The Magellan mound province in the Porcupine Basin

The Magellan mound province is one of the three known provinces of carbonate mounds or cold-water coral banks in the Porcupine Seabight, west of Ireland. It has been studied in detail using a large and varied data set: 2D and 3D seismic data, sidescan sonar imagery and video data collected during ROV deployment have been used to describe the mounds in terms of origin, growth processes and burial. The aim of this paper is to present the Magellan mounds and their setting in an integrated, holistic way. More than 1,000 densely spaced and mainly buried mounds have been identified in the area. They all seem to be rooted on one seismic reflection, suggesting a sudden mound start-up. Their size and spatial distribution characteristics are presented, together with the present-day appearance of the few mounds that reach the seabed. The underlying geology has been studied by means of fault analysis and numerical basin modelling in an attempt to identify possible hydrocarbon migration pathways below or in the surroundings of the Magellan mounds. Although conclusive evidence concerning the processes of mound initiation proves to be elusive, the results of both fault analysis and 2D numerical modelling failed to identify, with confidence, any direct pathways for focused hydrocarbon flow to the Magellan province. Diffuse seepage however may have taken place, as drainage area modelling suggests a possible link between mound position and structural features in the Hovland-Magellan area. During mound development and growth, the interplay of currents and sedimentation seems to have been the most important control. Mounds which could not keep pace with the sedimentation rates were buried, and on the few mounds which maintained growth, only a few corals survive at present.     

Improved earthquake locations in the Koyna-Warna seismic zone

In estimating the likelihood of an earthquake hazard for a seismically active region, information on the geometry of the potential source is important in quantifying the seismic hazard. The damage from an earthquake varies spatially and is governed by the fault geometry and lithology. As earthquake damage is amplified by guided seismic waves along fault zones, it is important to delineate the disposition of the fault zones by precisely determined hypocentral parameters. We used the double difference (DD) algorithm to relocate earthquakes in the Koyna-Warna seismic zone (KWSZ) region, with the P- and S-wave catalog data from relative arrival time pairs constituting the input. A significant improvement in the hypocentral estimates was achieved, with the epicentral errors <30 m and focal depth errors <75 m i.e. errors have been significantly reduced by an order of magnitude from the parameters determined by HYPO71. The earthquake activity defines three different fault segments. The seismogenic volume is shallower in the south by 3 km, with seismicity in the north extending to a depth of 11 km while in the south the deepest seismicity observed is at a depth of 8 km. By resolving the structure of seismicity in greater detail, we address the salient issues related to the seismotectonics of this region.     

黄骅坳陷港西断裂带流体包裹体的地球化学特征

通过对黄骅坳陷港西断裂带奥陶系灰岩和新近系沙河街组砂岩中11个钻井的岩心包裹体的特征,均一温度和组分等方面的分析,对其所反映的气体来源,形成环境,油气演化以及地质意义进行研究。研究区的包裹体均为次生成因包裹体,气液比在5%～10%之间,根据激光拉曼光谱技术分析组分主要为 H_2O,CO_2和 CH_4。利用均一温度,结合古地温和埋藏史,发现奥陶系灰岩和新近系沙河街组砂岩中包裹体中流体均捕获于新近纪。对氦同位素的分析发现包裹体中均有幔源氦的侵入,侵入的份额受到 NE 向港西断层和 NWW 向徐庄子断层的控制靠近断裂带的灰岩和砂岩中的包裹体含有还原性气体,由断层交汇中心向四周减少。包裹体中烷烃气的成熟度也与断层活动相关,具有从断层交汇中心向四周减小的相似特征。研究区内港西断层和徐庄子断层交汇处不仅是幔源气体上涌的有利通道,也是地热活动强烈的地区,有利于烷烃气的成熟。     

Antithetic fault linkages in a deep water fold and thrust belt

Deep water fold and thrust belts consist of both forethrusts and backthrusts that can link along strike to form continuous folds in the overburden. The interaction of faults of opposing dip are termed ‘antithetic thrust fault linkages’ and share the common feature of a switch in vergence of overlying hangingwall anticlines. Using three-dimensional seismic data, on the toe-of-slope of the Niger Delta, linkages are classified into three distinct structural styles. This preliminary classification is based on the vertical extent of faulting within a transfer zones relative to the branch line of the antithetic faults. The stratigraphic level of the lateral tip of the fault, the shape of lateral tip region of a fault plane and the stratal deformation within the transfer zones is also distinctive in each type of fault linkage. A Type 1 linkage comprises faults that overlap exclusively above the level of the branch line. A ‘pop-up’ structure forms within the transfer zone with sediments below remaining planar. The lower tip lines of faults climb stratigraphically towards the linkage zone creating asymmetric, upward-tapering lateral tip regions. In Type 2 linkages fault overlap occurs lower than the level of the branch line such that lateral fault tips are located within the footwall of the counterpart fault. Faulting is thus limited to the deeper section within the transfer zone and creates unfaulted, symmetric, bell-shaped folds in the overburden. Upper tip lines of faults lose elevation within the transfer zone creating asymmetric, downwards-tapering lateral tip regions. In Type 3 linkages both faults continue above and below the branch line within the transfer zone resulting in cross-cutting fault relationships. Horizon continuity across the folds, through the transfer zones, varies significantly with depth and with the type of fault intersection.     

Late Panafrican evolution of the main Hoggar fault zones: Implications of magnetic fabric study in the In Telloukh pluton (Tin Serririne basin, Algeria)

The Late Panafrican evolution of the Hoggar shield is characterized by emplacement of magmatic intrusions and by occurrence of major shear zones separating different terranes. In Telloukh granite is close to the In Guezzam faults (western border of the Tin Serririne basin). Analysis of its visible and magnetic fabrics suggests an emplacement mode and deformation that are not related to the In Guezzam faults, but most likely to a N–S compression, an event not yet identified. Dioritic dykes crosscutting the granite have a very different magnetic fabric, which is related on the contrary to dextral strike-slip movements along the In Guezzam faults. In both cases, no visible fabric can be correlated with the magnetic fabric, which has been likely acquired during late magmatic stages. This magnetic fabric was not significantly affected by the tectonic events that took place after entire crystallization of the magma. The In Guezzam faults and the major 7°30 and 4°50 shear zones are close to intrusions such as In Telloukh dykes and the Alous En Tides and Tesnou plutons where quite similar magnetic fabrics are observed, all related with dextral strike-slip movements along these structures.     

Active tectonic influence on the evolution of drainage and landscape: Geomorphic signatures from frontal and hinterland areas along the Northwestern Himalaya, India

The Kangra Re-entrant in the NW Himalaya is one of the most seismically active regions, falling into Seismic Zone V along the Himalaya. In 1905 the area experienced one of the great Himalayan earthquakes with magnitude 7.8. The frontal fault system – the Himalayan Frontal Thrust (HFT) associated with the foreland fold – Janauri Anticline, along with other major as well as secondary hinterland thrust faults, provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region. The present study suggests that the flat-uplifted surface in the central portion of the Janauri Anticline represents the paleo-exit of the Sutlej River. It is suggested that initially when the tectonic activity propagated southward along the HFT the Janauri Anticline grew along two separate fault segments (north and south faults), the gap between these two fault and the related folds allowed the Sutlej River to flow across this area. Later, the radial propagation of the faults towards each other resulted in an interaction of the fault tips, which caused the rapid uplift of the area. Rapid uplift resulted in the disruption and longitudinal deflection of the Sutlej river channel. Fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past. Geomorphic signatures, like the sharp mountain fronts along the HFT in some places, as well as along various hinterland subordinate faults like the Nalagarh Thrust (NaT), the Barsar Thrust (BaT) and the Jawalamukhi Thrust (JMT); the change in the channel pattern, marked by a tight incised meander of the Beas channel upstream of the JMT indicate active tectonic movements in the area. The prominent V-shaped valleys of the Beas and Sutlej rivers, flowing across the thrust fronts, with Vf values ranging from <1.0–1.5 are also suggestive of ongoing tectonic activity along major and hinterland faults. This suggests that not only is the HFT system active, but also the other major and secondary hinterland faults, viz. the MBT, MCT, SnT, NaT, BaT, and the JMT can be shown to have undergone recent tectonic displacement.     

Geometry and kinematics of the Mosha Fault, south central Alborz Range, Iran: An example of basement involved thrusting

Field investigation of the western part of the Mosha Fault in several structural sections in the south central Alborz Range showed that the fault has a high angle of dip to the north, and emplaces Precambrian to Cenozoic rocks over the Eocene Karaj Formation. Study of the kinematics of the Mosha Fault in this area, based on S–C fabric and microstructures, demonstrates that it is a deep-seated semi-ductile thrust. Strain analysis on rock samples from different sections across the Mosha Fault shows a flattening pattern of deformation in which the long axis of the strain ellipsoid is aligned in the fault shear sense. The Mosha Fault is associated with a large hanging-wall anticline, cored by Precambrian rocks, and series of footwall synclines, formed of late Tertiary rocks. This geometry, together with several low angle short-cut thrusts in the fault footwall, implies that the Mosha Fault is an inverted normal fault which has been reactivated since the late Tertiary. In the study area, the reverse fault mechanism was associated with the rapid uplift and igneous activity in the central Alborz Range during the late Tertiary, unlike in the eastern portion of the fault, where the fault kinematics was replaced by a strike-slip mechanism in the Late Miocene.     

Fluids migration and dynamics of a blocks-and-faults system

We explore the impact of fluids migrating through a fault network on the dynamics of lithosphere, both on slow movements and seismicity. For that purpose fluids in the fault zones are incorporated into modelling of blocks-and-faults systems, which takes into account driving forces and the system's geometry. Simulations have been performed for two-dimensional models: an idealised “brick wall” structure, and a coarse image of Sinai Subplate. Migrating fluids originating in different locations are considered, as well as fluids trapped in closed pockets. Basic features of the modelled and observed seismicity are in good accord, as shown by comparison with the earthquake catalog compiled by Geophysical Institute of Israel.     

Recurrence Behaviors of Earthquakes along the Kefallinia Transform Fault, Ionian Sea, Greece

We examined the whole strong earthquake recurrence behaviors of two fault zones along the Kefallinia Transform, Ionian Sea, Greece, using seismological data and statistical methods. Our data include 29 events with %M%>5^5 for the period 1636～2003. We found different recurrence behaviors for the Kefallinia Fault Zone (clustering and time-predictable recurrence behaviors) and the Lefkada Fault Zone (near random and non-slip-predictable or non-time-predictable recurrence nature). The different modes may be attributed to: (a) segment interaction along-strike (Kefallinia) by static triggering and (b) the influence of fault systems to the north and east on the recurrence on Lefkada. Within the active periods, earthquake recurrence intervals are distributed in a more dispersed fashion, and can be fitted well by a Weibull distribution. In contrast, the distribution of the quiet periods is relatively less dispersed and difficult to describe by suitable probability functions.     

Mountain Front Development by Folding and Crustal Thickening in the Internal Zone of the Betic Cordillera-Alboran Sea Boundary

The boundary between the Alboran Sea and Betic Cordillera is a good example of a fold related mountain front in the Internal Zone of an alpine mountain range. Since the late Miocene, NNW-SSE convergence between the Eurasian and African plates has produced shortening and related orthogonal extension. To improve the characterisation of the geometry of the deep structure in the region and to establish the recent tectonic evolution of the mountain front, well logs and newly acquired geophysical data (multichannel reflection seismic and gravimetric surveys) have been interpreted and integrated with available surface data. The most marked tectonic structure corresponds to large antiforms and synforms of ENE-WSW trend which are related to mountain ranges and basins, respectively. The fold belt continues toward the northern continental shelf of the Alboran Sea. The fold vergence is generally northwards and its amplitude decreases progressively towards SSE, until disappearring in a sharp boundary where the reflectors are undeformed. The deep geometry suggests that fold growth started during upper Tortonian times and continued its activity up to Pliocene or even Quaternary times. The NNW-SSE compression produces crustal thickening and a regional and progressive southwards emersion. The location of main present-day deformation fronts in the Internal Zones contrasts with classical models where the deformation progresses towards the frontal part of External Zones of cordilleras. In addition, this fold-related deformation mountain front has features different from fault related fronts, as it does not show a sharp boundary, and folds that determine rectilinear mountain boundaries decrease progressively in amplitude or in wavelength up to undeformed areas.