The role of fluids in faulting deformation:a case study from the Dead Sea Transform (Jordan)

The geochemistry of carbonate fault rocks has been examined in two areas of the Arava Fault segment, which forms the major branch of the Dead Sea Transform between the Dead Sea and the Gulf of Aquaba. The role of fluids in faulting deformation in the selected fault segment is remarkably different from observations at other major fault zones. Our data suggest reduced fluid rock interactions in both areas and limited fluid flow. The fault did not act as an important fluid conduit. There are no indications that hydrothermal reactions (cementation, dissolution) did change the strength and behavior of the fault zone, although the two areas show considerable differences with respect to fluid sources and fluid flow. In one area, the investigated calcite mineralization reveals an open fluid system with fluids originating from a variety of sources. Stable isotopes (¹³C, ¹⁸O), strontium isotopes, and trace elements indicate both infiltration of descending (meteoric and/or sea water) and ascending hydrothermal fluids. In the other area, all geochemical data indicate only local (small scale) fluid redistribution. These fluids were derived from the adjacent limestones under nearly closed-system conditions.     

由现今地震活动分析鲜水河断裂带中-南段活动习性与强震危险地段

利用最近25年的区域台网地震资料, 基于沿鲜水河断裂带中-南段的b值分布以及多个地震活动参数值的不同组合, 结合震源深度分布、 历史强震背景等, 分析了不同断裂段落的现今活动习性, 进而初步判别该断裂带潜在的强震危险地段。 结果表明, 鲜水河断裂带中-南段目前存在6个不同活动习性的段落。 其中, 道孚段自1981年强震后已再次趋于闭锁, 原因可能与断层面存在“凹凸体”有关, 但应变可能还会进一步积累; 八美段目前处于中偏高应力下的相对静止状态, 推测其断面正处于新的应力积累阶段; 塔公段已有255~300年的无强震期, 目前正处于高应力下的相对闭锁状态, 震源深度剖面上的小震空白区显示出闭锁断层面的轮廓, 应属于未来最可能发生强震的危险地段; 康定、 磨西二个段落表现出中偏低应力下的稀疏小震滑动及较频繁小震滑动的状态, 意味着最晚的一次大地震破裂后断层面尚未重新耦合; 石棉段表现出偏高应力下的频繁中-小地震活动与该段的多条断裂交汇有关。     

Distinctive diamagnetic fabrics in dolostones evolved at fault cores,the Dead Sea Transform

We resolve the anisotropy of magnetic susceptibility (AMS) axes along fault planes, cores and damage zones in rocks that crop out next to the Dead Sea Transform (DST) plate boundary. We measured 261 samples of mainly diamagnetic dolostones that were collected from 15 stations. To test the possible effect of the iron content on the AMS we analyzed the Fe concentrations of the samples in different rock phases. Dolostones with mean magnetic susceptibility value lower than −4 × 10⁻⁶ SI and iron content less than ∼1000 ppm are suitable for diamagnetic AMS-based strain analysis. The dolostones along fault planes display AMS fabrics that significantly deviate from the primary “sedimentary fabric”. The characteristics of these fabrics include well-grouped, sub-horizontal, minimum principal AMS axes (k₃) and sub-vertical magnetic foliations commonly defined by maximum and intermediate principal AMS axes (k₁ and k₂ axes, respectively). These fabrics are distinctive along fault planes located tens of kilometers apart, with strikes ranging between NNW-SSE and NNE-SSW and different senses of motion. The obtained magnetic foliations (k₁–k₂) are sub-parallel (within ∼20°) to the fault planes. Based on rock magnetic and geochemical analyses, we interpret the AMS fabrics as the product of both shape and crystallographic anisotropy of the dolostones. Preferred shape alignment evolves due to mechanical rotation of subordinate particles and rock fragments at the fault core. Preferred crystallographic orientation results from elevated frictional heating (>300 °C) during faulting, which enhances c-axes alignment in the cement-supported dolomite breccia due to crystal-plastic processes. The penetrative deformation within fault zones resulted from the local, fault-related strain field and does not reflect the regional strain field. The analyzed AMS fabrics together with fault-plane kinematics provide valuable information on faulting characteristics in the uppermost crust.     

东营凹陷盐底辟作用与中央隆起带断裂构造成因

华北渤海湾盆地济阳坳陷的东营凹陷中央隆起带同生断层非常发育,断层数量较多。主干正断层的下降盘上形成“逆牵引”构造,组成“负花状”地堑断裂系。这些断裂系将中央隆起带分割为一系列小断块。本文将这些断裂系和相关的小断块划分为3个构造,分别称为辛镇、东营和郝家—现河庄(简称郝—现)构造。研究证明,复杂断裂与断块组合构造主要为盐底辟作用的结果,伴生的逆牵引作用形成“包心状”的复杂断裂构造形态,总体上,东营凹陷中央隆起带构造成因是区域北北西—南南东向伸展作用下局部底辟作用和逆牵引作用共同形成的,而不是走滑成因。据强度,底辟构造可分为低幅度隆起和隐刺穿构造。其形成时期主要为沙河街组三段沉积期开始持续到馆陶组沉积前。底辟物质由盐岩为主的塑性层组成。     

新平大红山铜矿二期基建探矿控矿构造特征

二期基建揭露的断层按其产出方向分为四个组：NWW向的正断层,NNE向的平移正断层,NE～NEE向的正断层,NW向的矿区断层F3;按形成时间可分为早期断层和晚期断层,除边界断层F3外均为早期断层。早期断层又按其切错关系,可分为5个活动期次。断层构造将矿体沿走向切错成条块状,沿倾向切错成阶梯状排列,形成堑、垒式构造,对矿床开采产生较大的影响。     

Ruptures in a Highly Fractured Upper Crust

The 1999 Chiayi M 6.4 earthquake sequence that occurred about one month after the 1999 Chi-Chi M 7.6 earthquake is remarkably similar to the Ruey-Li M 6.2 earthquake sequence which occurred one year before the big Chi-Chi event. Both sequences were energetic and short in duration; with events confined in small source volumes, and the fault-plane orientation of individual events in these sequences varied abruptly during the development of the dynamic rupture. Both occurred on the southern extension of the large Chelungpu rupture causal to the Chi-Chi event, and in an area of highly fractured upper crust. We consider that this faulting behavior is due to the rupture-induced dynamic stress that interacts with the pre-existing highly fractured upper crust and continually perturbs the local stress field. This phenomenon appears to be typical of particularly active plate boundary regions with a highly fractured upper crust under intense tectonic loading.     

济阳坳陷古近系沙四段上亚段烃源岩沉积有机相研究

根据沉积构造、古生物组合、有机质赋存方式等特征研究,明确了沉积过程底水含氧量对古近系湖相烃源岩中有机 质的组成和含量的控制作用。在此基础上借鉴沉积有机相和古氧相研究的成果,将济阳坳陷古近系沙四段上亚段湖相烃源 岩划分为四种沉积有机相,分别为缺氧相、短暂充氧相、低氧相、充氧相,并且确定了不同类型沉积有机相的判识标志。 并结合测井资料开展了烃源岩沉积有机相的单井、连井及平面分布特征分析,提出沙四段上亚段烃源岩的发育存在着明显 的东西差异,东部地区明显优于西部地区,而不同走向断裂的活动差异控制了优质烃源岩的分布。沙四段上亚段烃源岩的 分布规律对于下一步勘探决策的制定和深层隐蔽油气藏成藏规律研究具有重要意义。     

河北矾山盆地北缘断层八营段的古地震重复模型

通过实测断错地貌面,开挖在探槽以及系统的地层年代采样,推断和揭露出矾出盆地北缘断层八营段９万年来总移量量为３４ｍ。经７．５万年来共发生过９次古位移事件。其中大探槽揭露的４次事件分别发生在距今：Ａ,２．８万年;Ｂ．１．４万年;Ｃ,０．７５万年和Ｄ,６５６年（？）左右。该段落古地震地重复模型分为两个阶段：９￣１．４万年间符合“时间可推测模型”;１．４万年来以来则为“位称衰减模型”。     

南海北部陆缘地震带的深部结构和孕震机制

南海北部陆缘地震带的地震震源基本上分布在地壳内６￣１３ｋｍ和１７￣２２ｋｍ两个深度范围内,发震层恰好位于区内中地震低速层和下地壳低速层的顶部附近。地壳深部结构的不稳定性以及侧向应力和垂向应力共同作用下的平移正断层错动,可能是该带地震孕育、发生的一种重要机制。     

Tectonic vs. gravitational morphostructures in the central Eastern Alps (Italy): Constraints on the recent evolution of the mountain range

Deep-seated gravitational slope deformations (DSGSDs) influence landscape development in tectonically active mountain ranges. Nevertheless, the relationships among tectonics, DSGSDs, and topography are poorly known. In this paper, the distribution of DSGSDs and their relationships with tectonic structures and active processes, surface processes, and topography were investigated at different scales. Over 100 DSGSDs were mapped in a 5000 km² sector of the central Eastern Alps between the Valtellina, Engadine and Venosta valleys. Detailed lineament mapping was carried out by photo-interpretation in a smaller area (about 750 km²) including the upper Valtellina and Val Venosta. Fault populations were also analysed in the field and their mechanisms unravelled, allowing to identify different structural stages, the youngest being consistent with the regional pattern of the ongoing crustal deformation. Finally, four DSGSD examples have been investigated in detail by geological and 2D geomechanical modelling.DSGSDs affect more than 10% of the study area, and mainly cluster in areas where anisotropic fractured rock mass and high local relief occur. Their onset and development is subjected to a strong passive control by mesoscopic and major tectonic features, including regional nappe boundaries as well as NW–SE, N–S and NE–SW trending recent brittle structures. The kinematic consistency between these structures and the pattern of seismicity suggests that active tectonics may force DSGSDs, although field evidence and numerical models indicate slope debuttressing related to deglaciation as a primary triggering mechanism.