴迁移规律,本文将拆离断层和洋底核杂岩的演化过程划分为6个阶段,并参照洋中脊拆离断层和洋底核杂岩演化阶段的划分,将全球27处拆离断层进行分类。现今全球洋中脊拆离断层多属于非活动性拆离断层,位于阶段VI（如Logachev Massif拆离断层和Kane Megamullion拆离断层）;但部分拆离断层仍在活动,即属于发展期和成熟期（阶段III/IV,如MAR, 13°19′N拆离断层和MtDent拆离断层）,以及衰亡期（阶段V,如MAR, 13°30′N拆离断层和Atlantis Massif拆离断层）。在洋中脊拆离断层和洋底核杂岩形成-演化-衰亡-再次形成的循环过程中,中央裂谷的岩浆作用发生周期性循环,洋中脊扩张中心亦发生新生火山岩区中线-拆离断层终止线-重新活动的新生火山岩区中线的位置变化,并先后产生离轴和向轴的位移。     

河北沽源460铀矿床主矿段矿体空间定位机制

460矿床构造几何学和运动学特征研究表明,460矿床构造格架是在大致自北西而南东的构造应力作用下,F45断裂带右行扭动并与F’45相互作用所形成。结合主矿段容矿构造产状和分布特征,提出矿区北西向反S形或弧形张-张扭性断裂是F45断裂的派生构造,是矿床定位的决定性因素;由陡倾断裂和缓倾地层组成的"断裂-地层圈闭"是矿床定位的另一重要因素。铀成矿作用与晚侏罗世—早白垩世火山作用没有直接的成因联系,而是与区域上强烈构造活动时期的构造活动密切相关。次流纹斑岩的侵入和两次铀成矿作用在时间上与区域上的强烈构造运动时期相对应,是区域构造演化不同阶段的产物,二者没有必然的因果关系。     

The analyses focusing on formation mechanism of Nanzhangzhuang ground fissure in Hengshui City,China

The paper focuses on the formation of Nanzhangzhuang ground fissure through emphatically analysing factors including the intersection fault dislocation, the deep ground-water over-exploitation together with the landform and lithology features. Features of the ground fissure are explained in detail after describing the geological setting in the study area. The paper also provides dynamic mode of the ground fissure formation via force analysis of the soil body unit at ground fissures. Conclusions can be drawn that the stress state of soil bodies changed with the activities of two intersection faults, namely Hengshui fault and Hubei fault. In addition, the stress fields control the development of ground fissure. The deep groundwater in Hengshui area dropped considerably in recent years, to be precise, the water elevation of deep groundwater dropped from -26 m to -94 m by 2010 at the centre of groundwater funnel. The over-exploitation of deep groundwater in Hengshui area enlarged the ground fissures. The data concerning shallow borehole show that the vertical lithology mainly consists of silt, silty clay and silty sandy soil, which all belong to the middle-compressed soil. The lateral extension of the soil bodies occur with pumping and tectonic creep, and the clay layers on both sides of the cracks can stay upright. Thus the ground fissure came visible.