WorldWideScience

Sample records for strike-slip shear zone

  1. Viscoelastic shear zone model of a strike-slip earthquake cycle

    Science.gov (United States)

    Pollitz, F.F.

    2001-01-01

    I examine the behavior of a two-dimensional (2-D) strike-slip fault system embedded in a 1-D elastic layer (schizosphere) overlying a uniform viscoelastic half-space (plastosphere) and within the boundaries of a finite width shear zone. The viscoelastic coupling model of Savage and Prescott [1978] considers the viscoelastic response of this system, in the absence of the shear zone boundaries, to an earthquake occurring within the upper elastic layer, steady slip beneath a prescribed depth, and the superposition of the responses of multiple earthquakes with characteristic slip occurring at regular intervals. So formulated, the viscoelastic coupling model predicts that sufficiently long after initiation of the system, (1) average fault-parallel velocity at any point is the average slip rate of that side of the fault and (2) far-field velocities equal the same constant rate. Because of the sensitivity to the mechanical properties of the schizosphere-plastosphere system (i.e., elastic layer thickness, plastosphere viscosity), this model has been used to infer such properties from measurements of interseismic velocity. Such inferences exploit the predicted behavior at a known time within the earthquake cycle. By modifying the viscoelastic coupling model to satisfy the additional constraint that the absolute velocity at prescribed shear zone boundaries is constant, I find that even though the time-averaged behavior remains the same, the spatiotemporal pattern of surface deformation (particularly its temporal variation within an earthquake cycle) is markedly different from that predicted by the conventional viscoelastic coupling model. These differences are magnified as plastosphere viscosity is reduced or as the recurrence interval of periodic earthquakes is lengthened. Application to the interseismic velocity field along the Mojave section of the San Andreas fault suggests that the region behaves mechanically like a ???600-km-wide shear zone accommodating 50 mm/yr fault

  2. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas fault zone

    Science.gov (United States)

    Thatcher, W.; England, P.C.

    1998-01-01

    We have carried out two-dimensional (2-D) numerical experiments on the bulk flow of a layer of fluid that is driven in a strike-slip sense by constant velocities applied at its boundaries. The fluid has the (linearized) conventional rheology assumed to apply to lower crust/upper mantle rocks. The temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations, as has thermal conduction in an overlying crustal layer. Two end-member boundary conditions have been considered, corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive, weak crust. In many cases of practical interest, shear heating is concentrated close to the axial plane of the shear zone for either boundary condition. For these cases, the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half-space at a depth corresponding to the top of the fluid layer. This approximation, along with the application of a theoretical result for one-dimensional shear zones, permits us to obtain simple analytical approximations to the thermal effects of 2-D ductile shear zones for a range of assumed rheologies and crustal geotherms, making complex numerical calculations unnecessary. Results are compared with observable effects on heat flux near the San Andreas fault using constraints on the slip distribution across the entire fault system. Ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the Mendocino triple junction and match the amplitude of the regional heat flux anomaly in the California Coast Ranges. Because ductile dissipation depends only weakly on slip rate, faults moving only a few millimeters per year can be important heat sources, and the superposition of effects of localized ductile shearing on both currently active and now

  3. E–W strike slip shearing of Kinwat granitoid at South East Deccan ...

    Indian Academy of Sciences (India)

    R D Kaplay

    2017-07-21

    Jul 21, 2017 ... cO Indian Academy of Sciences. DOI 10.1007/s12040-017-0853-8. E–W strike slip shearing of Kinwat granitoid at South East. Deccan ...... shear zone, Sutlej section-structural geology and extrusion mechanism by various combinations of simple shear, pure shear and channel flow in shifting modes; Int. J.

  4. Slip events propagating along a ductile mid-crustal strike-slip shear zone (Malpica-Lamego line, Variscan Orogen, NW Iberia)

    Science.gov (United States)

    Llana-Fúnez, Sergio; de Paola, Nicola; Pozzi, Giacomo; Lopez-Sanchez, Marco Antonio

    2017-04-01

    The current level of erosion in NW Iberian peninsula exposes Variscan mid-crustal depths, where widespread deformation during orogenesis produced dominantly ductile structures. It constitutes an adequate window for the observation of structures close to the brittle-plastic transition in the continental crust. The shear zone object of this work is the Malpica-Lamego line (MLL), a major Variscan structure formed in the late stages of the Variscan collision. The MLL is a mostly strike-slip major structure that offsets laterally by several kilometres the assembly of allochthonous complexes, that contain a sub-horizontal suture zone, which are the remnants of the plate duplication during the Variscan convergence. The shear zone is exposed along the northern coast of Galicia (NW Spain). It is characterized by phyllonites and quartz-mylonites in a zone which is tens of meters in thickness. Within the phyllonites, a few seams of cataclastic rocks have been found in bands along the main fabric. Their cohesive character, the parallelism between the different bands, the fact that host rocks maintain mineral assemblage and that no cross-cutting relations in the field were identified, are considered indicative of these brittle structures forming coetaneously with the ductile shearing producing the phyllonites. Samples from the phyllonites, also from quartz-mylonites, were prepared and powdered to characterize friction properties in a rotary shear apparatus at high, seismic velocities (m/s). Preliminary experiments run at room temperature and effective normal stresses between 10 to 25 MPa, show that friction coefficients µ are relatively high and a limited drop in friction coefficient occurs after 10-20 cm of slip, with µ decreasing from 0.7 to 0.5. Fracturing seems coetaneous with dominant ductile shearing within the shear zone, however, given the frictional properties of the phyllonites, it is unlikely that brittle deformation nucleates within these fault rocks. Instead, it

  5. Recent geodynamics of major strike-slip zones

    Directory of Open Access Journals (Sweden)

    Vladimir G. Trifonov

    2015-09-01

    In all of the cases mentioned above, strike-slip deformation was expressed only or mainly during strong earthquakes. At other times, the rate of its accumulation was small and the dominant stress conditions led to transverse shortening, rarely resulting in local lengthening of the tectonic zone. These variations are caused by the tectonic peculiarities of these zones. The sinistral component of the deformation is related to the shift of the Arabian Plate relative to the African one, but also the transverse component is related to the continental slope and is expressed by the Coastal range shortening that exists in the El Ghab segment zone. There is not only a dextral deformation component, but also a transverse component, expressed by shortening of the Fergana and Talas ranges existing in the Talas-Fergana fault zone. In both zones, the shortening component became appreciable or dominant when the strike-slip deformation rate decreased. Similar, but more local, relationships were expressed in the epicentral area of the 2003 Altai earthquake and in the Western Palmyrides.

  6. Seismic attribute detection of faults and fluid pathways within an active strike-slip shear zone: New insights from high-resolution 3D P-Cable™ seismic data along the Hosgri Fault, offshore California

    Science.gov (United States)

    Kluesner, Jared W.; Brothers, Daniel

    2016-01-01

    Poststack data conditioning and neural-network seismic attribute workflows are used to detect and visualize faulting and fluid migration pathways within a 13.7 km2 13.7 km2 3D P-Cable™ seismic volume located along the Hosgri Fault Zone offshore central California. The high-resolution 3D volume used in this study was collected in 2012 as part of Pacific Gas and Electric’s Central California Seismic Imaging Project. Three-dimensional seismic reflection data were acquired using a triple-plate boomer source (1.75 kJ) and a short-offset, 14-streamer, P-Cable system. The high-resolution seismic data were processed into a prestack time-migrated 3D volume and publically released in 2014. Postprocessing, we employed dip-steering (dip and azimuth) and structural filtering to enhance laterally continuous events and remove random noise and acquisition artifacts. In addition, the structural filtering was used to enhance laterally continuous edges, such as faults. Following data conditioning, neural-network based meta-attribute workflows were used to detect and visualize faults and probable fluid-migration pathways within the 3D seismic volume. The workflow used in this study clearly illustrates the utility of advanced attribute analysis applied to high-resolution 3D P-Cable data. For example, results from the fault attribute workflow reveal a network of splayed and convergent fault strands within an approximately 1.3 km wide shear zone that is characterized by distinctive sections of transpressional and transtensional dominance. Neural-network chimney attribute calculations indicate that fluids are concentrated along discrete faults in the transtensional zones, but appear to be more broadly distributed amongst fault bounded anticlines and structurally controlled traps in the transpressional zones. These results provide high-resolution, 3D constraints on the relationships between strike-slip fault mechanics, substrate deformation, and fluid migration along an active

  7. Continental strike slip fault zones in geologically complex lithosphere: the North Anatolian Fault, Turkey.

    Science.gov (United States)

    Cornwell, David; Thompson, David; Papaleo, Elvira; Rost, Sebastian; Houseman, Gregory; Kahraman, Metin; Turkelli, Niyazi; Teoman, Ugur; Altuncu Poyraz, Selda; Gulen, Levent; Utkucu, Murat

    2016-04-01

    As part of the multi-disciplinary Faultlab project, we present new detailed images in a geologically complex region where the crust and upper mantle is bisected by a major continental strike-slip fault system. Our study region samples the north Anatolian fault zone (NAFZ) near the epicentres of two large earthquakes that occurred in 1999 at Izmit (M7.5) and Düzce (M7.2) and where estimates of present day slip rate are 20-25 mm/yr. Using recordings of teleseismic earthquakes from a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield, we build a detailed 3-D image of structure and anisotropy using receiver functions, tomography and shear wave splitting and illuminate major changes in the architecture and properties of the upper crust, lower crust and upper mantle, both across and along the two branches of the NAFZ, at length scales of less than 20 km. We show that the northern NAFZ branch depth extent varies from the mid-crust to the upper mantle and it is likely to be less than 10 km wide. A high velocity lower crust and a region of crustal underthrusting appear to add strength to a heterogeneous crust and play a role in dictating the variation in faulting style and postseismic deformation. Sharp changes in lithospheric mantle velocity and anisotropy are constrained as the NAFZ is crossed, whereas crustal structure and anisotropy vary considerably both parallel and perpendicular to the faulting. We use our observations to test current models of the localisation of strike-slip deformation and develop new ideas to explain how narrow fault zones develop in extremely heterogeneous lithosphere.

  8. Structural evidence for strike-slip deformation in the Izmir-Balikesir transfer zone and consequences for late Cenozoic evolution of western Anatolia (Turkey)

    NARCIS (Netherlands)

    Uzel, B.; Sözbilir, H.; Özkaymak, T.; Kaymakci, N.; Langereis, C.G.

    2013-01-01

    The Izmir-Balikesir transfer zone (IBTZ) is a recently recognized strike-slip dominated shear zone that accommodates the differential deformation between the Cycladic and Menderes core complexes within the Aegean Extensional System. Here, we present new structural and kinematic data obtained from

  9. Crimea-Kopet Dagh zone of concentrated orogenic deformations as a transregional late collisional right-lateral strike-slip fault

    Science.gov (United States)

    Patina, I. S.; Leonov, Yu. G.; Volozh, Yu. A.; Kopp, M. L.; Antipov, M. P.

    2017-07-01

    It is shown that the Crimea, Caucasus, and Kopet Dagh fold systems make up a single whole unified by a lithospheric strike-slip fault zone of concentrated dislocations. The strike-slip fault that dissects the sedimentary cover and consolidated crust is rooted in subcrustal layers of the mantle. The notions about strike-slip dislocations in the structure of the Crimea-Kopet Dagh System are considered. Comparative analysis of structure, age, and amplitude of strike-slip fault segments is carried out. The effect of strike-slip faulting on the deep-seated and near-surface structure of the Earth's crust is considered. Based on estimation of strike-slip offsets, the paleogeography of Paleogene basins is refined; their initial contours, which have been disturbed and fragmented by slipping motion strike-slip displacement, have been reconstructed.

  10. Carpathian Shear Corridor – A strike-slip boundary of an extruded crustal segment

    Czech Academy of Sciences Publication Activity Database

    Marko, F.; Andriessen, P.A.M.; Tomek, Č.; Bezák, V.; Fojtíková, Lucia; Bošanský, M.; Piovarči, M.; Reichenwalder, P.

    703-704, APR 22 (2017), s. 119-134 ISSN 0040-1951 Grant - others:Slovak Foundation Grant(SK) VEGA 2/0188/15 Institutional support: RVO:67985891 Keywords : extrusion * Neo-alpine evolution * strike-slip faulting * uplift history * Western Carpathians Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Geology Impact factor: 2.693, year: 2016

  11. Right-lateral shear and rotation as the explanation for strike-slip faulting in eastern Tibet

    Science.gov (United States)

    England, Philip; Molnar, Peter

    1990-01-01

    Bounds are placed here on the rate of rotation proposed by Cobbold and Davy (1988) for the major strike-slip faults in the eastern Tibetan Plateau. It is also concluded here that the image of lateral transport on such faults, known also as continental escape, extrusion, or expulsion, is an illusion, and that instead the left-lateral slip on east-striking plates in eastern Tibet is a manifestation of north-striking right-lateral simple shear. If this conclusion is correct, the east-striking left-lateral faults and the crustal blocks between them are rotating clockwise at 1-2 deg/Myr, the east-west dimension of eastern Tibet is shortening at 10-20 mm/yr, and little material is moving eastward out of India's path into Eursasia by left-lateral simple shear.

  12. Structural evolution of the La Trocha fault zone: Oblique collision and strike-slip basins in the Cuban Orogen

    Science.gov (United States)

    Cruz-Orosa, Israel; Sã Bat, Francesc; Ramos, Emilio; Rivero, LluíS.; VáZquez-Taset, Yaniel M.

    2012-10-01

    The La Trocha fault zone acted as a major left-lateral transfer zone and is bounded by the La Trocha (LTF), Zaza-Tuinicú (ZTF), Cristales (CTF) and Taguasco (TGF) faults. These faults were consistent with the clockwise rotation of convergence and shortening in central Cuba. From the Paleocene to the Early Eocene (65-48 Ma), a SSW-NNE shortening produced transtension in the LTF and transpression in the ZTF. Subsequently, during the Middle Eocene (48-37 Ma), shortening shifted to a SW-NE direction, resulting in the normal component of the LTF and transpression in the ZTF and CTF. Since the Late Eocene (37 Ma), central Cuba has been welded to the North American Plate. The post-welding deformation gave rise to transtension of the LTF and TGF. This deformation is consistent with a WSW-ENE shortening and reflects activity in the transform boundary of the Cayman Trough. Both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left-lateral displacement is deduced from the concordance between oblique collision and structural features. Plate-kinematics and the structural evolution of the La Trocha fault zone indicate that the related Central Basin is a strike-slip polygenetic basin and that the formation of this system (i.e., fault zone - strike-slip basin) was a consequence of the Paleogene oblique collision between the Caribbean Volcanic Arc and the Bahamas Borderland (North American plate).

  13. Late Pleistocene-Holocene Activity of the Strike-slip Xianshuihe Fault Zone, Tibetan Plateau, Inferred from Tectonic Landforms

    Science.gov (United States)

    Lin, A.; Yan, B.

    2017-12-01

    Knowledges on the activity of the strike-slip fault zones on the Tibetan Plateau have been promoted greatly by the interpretation of remote sensing images (Molnar and Tapponnier, 1975; Tapponnier and Molnar, 1977). The active strike-slip Xianshuihe-Xiaojiang Fault System (XXFS), with the geometry of an arc projecting northeastwards, plays an important role in the crustal deformation of the Tibetan Plateau caused by the continental collision between the Indian and Eurasian plates. The Xianshuihe Fault Zone (XFZ) is located in the central segment of the XXFS and extends for 370 km, with a maximum sinistral offset of 60 km since 13‒5 Ma. In this study, we investigated the tectonic landforms and slip rate along the central segment of the left-lateral strike-slip XFZ. Field investigations and analysis of ttectonic landforms show that horizontal offset has been accumulated on the topographical markers of different scales that developed since the Last Glacial Maximum (LGM). The central segment of the XFZ is composed of three major faults: Yalahe, Selaha, and Zheduotang faults showing a right-stepping echelon pattern, that is characterized by systematical offset of drainages, alluvial fans and terrace risers with typical scissoring structures, indicating a structural feature of left-lateral strike-slip fault. Based on the offset glacial morphology and radiocarbon dating ages, we estimate the Late Pleistocene-Holocene slip rate to be 10 mm/yr for the central segment of the XFZ, which is consistent with that estimated from the GPS observations and geological evidence as reported previously. Across the central segment of the XFZ, the major Selaha and Zheduotang faults participate a slip rate of 5.8 mm/yr and 3.4 mm/yr, respectively. Detailed investigations of tectonic landforms are essential for the understanding the activity of active faults. Our findings suggest that the left-lateral slipping of the XFZ partitions the deformation of eastward extrusion and northeastward

  14. The Iceland Plate Boundary Zone: Propagating Rifts, Migrating Transforms, and Rift-Parallel Strike-Slip Faults

    Science.gov (United States)

    Karson, J. A.

    2017-11-01

    Unlike most of the Mid-Atlantic Ridge, the North America/Eurasia plate boundary in Iceland lies above sea level where magmatic and tectonic processes can be directly investigated in subaerial exposures. Accordingly, geologic processes in Iceland have long been recognized as possible analogs for seafloor spreading in the submerged parts of the mid-ocean ridge system. Combining existing and new data from across Iceland provides an integrated view of this active, mostly subaerial plate boundary. The broad Iceland plate boundary zone includes segmented rift zones linked by transform fault zones. Rift propagation and transform fault migration away from the Iceland hotspot rearrange the plate boundary configuration resulting in widespread deformation of older crust and reactivation of spreading-related structures. Rift propagation results in block rotations that are accommodated by widespread, rift-parallel, strike-slip faulting. The geometry and kinematics of faulting in Iceland may have implications for spreading processes elsewhere on the mid-ocean ridge system where rift propagation and transform migration occur.

  15. Turkish earthquakes reveal dynamics of fracturing along a major strike-slip fault zone

    Science.gov (United States)

    Çemen, Ibrahim; Gökten, Ergun; Varol, Baki; Kiliç, Recep; Özaksoy, Volkan; Erkmen, Cenk; Pinar, Ali

    During the last 5 months of 1999, northwestern Turkey experienced two major earthquakes along the North Anatolian Fault Zone (NAFZ). The first earthquake struck the country at 3:01 A.M. local time on August 17, and caused extensive damage in the towns of Yalova, Gölcük, Izmit, Adapazari, and Düzce (Figure 1). The second earthquake occurred at 6:57 P.M. local time on November 12 and caused damage mostly in Düzce and Kaynasli.The 7.4-Mw main shock of the August 17 Izmit earthquake was centered at 40.702°N, 29.987°E and originated at a depth of 17 km. The center was about 11 km southeast of Izmit, a major industrial town (Figure 1). The earthquake was a devastating natural disaster that claimed close to 20,000 lives and left more than 100,000 people homeless.

  16. (Plio-)Pleistocene alluvial-lacustrine basin infill evolution in a strike-slip active zone (Northern Andes, Western-Central Cordilleras, Colombia)

    OpenAIRE

    SUTER, F.; NEUWERTH, R.; GORIN, G.; GUZMÁN, C.

    2009-01-01

    The (Plio)-Pleistocene Zarzal Formation was deposited in the Cauca Depression and Quindío-Risaralda Basin between the Western and Central Cordilleras (Northern Andes). This area is structurally located on the transcurrent Romeral Fault System (RFS). Because of the interaction between the Nazca plate and the Chocó-Panamá block (an active indenter), the RFS strike-slip component changes direction around the study zone (dextral in the south, senestral in the north). Zarzal sediments are the olde...

  17. THE ILICA BRANCH OF THE SOUTHEASTERN ESKIŞEHIR FAULT ZONE: AN ACTIVE RIGHT LATERAL STRIKE-SLIP STRUCTURE IN CENTRAL ANATOLIA, TURKEY

    Directory of Open Access Journals (Sweden)

    Korhan ESAT

    2016-12-01

    Full Text Available The Eskişehir Fault Zone is one of the prominent neotectonic structures of Turkey. It separates the west  Anatolian extensional province and the strike-slip induced northwest central Anatolian contractional area in the Anatolian Block. Its southeastern part is generally divided into three branches, namely the Ilıca, Yeniceoba, and Cihanbeyli from north to south, respectively. The right lateral strike-slip Ilıca branch (IB is an approximately 100-km-long fault and it is composed of several segments in a northwest-southeast direction. The slickensides, subsidiary fractures, cataclastic zone, fracture-controlled drainage pattern, right lateral stream deflections, deformation in the Quaternary unit observing in the seismic reflection sections, and seismicity of the region all indicate that the IB is an active right lateral strike-slip fault. The IB has also a regional tectonic importance as a boundary fault between the contractional and the extensional regions in central Anatolia considering that it is the southern limit of the contraction-related structures in the west-southwest of Ankara.

  18. Active and recent strike-slip tectonics

    Science.gov (United States)

    Nur, Amos; Boccaletti, Mario

    An international workshop cosponsored by the Department of Geology, University of Florence, Italy and the Department of Geophysics, Stanford University, Stanford, Calif., was held in Florence, Italy, April 18-20, 1989,on the topic of active and recent strike-slip tectonics in the continental crust. Workshop participants from Turkey, Ethiopia, Israel, Greece, and various universities in Italy, Spain, West Germany, France, the United Kingdom, Brazil, and the United States reported on a broad range of studies involving strike-slip faulting in continental crustal setting. As it turned out, much of the work reported on involved aspects of strike-slip faulting that are only poorly understood, especially crustal deformation, which is distributed over a multiplicity of faults, or even fault domains.One of the rewarding aspects of this workshop was the diversity of geographic areas and geological settings covered by the reporters. The north and east Anatolian faults, the Dead Sea transform zone, western Turkey, north and central Greece, Malta, Sicily, southern Italy, the bethic Cordillera in southern Spain, Tunisia, Tibet and southwest China, offshore Brazil, Alaska, Nevada, and California. A recurring observation reported for all those areas was mixed mode faulting, i.e., the coterminous or sequential occurrence of strike-slip and normal faulting, or strike-slip and thrust, and in many instances also strikeslip, normal and thrust faulting in a single tectonic setting.

  19. Role of the offshore Pedro Banks left-lateral strike-slip fault zone in the plate tectonic evolution of the northern Caribbean

    Science.gov (United States)

    Ott, B.; Mann, P.; Saunders, M.

    2013-12-01

    Previous workers, mainly mapping onland active faults on Caribbean islands, defined the northern Caribbean plate boundary zone as a 200-km-wide bounded by two active and parallel strike-slip faults: the Oriente fault along the northern edge of the Cayman trough with a GPS rate of 14 mm/yr, and and the Enriquillo-Plaintain Garden fault zone (EPGFZ) with a rate of 5-7 mm/yr. In this study we use 5,000 km of industry and academic data from the Nicaraguan Rise south and southwest of the EPGFZ in the maritime areas of Jamaica, Honduras, and Colombia to define an offshore, 700-km-long, active, left-lateral strike-slip fault in what has previously been considered the stable interior of the Caribbean plate as determined from plate-wide GPS studies. The fault was named by previous workers as the Pedro Banks fault zone because a 100-km-long segment of the fault forms an escarpment along the Pedro carbonate bank of the Nicaraguan Rise. Two fault segments of the PBFZ are defined: the 400-km-long eastern segment that exhibits large negative flower structures 10-50 km in width, with faults segments rupturing the sea floor as defined by high resolution 2D seismic data, and a 300-km-long western segment that is defined by a narrow zone of anomalous seismicity first observed by previous workers. The western end of the PBFZ terminates on a Quaternary rift structure, the San Andres rift, associated with Plio-Pleistocene volcanism and thickening trends indicating initial rifting in the Late Miocene. The southern end of the San Andreas rift terminates on the western Hess fault which also exhibits active strands consistent with left-lateral, strike-slip faults. The total length of the PBFZ-San Andres rift-Southern Hess escarpment fault is 1,200 km and traverses the entire western end of the Caribbean plate. Our interpretation is similar to previous models that have proposed the "stable" western Caribbean plate is broken by this fault whose rate of displacement is less than the threshold

  20. Palaeopermeability anisotropies of a strike-slip fault damage zone: 3D Insights of quantitative fluid flow from µCT analysis.

    Science.gov (United States)

    Gomila, R.; Arancibia, G.; Nehler, M.; Bracke, R.; Morata, D.

    2017-12-01

    Fault zones and their related structural permeability are a key aspect in the migration of fluids through the continental crust. Therefore, the estimation of the hydraulic properties (palaeopermeability conditions; k) and the spatial distribution of the fracture mesh within the damage zone (DZ) are critical in the assessment of fault zones behavior for fluids. The study of the real spatial distribution of the veinlets of the fracture mesh (3D), feasible with the use of µCT analyses, is a first order factor to unravel both, the real structural permeability conditions of a fault-zone, and the validation of previous (and classical) estimations made in 2D analyses in thin-sections. This work shows the results of a fault-related fracture mesh and its 3D spatial distribution in the damage-zone of the Jorgillo Fault (JF), an ancient subvertical left-lateral strike-slip fault exposed in the Atacama Fault System in northern Chile. The JF is a ca. 20 km long NNW-striking strike-slip fault with sinistral displacement of ca. 4 km. The methodology consisted of drilling 5 mm vertically oriented plugs at several locations within the JF damage zone. Each specimen was scanned with an X-Ray µCT scanner, to assess the fracture mesh, with a voxel resolution of ca. 4.5 µm in the 3D reconstructed data. Tensor permeability modeling, using Lattice-Boltzmann Method, through the segmented microfracture mesh show GMkmin (geometric mean values) of 2.1x10-12 and 9.8x10-13 m2, and GMkmax of 6.4x10-12 and 2.1x10-12 m2. A high degree of anisotropy of the DZ permeability tensor both sides of the JF (eastern and western side, respectively) is observed, where the k values in the kmax plane are 2.4 and 1.9 times higher than the kmin direction at the time of fracture sealing. This style of anisotropy is consistent with the obtained for bedded sandstones supporting the idea that damage zones have an analogous effect - but vertically orientated - on bulk permeability (in low porosity rocks) as

  1. Reconstructing the magnitude and timing of late Pleistocene and Holocene strike-slip events within the Marlborough Fault Zone, New Zealand

    Science.gov (United States)

    Rhodes, Ed; Dolan, James; Van Dissen, Russ; Langridge, Rob; Zinke, Rob; Hatem, Alex; McGuire, Chris; Brown, Nathan

    2017-04-01

    In most instances, information about the timing of pre-historic earthquake events comes from palaeoseismic trenches located within sediments that were deposited gradually and are close to the fault. Earthquake events are recognised by disturbed stratigraphy, and the timing provided by radiocarbon dating of organic materials that constrain the youngest disturbances for each event. In contrast, fault slip rates are typically derived from the dating of geomorphic features that are offset by one or more slip events. In this latter case, it is often hard to locate suitable organic material for dating these features which often comprise fluvial terraces or channels, and a variety of alternative chronological approaches has been taken including the use of terrestrial cosmogenic nuclides (TCNs; 10Be, 36Cl), U-series dating of carbonate overgrowths on pebbles, and/or luminescence dating of sediments. Using luminescence dating based on single grains of K-feldspar and a post-IR IRSL (Infra-Red Stimulated Luminescence) measurement protocol, we have been able to control the age of several offset terrace units from a number of major strike slip faults of the Marlborough Fault Zone, New Zealand. In the past, arguments concerning the selection of which geomorphic terrace feature to date have been presented, and typically a single age estimate, or small number of dates were used to constrain the derived slip rate. In the Marlborough region, we have sampled several locations characterised by multiple fluvial terraces dating from the late Glacial period (c. 16,000 years ago) through the Holocene. By using a high sampling density involving multiple age estimates within each terrace, dating each one of the terraces, and applying a Bayesian statistical approach to constrain the age of deposition and incision events, we are able to approach a situation where we can derive slip-per-event data and event timing from the same dataset. This can overcome problems of relating observed slip

  2. Structural setting and kinematics of Nubian fault system, SE Western Desert, Egypt: An example of multi-reactivated intraplate strike-slip faults

    Science.gov (United States)

    Sakran, Shawky; Said, Said Mohamed

    2018-02-01

    Detailed surface geological mapping and subsurface seismic interpretation have been integrated to unravel the structural style and kinematic history of the Nubian Fault System (NFS). The NFS consists of several E-W Principal Deformation Zones (PDZs) (e.g. Kalabsha fault). Each PDZ is defined by spectacular E-W, WNW and ENE dextral strike-slip faults, NNE sinistral strike-slip faults, NE to ENE folds, and NNW normal faults. Each fault zone has typical self-similar strike-slip architecture comprising multi-scale fault segments. Several multi-scale uplifts and basins were developed at the step-over zones between parallel strike-slip fault segments as a result of local extension or contraction. The NNE faults consist of right-stepping sinistral strike-slip fault segments (e.g. Sin El Kiddab fault). The NNE sinistral faults extend for long distances ranging from 30 to 100 kms and cut one or two E-W PDZs. Two nearly perpendicular strike-slip tectonic regimes are recognized in the NFS; an inactive E-W Late Cretaceous - Early Cenozoic dextral transpression and an active NNE sinistral shear.

  3. Strike-slip tectonics during rift linkage

    Science.gov (United States)

    Pagli, C.; Yun, S. H.; Ebinger, C.; Keir, D.; Wang, H.

    2017-12-01

    The kinematics of triple junction linkage and the initiation of transforms in magmatic rifts remain debated. Strain patterns from the Afar triple junction provide tests of current models of how rifts grow to link in area of incipient oceanic spreading. Here we present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary deformation in Afar is accommodated primarily by extensional tectonics in the Red Sea and Gulf of Aden rifts, and does not require large rotations about vertical axes (bookshelf faulting). Additionally, models of stress changes and seismicity induced by recent dykes in one sector of the Afar triple junction provide poor fit to the observed strike-slip earthquakes. Instead we explain these patterns as rift-perpendicular shearing at the tips of spreading rifts where extensional strains terminate against less stretched lithosphere. Our results demonstrate that rift-perpendicular strike-slip faulting between rift segments achieves plate boundary linkage during incipient seafloor spreading.

  4. Propagation of strike-slip faults across Holocene volcano-sedimentary deposits, Pasto, Colombia

    Science.gov (United States)

    Rovida, Andrea; Tibaldi, Alessandro

    2005-10-01

    This study contributes to the understanding of shear failure development on the basis of macroscopic field data collected in latest Pleistocene-Holocene pyroclastic and fluvio-lacustrine deposits in the Pasto Valley, SW Colombia. Here there is a pervasive system of microfaults and joints. Right-lateral strike-slip microfaults strike N065°, whereas left-lateral strike-slip microfaults strike N120°. Three main joint sets strike N, N065° and N020° in decreasing order of frequency. Stress computation gives a horizontal σ1 trending ˜N060° and a horizontal σ3 trending ˜N150°, consistent with earthquake focal mechanisms and stress inversion of main faults. Synthetic shears dominate resulting from nucleation of older cracks. In the basement cropping out northeast of Pasto, the NE- to ENE-striking Buesaco, Aranda and Pasto Faults show evidence of latest Pleistocene-Holocene right-lateral strike-slip motions. The structures in the Pasto Valley can be interpreted as a Mode III damage zone representing the up-dip propagation of the main faults across the young volcano-sedimentary deposits.

  5. Mesozoic strike-slip movement of the Dunhua-Mishan Fault Zone in NE China: A response to oceanic plate subduction

    Science.gov (United States)

    Liu, Cheng; Zhu, Guang; Zhang, Shuai; Gu, Chengchuan; Li, Yunjian; Su, Nan; Xiao, Shiye

    2018-01-01

    The NE-striking Dunhua-Mishan Fault Zone (DMFZ) is one of two branches of the continental-scale sinistral Tan-Lu Fault Zone in NE China. The field data presented here indicate that the ca. 1000 km long DMFZ records two phases of sinistral faulting. The structures produced by these two phases of faulting include NE-SW-striking ductile shear belts and brittle faults, respectively. Mylonite-hosted microstructures and quartz c-axis fabrics suggest deformation temperatures of 450 °C-500 °C for the ductile shear belts. Combining new zircon U-Pb dates for 14 igneous rock samples analyzed during this study with the geology of this region indicates these shear belts formed during the earliest Early Cretaceous. This phase of sinistral displacement represents the initial formation of the DMFZ in response to the northward propagation of the Tan-Lu Fault Zone into NE China. A phase of Early Cretaceous rifting was followed by a second phase of sinistral faulting at 102-96 Ma, as evidenced by our new U-Pb ages for associated igneous rocks. Combining our new data with the results of previous research indicates that the DFMZ records a four-stage Cretaceous evolutionary history, where initial sinistral faulting at the beginning of the Early Cretaceous gave way to rifting during the rest of the Early Cretaceous. This was followed by a second phase of sinistral faulting at the beginning of the Late Cretaceous and a second phase of local rifting during the rest of the Late Cretaceous. The Cretaceous evolution of the DMFZ records the synchronous tectonic evolution of the NE China continent bordering the Pacific Ocean. Two phases of regional N-S compression generated the two phases of sinistral faulting within the DMFZ, whereas two-stage regional extension generated the two phases of rifting. The two compressive events were the result of the rapid low-angle subduction of the Izanagi and Pacific plates, whereas the two-stage extension was caused by the roll-back of these respective

  6. A new perspective on the significance of the Ranotsara shear zone in Madagascar

    DEFF Research Database (Denmark)

    Schreurs, Guido; Giese, Jörg; Berger, Alfons

    2010-01-01

    The Ranotsara shear zone in Madagascar has been considered in previous studies to be a >350-km-long, intracrustal strike-slip shear zone of Precambrian/Cambrian age. Because of its oblique strike to the east and west coast of Madagascar, the Ranotsara shear zone has been correlated with shear zones...... only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of E-W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar Block during a late phase of the Neoproterozoic/Cambrian East...... is not a megascale intracrustal strike-slip shear zone that crosscuts the entire basement of southern Madagascar. It can therefore not be used as a piercing point in Gondwana reconstructions...

  7. A preliminary study on surface ground deformation near shallow foundation induced by strike-slip faulting

    Science.gov (United States)

    Wong, Pei-Syuan; Lin, Ming-Lang

    2016-04-01

    According to investigation of recent earthquakes, ground deformation and surface rupture are used to map the influenced range of the active fault. The zones of horizontal and vertical surface displacements and different features of surface rupture are investigated in the field, for example, the Greendale Fault 2010, MW 7.1 Canterbury earthquake. The buildings near the fault rotated and displaced vertically and horizontally due to the ground deformation. Besides, the propagation of fault trace detoured them because of the higher rigidity. Consequently, it's necessary to explore the ground deformation and mechanism of the foundation induced by strike-slip faulting for the safety issue. Based on previous study from scaled analogue model of strike-slip faulting, the ground deformation is controlled by material properties, depth of soil, and boundary condition. On the condition controlled, the model shows the features of ground deformation in the field. This study presents results from shear box experiment on small-scale soft clay models subjected to strike-slip faulting and placed shallow foundations on it in a 1-g environment. The quantifiable data including sequence of surface rupture, topography and the position of foundation are recorded with increasing faulting. From the result of the experiment, first en echelon R shears appeared. The R shears rotated to a more parallel angle to the trace and cracks pulled apart along them with increasing displacements. Then the P shears crossed the basement fault in the opposite direction appears and linked R shears. Lastly the central shear was Y shears. On the other hand, the development of wider zones of rupture, higher rising surface and larger the crack area on surface developed, with deeper depth of soil. With the depth of 1 cm and half-box displacement 1.2 cm, en echelon R shears appeared and the surface above the fault trace elevated to 1.15 mm (Dv), causing a 1.16 cm-wide zone of ground-surface rupture and deformation

  8. The Mechanics, Geometry and Distribution of Strike Slip Faults in a Fold and Thrust Belt, County Clare, Ireland

    Science.gov (United States)

    Nenna, F. A.; Aydin, A.

    2010-12-01

    Fundamental structures such as opening mode joints and veins, and closing mode pressure solution seams (PSSs) can form dense orthogonal arrays in collisional deformation belts and play important roles in the initiation and development of larger scale faults. We describe the deformation processes and the evolution of fault architecture using systematic documentation of field observations from arrays of strike-slip faults in the Carboniferous Ross Sandstone. This unit is exposed on the Loop Head Peninsula, County Clare, Ireland and was subject to compressive stresses associated with the Variscan orogeny at the end of the Carboniferous producing broad regional east-west trending folds and also tight low-amplitude folds cored by thrust faults. Near these faults, orthogonal sets of PSSs and joints/veins form contemporaneous arrays with pressure solution seams that are sub-parallel to the thrust fault traces and fold axes. A stress or material rotation during the Variscan Orogeny (or perhaps a major second stage of deformation either in late phase of the orogeny or post-orogeny) has lead to left-lateral shear of the PSSs evidenced by pressure solution splays and pull-aparts between their sheared segments, and right-lateral shear on the joints/veins evidenced by splay fractures. The splays of the sheared joints are in the same orientation of the joints in the pull-aparts of the sheared PSSs with which they merge. This indicates that the shearing of the joints/veins and the PSSs was likely to have occurred simultaneously under the same remote loading conditions. With increased shear, extensive splay fractures and pull-apart networks form weak damage zones through which strike-slip faults systems develop with slip of up to 2km. As a higher proportion of the shear is resolved on the joint system than that of the PSS system, the more prominent strike-slip faults are sub-parallel to or slightly inclined to the pre-existing joint/vein set and have a right-lateral sense of slip

  9. Intra-Continental Deformation by Mid-Crustal Shearing and Doming in a Cenozoic Compressive Setting Along the Ailao Shan-Red River Shear Zone

    Science.gov (United States)

    Zhang, B.

    2016-12-01

    Large-scale lateral strike-slip shear zones have been a key point in the debate about the deformation mechanisms of Asia in response to the India-Asia collision. The exhumed gneiss has been attributed to lateral strike-slip shear zone. This hypothesis has been challenged by recent discoveries indicating that a contractional doming deformation prior to the initiation of lateral strike-slip shearing. The Cenozoic Xuelong Shan antiformal dome is located at the northern segment of the Ailao Shan-Red River shear zone. Subhorizontal foliation in the gneiss core are recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagated into greenschist facies in the mantling schist and strike-slip shear zone. Quartz CPOs and opening angles of crossed girdle fabrics in quartz suggest that the deformation temperatures increased with increasing structural depth from 300-500 °C in the mantling schist to ≥650 °C in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which ranges from garnet + amphibole + biotite + sillimanite + rutite + feldspar in the core to garnet + staurolite + biotite + epidote + muscovite within the limb units. Five-stage deformation is identified: (1) a broad top-to-NE shear in the subhorizontal level (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2-D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The antiformal dome formation had been roughly coeval with top-to-NE ductile shearing in the mid-crust at 32 Ma or earlier. The geometries of the antiformal dome in the Xuelong Shan dome are similar to those associated with the antiform in the Dai Nui Con Voi, Diancang Shan and Ailao Shan zones. It is likely that the complex massifs, which define a regional linear gneiss dome zone in Cenozoic intra

  10. Analog modeling of strike-slip surface ruptures: Implications for Greendale Fault (New Zealand) mechanics and paleoseismology

    Science.gov (United States)

    Sasnett, P.; Quigley, M.; Cruden, A. R.; Boutelier, D. A.; Villamor, P.

    2013-12-01

    Analog modeling of strike-slip faulting provides insight into the development and behavior of surface ruptures with progressive slip, with relevance for understanding how coseismic displacements from fault ruptures are recorded in paleoseismic trenches. Patterns of surface deformation were investigated in analogue experiments using cohesive and non-cohesive granular materials above a vertical, planar, strike-slip basement fault. Surface deformation during the experiments was monitored by 3D PIV (Particle Imaging Velocimetry) and 2D time-lapse photography. Analysis of the experiments focused on fault zone morphology and development, as well as comparisons between the models and surface deformation observed along the Greendale Fault that resulted from the 2010 Darfield earthquake, New Zealand. Complex surface rupture patterns with similar characteristics to the Greendale Fault (en echelon fractures, Riedel shears, pop-up structures, etc.) were generated by a simple fault plane of uniform dip, slip, and frictional properties. The main controls on surface rupture morphology were found to be the properties and thickness of the overburden, the nature of the material surface, and the overall displacement of the underlying fault. Mapping the evolution of fracture patterns with progressive shear strain reveals that Riedel shears, striking 0-30° from the underlying basement fault, are more frequently reactivated during multiple displacement (earthquake) cycles, and are thus most likely to provide reliable paleoseismic records. This information will assist in the identification of suitable locations for paleoseismic trenches and in the interpretation of trench records from the Greendale Fault and other active, strike-slip faults in analogous geologic settings. The results also highlight the tendency of trenching studies of faults of this type to underestimate the number of and displacements on previous ruptures, which potentially leads to an underestimate of the magnitude

  11. How seismicity impacts the evolution and branching of strike-slip faults

    Science.gov (United States)

    Preuss, S.; van Dinther, Y.; Ampuero, J. P.; Herrendoerfer, R.; Gerya, T.

    2017-12-01

    Strike-slip fault systems are capable of producing large earthquakes on both their main fault and on secondary and potentially unknown faults. A recent example is the 2016 Mw 7.8 Kaikōura earthquake that resulted in surface ruptures along at least 12 major crustal faults. Strike-slip faults are surrounded by inelastic off-fault deformation zones whose displacement accounts for up to 60% of the total displacement. Secondary faults in California accommodate up to 43% of the total fault slip rate of mapped faults taken from the SCEC catalog, while unknown faults arguably accommodate up to 30% of the long-term strain. To better understand these complexities and the long-term evolution of branching fault structures, we quantify the parameters influencing branching structure with a particular focus on the role of seismicity. We incorporate the relevant dynamics of both long-term fault evolution and short-term seismogenesis using the continuum visco-elasto-plastic tools of Seismo-Thermo-Mechanical (STM) modeling approach (van Dinther et al., 2013, Herrendörfer et al., in prep). Long-term fault evolution is governed by Drucker-Prager plasticity and plastic strain weakening of cohesion, while frictional weakening and rapid slip is governed by either strongly rate-dependent (RDF) or rate-and-state friction (RSF). We use a 2D, plane view, natural scale model setup (1200 km x 1000 km), which contains the end of a dextral mature strike-slip fault on one side. Episodic slip events on this pre-existing fault patch propagate into the undamaged host rock. As faults grow they develop a fan-like plastic strain envelope, whose width keeps growing with fault length and accumulated on-fault slip. We interpret this zone as a splay-fault network, which is typically seen ahead of propagating fault tips. We analyze the evolving faults in terms of dissipated strain energy GC, accumulated slip D and fault length L. Results show that a single event is capable of producing a several hundreds

  12. Analysis of the growth of strike-slip faults using effective medium theory

    Energy Technology Data Exchange (ETDEWEB)

    Aydin, A.; Berryman, J.G.

    2009-10-15

    Increases in the dimensions of strike-slip faults including fault length, thickness of fault rock and the surrounding damage zone collectively provide quantitative definition of fault growth and are commonly measured in terms of the maximum fault slip. The field observations indicate that a common mechanism for fault growth in the brittle upper crust is fault lengthening by linkage and coalescence of neighboring fault segments or strands, and fault rock-zone widening into highly fractured inner damage zone via cataclastic deformation. The most important underlying mechanical reason in both cases is prior weakening of the rocks surrounding a fault's core and between neighboring fault segments by faulting-related fractures. In this paper, using field observations together with effective medium models, we analyze the reduction in the effective elastic properties of rock in terms of density of the fault-related brittle fractures and fracture intersection angles controlled primarily by the splay angles. Fracture densities or equivalent fracture spacing values corresponding to the vanishing Young's, shear, and quasi-pure shear moduli were obtained by extrapolation from the calculated range of these parameters. The fracture densities or the equivalent spacing values obtained using this method compare well with the field data measured along scan lines across the faults in the study area. These findings should be helpful for a better understanding of the fracture density/spacing distribution around faults and the transition from discrete fracturing to cataclastic deformation associated with fault growth and the related instabilities.

  13. Transpressional segment boundaries in strike-slip fault systems offshore southern California: Implications for fluid expulsion and cold seep habitats

    Science.gov (United States)

    Maloney, Jillian M.; Grupe, Benjamin M.; Pasulka, Alexis L.; Dawson, Katherine S.; Case, David H.; Frieder, Christina A.; Levin, Lisa A.; Driscoll, Neal W.

    2015-05-01

    The importance of tectonics and fluid flow in controlling cold seep habitats has long been appreciated at convergent margins but remains poorly understood in strike-slip systems. Here we present geophysical, geochemical, and biological data from an active methane seep offshore from Del Mar, California, in the inner California borderlands (ICB). The location of this seep appears controlled by localized transpression associated with a step in the San Diego Trough fault zone and provides an opportunity to examine the interplay between fluid expulsion and restraining step overs along strike-slip fault systems. These segment boundaries may have important controls on seep locations in the ICB and other margins characterized by strike-slip faulting (e.g., Greece, Sea of Marmara, and Caribbean). The strike-slip fault systems offshore southern California appear to have a limited distribution of seep sites compared to a wider distribution at convergent plate boundaries, which may influence seep habitat diversity and connectivity.

  14. Modeling the evolution of the lower crust with laboratory derived rheological laws under an intraplate strike slip fault

    Science.gov (United States)

    Zhang, X.; Sagiya, T.

    2015-12-01

    The earth's crust can be divided into the brittle upper crust and the ductile lower crust based on the deformation mechanism. Observations shows heterogeneities in the lower crust are associated with fault zones. One of the candidate mechanisms of strain concentration is shear heating in the lower crust, which is considered by theoretical studies for interplate faults [e.g. Thatcher & England 1998, Takeuchi & Fialko 2012]. On the other hand, almost no studies has been done for intraplate faults, which are generally much immature than interplate faults and characterized by their finite lengths and slow displacement rates. To understand the structural characteristics in the lower crust and its temporal evolution in a geological time scale, we conduct a 2-D numerical experiment on the intraplate strike slip fault. The lower crust is modeled as a 20km thick viscous layer overlain by rigid upper crust that has a steady relative motion across a vertical strike slip fault. Strain rate in the lower crust is assumed to be a sum of dislocation creep and diffusion creep components, each of which flows the experimental flow laws. The geothermal gradient is assumed to be 25K/km. We have tested different total velocity on the model. For intraplate fault, the total velocity is less than 1mm/yr, and for comparison, we use 30mm/yr for interplate faults. Results show that at a low slip rate condition, dislocation creep dominates in the shear zone near the intraplate fault's deeper extension while diffusion creep dominates outside the shear zone. This result is different from the case of interplate faults, where dislocation creep dominates the whole region. Because of the power law effect of dislocation creep, the effective viscosity in the shear zone under intraplate faults is much higher than that under the interplate fault, therefore, shear zone under intraplate faults will have a much higher viscosity and lower shear stress than the intraplate fault. Viscosity contract between

  15. The role of post-collisional strike-slip tectonics in the geological evolution of the late Neoproterozoic volcano-sedimentary Guaratubinha Basin, southern Brazil

    Science.gov (United States)

    Barão, Leonardo M.; Trzaskos, Barbara; Vesely, Fernando F.; de Castro, Luís Gustavo; Ferreira, Francisco J. F.; Vasconcellos, Eleonora M. G.; Barbosa, Tiago C.

    2017-12-01

    The Guaratubinha Basin is a late Neoproterozoic volcano-sedimentary basin included in the transitional-stage basins of the South American Platform. The aim of this study is to investigate its tectonic evolution through a detailed structural analysis based on remote sensing and field data. The structural and aerogeophysics data indicate that at least three major deformational events affected the basin. Event E1 caused the activation of the two main basin-bounding fault zones, the Guaratubinha Master Fault and the Guaricana Shear Zone. These structures, oriented N20-45E, are associated with well-defined right-lateral to oblique vertical faults, conjugate normal faults and vertical flow structures. Progressive transtensional deformation along the two main fault systems was the main mechanism for basin formation and the deposition of thick coarse-grained deposits close to basin-borders. The continuous opening of the basin provided intense intermediate and acid magmatism as well as deposition of volcaniclastic sediments. Event E2 characterizes generalized compression, recorded as minor thrust faults with tectonic transport toward the northwest and left-lateral activation of the NNE-SSW Palmital Shear Zone. Event E3 is related to the Mesozoic tectonism associated with the South Atlantic opening, which generated diabase dykes and predominantly right-lateral strike-slip faults oriented N10-50W. Its rhomboidal geometry with long axis parallel to major Precambrian shear zones, the main presence of high-angle, strike-slip or oblique faults, the asymmetric distribution of geological units and field evidence for concomitant Neoproterozoic magmatism and strike-slip movements are consistent with pull-apart basins reported in the literature.

  16. Shell Tectonics: A Mechanical Model for Strike-slip Displacement on Europa

    Science.gov (United States)

    Rhoden, Alyssa Rose; Wurman, Gilead; Huff, Eric M.; Manga, Michael; Hurford, Terry A.

    2012-01-01

    We introduce a new mechanical model for producing tidally-driven strike-slip displacement along preexisting faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history.

  17. Neotectonics of a subduction/strike-slip transition: the northeastern Dominican Republic

    Energy Technology Data Exchange (ETDEWEB)

    Winslow, M.A.; McCann, W.R.

    1985-01-01

    The Septentrional fault system in the northeastern Dominican Republic marks the zone where the North American-Carribean plate boundary is evolving from subduction to strike-slip motion, and where terranes appear to be forming and migrating laterally in a subduction complex/forearc region. On the Island of Hispaniola, slip vectors are oblique to the strike of the Puerto Rico trench, and oblique subduction thrusts the upper plate over normal seafloor. The offshore geology and seismicity of the northern Caribbean suggest that uplift, broad crustal warping, thrusting, and strike-slip faulting (ie. collisional tectonics) should be present in the northern part of the Dominican Republic. The high topography (>1000m), high levels of seismicity, and large earthquakes support the hypothesis of contemporary deformation in Hispaniola. In this region, the subduction regime dies out toward the west, and deformation is transferred to onshore, oblique-slip faults. As this change in tectonic style has occurred in Neogene to Recent times, we are investigating the modern evolution of a plate boundary. We have already documented: (1) the presence of a strike-slip faulting in the northeastern Dominican Republic; (2) an anomalous push-up structure; and (3) a region of numerous splay faults. In conclusion, recent seismicity suggest a wide zone of deformation and variations in interplate motions near Hispaniola. This island lies at the western limit of active underthrusting and at the eastern limit of onshore faulting, i.e., at an important transition from a subduction to strike-slip regime.

  18. Geological and structural characterization and microtectonic study of shear zones Colonia

    International Nuclear Information System (INIS)

    Gianotti, V.; Oyhantcabal, P.; Spoturno, J.; Wemmer, K.

    2010-01-01

    The “Colonia Shear Zone System”, characterized by a transcurrent system of predominant sinistral shear sense, is defined by two approximately parallel shear zones, denominated Isla San Gabriel-Juan Lacaze Shear Zone (ISG-JL S.Z.) and Islas de Hornos-Arroyo Riachuelo Shear Zone (IH-AºR S. Z.). Represented by rocks with ductile and brittle deformation, are defined as a strike slip fault system, with dominant subvertical foliation orientations: 090-100º (dip-direction 190º) and 090-100º (dip-direction 005º). The K/Ar geochronology realized, considering the estimates temperatures conditions for shear zones (450-550º), indicate that 1780-1812 Ma should be considered a cooling age and therefore a minimum deformation age. The observed microstructures suggest deformation conditions with temperatures between 450-550º overprinted by cataclastic flow structures (reactivation at lower temperature)

  19. San Andreas-sized Strike-slip Fault on Europa

    Science.gov (United States)

    1998-01-01

    This mosaic of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, about the size of the California portion of the San Andreas fault, which runs from the California-Mexico border north to the San Francisco Bay. In a strike-slip fault, two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. Overall motion along the fault seems to have followed a continuous narrow crack along the feature's entire length, with a path resembling steps on a staircase crossing zones that have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. The fault's opposite sides can be reconstructed like a puzzle, matching the shape of the sides and older, individual cracks and ridges broken by its movements. [figure removed for brevity, see original site] The red line marks the once active central crack of the fault. The black line outlines the fault zone, including material accumulated in the regions which have been pulled apart. Bends in the fault have allowed the surface to be pulled apart. This process created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling-apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, in Death Valley and the Dead Sea. In those cases, the pulled-apart regions can include upwelled materials, but may be filled mostly by sedimentary and eroded material from above. One theory is that fault motion on Europa is induced by the pull of variable daily tides generated by Jupiter's gravitational tug on Europa. Tidal tension opens the fault and

  20. Fabric evolution of polydeformed orthogneisses and quartzites along the Curitiba Shear Zone, Curitiba Domain, Southern Brazil

    Science.gov (United States)

    Cabrita, Dina; Salamuni, Eduardo; Lagoeiro, Leonardo

    2017-08-01

    In Southern Brazil there is a series of strike-slip shear zones that represent the late-collisional event of Western Gondwana in the Neoproterozoic-Eopaleozoic transition. The Curitiba Shear Zone (CSZ) is a part of this strike-slip regime separating two different domains: the supracrustal metasedimentary rocks and the basement composed of orthogneiss, migmatite and quartzite. The absence of detailed structural data for this discontinuity has motivated us to study this important part of the geology of southern of Brazil. The main purpose of this work is the characterization of meso and microstructures and determination of crystallographic fabric of quartz in orthogneisses and quartzites along the CSZ southern block. Structural data suggest that the CSZ consists of one ductile-brittle strike-slip deformation phase leading to the deformation of orthogneiss and quartzites of the Atuba Complex. The ductile regime was responsible for the formation of low-grade mylonite in greenschist facies. Crystallographic texture indicate a restricted recrystallization of quartz mainy via dislocation creep through activation ob basal slip system. The brittle regime led to the formation of cataclasites, faults and joints, with a mean orientation of N50E/75SE and N33E/80SE, respectively. Extensive dissolution-precipitation creep affected the rocks and infilled veins with carbonate and quartz.

  1. Sense of shear and displacement estimates in the Abeibara-Rarhous late Pan-African shear zone, Adrar des Iforas, Mali

    Science.gov (United States)

    Boullier, Anne-Marie

    The late Pan-African Abeibara-Rarhous shear zone in the Adrar des Iforas (Mali) is described and studied with the aim of defining the direction, sense of movement and amount of displacement along the zone. It is a strike-slip shear zone, the dextral sense of which is demonstrated at the scale of the map by the rotation of the related mylonitic foliation and at the scale of the thin section with characteristic microstructures. Preferred orientation of quartz c-axes is tentatively used; three quartz-rich samples of 35% or more quartz indicate dextral strike-slip movement, but other samples do not show preferred orientation of quartz c-axes. Strain measurements have been performed on one half of the shear zone using established techniques and a new technique using the thickness of mylonitic layering. The results vary along the length of the shear zone when using the same method and for the same cross-section when using the three methods together. A mean value of 4 km is obtained for total displacement which is low when considering the apparent width of the shear zone. This result is discussed in view of the assumptions involved in the strain estimation. The tectonic history of the Abeibara-Rarhous shear zone and its significance in the Trans-Saharan Pan-African collisional belt are discussed.

  2. Incipient Evolution of the Eastern California Shear Zone through a Transpressional Zone along the San Andreas Fault in the San Bernardino Mountains, California

    Science.gov (United States)

    Cochran, W. J.; Spotila, J. A.

    2017-12-01

    Measuring long-term accumulation of strike-slip displacements and transpressional uplift is difficult where strain is accommodated across wide shear zones, as opposed to a single major fault. The Eastern California Shear Zone (ECSZ) in southern California accommodates dextral shear across several strike-slip faults, and is potentially migrating and cutting through a formerly convergent zone of the San Bernardino Mountains (SBM). The advection of crust along the San Andreas fault to the SE has forced these two tectonic regimes into creating a nexus of interacting strike-slip faults north of San Gorgonio Pass. These elements make this region ideal for studying complex fault interactions, evolving fault geometries, and deformational overprinting within a wide shear zone. Using high-resolution topography and field mapping, this study aims to test whether diffuse, poorly formed strike-slip faults within the uplifted SBM block are nascent elements of the ECSZ. Topographic resolution of ≤ 1m was achieved using both lidar and UAV surveys along two Quaternary strike-slip faults, namely the Lake Peak fault and Lone Valley faults. Although the Lone Valley fault cuts across Quaternary alluvium, the geomorphic expression is obscured, and may be the result of slow slip rates. In contrast, the Lake Peak fault is located high elevations north of San Gorgonio Peak in the SBM, and displaces Quaternary glacial deposits. The deposition of large boulders along the escarpment also obscures the apparent magnitude of slip along the fault. Although determining fault offset is difficult, the Lake Peak fault does display evidence for minor right-lateral displacement, where the magnitude of slip would be consistent with individual faults within the ECSZ (i.e. ≤ 1 mm/yr). Compared to the preservation of displacement along strike-slip faults located within the Mojave Desert, the upland region of the SBM adds complexity for measuring fault offset. The distribution of strain across the entire

  3. The morphology of strike-slip faults - Examples from the San Andreas Fault, California

    Science.gov (United States)

    Bilham, Roger; King, Geoffrey

    1989-01-01

    The dilatational strains associated with vertical faults embedded in a horizontal plate are examined in the framework of fault kinematics and simple displacement boundary conditions. Using boundary element methods, a sequence of examples of dilatational strain fields associated with commonly occurring strike-slip fault zone features (bends, offsets, finite rupture lengths, and nonuniform slip distributions) is derived. The combinations of these strain fields are then used to examine the Parkfield region of the San Andreas fault system in central California.

  4. A PHYSICAL MODEL OF THE EFFECT OF A SHALLOW WEAK LAYER ON STRONG GROUND MOTION FOR STRIKE-SLIP RUPTURES

    Energy Technology Data Exchange (ETDEWEB)

    JAMES N. BRUNE AND ABDOLRASOOL ANOOSHEHPOOR

    1998-02-23

    We report results of foam-rubber modeling of the effect of a shallow weak layer on ground motion from strike-slip ruptures. Computer modeling of strong ground motion from strike-slip earthquakes has involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault (e.g., fixing the slip to be zero along the upper 2 kilometers of the fault plane) in order to match certain strong motion accelerograms. Most modeling studies of earthquake strong ground motion have used what is termed kinematic dislocation modeling. In kinematic modeling the time function for slip on the fault is prescribed, and the response of the layered medium is calculated. Unfortunately, there is no guarantee that the model and the prescribed slip are physically reasonable unless the true nature of the medium and its motions are known ahead of time. There is good reason to believe that in many cases faults are weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes. Physical models of faulting, as distinct from numerical or mathematical models, are guaranteed to obey static and dynamic mechanical laws. Foam-rubber modeling studies have been reported in a number of publications. The object of this paper is to present results of physical modeling using a shallow weak layer, in order to verify the physical basis for assuming a long rise time and a reduced high frequency pulse for the slip on the shallow part of faults. It appears a 2-kilometer deep, weak zone along strike-slip faults could indeed reduce the high frequency energy radiated from shallow slip, and that this effect can best be represented by superimposing a small amplitude, short rise-time pulse at the onset of a much longer rise-time slip. A weak zone was modeled by inserting weak plastic layers of a few inches in thickness into the foam rubber model. For the 15 cm weak zone the average

  5. Lower Miocene coeval thrusting and strike-slip faulting in the Western Betics

    Science.gov (United States)

    Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre

    2015-04-01

    In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper subduction plate deformation since 30 Ma. The western end of the system shows an arcuate geometry across the Gibraltar arc, the Betico-Rifean belt, in which the relationship between slab dynamics and onshore tectonics is poorly constrained. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1/ the Alboran Front limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts involving the Mesozoic cover of the Iberian margin (Subbetics Domain); 2/ the Alboran Internal Thrust allows the juxtaposition of a strongly attenuated lithosphere section, containing the large Ronda subcontinental mantle bodies, on top of crustal rocks. New structural data show that two major E-W strike-slip corridors controlled the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60° thrusts and N140° normal faults developed simultaneously during dextral strike-slip simple shear. The Alozaina piggy-back Basin, mainly formed by olistotromic deposits of Lower Miocene age, provides an age estimate for the continuous westward translation of the Alboran Domain, with reference to Iberia, that is accommodated mainly by an E-W lateral strike-slip ramp and a N60° frontal thrust ramp. In this context, a thrust sequence led to the piling up of thrust units in the Western Betics and to the crustal emplacement of the Ronda Peridotites bodies.

  6. Assemblage of strike-slip faults and tectonic extension and ...

    Indian Academy of Sciences (India)

    12

    and its effect on the productivity of the tight reservoirs. The study will not only guide. 95 the oil-gas ..... 5 Effect of tectonic extension and compression on coal reservoir productivity. 288. 5.1 Strike-slip compression and ..... staff of all the authors that cooperated in performing the analyses. We are also. 425 grateful to the ...

  7. Assemblage of strike-slip faults and tectonic extension and ...

    Indian Academy of Sciences (India)

    12

    Assemblage of strike-slip faults and tectonic. 1 extension and compression analysis: A case. 2 study of a Lower Permian commercial coal. 3 reservoir in China. 4. 5. Shuai Yina,*, Dawei Lvb, Zhonghu Wu c .... high-quality reservoirs, and tectonic action is a leading factor for oil and gas. 70 enrichment. Therefore, it is of great ...

  8. Source study of the Jan Mayen transform fault strike-slip earthquakes

    Science.gov (United States)

    Rodríguez-Pérez, Q.; Ottemöller, L.

    2014-07-01

    Seismic source parameters of oceanic transform zone earthquakes have been relatively poorly studied. Previous studies showed that this type of earthquakes has unique characteristics such as not only the relatively common occurrence of slow events with weak seismic radiation at high frequencies but also the occurrence of some events that have high apparent stress indicating strong high frequency radiation. We studied 5 strike-slip earthquakes in the Jan Mayen fracture zone with magnitudes in the range of 5.9 centroid time delay compared to other oceanic transform fault earthquakes.

  9. The 2015 M7.2 Sarez, Central Pamir, Earthquake And The Importance Of Strike-Slip Faulting In The Pamir Interior: Insights From Geodesy And Field Observations

    Science.gov (United States)

    Metzger, Sabrina; Schurr, Bernd; Ratschbacher, Lothar; Schöne, Tilo; Kufner, Sofia-Katerina; Zhang, Yong; Sudhaus, Henriette

    2017-04-01

    The Pamir mountain range, located in the Northwest of the India-Asia collision zone, accommodates approximately one third of the northward advance of the Indian continent at this longitude (i. e. ˜34 mm/yr) mostly by shortening at its northern thrust system. Geodetic and seismic data sets reveal here a narrow zone of high deformation and M7+ earthquakes of mostly thrust type with some dextral strike-slip faulting observed, too. The Pamir interior shows sinistral strike-slip and normal faulting indicating north-south compression and east-west extension. In this tectonic setting the two largest instrumentally recorded earthquakes, the M7+ 1911 and 2015 earthquake events in the central Pamir occurred with left-lateral shear along a NE-SW rupture plane. We present the co-seismic deformation field of the 2015 earthquake observed by radar satellite interferometry (InSAR), SAR amplitude pixel offsets and high-rate Global Positioning System (GPS). The InSAR and pixel offset results suggest a 50+ km long rupture with sinistral fault offsets at the surface of more than 2 m on a yet unmapped fault trace of the Sarez Karakul Fault System (SKFS). A distributed slip model with a data-driven slip patch resolution yields a sub-vertical fault plane with a strike of N39.5 degrees and a rupture area of ˜80 x 40 km with a maximum slip of 2 m in the upper 10 km of the crust near the surface rupture. Field observations collected some nine months after the earthquake confirm the rupture mechanism, surface trace location and fault offset measurements as constrained by geodetic data. Diffuse deformation was observed across a 1-2 km wide zone, hosting primary fractures sub-parallel to the rupture strike with offsets of 2 m and secondary, en echelon fractures including Riedel shears and hybrid fractures often related to gravitational mass movements. The 1911 and 2015 earthquakes demonstrate the importance of sinistral strike-slip faulting on the SKFS, contributing both to shear between the

  10. Aseismic strike-slip associated with the 2007 dike intrusion episode in Tanzania

    Science.gov (United States)

    Himematsu, Yuji; Furuya, Masato

    2015-08-01

    In July 2007, an earthquake swarm initiated in northern Tanzania near Lake Natron and lasted for about two months. Mt. Oldoinyo Lengai, located to the southwest of the swarm, began to erupt effusively about a month prior to the swarm, and increased its eruption intensity on September when the swarm almost ceased. Several previous studies have already reported the crustal deformation signals associated with the swarm using Interferometric Synthetic Aperture Radar (InSAR). However, nearly all the published data are based on the C-band ENVISAT/ASAR images acquired only from the descending path. We use the L-band ALOS/PALSAR images acquired from both ascending and descending paths, which allow us to examine the deformation signals in more detail. In addition to the InSAR data, we employ the offset-tracking technique to detect the signals along the azimuth direction. Using InSAR and offset-tracking data, we obtain the full 3D displacement fields associated with the episode. Besides the horizontal extension and subsidence signals due to the dike intrusion as already reported, the inferred full 3D displacements further indicate that the subsiding zone was horizontally moving by ~ 48 cm toward SSW. To explain the displacements, we performed fault source modeling, assuming an elastic half space. The fault slip distribution indicates that the contribution of the strike-slip component is about 20% of total moment release. Because almost all the focal mechanisms of earthquakes during the 2007 event indicate nearly pure normal faulting, aseismic strike-slip must have been responsible for the horizontal movement of the subsiding zone. The strike-slip at the shallowest depths suggests the presence of transtensive stress, which seems to be reasonable to generate the relay zones that are widely observed in the East African Rift. We also confirmed that the stress changes due to the dike intrusion were consistent with the inferred fault slip distributions.

  11. Inelastic off-fault response and three-dimensional dynamics of earthquake rupture on a strike-slip fault

    Science.gov (United States)

    Andrews, D.J.; Ma, Shuo

    2010-01-01

    Large dynamic stress off the fault incurs an inelastic response and energy loss, which contributes to the fracture energy, limiting the rupture and slip velocity. Using an explicit finite element method, we model three-dimensional dynamic ruptures on a vertical strike-slip fault in a homogeneous half-space. The material is subjected to a pressure-dependent Drucker-Prager yield criterion. Initial stresses in the medium increase linearly with depth. Our simulations show that the inelastic response is confined narrowly to the fault at depth. There the inelastic strain is induced by large dynamic stresses associated with the rupture front that overcome the effect of the high confining pressure. The inelastic zone increases in size as it nears the surface. For material with low cohesion (~5 MPa) the inelastic zone broadens dramatically near the surface, forming a "flowerlike" structure. The near-surface inelastic strain occurs in both the extensional and the compressional regimes of the fault, induced by seismic waves ahead of the rupture front under a low confining pressure. When cohesion is large (~10 MPa), the inelastic strain is significantly reduced near the surface and confined mostly to depth. Cohesion, however, affects the inelastic zone at depth less significantly. The induced shear microcracks show diverse orientations near the surface, owing to the low confining pressure, but exhibit mostly horizontal slip at depth. The inferred rupture-induced anisotropy at depth has the fast wave direction along the direction of the maximum compressive stress.

  12. San-in shear zone in southwest Japan, revealed by GNSS observations

    Science.gov (United States)

    Nishimura, Takuya; Takada, Youichiro

    2017-06-01

    A right-lateral shear zone in the San-in region, southwest Japan, has been proposed by previous geological and seismological studies. It locates 350 km north of the Nankai Trough, that is, the main plate boundary between the subducting Philippine Sea and overriding Amurian plates and presumably accommodates a part of the relative plate motion. We present a geodetic evidence of the proposed shear zone using GNSS velocity data. Distinct shear deformation is identified only between 132.5°E and 135°E along a coastline which is a part of the proposed shear zone, and we propose to call the geodetically identified shear zone as the San-in shear zone (SSZ). The SSZ is a concentrated deformation zone with a width of 50 km and can be modeled by a deep creep on a vertical strike slip fault with a creep rate of 5 mm/year. There are some active faults parallel and oblique to the overall trend of the SSZ, but no single active fault coincides with the SSZ. Lineaments of microseismicity and source faults of large earthquakes are almost oriented in NNW-SSE in the SSZ and oblique to the overall trend of the SSZ. They are interpreted as conjugate Riedel shears. Based on these geodetic, seismological, and geomorphological observations, we suggest that the SSZ is a developing and young shear zone in a geological time scale.[Figure not available: see fulltext.

  13. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    KAUST Repository

    Ruch, Joel

    2016-01-23

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic and structural field data along the strike-slip Central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion; consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activity steadily migrated eastward and currently focus on a 10 km long x 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter-term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the Central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  14. The Strike-slip Systems in Northern Venezuela Review of Neotectonic, Paleoseismological and Seismic Investigations

    Science.gov (United States)

    Audemard, F.; Schmitz, M.; Levander, A.

    2006-12-01

    The complex Caribbean-South America plate boundary zone in northern Venezuela, which extends from the Southern Caribbean Deformation Front in the north to the Guayana Shield in the south, is the result of stress transfer generated by the relative movement of 2 cm/a between both plates. The movement is active since Cretaceous time and progressively migrates from west to east, and the major movement is accommodated along a roughly 1000 km long strike-slip system in northern Venezuela, comprising the Oca-Ancon, San Sebastian and El Pilar right-lateral fault systems. Neotoectonic and paleoseismological investigations have been carried out during the last two decades, and recently have been complemented by research activities within the interdisciplinary projects BOLIVAR (Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region) and GEODINOS (Recent Geodynamics of the Northern Limit of the South American Plate). By means of geological, seismicity and structural seismic investigations, the structures of the strike- slip zones are investigated from their surface expression through the crust and into the upper mantle. High velocity zones are identified at crustal levels and near surface investigations give insight to the detailed tectonic structures. Contribution from GEODINOS (FONACIT-2002000478) and BOLIVAR working groups.

  15. Onset of aseismic creep on major strike-slip faults

    KAUST Repository

    Çakir, Ziyadin

    2012-10-02

    Time series analysis of spaceborne synthetic aperture radar (SAR) data, GPS measurements, and fi eld observations reveal that the central section of the Izmit (Turkey) fault that slipped with a supershear rupture velocity in the A.D. 1999, Mw7.4, Izmit earthquake began creeping aseismically following the earthquake. Rapid initial postseismic afterslip decayed logarithmically with time and appears to have reached a steady rate comparable to the preearthquake full fault-crossing rate, suggesting that it may continue for decades and possibly until late in the earthquake cycle. If confi rmed by future monitoring, these observations identify postseismic afterslip as a mechanism for initiating creep behavior along strike-slip faults. Long-term afterslip and/or creep has signifi cant implications for earthquake cycle models, recurrence intervals of large earthquakes, and accordingly, seismic hazard estimation along mature strike-slip faults, in particular for Istanbul which is believed to lie adjacent to a seismic gap along the North Anatolian fault in the Sea of Marmara. © 2012 Geological Society of America.

  16. Strike-slip and extrusion tectonics of the Greater Caucasus-Kopetdagh region

    Science.gov (United States)

    Kopp, M. L.

    2012-04-01

    In the Paleogene-Early Miocene, the areas of the modern Greater Caucasus and Kopetdagh were occupied by marginal seas (parts of the Paratethys intracontinental sea) inheriting the Cretaceous back-arc basins. In the Early Miocene, a collisional compression of the seas began at the time when the Arabian plate detached from Africa to move northward. The compression proceeded in a good accordance with the Arabia movement that was manifested in a general synchroneity of the Late Alpine orogenies in the Caucasus and Kopetdagh with the rifting and spreading phases in the Aden Gulf and the Red Sea. The earliest orogeny was the Styrian one of the terminal Early Miocene. It corresponds to the initial stage of the rift opening and was mostly pronounced in the east, in Kopetdagh and East Iran, where a recent structure has been formed by the initial Middle Miocene. In the Greater Caucasus, the Styrian deformations occurred in its central part only (i.e., in front of the Arabian plate northern tip) where the main Caucasian thrusts and conjugate asymmetrical megaanticline of the Central Caucasus were formed. An essential feature of the earliest, Styrian, structure of the whole Caucasus-Kopetdagh region was a series of regional right-lateral strike-slip faults. In the Kopetdagh, the strike-slips have no submeridional but northwestern direction although they occurred in the northern continuation of the submeridional right-lateral strike-slip faults framing the Lut block. In the Caucasus, they became even sublatitudinal, in parallel with the North Anatolian fault, thus constituting a single domain with the latter. So, the right-lateral strike-slip faults of East Iran, Kopetdagh, and the Caucasus compose an extensive arc convex to the north and appeared probably as a result of the right-lateral shear caused by the known counterclockwise rotation of the Arabian lithospheric plate. The Middle Miocene was characterized by a tectonic pause both in the Red Sea-Aden rift system and in the

  17. Rupture model of the 2015 M7.2 Sarez, Central Pamir, earthquake and the importance of strike-slip faulting in the Pamir interior

    Science.gov (United States)

    Metzger, S.; Schurr, B.; Schoene, T.; Zhang, Y.; Sudhaus, H.

    2016-12-01

    The Pamir mountain range, located in the Northwest of the India-Asia collision zone, accommodates approximately one third of the northward advance of the Indian continent at this longitude (i.e. 34 mm/yr) mostly by shortening at its northern thrust system. Geodetic and seismic data sets reveal here a narrow zone of high deformation and M7+ earthquakes of mostly thrust type with some dextral strike-slip faulting observed, too. The Pamir interior shows sinistral strike-slip and normal faulting indicating north-south compression and east-west extension. In this tectonic setting the two largest instrumentally recorded earthquakes, the M7+ 1911 and 2015 earthquake events in the central Pamir occurred with left-lateral shear along a NE-SW rupture plane. We present the co-seismic deformation field of the 2015 earthquake observed by Radar satellite interferometry (InSAR), SAR amplitude offsets and high-rate Global Positioning System (GPS). The InSAR and offset results reveal that the earthquake created a 50 km long surface rupture with maximum left-lateral offsets of more than two meters on a yet unmapped fault trace of the Sarez Karakul Fault System (SKFS). We further derive a distributed slip-model including a thorough model parameter uncertainty study. Using a two-step approach to first find the optimal rupture geometry and then invert for slip on discrete patches, we show that a data-driven patch resolution produces yields a better representation of the near-surface slip and an increased slip precision than a uniform patch approach without increasing the number of parameters and thus calculation time. Our best-fit model yields a sub-vertical fault plane with a strike of N39.5 degrees and a rupture area of 80 x 40 km2 with a maximum slip of 2 meters in the upper 10 km of the crust near the surface rupture. The 1911 and 2015 earthquakes demonstrate the importance of sinistral strike-slip faulting on the SKFS, contributing both to shear between the western and eastern

  18. Th-Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland

    Science.gov (United States)

    Bergemann, C.; Gnos, E.; Berger, A.; Whitehouse, M.; Mullis, J.; Wehrens, P.; Pettke, T.; Janots, E.

    2017-04-01

    Th-Pb age dating of zoned hydrothermal monazite from alpine-type fissures/clefts is a powerful tool for constraining polyphase deformation at temperatures below 350°C and presents an alternative to K/Ar and 40Ar/39Ar dating techniques for dating brittle tectonics. This study considers the relationship between cleft orientations in ductile shear zones and cleft mineral crystallization during subsequent brittle overprinting. In the Grimsel area, located in the Aar Massif of the Central Alps, horizontal clefts formed during a primary thrust dominated deformation, while younger and vertically oriented clefts developed during secondary strike-slip movements. The change is due to a switch in orientation between the principal stress axes σ2 and σ3. The transition is associated with monazite crystallization and chloritization of biotite at around 11.5 Ma. Quartz fluid inclusion data allow a link between deformation stages and temperatures to be established and indicate that primary monazite crystallization occurred in both cleft systems at 300-350°C. While cleft monazite crystallization ceases at 11 Ma in inactive shear zones, monazite growth, and/or dissolution-reprecipitation continues under brittle deformation conditions in vertical clefts during later deformation until 7 Ma. This younger shear zone activity occurs in association with dextral strike-slip movement of the Rhone-Simplon fault system. With the exception of varying Th/U values correlated with the degree of oxidation, there is only limited compositional variation in the studied cleft monazites.

  19. Role of N-S strike-slip faulting in structuring of north-eastern Tunisia; geodynamic implications

    Science.gov (United States)

    Arfaoui, Aymen; Soumaya, Abdelkader; Ben Ayed, Noureddine; Delvaux, Damien; Ghanmi, Mohamed; Kadri, Ali; Zargouni, Fouad

    2017-05-01

    Three major compressional events characterized by folding, thrusting and strike-slip faulting occurred in the Eocene, Late Miocene and Quaternary along the NE Tunisian domain between Bou Kornine-Ressas-Msella and Cap Bon Peninsula. During the Plio-Quaternary, the Grombalia and Mornag grabens show a maximum of collapse in parallelism with the NNW-SSE SHmax direction and developed as 3rd order distensives zones within a global compressional regime. Using existing tectonic and geophysical data supplemented by new fault-kinematic observations, we show that Cenozoic deformation of the Mesozoic sedimentary sequences is dominated by first order N-S faults reactivation, this sinistral wrench system is responsible for the formation of strike-slip duplexes, thrusts, folds and grabens. Following our new structural interpretation, the major faults of N-S Axis, Bou Kornine-Ressas-Messella (MRB) and Hammamet-Korbous (HK) form an N-S first order compressive relay within a left lateral strike-slip duplex. The N-S master MRB fault is dominated by contractional imbricate fans, while the parallel HK fault is characterized by a trailing of extensional imbricate fans. The Eocene and Miocene compression phases in the study area caused sinistral strike-slip reactivation of pre-existing N-S faults, reverse reactivation of NE-SW trending faults and normal-oblique reactivation of NW-SE faults, creating a NE-SW to N-S trending system of east-verging folds and overlaps. Existing seismic tomography images suggest a key role for the lithospheric subvertical tear or STEP fault (Slab Transfer Edge Propagator) evidenced below this region on the development of the MRB and the HK relay zone. The presence of extensive syntectonic Pliocene on top of this crustal scale fault may be the result of a recent lithospheric vertical kinematic of this STEP fault, due to the rollback and lateral migration of the Calabrian slab eastward.

  20. Fifty years of shear zones

    Science.gov (United States)

    Graham, Rodney

    2017-04-01

    We are here, of course, because 1967 saw the publication of John Ramsay's famous book. Two years later a memorable field trip from Imperial College to the Outer Hebrides saw John on a bleak headland on the coast of North Uist where a relatively undeformed metadolerite within Lewisian (Precambrian) gneisses contained ductile shear zones with metamorphic fabrics in amphibolite facies. One particular outcrop was very special - a shear zone cutting otherwise completely isotropic, undeformed metadolerite, with an incremental foliation starting to develop at 45° to the deformation zone, and increasing in intensity as it approached the shear direction. Here was proof of the process of simple shear under ductile metamorphic conditions - the principles of simple shear outlined in John Ramsay's 1967 book clearly visible in nature, and verified by Ramsay's mathematical proofs in the eventual paper (Ramsay and Graham, 1970). Later work on the Lewisian on the mainland of Scotland, in South Harris, in Africa, and elsewhere applied Ramsay's simple shear principles more liberally, more imprecisely and on larger scale than at Caisteal Odair, but in retrospect it documented what seems now to be the generality of mid and lower crustal deformation. Deep seismic reflection data show us that on passive margins hyper-stretched continental crust (whether or not cloaked by Seaward Dipping Reflectors) seems to have collapsed onto the mantle. Crustal faults mostly sole out at or above the mantle - so the Moho is a detachment- an 'outer marginal detachment', if you like, and, of course, it must be a ductile shear. On non-volcanic margins this shear zone forms the first formed ocean floor before true sea floor spreading gets going to create real oceanic crust. Gianreto Manatschal, Marcel Lemoine and others realised that the serpentinites described in parts of the Alps are exposed remnants of this ductile shear zone. Associated ophicalcite breccias tell of sea floor exposure, while high

  1. Are "uncharacteristic" earthquakes spatially linked to strike-slip restraining bends?

    Science.gov (United States)

    Mann, P.

    2011-12-01

    On the basis of a compilation of paleoseismological data from the Wasatch and San Andreas faults, Schwartz and Coppersmith (1984) proposed that both plate boundary and intraplate faults tend to generate essentially same size earthquakes having a relatively narrow range of magnitudes near the maximum. They referred to these earthquakes as "characteristic earthquakes". Their hypothesis suggests that the historical record of earthquakes documented for periods of time ranging from centuries to millennia in different parts of the world that could allow predictions of future ruptures. The characteristic earthquake model works surprisingly well for major strike-slip faults like the North Anatolian fault of Turkey and the North Tabriz strike-slip fault in Iran which both show a progressive, uni-direction pattern of rupture starting at one point and "unzippering" over a distance of hundreds of kilometers in a series of earthquakes. This regular periodicity has been attributed to systematic changes in Coulomb failure stress on individual faults or interconnected fault networks defined by distinctive changes in fault strike, or stepover faults, or by the intersection of a neighboring fault. However, studies of the San Andreas, Wasatch, and Dead Sea faults show that earthquake ruptures are not periodic and instead form clusters of events with no obvious "recurrence interval" as predicted by the characteristic earthquake model. Some of these hard-to-forecast "uncharacteristic" earthquakes initiate as blind thrust faults formed at deeper levels in the crust near the brittle-plastic transition zone as illustrated by the 1989 M 6.9 Loma Prieta earthquake of California. Such events would produce little or no surface rupture of the main fault plane so the effects of this type of earthquake would remain impossible for future paleoseismologists to discern (other than from shaking effects and the broad vertical uplift related to vertical motions on deeply buried faults). More recently

  2. Strike-slip earthquakes in the oceanic lithosphere: Observations of exceptionally high apparent stress

    Science.gov (United States)

    Choy, George; McGarr, A.

    2002-01-01

    The radiated energies, ES, and seismic moments, M0, for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses (τa=μES/M0, where μ is the modulus of rigidity). The globally averaged τa for shallow earthquakes in all tectonic environments and seismic regions is 0.3 MPa. However, the subset of 49 earthquakes with the highest apparent stresses (τa greater than about 5.0 MPa) is dominated almost exclusively by strike-slip earthquakes that occur in oceanic environments. These earthquakes are all located in the depth range 7–29 km in the upper mantle of the young oceanic lithosphere. Many of these events occur near plate-boundary triple junctions where there appear to be high rates of intraplate deformation. Indeed, the small rapidly deforming Gorda Plate accounts for 10 of the 49 high-τa events. The depth distribution of τa, which shows peak values somewhat greater than 25 MPa in the depth range 20–25 km, suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere. A recently proposed envelope for apparent stress, derived by taking 6 per cent of the strength inferred from laboratory experiments for young (less than 30 Ma) deforming oceanic lithosphere, agrees well with the upper-bound envelope of apparent stresses over the depth range 5–30 km. The corresponding depth-dependent shear strength for young oceanic lithosphere attains a peak value of about 575 MPa at a depth of 21 km and then diminishes rapidly as the depth increases. In addition to their high apparent stresses, which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10–30 km, our set of high-τa earthquakes show other features that constrain the nature of the forces that cause interplate motion. First, our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions

  3. Models of recurrent strike-slip earthquake cycles and the state of crustal stress

    Science.gov (United States)

    Lyzenga, Gregory A.; Raefsky, Arthur; Mulligan, Stephanie G.

    1991-01-01

    Numerical models of the strike-slip earthquake cycle, assuming a viscoelastic asthenosphere coupling model, are examined. The time-dependent simulations incorporate a stress-driven fault, which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent. Single-fault simulations with constant far-field plate motion lead to a nearly periodic earthquake cycle and a distinctive spatial distribution of crustal shear stress. The predicted stress distribution includes a local minimum in stress at depths less than typical seismogenic depths. The width of this stress 'trough' depends on the magnitude of crustal stress relative to asthenospheric drag stresses. The models further predict a local near-fault stress maximum at greater depths, sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere. Models incorporating both low-stress and high-stress fault strength assumptions are examined, under Newtonian and non-Newtonian rheology assumptions. Model results suggest a preference for low-stress (a shear stress level of about 10 MPa) fault models, in agreement with previous estimates based on heat flow measurements and other stress indicators.

  4. Characterizing a middle to upper crustal shear zone: Microstructures, quartz c-axis fabrics, deformation temperatures and flow vorticity analysis of the northern Ailao Shan-Red River shear zone, China

    Science.gov (United States)

    Wu, Wenbin; Liu, Junlai; Zhang, Lisheng; Qi, Yinchuan; Ling, Chengyang

    2017-05-01

    Structural and microstructural characteristics, deformation temperatures and flow vorticities of the northern Ailao Shan (ALS) high-grade metamorphic belt provide significant information regarding the nature and tectonic evolution of the Ailao Shan-Red River (ASRR) shear zone. Mineral deformation mechanisms, quartz lattice-preferred orientation (LPO) patterns and the opening angles of quartz c-axis fabrics of samples from the Gasa section indicate that the northern ALS high-grade metamorphic belt has experienced progressive shear deformation. The early stage shearing is characterized by a gradual decrease of deformation temperatures from >650 °C at the northeastern unit to ca. 300 °C at the southwestern unit, that results in the formation of migmatites, mylonitic gneisses, thin bedded mylonites, mylonitic schists and phyllonites from the NE to SW across the strike of the shear zone. The late stage low-temperature (300-400 °C) shearing is superimposed on the early deformation throughout the belt with the formation of discrete, small-scale shear zones, especially in the thin-banded mylonitic rocks along both margins. The kinematic vorticity values estimated by rotated rigid porphyroclast method and oblique grain-shaped/quartz c-axis-fabric method imply that the general shear-dominated flow (0.49-0.77) progressively changed to a simple shear-dominated flow (0.77-1) toward the late stage of ductile deformation. The two stages of shearing are consistent with early shortening-dominated and late extrusion-controlled regional tectonic processes. The transition between them occurred at ca. 27 Ma in the ALS high-grade metamorphic belt along the ASRR shear zone. The large amount of strike-slip displacement along the ASRR shear zone is predominantly attributed to accelerated flow along the shear zone during the late extrusion-controlled tectonic process.

  5. Strike-slip tectonics within the northernmost Philippine Sea plate in an arc-continent collisional setting

    Science.gov (United States)

    Gong, Wei; Jiang, Xiaodian; Guo, Yufan; Xing, Junhui; Li, Congying; Sun, Yang

    2017-09-01

    The geological processes in the northernmost Philippine Sea plate, which is bounded by the Suruga and Sagami troughs, are a typical example of an active collision zone. We attempt to illustrate the stress field through seismic estimations and geodetic analysis and propose the kinematic mode of the northernmost tip of the Philippine Sea plate. Seven events (M ≥ 4.0) are chosen for waveform inversion by the ISOLA software to distinguish the stress field. In particular, six of the chosen events, which exhibit strike-slip motion, are distributed in the eastern area, where few focal mechanisms have been reported by previous studies. According to the available focal mechanisms, strike-slip faults with similar P and T axes are widely distributed in the study area. The stress inversion suggests that the northern area is characterized by a NW-SE compression and a NE-SW extension stress regime, although some spatial differences exist. As indicated by an analysis of the geodesy, epicenters, focal mechanisms, gravity anomalies and velocity structure, the deformation in the northernmost tip is mainly accommodated by several conjugate strike-slip fault systems with steep dips that center on the Izu volcanic line. Generally, the maximum principal stress of the kinematics is derived from the collision between the Philippine Sea plate and Central Japan. Because of the different subduction angles, rates and directions of the down-going plate, diverging slab-pull forces along the Suruga and Sagami troughs may be causing the NE-NNE extension in most of the areas that are bounded by the two troughs. The extension propagates southwards along the Izu volcanic line and reaches the area adjacent to Miyake-jima.

  6. Fault and fracture patterns around a strike-slip influenced salt wall

    Science.gov (United States)

    Alsop, G. I.; Weinberger, R.; Marco, S.; Levi, T.

    2018-01-01

    The trends of faults and fractures in overburden next to a salt diapir are generally considered to be either parallel to the salt margin to form concentric patterns, or at right angles to the salt contact to create an overall radial distribution around the diapir. However, these simple diapir-related patterns may become more complex if regional tectonics influences the siting and growth of a diapir. Using the Sedom salt wall in the Dead Sea Fault system as our case study, we examine the influence of regional strike-slip faulting on fracture patterns around a salt diapir. This type of influence is important in general as the distribution and orientation of fractures on all scales may influence permeability and hence control fluid and hydrocarbon flow. Fractures adjacent to the N-S trending salt wall contain fibrous gypsum veins and injected clastic dykes, attesting to high fluid pressures adjacent to the diapir. Next to the western flank of the salt wall, broad (∼1000 m) zones of upturn or 'drape folds' are associated with NW-SE striking conjugate extensional fractures within the overburden. Within 300 m of the salt contact, fracture patterns in map view display a progressive ∼30°-35° clockwise rotation with more NNW-SSE strikes immediately adjacent to the salt wall. While some extensional faults display growth geometries, indicating that they were syn-depositional and initiated prior to tilting of beds associated with drape folding, other fractures display increasing dips towards the salt, suggesting that they have formed during upturn of bedding near the diapir. These observations collectively suggest that many fractures developed to accommodate rotation of beds during drape folding. Extensional fractures in the overburden define a mean strike that is ∼45° anticlockwise (counter-clockwise) of the N-S trending salt wall, and are therefore consistent with sinistral transtension along the N-S trending Sedom Fault that underlies the salt wall. Our outcrop

  7. A nonlinear least-squares inverse analysis of strike-slip faulting with application to the San Andreas fault

    Science.gov (United States)

    Williams, Charles A.; Richardson, Randall M.

    1988-01-01

    A nonlinear weighted least-squares analysis was performed for a synthetic elastic layer over a viscoelastic half-space model of strike-slip faulting. Also, an inversion of strain rate data was attempted for the locked portions of the San Andreas fault in California. Based on an eigenvector analysis of synthetic data, it is found that the only parameter which can be resolved is the average shear modulus of the elastic layer and viscoelastic half-space. The other parameters were obtained by performing a suite of inversions for the fault. The inversions on data from the northern San Andreas resulted in predicted parameter ranges similar to those produced by inversions on data from the whole fault.

  8. The Implications of Strike-Slip Earthquake Source Properties on the Transform Boundary Development Process

    Science.gov (United States)

    Neely, J. S.; Huang, Y.; Furlong, K.

    2017-12-01

    Subduction-Transform Edge Propagator (STEP) faults, produced by the tearing of a subducting plate, allow us to study the development of a transform plate boundary and improve our understanding of both long-term geologic processes and short-term seismic hazards. The 280 km long San Cristobal Trough (SCT), formed by the tearing of the Australia plate as it subducts under the Pacific plate near the Solomon and Vanuatu subduction zones, shows along-strike variations in earthquake behaviors. The segment of the SCT closest to the tear rarely hosts earthquakes > Mw 6, whereas the SCT sections more than 80 - 100 km from the tear experience Mw7 earthquakes with repeated rupture along the same segments. To understand the effect of cumulative displacement on SCT seismicity, we analyze b-values, centroid-time delays and corner frequencies of the SCT earthquakes. We use the spectral ratio method based on Empirical Green's Functions (eGfs) to isolate source effects from propagation and site effects. We find high b-values along the SCT closest to the tear with values decreasing with distance before finally increasing again towards the far end of the SCT. Centroid time-delays for the Mw 7 strike-slip earthquakes increase with distance from the tear, but corner frequency estimates for a recent sequence of Mw 7 earthquakes are approximately equal, indicating a growing complexity in earthquake behavior with distance from the tear due to a displacement-driven transform boundary development process (see figure). The increasing complexity possibly stems from the earthquakes along the eastern SCT rupturing through multiple asperities resulting in multiple moment pulses. If not for the bounding Vanuatu subduction zone at the far end of the SCT, the eastern SCT section, which has experienced the most displacement, might be capable of hosting larger earthquakes. When assessing the seismic hazard of other STEP faults, cumulative fault displacement should be considered a key input in

  9. Integration of remote sensing, geochemical and field data in the Qena-Safaga shear zone: Implications for structural evolution of the Eastern Desert, Egypt

    Science.gov (United States)

    El-Din, Gamal Kamal; Abdelkareem, Mohamed

    2018-05-01

    The Qena-Safaga shear zone (QSSZ) represents a significant structural characteristic in the Eastern Desert of Egypt. Remote Sensing, field and geochemical data were utilized in the present study. The results revealed that the QSSZ dominated by metamorphic complex (MC) that intruded by syn-tectonic granitoids. The low angle thrust fault brings calc-alkaline metavolcanics to overlie MC and its association. Subsequently, the area is dissected by strike-slip faults and the small elongated basins of Hammamat sediments of Precambrian were accumulated. The MC intruded by late-to post-tectonic granites (LPG) and Dokhan Volcanics which comprise felsic varieties forming distinctive columnar joints. Remote sensing analysis and field data revealed that major sub-vertical conspicuous strike-slip faults (SSF) including sinistral NW-SE and dextral ca. E-W shaped the study area. Various shear zones that accompanying the SSF are running NW-SE, NE-SW, E-W, N-S and ENE-WSW. The obtained shear sense presented a multiphase of deformation on each trend. i.e., the predominant NW-SE strike-slip fault trend started with sinistral displacement and is reactivated during later events to be right (dextral) strike slip cutting with dextral displacement the E-W trending faults; while NE-SW movements are cut by both the N-S and NNW - SSE trends. Remote sensing data revealed that the NW-SE direction that dominated the area is associated with hydrothermal alteration processes. This allowed modifying the major and trace elements of the highly deformed rocks that showed depletion in SiO2 and enrichments in Fe2O3, MnO, Al2O3, TiO2, Na2O, K2O, Cu, Zn and Pb contents. The geochemical signatures of major and trace elements revealed two types of granites including I-type calc-alkaline granites (late-to post-tectonic) that formed during an extensional regime. However, syn-tectonic granitoids are related to subduction-related environment.

  10. Shear zones of the Verkhoyansk fold-and-thrust belt, Northeast Russia

    Science.gov (United States)

    Fridovsky, Valery; Polufuntikova, Lena

    2017-04-01

    The Verkhoyansk fold-and-thrust belt is situated on the submerged eastern margin of the North Asian craton, and is largely composed of the Ediacaran - Middle Paleozoic carbonate and the Upper Paleozoic-Mesozoic terrigenous rocks. The Upper Carboniferous - Jurassic sediments constitute the Verkhoyansk terrigenous complex containing economically viable orogenic gold deposits. The structure of the belt is mainly controlled by thrusts and associated diagonal strike slips. Linear concentric folds are common all over the area of the belt. Shear zones with associated similar folds are confined to long narrow areas. Shear zones were formed during the early stages of the Oxfordian-Kimmeridgian collisional and accretionary events prior to the emplacement of large orogenic granitoid plutons. The main ore-controlling structures are shear zones associated with slaty cleavage, shear folds, mullion- and boudinage-structures, and transposition features. The shear zones are listric-type, and represent branches of a detachment structure, which is assumed to be present at the base of the Verkhoyansk fold-and-thrust belt. A vertical zonation of shear zones is correlated with the distance to the detachment. Changes in the dip angle of the shear zones (as indicated mainly by cleavage), structural paragenesis, the degree of microdeformation of the host rocks, and the type of ore-controlling structures can be clearly observed in the direction away from the detachment. Structural zoning is evidenced, among other things, by changing morphologic types of microstructures and by strain-indicators of the degree of rock metamorphism. Four morphologic types of microstructures are identified. The first platy-shear type is characterized by aggregate cleavage and the coefficient of deformation (Cd) of single grains from 1.0 to 2.0. Irregular angular fragments of variously oriented grains can be observed in thin sections. The second shear-cataclastic morphologic type (Cd from 2.0 to 3.0) exhibits

  11. High tsunami frequency as a result of combined strike-slip faulting and coastal landslides

    Science.gov (United States)

    Hornbach, Matthew J.; Braudy, Nicole; Briggs, Richard W.; Cormier, Marie-Helene; Davis, Marcy B.; Diebold, John B.; Dieudonne, Nicole; Douilly, Roby; Frohlich, Cliff; Gulick, Sean P.S.; Johnson, Harold E.; Mann, Paul; McHugh, Cecilia; Ryan-Mishkin, Katherine; Prentice, Carol S.; Seeber, Leonardo; Sorlien, Christopher C.; Steckler, Michael S.; Symithe, Steeve Julien; Taylor, Frederick W.; Templeton, John

    2010-01-01

    Earthquakes on strike-slip faults can produce devastating natural hazards. However, because they consist predominantly of lateral motion, these faults are rarely associated with significant uplift or tsunami generation. And although submarine slides can generate tsunami, only a few per cent of all tsunami are believed to be triggered in this way. The 12 January Mw 7.0 Haiti earthquake exhibited primarily strike-slip motion but nevertheless generated a tsunami. Here we present data from a comprehensive field survey that covered the onshore and offshore area around the epicentre to document that modest uplift together with slope failure caused tsunamigenesis. Submarine landslides caused the most severe tsunami locally. Our analysis suggests that slide-generated tsunami occur an order-of-magnitude more frequently along the Gonave microplate than global estimates predict. Uplift was generated because of the earthquake's location, where the Caribbean and Gonave microplates collide obliquely. The earthquake also caused liquefaction at several river deltas that prograde rapidly and are prone to failure. We conclude that coastal strike-slip fault systems such as the Enriquillo-Plantain Garden fault produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunami - a risk that is underestimated at present.

  12. A note on 2-D lithospheric deformation due to a blind strike-slip fault

    Indian Academy of Sciences (India)

    mic deformation. Several researchers have devel- oped models of coseismic lithospheric deformation. Rybicki (1971) found a closed-form analytical solu- tion for the problem of a long vertical strike-slip fault in a two-layer model of the earth. Chinnery and Jovanovich (1972) extended the solution to a three-layer model.

  13. Strike-slip deformation reflects complex partitioning of strain in the Nankai Accretionary Prism (SE Japan)

    Science.gov (United States)

    Azevedo, Marco C.; Alves, Tiago M.; Fonseca, Paulo E.; Moore, Gregory F.

    2018-01-01

    Previous studies have suggested predominant extensional tectonics acting, at present, on the Nankai Accretionary Prism (NAP), and following a parallel direction to the convergence vector between the Philippine Sea and Amur Plates. However, a complex set of thrusts, pop-up structures, thrust anticlines and strike-slip faults is observed on seismic data in the outer wedge of the NAP, hinting at a complex strain distribution across SE Japan. Three-dimensional (3D) seismic data reveal three main families of faults: (1) NE-trending thrusts and back-thrusts; (2) NNW- to N-trending left-lateral strike-slip faults; and (3) WNW-trending to E-W right-lateral strike-slip faults. Such a fault pattern suggests that lateral slip, together with thrusting, are the two major styles of deformation operating in the outer wedge of the NAP. Both styles of deformation reflect a transpressional tectonic regime in which the maximum horizontal stress is geometrically close to the convergence vector. This work is relevant because it shows a progressive change from faults trending perpendicularly to the convergence vector, to a broader partitioning of strain in the form of thrusts and conjugate strike-slip faults. We suggest that similar families of faults exist within the inner wedge of the NAP, below the Kumano Basin, and control stress accumulation and strain accommodation in this latter region.

  14. A note on 2-D lithospheric deformation due to a blind strike-slip fault

    Indian Academy of Sciences (India)

    Chinnery and Jovanovich (1972) extended the solution to a three-layer model. Savage and Prescott (1978) constructed a simple two-dimensional model of an earthquake cycle that takes place on a transform fault. Singh and Rani (1994) obtained an analytical solution for the problem of a long inclined strike- slip fault in an ...

  15. The Role of Near-Fault Relief in Creating and Maintaining Strike-Slip Landscape Features

    Science.gov (United States)

    Harbert, S.; Duvall, A. R.; Tucker, G. E.

    2016-12-01

    Geomorphic landforms, such as shutter ridges, offset river terraces, and deflected stream channels, are often used to assess the activity and slip rates of strike-slip faults. However, in some systems, such as parts of the Marlborough Fault System (South Island, NZ), an active strike-slip fault does not leave a strong landscape signature. Here we explore the factors that dampen or enhance the landscape signature of strike-slip faulting using the Channel-Hillslope Integrated Landscape Development model (CHILD). We focus on variables affecting the length of channel offsets, which enhance the signature of strike-slip motion, and the frequency of stream captures, which eliminate offsets and reduce this signature. We model a strike-slip fault that passes through a mountain ridge, offsetting streams that drain across this fault. We use this setup to test the response of channel offset length and capture frequency to fault characteristics, such as slip rate and ratio of lateral to vertical motion, and to landscape characteristics, such as relief contrasts controlled by erodibility. Our experiments show that relief downhill of the fault, whether generated by differential uplift across the fault or by an erodibility contrast, has the strongest effect on offset length and capture frequency. This relief creates shutter ridges, which block and divert streams while being advected along a fault. Shutter ridges and the streams they divert have long been recognized as markers of strike-slip motion. Our results show specifically that the height of shutter ridges is most responsible for the degree to which they create long channel offsets by preventing stream captures. We compare these results to landscape metrics in the Marlborough Fault System, where shutter ridges are common and often lithologically controlled. We compare shutter ridge length and height to channel offset length in order to assess the influence of relief on offset channel features in a real landscape. Based on our

  16. Relationships between along-fault heterogeneous normal stress and fault slip patterns during the seismic cycle: Insights from a strike-slip fault laboratory model

    Science.gov (United States)

    Caniven, Yannick; Dominguez, Stéphane; Soliva, Roger; Peyret, Michel; Cattin, Rodolphe; Maerten, Frantz

    2017-12-01

    We use a strike-slip fault analog model to study experimentally the role played by along-fault non-uniform and asymmetric applied normal stress on both coseismic slip and long-term fault behavior. Our model is based on a visco-elasto-plastic multi-layered rheology that allows to produce several hundreds of scaled analog microquakes and associated seismic cycles. Uniform or heterogeneous applied normal stress along the fault plane is imposed and maintained constant during the whole experiment durations. Our results suggest that coseismic slip patterns are strongly controlled by spatial normal stress variations and subsequent accumulated shear stress along fault strike. Major microquakes occur preferentially in zones of major shear stress asperities. Coseismic slip distributions exhibit a pattern similar to the along-fault applied normal stress distribution. The occurrence of isolated low to moderate microquakes where residual stresses persist around secondary stress asperities, indicates that stress conditions along the fault also control the whole variability of fault slip events. Moreover, when fault slip stability conditions are modulated by normal stress distribution, our experiments suggest that the along-fault stress heterogeneity influences the seismic cycle regularity and, consequently, long-term fault slip behavior. Uniform applied normal stress favors irregular seismic cycles and the occurrence of earthquakes clustering, whereas non-uniform normal stress with a single high amplitude stress asperity generates strong characteristic microquake events with stable return periods. Together our results strengthen the assumption that coseismic slip distribution and earthquake variability along an active fault may provide relevant information on long term tectonic stress and could thus improve seismic hazard assessment.

  17. Kinematics of transition from subduction to strike-slip: an example from the New Zealand plate boundary (Invited)

    Science.gov (United States)

    Wallace, L. M.; Barnes, P.; Beavan, R. J.; van Dissen, R.; Pondard, N.; Litchfield, N. J.; Lamarche, G.; Little, T. A.

    2009-12-01

    We develop a kinematic model for the transition from oblique subduction beneath the North Island to strike-slip in the South Island, New Zealand, constrained by GPS velocities and onshore and new offshore active fault slip rate and location data. To interpret these data, we simultaneously invert the kinematic data for poles of rotation of tectonic blocks (block boundaries chosen to coincide with known active faults) and the degree of interseismic coupling on faults in the region, including the Hikurangi subduction thrust. Our best-fitting kinematic models require that the northeastern corner of the South Island undergoes significant vertical axis rotation as a part of the rapidly rotating (3-4°/Myr) North Island forearc block, while the remainder of the tectonic blocks in the South Island undergo negligible vertical axis rotation relative to the Pacific Plate. This result agrees well with clockwise paleomagnetic declinations from ~4 Ma rock samples in the northeastern South Island, and suggests that paleomagnetically-observed rotation of that region is continuing today. The poles of rotation between the more rapidly rotating northeastern South Island blocks and the non-rotating South Island blocks (further south) coincide with the boundary between the rotating and non-rotating domains of the South Island. This result is consistent with structural mapping of the rotation/non-rotation boundary by Little and Roberts (1997), and suggests that the transition from the rapidly rotating forearc of the Hikurangi subduction margin to a strike-slip dominated plate boundary in the South Island is accommodated by a crustal-scale kink or hinge in the upper plate of that subduction zone. This result highlights a remarkable consistency between datasets spanning decades (GPS), thousands of years (active fault data), and millions of years (paleomagnetic data and bedrock structure) in the northeastern South Island. Although the interseismic coupling coefficients that we estimate for

  18. The San Andreas Fault and a Strike-slip Fault on Europa

    Science.gov (United States)

    1998-01-01

    The mosaic on the right of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, the size of the California portion of the San Andreas fault on Earth which runs from the California-Mexico border north to the San Francisco Bay. The left mosaic shows the portion of the San Andreas fault near California's san Francisco Bay that has been scaled to the same size and resolution as the Europa image. Each covers an area approximately 170 by 193 kilometers(105 by 120 miles). The red line marks the once active central crack of the Europan fault (right) and the line of the San Andreas fault (left). A strike-slip fault is one in which two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. The overall motion along the Europan fault seems to have followed a continuous narrow crack along the entire length of the feature, with a path resembling stepson a staircase crossing zones which have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. Opposite sides of the fault can be reconstructed like a puzzle, matching the shape of the sides as well as older individual cracks and ridges that had been broken by its movements. Bends in the Europan fault have allowed the surface to be pulled apart. This pulling-apart along the fault's bends created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, and in Death Valley and the Dead Sea. In those cases, the pulled apart regions can include upwelled materials, but may

  19. The San Andreas Fault and a Strike-slip Fault on Europa

    Science.gov (United States)

    1998-01-01

    The mosaic on the right of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, the size of the California portion of the San Andreas fault on Earth which runs from the California-Mexico border north to the San Francisco Bay. The left mosaic shows the portion of the San Andreas fault near California's san Francisco Bay that has been scaled to the same size and resolution as the Europa image. Each covers an area approximately 170 by 193 kilometers(105 by 120 miles). The red line marks the once active central crack of the Europan fault (right) and the line of the San Andreas fault (left). A strike-slip fault is one in which two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. The overall motion along the Europan fault seems to have followed a continuous narrow crack along the entire length of the feature, with a path resembling stepson a staircase crossing zones which have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. Opposite sides of the fault can be reconstructed like a puzzle, matching the shape of the sides as well as older individual cracks and ridges that had been broken by its movements. Bends in the Europan fault have allowed the surface to be pulled apart. This pulling-apart along the fault's bends created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, and in Death Valley and the Dead Sea. In those cases, the pulled apart regions can include upwelled materials, but may

  20. Strike-slip faulting in the Inner California Borderlands, offshore Southern California.

    Science.gov (United States)

    Bormann, J. M.; Kent, G. M.; Driscoll, N. W.; Harding, A. J.; Sahakian, V. J.; Holmes, J. J.; Klotsko, S.; Kell, A. M.; Wesnousky, S. G.

    2015-12-01

    In the Inner California Borderlands (ICB), offshore of Southern California, modern dextral strike-slip faulting overprints a prominent system of basins and ridges formed during plate boundary reorganization 30-15 Ma. Geodetic data indicate faults in the ICB accommodate 6-8 mm/yr of Pacific-North American plate boundary deformation; however, the hazard posed by the ICB faults is poorly understood due to unknown fault geometry and loosely constrained slip rates. We present observations from high-resolution and reprocessed legacy 2D multichannel seismic (MCS) reflection datasets and multibeam bathymetry to constrain the modern fault architecture and tectonic evolution of the ICB. We use a sequence stratigraphy approach to identify discrete episodes of deformation in the MCS data and present the results of our mapping in a regional fault model that distinguishes active faults from relict structures. Significant differences exist between our model of modern ICB deformation and existing models. From east to west, the major active faults are the Newport-Inglewood/Rose Canyon, Palos Verdes, San Diego Trough, and San Clemente fault zones. Localized deformation on the continental slope along the San Mateo, San Onofre, and Carlsbad trends results from geometrical complexities in the dextral fault system. Undeformed early to mid-Pleistocene age sediments onlap and overlie deformation associated with the northern Coronado Bank fault (CBF) and the breakaway zone of the purported Oceanside Blind Thrust. Therefore, we interpret the northern CBF to be inactive, and slip rate estimates based on linkage with the Holocene active Palos Verdes fault are unwarranted. In the western ICB, the San Diego Trough fault (SDTF) and San Clemente fault have robust linear geomorphic expression, which suggests that these faults may accommodate a significant portion of modern ICB slip in a westward temporal migration of slip. The SDTF offsets young sediments between the US/Mexico border and the

  1. The cenozoic strike-slip faults and TTHE regional crust stability of Beishan area

    International Nuclear Information System (INIS)

    Guo Zhaojie; Zhang Zhicheng; Zhang Chen; Liu Chang; Zhang Yu; Wang Ju; Chen Weiming

    2008-01-01

    The remote sensing images and geological features of Beishan area indicate that the Altyn Tagh fault, Sanweishan-Shuangta fault, Daquan fault and Hongliuhe fault are distributed in Beishan area from south to north. The faults are all left-lateral strike-slip faults with trending of NE40-50°, displaying similar distribution pattern. The secondary branch faults are developed at the end of each main strike-slip fault with nearly east to west trending form dendritic oblique crossings at the angle of 30-50°. Because of the left-lateral slip of the branch faults, the granites or the blocks exposed within the branch faults rotate clockwisely, forming 'Domino' structures. So the structural style of Beishan area consists of the Altyn Tagh fault, Sanweishan-Shuangta fault, Daquan fault, Hongliuhe fault and their branch faults and rotational structures between different faults. Sedimentary analysis on the fault valleys in the study area and ESR chronological test of fault clay exhibit that the Sanweishan-Shuangta fault form in the late Pliocene (N2), while the Daquan fault displays formation age of l.5-1.2 Ma, and the activity age of the relevant branch faults is Late Pleistocene (400 ka). The ages become younger from the Altyn Tagh fault to the Daquan fault and strike-slip faults display NW trending extension, further revealing the lateral growth process of the strike-slip boundary at the northern margin during the Cenozoic uplift of Tibetan Plateau. The displacement amounts on several secondary faults caused by the activities of the faults are slight due to the above-mentioned structural distribution characteristics of Beishan area, which means that this area is the most stable active area with few seismic activities. We propose the main granitic bodies in Beishan area could be favorable preselected locations for China's high level radioactive waste repository. (authors)

  2. A note on 2-D lithospheric deformation due to a blind strike-slip fault

    Indian Academy of Sciences (India)

    Analytical solution for the problem of a surface-breaking long strike-slip fault in an elastic layer overlying an elastic half-space is well known. The purpose of this note is to obtain the corresponding solution for a blind fault. Since the solution is valid for arbitrary values of the fault-depth and the dip angle, the effects of these ...

  3. A Comparison of Geodetic and Geologic Rates Prior to Large Strike-Slip Earthquakes: A Diversity of Earthquake-Cycle Behaviors?

    Science.gov (United States)

    Dolan, James F.; Meade, Brendan J.

    2017-12-01

    Comparison of preevent geodetic and geologic rates in three large-magnitude (Mw = 7.6-7.9) strike-slip earthquakes reveals a wide range of behaviors. Specifically, geodetic rates of 26-28 mm/yr for the North Anatolian fault along the 1999 MW = 7.6 Izmit rupture are ˜40% faster than Holocene geologic rates. In contrast, geodetic rates of ˜6-8 mm/yr along the Denali fault prior to the 2002 MW = 7.9 Denali earthquake are only approximately half as fast as the latest Pleistocene-Holocene geologic rate of ˜12 mm/yr. In the third example where a sufficiently long pre-earthquake geodetic time series exists, the geodetic and geologic rates along the 2001 MW = 7.8 Kokoxili rupture on the Kunlun fault are approximately equal at ˜11 mm/yr. These results are not readily explicable with extant earthquake-cycle modeling, suggesting that they may instead be due to some combination of regional kinematic fault interactions, temporal variations in the strength of lithospheric-scale shear zones, and/or variations in local relative plate motion rate. Whatever the exact causes of these variable behaviors, these observations indicate that either the ratio of geodetic to geologic rates before an earthquake may not be diagnostic of the time to the next earthquake, as predicted by many rheologically based geodynamic models of earthquake-cycle behavior, or different behaviors characterize different fault systems in a manner that is not yet understood or predictable.

  4. Friction of Shear-Fracture Zones

    Science.gov (United States)

    Riikilä, T. I.; Pylväinen, J. I.; Åström, J.

    2017-12-01

    A shear fracture of brittle solids under compression undergoes a substantial evolution from the initial microcracking to a fully formed powder-filled shear zone. Experiments covering the entire process are relatively easy to conduct, but they are very difficult to investigate in detail. Numerically, the large strain limit has remained a challenge. An efficient simulation model and a custom-made experimental device are employed to test to what extent a shear fracture alone is sufficient to drive material to spontaneous self-lubrication. A "weak shear zone" is an important concept in geology, and a large number of explanations, specific for tectonic conditions, have been proposed. We demonstrate here that weak shear zones are far more general, and that their emergence only demands that a microscopic, i.e., fragment-scale, stress relaxation mechanism develops during the fracture process.

  5. Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

    Science.gov (United States)

    van der Werf, Thomas; Chatzaras, Vasileios; Marcel Kriegsman, Leo; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

    2017-12-01

    The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene-Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750-890 °C and pressures of 400-560 MPa, corresponding to 15-22 km depth. A hot crustal geotherm of 40 ° C km-1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12-33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12-17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1-1.3×1020 Pa ṡ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016-1019 Pa ṡ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ṡ s

  6. Size distribution and roundness of clasts within pseudotachylytes of the Gangavalli Shear Zone, Salem, Tamil Nadu: An insight into its origin and tectonic significance

    Science.gov (United States)

    Behera, Bhuban Mohan; Thirukumaran, V.; Soni, Aishwaraya; Mishra, Prasanta Kumar; Biswal, Tapas Kumar

    2017-06-01

    Gangavalli (Brittle) Shear Zone (Fault) near Attur, Tamil Nadu exposes nearly 50 km long and 1-3 km wide NNE-SSW trending linear belt of cataclasites and pseudotachylyte produced on charnockites of the Southern Granulite Terrane. Pseudotachylytes, as well as the country rock, bear the evidence of conjugate strike slip shearing along NNE-SSW and NW-SE directions, suggesting an N-S compression. The Gangavalli Shear Zone represents the NNE-SSW fault of the conjugate system along which a right lateral shear has produced seismic slip motion giving rise to cataclasites and pseudotachylytes. Pseudotachylytes occur as veins of varying width extending from hairline fracture fills to tens of meters in length. They carry quartz as well as feldspar clasts with sizes of few mm in diameter; the clast sizes show a modified Power law distribution with finer ones (0.4) due to thermal decrepitation. In a large instance, devitrification has occurred producing albitic microlites that suggest the temperature of the pseudotachylyte melt was >1000^{circ }\\hbox {C}. Thus, pseudotachylyte veins act as a proxy to understand the genetic process involved in the evolution of the shear zone and its tectonic settings.

  7. Strike-slip pull-apart process and emplacement of Xiangshan uranium-producing volcanic basin

    International Nuclear Information System (INIS)

    Qiu Aijin; Guo Lingzhi; Shu Liangshu

    2001-01-01

    Xiangshan volcanic basin is one of the famous uranium-producing volcanic basins in China. Emplacement mechanism of Xiangshan uranium-producing volcanic basin is discussed on the basis of the latest research achievements of deep geology in Xiangshan area and the theory of continental dynamics. The study shows that volcanic activity in Xiangshan volcanic basin may be divided into two cycles, and its emplacement is controlled by strike-ship pull-apart process originated from the deep regional faults. Volcanic apparatus in the first cycle was emplaced in EW-trending structure activated by clockwise strike-slipping of NE-trending deep fault, forming the EW-trending fissure-type volcanic effusion belt. Volcanic apparatus in the second cycle was emplaced at junction points of SN-trending pull-apart structure activated by sinistral strike-slipping of NE-trending deep faults and EW-trending basement faults causing the center-type volcanic magma effusion and extrusion. Moreover, the formation mechanism of large-rich uranium deposits is discussed as well

  8. E-W strike slip shearing of Kinwat Granitoid at South East Deccan ...

    Indian Academy of Sciences (India)

    53

    detail/photo evidences nor any attitude data were presented. Tectonically active-, moderately active- and inactive basins have elongation ratios 0.75 ..... various types of interaction between coexisting felsic and mafic magmas. Earth and. Environmental Science Trans. Royal Soc. Edin. 83 145-153.

  9. E–W strike slip shearing of Kinwat granitoid at South East Deccan ...

    Indian Academy of Sciences (India)

    R D Kaplay

    2017-07-21

    Jul 21, 2017 ... Roy S and Rao R U M 1999 Geothermal investigations in the. 1993 Latur earthquake area, Deccan Volcanic Province,. India; Tectonophys. 306 237–252. Sangode S J, Mesharm D C, Kulkarni Y R, Gudadhe. S S, Malpe D B and Herlekar M A 2013 Neotectonic response of the Godavari and Kaddam Rivers ...

  10. Pseudodynamic Source Characterization for Strike-Slip Faulting Including Stress Heterogeneity and Super-Shear Ruptures

    KAUST Repository

    Mena, B.

    2012-08-08

    Reliable ground‐motion prediction for future earthquakes depends on the ability to simulate realistic earthquake source models. Though dynamic rupture calculations have recently become more popular, they are still computationally demanding. An alternative is to invoke the framework of pseudodynamic (PD) source characterizations that use simple relationships between kinematic and dynamic source parameters to build physically self‐consistent kinematic models. Based on the PD approach of Guatteri et al. (2004), we propose new relationships for PD models for moderate‐to‐large strike‐slip earthquakes that include local supershear rupture speed due to stress heterogeneities. We conduct dynamic rupture simulations using stochastic initial stress distributions to generate a suite of source models in the magnitude Mw 6–8. This set of models shows that local supershear rupture speed prevails for all earthquake sizes, and that the local rise‐time distribution is not controlled by the overall fault geometry, but rather by local stress changes on the faults. Based on these findings, we derive a new set of relations for the proposed PD source characterization that accounts for earthquake size, buried and surface ruptures, and includes local rise‐time variations and supershear rupture speed. By applying the proposed PD source characterization to several well‐recorded past earthquakes, we verify that significant improvements in fitting synthetic ground motion to observed ones is achieved when comparing our new approach with the model of Guatteri et al. (2004). The proposed PD methodology can be implemented into ground‐motion simulation tools for more physically reliable prediction of shaking in future earthquakes.

  11. E–W strike slip shearing of Kinwat granitoid at South East Deccan ...

    Indian Academy of Sciences (India)

    School of Earth Sciences, S.R.T.M. University, Nanded, Maharashtra 431 606, India. Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra 400 076, India. Nanded Education Society's Science College, Nanded, Maharashtra 431 606, India. Dnyanopasak College, Parbhani ...

  12. Hydrothermal quartz formation during fluctuations of brittle shear-zone activity and fluid flow: grain growth and deformation structures of the Pfahl shear zone (Germany)

    Science.gov (United States)

    Yilmaz, T.; Prosser, G.; Liotta, D.; Kruhl, J. H.

    2012-12-01

    The Bavarian Pfahl shear zone is a WNW-ESE trending dextral strike-slip shear zone at the SW margin of the Bohemian Massif (Central Europe). It was discontinuously active during decreasing PT-conditions, i.e. from ductile to brittle, from the late-Carboniferous to the late-Cretaceous - Paleocene times. Triassic hydrothermal activity produced a 150 km long and 30-100 m wide quartz dyke along the main fault, surrounded by sheared basement rocks. Within a zone of >10 m metasomatism transformed the wall rocks to mostly kaolinite, chlorite and phyllosilicates. The quartz dyke exhibits a layered to lenticular and partly symmetric structure with different types of quartz masses, transected by a complex quartz vein network. This already indicates pulses of fluid flux and fragmentation during the lifetime of the shear zone. Analyses by optical microscopy, cathodoluminescence (CL) and SEM-EDX reveal at least four subsequent stages of quartz crystallization and fragmentation. (i) The oldest generation of quartz is represented by a homogeneous dark grey to reddish quartz mass made up by ~10-20 μm-sized crystals. It contains mm- to cm-sized angular wall-rock fragments, completely altered to kaolinite, indicating intense wall-rock alteration prior to the earliest event of silica precipitation. This rules out the possibility that the quartz mass developed from silicification of the wall rocks. This first type of quartz occurs as cm- to dm-large angular fragments in (ii) a light grey to pink quartz mass formed by ~10-50 μm-sized crystals. The different colours result from variable types and amounts of inclusions. Quartz of both generations shows random crystallographic orientations and complex inclusion structures. It probably developed during two fragmentation events and possibly from a silica gel precursor that crystallized after precipitation. (iii) The third quartz generation formed as a set of mm- to dm-wide veins roughly parallel to the trend of the Pfahl zone

  13. A recent Mw 4.3 earthquake proving activity of a shallow strike-slip fault in the northern part of the Western Desert, Egypt

    Science.gov (United States)

    Ezzelarab, Mohamed; Ebraheem, Mohamed O.; Zahradník, Jiří

    2018-03-01

    The Mw 4.3 earthquake of September 2015 is the first felt earthquake since 1900 A.D in the northern part of the Western Desert, Egypt, south of the El-Alamein City. The available waveform data observed at epicentral distances 52-391 km was collected and carefully evaluated. Nine broad-band stations were selected to invert full waveforms for the centroid position (horizontal and vertical) and for the focal mechanism solution. The first-arrival travel times, polarities and low-frequency full waveforms (0.03-0.08 Hz) are consistently explained in this paper as caused by a shallow source of the strike-slip mechanism. This finding indicates causal relation of this earthquake to the W-E trending South El-Alamein fault, which developed in Late Cretaceous as dextral strike slip fault. Recent activity of this fault, proven by the studied rare earthquake, is of fundamental importance for future seismic hazard evaluations, underlined by proximity (∼65 km) of the source zone to the first nuclear power plant planned site in Egypt. Safe exploration and possible future exploitation of hydrocarbon reserves, reported around El-Alamein fault in the last decade, cannot be made without considering the seismic potential of this fault.

  14. Equivalent strike-slip earthquake cycles in half-space and lithosphere-asthenosphere earth models

    Science.gov (United States)

    Savage, J.C.

    1990-01-01

    By virtue of the images used in the dislocation solution, the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike-slip fault in an Earth model consisting of an elastic plate (lithosphere) overlying a viscoelastic half-space (asthenosphere) can be duplicated by prescribed slip on a vertical fault embedded in an elastic half-space. Inversion of 1973-1988 geodetic measurements of deformation across the segment of the San Andreas fault in the Transverse Ranges north of Los Angeles for the half-space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm/yr below 30 km. One equivalent lithosphere-asthenosphere model would have a 30-km thick lithosphere and an asthenosphere relaxation time greater than 33 years, but other models are possible. -from Author

  15. A Possible Differentially Shortened Strike-slip Plate Boundary: the Okhotsk Plate Example.

    Science.gov (United States)

    Hindle, D.; Egorov, V.; Mackey, K. G.; Fujita, K.

    2004-12-01

    The Okhotsk plate has been postulated based on a combination of GPS geodetic inversions (REVEL1), seimsicity, geologic and lineament data. Lying between the North American and Eurasian plates, its northwestern corner would appear to be undergoing compression in a scissors motion between the two bounding plates. Extrusion tectonics along multiple, large strike-slip faults within the Okhotsk plate itself have been suggested to allow the escape of material away from the apex of Eurasia-North America. The plate boundary between Okhotsk and North America has been suggested to be diffuse, based on widely scattered minor seismicity. However, the large, left lateral, Ulakhan fault has also been suggested as a candidate plate boundary. We present field geological and geomorphological evidence of the partitioning of deformation between the Ulakhan fault, and several parallel and oblique, linked faults. The Ulakhan fault strand appears to have a maximum displacement of 24 km based on river valley offsets and closing large pull apart basins. Some of the displacement from the Ulakhan fault appears relayed into the plate margin along oblique trending, thrust/oblique slip faults. Estimated shortening over these faults is equivalent to the amount of shortening relayed into the plate margin from the plate boundary. There may be several thrust/oblique slip faults along the Ulakhan fault, which leads to the interesting situation of a segmented, strike-slip plate boundary being actively shortened in a margin parallel direction. This may be the result of postulated extrusion of the Okhotsk plate due to North America/Eurasia convergence. Such a situation would have important consequences for the interpretation of GPS data in a plate tectonic context.

  16. Multiple strike slip faults sets: A case study from the Dead Sea transform

    Science.gov (United States)

    Ron, Hagai; Nur, Amos; Eyal, Y.

    1990-01-01

    In many strike slip tectonic settings, large rotations of crust blocks about vertical axes have been inferred from paleomagnetic data. These blocks are bounded by sets of parallel faults which presumably accommodate the relative motion between the blocks as regional deformation progress. A mechanical model by Nur et al., (1986) suggests that rotations greater than phi sub c equals 25 to 45 degrees must be accommodated by more than one set of faults, with angle phi sub c between their direction; consequently the sum of the angles between sets must be roughly equal to the total tectonic material rotation. To test this model, the authors investigated the fault geometry and field relation of fault sets in the Mt. Hermon area in northern Israel, where paleomagnetic declination implies data 69 degrees plus or minus 13 degrees counter-clockwise block rotation. The statistical and field relation analysis of over 315 faults shows that the faulting is predominantly right lateral strike slip consisting of three distinct sets. The oldest set strikes 253 degrees, the second oldest set strikes 293 degrees and the youngest strikes 339 degrees. This last direction is consistent also with the current north-south direction of the maximum principle stress axis. The angle phi sub c between the first and second sets is 39 degrees and between the second and third sets 46 degrees, in good agreement with the phi sub c angle predicted from mechanical considerations. The sum of the two angles is 85 degrees, in good agreement with the 69 degrees plus or minus 13 degrees CCW paleomagnetically derived rotation. The results suggest specifically that the sequential development of multiple intersecting fault sets is responsible for the faulting in the Mt. Hermon area; and generally that the model of block rotation with multiple faults provides very good simple rules for analyzing very complex fault patterns.

  17. States of stress and slip partitioning in a continental scale strike-slip duplex: Tectonic and magmatic implications by means of finite element modeling

    Science.gov (United States)

    Iturrieta, Pablo Cristián; Hurtado, Daniel E.; Cembrano, José; Stanton-Yonge, Ashley

    2017-09-01

    Orogenic belts at oblique convergent subduction margins accommodate deformation in several trench-parallel domains, one of which is the magmatic arc, commonly regarded as taking up the margin-parallel, strike-slip component. However, the stress state and kinematics of volcanic arcs is more complex than usually recognized, involving first- and second-order faults with distinctive slip senses and mutual interaction. These are usually organized into regional scale strike-slip duplexes, associated with both long-term and short-term heterogeneous deformation and magmatic activity. This is the case of the 1100 km-long Liquiñe-Ofqui Fault System in the Southern Andes, made up of two overlapping margin-parallel master faults joined by several NE-striking second-order faults. We present a finite element model addressing the nature and spatial distribution of stress across and along the volcanic arc in the Southern Andes to understand slip partitioning and the connection between tectonics and magmatism, particularly during the interseismic phase of the subduction earthquake cycle. We correlate the dynamics of the strike-slip duplex with geological, seismic and magma transport evidence documented by previous work, showing consistency between the model and the inferred fault system behavior. Our results show that maximum principal stress orientations are heterogeneously distributed within the continental margin, ranging from 15° to 25° counter-clockwise (with respect to the convergence vector) in the master faults and 10-19° clockwise in the forearc and backarc domains. We calculate the stress tensor ellipticity, indicating simple shearing in the eastern master fault and transpressional stress in the western master fault. Subsidiary faults undergo transtensional-to-extensional stress states. The eastern master fault displays slip rates of 5 to 10 mm/yr, whereas the western and subsidiary faults show slips rates of 1 to 5 mm/yr. Our results endorse that favorably oriented

  18. Magma-assisted strain localization in an orogen-parallel transcurrent shear zone of southern Brazil

    Science.gov (United States)

    Tommasi, AndréA.; Vauchez, Alain; Femandes, Luis A. D.; Porcher, Carla C.

    1994-04-01

    . Synkinematic granitoids localize most, if not all, deformation in the studied shear zone. The regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies, consistently displaying similar plane and direction of flow, argue for accommodation of large amounts of orogen-parallel movement by viscous deformation of these magmas. Moreover, activation of high-temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and, consequently, contributed significantly to the localization of deformation. Finally, the small extent of the low-temperature deformation suggests that the strike-slip deformation ended approximately synchronously with the final cooling of the peraluminous granites. The evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone. Magma intrusion in an orogen-scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust. It triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated. Therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments.

  19. The 2015 Mw7.2 Sarez Strike-Slip Earthquake in the Pamir Interior: Response to the Underthrusting of India's Western Promontory

    Science.gov (United States)

    Metzger, Sabrina; Schurr, Bernd; Ratschbacher, Lothar; Sudhaus, Henriette; Kufner, Sofia-Katerina; Schöne, Tilo; Zhang, Yong; Perry, Mason; Bendick, Rebecca

    2017-11-01

    The Pamir orogen, Central Asia, is the result of the ongoing northward advance of the Indian continent causing shortening inside Asia. Geodetic and seismic data place the most intense deformation along the northern rim of the Pamir, but the recent 7 December 2015, Mw7.2 Sarez earthquake occurred in the Pamir's interior. We present a distributed slip model of this earthquake using coseismic geodetic data and postseismic field observations. The earthquake ruptured an ˜80 km long, subvertical, sinistral fault consisting of three right-stepping segments from the surface to ˜30 km depth with a maximum slip of three meters in the upper 10 km of the crust. The coseismic slip model agrees well with en échelon secondary surface breaks that are partly influenced by liquefaction-induced mass movements. These structures reveal up to 2 m of sinistral offset along the northern, low-offset segment of modeled rupture. The 2015 event initiated close to the presumed epicenter of the 1911 Mw˜7.3 Lake Sarez earthquake, which had a similar strike-slip mechanism. These earthquakes highlight the importance of NE trending sinistral faults in the active tectonics of the Pamir. Strike-slip deformation accommodates shear between the rapidly northward moving eastern Pamir and the Tajik basin in the west and is part of the westward (lateral) extrusion of thickened Pamir plateau crust into the Tajik basin. The Sarez-Karakul fault system and the two large Sarez earthquakes likely are crustal expressions of the underthrusting of the northwestern leading edge of the Indian mantle lithosphere beneath the Pamir.

  20. Shear zones between rock units with no relative movement

    DEFF Research Database (Denmark)

    Koyi, H.; Schmeling, H.; Burchardt, S.

    2012-01-01

    Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two "blocks" that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other...... magma body (stoping). From the fluid dynamics point of view these shear zones can be regarded as the low Reynolds number deformation zones within the wake of a body moving through a viscous medium. While compact (aspect ratio 1:1:1) moving bodies generate axial symmetric (cone like) shear zones...

  1. Shear zones between rock units with no relative movement

    DEFF Research Database (Denmark)

    Koyi, Hemin; Schmeling, Harro; Burchardt, Steffi

    2013-01-01

    Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two "blocks" that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other...... a partially molten magma body (stoping). From the fluid dynamics perspective these shear zones can be regarded as low Reynolds number deformation zones within the wake of a body moving through a viscous medium. While compact moving bodies (aspect ratio 1:1:1) generate axial symmetric (cone like) shear zones...

  2. Influence of fault steps on rupture termination of strike-slip earthquake faults

    Science.gov (United States)

    Li, Zhengfang; Zhou, Bengang

    2018-03-01

    A statistical analysis was completed on the rupture data of 29 historical strike-slip earthquakes across the world. The purpose of this study is to examine the effects of fault steps on the rupture termination of these events. The results show good correlations between the type and length of steps with the seismic rupture and a poor correlation between the step number and seismic rupture. For different magnitude intervals, the smallest widths of the fault steps (Lt) that can terminate the rupture propagation are variable: Lt = 3 km for Ms 6.5 6.9, Lt = 4 km for Ms 7.0 7.5, Lt = 6 km for Ms 7.5 8.0, and Lt = 8 km for Ms 8.0 8.5. The dilational fault step is easier to rupture through than the compression fault step. The smallest widths of the fault step for the rupture arrest can be used as an indicator to judge the scale of the rupture termination of seismic faults. This is helpful for research on fault segmentation, as well as estimating the magnitude of potential earthquakes, and is thus of significance for the assessment of seismic risks.

  3. Source characteristics of the 2015 Mw6.5 Lefkada, Greece, strike-slip earthquake

    Science.gov (United States)

    Melgar, Diego; Ganas, Athanassios; Geng, Jianghui; Liang, Cunren; Fielding, Eric J.; Kassaras, Ioannis

    2017-03-01

    We present a kinematic slip model from the inversion of 1 Hz GPS, strong motion, and interferometric synthetic aperture radar (InSAR) data for the 2015 Mw6.5 Lefkada, Greece, earthquake. We will show that most of the slip during this event is updip of the hypocenter (10.7 km depth) with substantial slip (>0.5 m) between 5 km depth and the surface. The peak slip is 1.6 m, and the inverted rake angles show predominantly strike-slip motion. Slip concentrates mostly to the south of the hypocenter, and the source time function indicates a total duration of 17 s with peak moment rate at 6 s. We will show that a 65° dipping geometry is the most plausible due to a lack of polarity reversals in the InSAR data and good agreement with Coulomb stress modeling, aftershock locations, and regional moment tensors. We also note that there was an 20 cm peak-to-peak tsunami observed at one tide gauge station 300 km away from the earthquake. We will discuss tsunami modeling results and study the possible source of the amplitude discrepancy between the modeled and the observed data at far-field tide gauges.

  4. Upper crustal earthquake swarms in São Caetano: Reactivation of the Pernambuco shear zone and trending branches in intraplate Brazil

    Science.gov (United States)

    Lima Neto, Heleno C.; Ferreira, Joaquim M.; Bezerra, Francisco Hilário R.; Assumpção, Marcelo S.; do Nascimento, Aderson F.; Sousa, Maria O. L.; Menezes, Eduardo A. S.

    2013-11-01

    Seismogenic fault reactivation of continental-scale structures has been observed in a few intraplate areas, but its cause is still a matter of debate. The objective of the present study is to analyze two seismic swarms that occurred along the EW-trending Pernambuco ductile shear zone and in a NE-trending branch, in 2007 and 2010 in São Caetano County, Northeastern Brazil. We studied both epicentral areas using a nine- and a seven-station network during 180 and 54 days, respectively. The results indicate that the 2007 swarm correspond to a right-lateral, strike-slip fault with a normal component of slip (strike 74°, dip 60°, and rake - 145°) and the 2010 swarm corresponds to a normal fault (strike 265°, dip 79°, and rake - 91°). The former reactivated a NE-trending branch, whereas the latter reactivated the main E-W-trending mylonitic belt of the Pernambuco shear zone. These results are consistent with seismogenic reactivation of this major structure, generated by the present-day EW-trending compression and NS-trending extension, as observed by previous studies. This shear zone was reactivated as rift faults in the Cretaceous during the South America-Africa breakup. However, our study confirms that the basement fabric such as continental-scale ductile shear zones, show evidence of crustal weakness outside areas of previous rifting, and it reveals the potential for large earthquakes along dormant rift segments associated with major basement shear belts.

  5. Magnetotelluric imaging of the crustal structure of the Great Slave Lake shear zone in Northwest Alberta

    Science.gov (United States)

    WANG, E.; Unsworth, M. J.; Chacko, T.

    2017-12-01

    The Alberta basement is part of the North American craton - Laurentia, which was assembled in the Paleoproterozoic era. The Great Slave Lake shear zone (GSLsz) is the major crustal-scale right-lateral strike-slip feature in northwest Laurentia. Because of the extensive coverage of the rocks of the WCSB, geological studies in northern Alberta are limited to studies of drill core samples. The crustal structures of northern Alberta were defined from potential field in combination with isotopic studies. Magnetotelluric method is helpful in this case, because it is sensitive to conductive bodies. New Broadband magnetotelluric data were collected across the GSLsz to give a clear image of the crustal structure. Dimensionality analyses showed that the data are two-dimensional at the crustal depth, even though 3-D effects are present at the lowest frequencies. Consequently, 2-D inversions were applied and a preferred resistivity model was achieved. The WCSB was imaged as a conductive layer on the top of the resistive Precambrian basement rocks. Four conductive bodies associate with terrane boundaries were identified. The largest conductor - KC is located coincident with the Kiskatinaw terrane at the mid-crustal depth. The second conductor - KCC is located at the boundary of the Ksituan and Chinchaga terranes at upper-crustal depth. The KC and KCC are suspected to be linear conductors that are consistent along the strikes of the Kiskatinaw terrane and the western boundary of the Chinchaga terrane, respectively. This is concluded when considering the result of this study in combination with the potential field data, a previously proposed 3-D resistivity model and a 2-D seismic reflection result. Both of the KC and KCC corresponds to seismically reflective zones. The third conductor - HC is imaged beneath the Hottah terrane. The GSLsz is close to the HC and they may be related in origin. The fourth conductor - CBHC is imaged at the boundary of the Chinchaga and Buffalo Head

  6. Dynamics of a strike-slip fault analog model : Effects of the tectonic loading rate

    Science.gov (United States)

    Caniven, Y.; Dominguez, S.; Soliva, R.; Cattin, R.; Peyret, M.; Chéry, J.; Romano, C.

    2013-12-01

    The average seismic cycle duration extends from hundred to a few thousands years but geodetic measurements and seismological data extend over less than one century. This short time observation scale renders difficult to constrain the role of key parameters such as fault friction and geometry, crust rheology, stress and strain rate that control the kinematics and mechanics of active faults. To solve this time scale issue, we have developed a new experimental set-up that reproduces scaled micro-earthquakes and several hundreds of seismic cycles along a strike-slip fault. The model is constituted by two polyurethane foam plates laterally in contact, lying on a basal silicone layer, which simulate the mechanical behaviour of an elastoplastic upper crust over a ductile lower crust, respectively. To simulate the boundary conditions of a strike-slip fault, a computerized motoreductor system moves the two compartments on an opposite sens at a constant low velocity (a few μm/s). The model scaling, deduces from analog material physical parameters, implies that 1 cm in the model represents 2-3 km in the nature and 1 s is equivalent to 5-15 years. Surface-horizontal strain field is quantified by sub-pixel correlation of digital camera pictures recorded every 16 μm of displacement. We record about 2000 horizontal-velocity field measurements for each experiment. The analysis of model-interseismic and coseismic surface displacements and their comparison to seismogenic natural faults demonstrate that our analog model reproduces correctly both near and far-field surface strains. To compare the experiments, we have developed several algorithms that allow studying the main spatial and temporal evolution of the physical parameters and surface deformation processes that characterise the seismic cycle (magnitudes, stress, strain, friction coefficients, interseismic locking depth, recurrence time, ...). We also performed surface-velocity field inversions to assess the spatial

  7. Left-Lateral Strike-Slip Faulting in the East Alborz, NE Iran

    Science.gov (United States)

    Hollingsworth, J.; Walker, R.; Jackson, J.; Bolourchi, M. J.; Eshraghi, S. A.

    2006-12-01

    The East Alborz mountains of NE Iran are actively deforming as a result of Arabia-Eurasia collision. We combine observations of the geomorphology made using high resolution satellite, topographic and field data, with historical and recent seismicity to map major active faults in this poorly studied region. Deformation on the north side of the range occurs by range-normal shortening on the Khazar thrust fault, which separates Central Iran from the South Caspian. South of the range, deformation involves both left-lateral slip on the previously undocumented Shahrud fault system, which comprises several range-bounding fault segments, and shortening on (probably minor) thrust faults. Faulting south of the range is responsible for major historical earthquakes at Damghan (856AD) and Shahrud (1890). Deformation accommodated across the East Alborz is estimated from the difference in GPS velocities north and south of the range. South of the Alborz, northward GPS velocities across Central Iran decrease eastwards and the strike of the deforming belt changes to become more sub-parallel to the direction of South Caspian- Iran relative motion. This reduces the shortening component across the East Alborz, resulting in lower elevations between 54--57°E. West of 55.5°E, the more arc-normal shortening is achieved by partitioning of deformation onto the Khazar thrust (~1 mm/yr) and the Astaneh and Firuzkuh strike-slip faults (~3 mm/yr). East of 55.5°E, the Khazar fault ends and East Alborz deformation is accommodated primarily on the left-lateral Shahrud fault system, which may slip up to 3~mm/yr. Due to the long gap in seismicity along the eastern Shahrud fault system, the city of Jajarm (15,000 pop.) is considered at high risk from future earthquakes.

  8. Earthquake Activities Along the Strike-Slip Fault System on the Thailand-Myanmar Border

    Directory of Open Access Journals (Sweden)

    Santi Pailoplee

    2014-01-01

    Full Text Available This study investigates the present-day seismicity along the strike-slip fault system on the Thailand-Myanmar border. Using the earthquake catalogue the earthquake parameters representing seismic activities were evaluated in terms of the possible maximum magnitude, return period and earthquake occurrence probabilities. Three different hazardous areas could be distinguished from the obtained results. The most seismic-prone area was located along the northern segment of the fault system and can generate earthquakes of magnitude 5.0, 5.8, and 6.8 mb in the next 5, 10, and 50 years, respectively. The second most-prone area was the southern segment where earthquakes of magnitude 5.0, 6.0, and 7.0 mb might be generated every 18, 60, and 300 years, respectively. For the central segment, there was less than 30 and 10% probability that 6.0- and 7.0-mb earthquakes will be generated in the next 50 years. With regards to the significant infrastructures (dams in the vicinity, the operational Wachiralongkorn dam is situated in a low seismic hazard area with a return period of around 30 - 3000 years for a 5.0 - 7.0 mb earthquake. In contrast, the Hut Gyi, Srinakarin and Tha Thung Na dams are seismically at risk for earthquakes of mb 6.4 - 6.5 being generated in the next 50 years. Plans for a seismic-retrofit should therefore be completed and implemented while seismic monitoring in this region is indispensable.

  9. Strike-Slip Fault Patterns on Europa: Obliquity or Polar Wander?

    Science.gov (United States)

    Rhoden, Alyssa Rose; Hurford, Terry A.; Manga, Michael

    2011-01-01

    Variations in diurnal tidal stress due to Europa's eccentric orbit have been considered as the driver of strike-slip motion along pre-existing faults, but obliquity and physical libration have not been taken into account. The first objective of this work is to examine the effects of obliquity on the predicted global pattern of fault slip directions based on a tidal-tectonic formation model. Our second objective is to test the hypothesis that incorporating obliquity can reconcile theory and observations without requiring polar wander, which was previously invoked to explain the mismatch found between the slip directions of 192 faults on Europa and the global pattern predicted using the eccentricity-only model. We compute predictions for individual, observed faults at their current latitude, longitude, and azimuth with four different tidal models: eccentricity only, eccentricity plus obliquity, eccentricity plus physical libration, and a combination of all three effects. We then determine whether longitude migration, presumably due to non-synchronous rotation, is indicated in observed faults by repeating the comparisons with and without obliquity, this time also allowing longitude translation. We find that a tidal model including an obliquity of 1.2?, along with longitude migration, can predict the slip directions of all observed features in the survey. However, all but four faults can be fit with only 1? of obliquity so the value we find may represent the maximum departure from a lower time-averaged obliquity value. Adding physical libration to the obliquity model improves the accuracy of predictions at the current locations of the faults, but fails to predict the slip directions of six faults and requires additional degrees of freedom. The obliquity model with longitude migration is therefore our preferred model. Although the polar wander interpretation cannot be ruled out from these results alone, the obliquity model accounts for all observations with a value

  10. A comparison of GPS solutions for strain and SKS fast directions: Implications for modes of shear in the mantle of a plate boundary zone

    Science.gov (United States)

    Houlie, N.; Stern, T. A.

    2012-12-01

    The strain rate and vertical velocity fields for New Zealand are computed using GPS data from GEONET (NZ) collected during the past decade. Two domains for shear in the mantle are inferred by comparing the principal shortening direction with the fast direction of shear wave splitting. Beneath the central- southern part of the South Island the strains are low and its unclear if irrotational strain is taking place or if the splitting here is dominated by anisotropy in the asthenosphere. In contrast, data for the central and northern South Island suggest simple shear is dominant and distributed over a zone 200 km wide. An analysis of the major strike-slip faults confirms that the strike of the major South Island fault systems makes a 60±15 deg. angle with the shortening direction. A map of the vertical component of GEONET GPS velocities shows regions of surface uplift >5mm/y in both the central South and North Islands. While the pattern of uplift in central South Island is consistent with known geology, the rate of uplift in the central North Island is an order of magnitude higher than the geological rate estimated on a my timescale.

  11. Petrology, chronology and sequence of vein systems: Systematic magmatic and hydrothermal history of a major intracontinental shear zone, Canadian Appalachians

    Science.gov (United States)

    Pe-Piper, Georgia; Piper, David J. W.; McFarlane, Chris R. M.; Sangster, Chris; Zhang, Yuanyuan; Boucher, Brandon

    2018-04-01

    Intra-continental shear zones developed during continental collision may experience prolonged magmatism and mineralization. The Cobequid Shear Zone formed part of a NE-SW-trending, orogen-parallel shear system in the late Devonian-early Carboniferous, where syn-tectonic granite-gabbro plutons and volcanic rocks 4 km thick were progressively deformed. In late Carboniferous to Permian, Alleghanian collision of Africa with Laurentia formed the E-W trending Minas Fault Zone, reactivating parts of the Cobequid Shear Zone. The 50 Ma history of hydrothermal mineralization following pluton emplacement is difficult to resolve from field relationships of veins, but SEM study of thin sections provides clear detail on the sequence of mineralization. The general paragenesis is: albite ± quartz ± chlorite ± monazite → biotite → calcite, allanite, pyrite → Fe-carbonates, Fe-oxides, minor sulfides, calcite and synchysite. Chronology was determined from literature reports and new U-Pb LA-ICPMS dating of monazite and allanite in veins. Vein mineralization was closely linked to magmatic events. Vein emplacement occurred preferentially during fault movement recognised from basin-margin inversion, as a result of fractures opening in the damage zone of master faults. The sequence of mineralization, from ca. 355 Ma riebeckite and albite veins to ca. 327 (-305?) Ma siderite-magnetite and sulfide mineralization, resembles Precambrian iron-oxide-copper-gold (IOCG) systems in the literature. The abundant magmatic Na, halogens and CO2 in veins and some magmatic bodies, characteristic of IOCG systems, were derived from the deeply subducted Rheic Ocean slab with little terrigenous sediment. Regional extension of the Magdalen Basin caused asthenospheric upwelling and melting of the previously metasomatized sub-continental lithospheric mantle. Crustal scale strike-slip faulting facilitated the rise of magmas, resulting in high heat flow driving an active hydrothermal system. Table S2

  12. Crustal Anisotropy Beneath the Western Segment of North Anatolian Fault Zone from Local Shear-Wave Splitting

    Science.gov (United States)

    Altuncu Poyraz, S.; Teoman, U.; Kahraman, M.; Turkelli, N.; Rost, S.; Thompson, D. A.; Houseman, G.

    2014-12-01

    Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the upper crust. Upper-crustal anisotropy is widely interpreted as due to aligned fluid-filled cracks or pores. Differential stress is thought to close cracks aligned perpendicular to the maximum principal stress and leaves cracks open that are aligned perpendicular to the minimum horizontal compressional stress. In other cases local shear-wave splitting has been found to be aligned with regional faulting. Temporal variations in local splitting patterns might provide hints of changes in stress orientation related to earthquakes or volcanoes. North Anatolian Fault Zone (NAFZ) is a large-scale continental strike slip fault system originating at the Karlıova Junction in the east where it intersects the East Anatolian Fault (EAF) and extends west cutting across the entire Northern Turkey towards the Aegean Sea and the mainland Greece. Our primary focus is to provide constraints on the crustal anisotropy beneath the western segment of the North Anatolian Fault Zone with the use of a data set collected from a dense temporary seismic network consisting of 70 stations that was deployed in early May 2012 and operated for 18 months in the Sakarya region and the surroundings during the Faultlab experiment. For the local shear wave splitting analysis, out of 1344 events, we extracted 90 well located earthquakes with magnitudes greater than 2.0. Local shear-wave splitting makes use of earthquakes close to and nearly directly below the recording station. Incidence angles of less than 45 degrees were used to avoid the free-surface effect and resulting non-linear particle motion. Basically, two essential parameters for each station-event pair is needed for shear wave splitting calculations. One of them is fast polarization direction (ɸ) and the other is delay time (δt) between the fast and slow components of the shear wave. In this study, delay times vary between 0,02 and 0,25 seconds

  13. COMPARISON OF COSEISMIC IONOSPHERIC DISTURBANCE WAVEFORMS REVISITED: STRIKE-SLIP, NORMAL, AND REVERSE FAULT EARTHQUAKE

    Directory of Open Access Journals (Sweden)

    Mokhamad Nur Cahyadi

    2015-02-01

    Full Text Available Using Total Electron Content (TEC measurements with Global Positioning System we studied ionospheric responses to three large earthquakes with difference focal mechanism that occurred in the Sumatra Andaman 26 December 2004, North off Sumatra 11 April 2012, and North Japan 7 December 2012. These earthquakes have different focal mechanisms, i.e. high-angle reverse, strike-slip, and normal faulting, respectively. TEC responses to the Sumatra Andaman 2004 and north Japan 2012 events initiated with positive changes. On the other hand, the initial TEC changes in the Sumatra 2012 earthquake showed both positive and negative polarities depending on the azimuth around the focal area. Such a variety may reflect differences in coseismic vertical crustal displacements, which are dominated by uplift and subsidence in the Sumatra 2012 event. This phenomena has same characteristic with 1994 Kuril Arch earthquake. There are three different propagation velocity in the Sumatra 2012 earthquake, within the first 300 km until 430 km, the CID propagation velocity was ~3 km/s, which is equal to the secod sound speed at the height of the ionospheric F-layer. Starting from 380 km until 750 km out from the epicenter, the disturbance seems to divide into two separate perturbations, with each propagating at a different velocity, about 1 km/s for the one and about 0.4 m/s for the other. The apparent velocity in the Sumatra Andaman 2004 and Japan 2012 propagated ~ 1 km/s and ~ 0.3 km/s, consistent with the sound speed at the ionospheric F layer height and internal gravity wave respectively. Resonant oscillation of TEC with a frequency of ~ 3.7 mHZ and ~4.4 mHz have been found in the Sumatra 2012 and Sumatra Andaman 2004 events. Those earthquakes, which occurred during a period of quiet geomagnetic activity, also showed clear preseismic TEC anomalies similar to those before the 2011 Tohoku-Oki and 2007 Bengkulu earthquake.   The positive anomalies started 30-60 minutes

  14. Holocene paleoearthquakes on the strike-slip Porters Pass Fault, Canterbury, New Zealand

    International Nuclear Information System (INIS)

    Howard, M.; Nicol, A.; Campbell, J.; Pettinga, J.R.

    2005-01-01

    The Porters Pass Fault comprises a series of discontinuous Holocene active traces which extend for c. 40 km between the Rakaia and Waimakariri Rivers in the foothills of the Southern Alps. There have been no historical earthquakes on the Porters Pass Fault (i.e., within the last 150 yr), and the purpose of this paper is to establish the timing and magnitudes of displacements on the fault at the ground surface during Holocene paleoearthquakes. Displaced geomorphic features (e.g., relict streams, stream channels, and ridge crests), measured using either tape measure (n = 20) or surveying equipment (n = 5), range from 5.5 to 33 m right lateral strike slip and are consistent with six earthquakes characterised by slip per event of c. 5-7 m. The timing of these earthquakes is constrained by radiocarbon dates from four trenches excavated across the fault and two auger sites from within swamps produced by ponding of drainage along the fault scarp. These data indicate markedly different Holocene earthquake histories along the fault length separated by a behavioural segment boundary near Lake Coleridge. On the eastern segment at least six Holocene earthquakes were identified at 8400-9000, 5700-6700, 4500-6000, 2300-2500, 800-1100, and 500-600 yr BP, producing an average recurrence interval of c. 1500 yr. On the western segment of the fault in the Rakaia River valley, a single surface-rupturing earthquake displaced Acheron Advance glacial deposits (c.10,000-14,000 yr in age) and may represent the southward continuation of the 2300-2500 yr event identified on the eastern segment. These data suggest Holocene slip rates of 3.2-4.1 mm/yr and 0.3-0.9 mm/yr on the eastern and western sections of the fault, respectively. Displacement and timing data suggest that earthquakes ruptured the western segment of the fault in no more than one-sixth of cases and that for a sample period of 10,000 yr the recurrence intervals were not characteristic. (auth). 45 refs., 10 figs., 3 tabs

  15. The late Quaternary slip history of the North Anatolian Fault, Turkey: Implications for the spatial and temporal behaviour of large strike-slip fault belts

    Science.gov (United States)

    Zabcı, Cengiz; Akyüz, H. Serdar; Sançar, Taylan; Güneç Kıyak, Nafiye

    2015-04-01

    The study of the spatial and temporal behaviour of active faults by estimating the geologic and geodetic slip rates is critical not only for assessing the seismic potential of these tectonic structures, but also for understanding their geodynamics. Geodetic data can provide detailed spatial coverage but represent a short time interval of a single earthquake cycle, while geologic rates are derived as average values for multiple events at spatially limited sites. In the complex tectonic setting of the eastern Mediterranean, the westward extrusion of the Anatolian scholle is mainly accommodated by two major tectonic structures, the North Anatolian (NASZ) and the East Anatolian (EASZ) shear zones, respectively forming the northern and eastern boundaries. The rate of deformation all along the North Anatolian Fault (NAF) is spatially well documented mainly by GPS and InSAR based geodetic studies during the last two decades. Furthermore, the number of the morphochronology-based geologic slip rate studies significantly increased, covering the different sections of this large strike slip fault for various time intervals. In this study, we do not only compile all previous geologic slip rate estimates, but we also present data for three new and two revised sites from central to the most eastern parts of the NAF in order to understand the spatial and temporal behaviour of this important fault system. The integrated dataset of geologic studies were classified into two groups to represent the central to eastern sections (Model I) and the western part (Model II). The geographical diversion between two models is about at the 31° E longitude, where the NAF bifurcates into two branches from this point toward west into the Marmara Region. To test any secular variation in fault's slip history, we used the Monte Carlo approach of Gold and Cowgill (2011). After the removal of rates, which do not account the near fault deformation or the existing parallel/sub-parallel faults, the Model

  16. Rheological weakening of high-grade mylonites during low-temperature retrogression: The exhumed continental Ailao Shan-Red River fault zone, SE Asia

    Science.gov (United States)

    Cao, Shuyun; Neubauer, Franz; Liu, Junlai; Bernroider, Manfred; Cheng, Xuemei; Li, Junyu; Yu, Zunpu; Genser, Johann

    2017-05-01

    We present a detailed case study of an exhumed continental strike-slip fault zone, the Ailao Shan-Red River (ASRR) strike-slip fault zone, to investigate how deformation promotes strain localization, and how the weak second phases and fluids trigger rheological weakening during retrogression near the ductile to brittle transition during exhumation. Along the ASRR strike-slip fault zone, in the Diancang Shan (DCS) metamorphic massif, high-temperature ductile deformation (D1) pervasively occurred during shearing and exhumation since late Oligocene. The high-temperature microstructures and textures are in part or entirely altered by subsequent low-temperature shearing (D2) since late Miocene, which is under the conditions of frictional-viscous transition of K-feldspar (ca. 450 °C) during further exhumation to the upper crustal levels. The formation of D2 microstructures and shear bands overprinted high-temperature intracrystalline plasticity phases (D1) in mylonitic rocks. Depending on the main rock-forming minerals, the results also demonstrate that the brittle-ductile transition involves a combination of different deformation mechanisms and possible rheological paths. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to exhumation. As a result, grain-size reduction associated with fluids circulating within the ASRR strike-slip fault zone at brittle-ductile transition leads to reaction and texture weakening. Rheological weakening is the consequence of the syntectonic deformation, fluid flow, reaction softening, reaction creep and textural softening. The hydrous fluids resulted in hydration of silicates. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the exhumation through the ductile to ductile-brittle transition involves a combination of different

  17. Geochemical and isotopic characterization of the granitic magmatism along the Remígio - Pocinhos shear zone, Borborema Province, NE Brazil

    Science.gov (United States)

    de Lima, Jefferson V.; Guimarães, Ignez de P.; Santos, Lucilene; Amorim, José Victor A.; Farias, Douglas José S.

    2017-04-01

    Two granitoid plutons (Pilõezinhos and Curral de Cima) intruded along the Remígio - Pocinhos shear zone, eastern part of the Borborema Province. The Pilõezinhos and Curral de Cima granites were dated at 566 ± 3 Ma and 618 ± 5 Ma respectively. The granitoids from both plutons have distinct initial 143Nd/144Nd ratios, expressed by εNd(t) values, i.e. the granitoids of Pilõezinhos pluton have lower εNd(t) values (-15.47 to -15.81) and negative εHf (t = 570 Ma) values (-16.0 to -18.6), while the granitoids of the Curral de Cima pluton have εNd(t) values between -1.12 and -5.23. The granitoids of the Curral de Cima pluton are epidote bearing, magnesian calcalkaline I-type granitoids, crystallized under high fO2 conditions. The granitoids of the Pilõezinhos pluton are alkaline, low-fO2, ferroan, ilmenite-series, A2-type granite intrusions. The geochemical and isotopic signatures suggest that the origin of magma of the Curral de Cima granitoids involved mixing/mingling at depth between crustal and mantle magmas, associated to decompression (lateral escape) during the convergent stage of Brasiliano/Pan/African orogeny, which lead the asthenosphere melts to rise into the lower crust. The source of magma of the granitoids of the Pilõezinhos pluton involved a strong crustal component with geochemical and isotopic signatures similar to the orthogneisses of the Serrinha-Pedro Velho Complex, and small mantle component. The emplacement of the Pilõezinhos pluton is associated to an extensional space formed during high-T strike-slip shearing developed by the synchronic movement of the Matinhas sinistral shear zone and Remígio - Pocinhos dextral shear zone.

  18. Contrasting metamorphism across Cauvery Shear Zone, south India

    Indian Academy of Sciences (India)

    The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating ...

  19. Deformation of footwall rock of Phulad Shear Zone, Rajasthan ...

    Indian Academy of Sciences (India)

    Phulad Shear Zone (PSZ) of Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e. ...

  20. Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

    Directory of Open Access Journals (Sweden)

    T. van der Werf

    2017-12-01

    Full Text Available The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene–Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750–890 °C and pressures of 400–560 MPa, corresponding to 15–22 km depth. A hot crustal geotherm of 40 ° C km−1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12–33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12–17 MPa in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1–1.3×1020 Pa ⋅ s for the high temperature conditions (890 °C in the lower crust. Significantly lower viscosities in the range of 1016–1019 Pa ⋅ s, were estimated using flow laws for wet plagioclase. The

  1. The 2014 Mw6.9 Gokceada and 2017 Mw6.3 Lesvos Earthquakes in the Northern Aegean Sea: The Transition from Right-Lateral Strike-Slip Faulting on the North Anatolian Fault to Extension in the Central Aegean

    Science.gov (United States)

    Cetin, S.; Konca, A. O.; Dogan, U.; Floyd, M.; Karabulut, H.; Ergintav, S.; Ganas, A.; Paradisis, D.; King, R. W.; Reilinger, R. E.

    2017-12-01

    The 2014 Mw6.9 Gokceada (strike-slip) and 2017 Mw6.3 Lesvos (normal) earthquakes represent two of the set of faults that accommodate the transition from right-lateral strike-slip faulting on the North Anatolian Fault (NAF) to normal faulting along the Gulf of Corinth. The Gokceada earthquake was a purely strike-slip event on the western extension of the NAF where it enters the northern Aegean Sea. The Lesvos earthquake, located roughly 200 km south of Gokceada, occurred on a WNW-ESE-striking normal fault. Both earthquakes respond to the same regional stress field, as indicated by their sub-parallel seismic tension axis and far-field coseismic GPS displacements. Interpretation of GPS-derived velocities, active faults, crustal seismicity, and earthquake focal mechanisms in the northern Aegean indicates that this pattern of complementary faulting, involving WNW-ESE-striking normal faults (e.g. Lesvos earthquake) and SW-NE-striking strike-slip faults (e.g. Gokceada earthquake), persists across the full extent of the northern Aegean Sea. The combination of these two "families" of faults, combined with some systems of conjugate left-lateral strike-slip faults, complement one another and culminate in the purely extensional rift structures that form the large Gulfs of Evvia and Corinth. In addition to being consistent with seismic and geodetic observations, these fault geometries explain the increasing velocity of the southern Aegean and Peloponnese regions towards the Hellenic subduction zone. Alignment of geodetic extension and seismic tension axes with motion of the southern Aegean towards the Hellenic subduction zone suggests a direct association of Aegean extension with subduction, possibly by trench retreat, as has been suggested by prior investigators.

  2. Deformation at a Complex Strike-Slip Plate Boundary: Modeling the Southern California GPS Velocity Field

    Science.gov (United States)

    Thatcher, W. R.; Murray-Moraleda, J. R.

    2009-12-01

    a simple block description may not be useful. It is notable that a number of documented disagreements between GPS and geologic slip rates occur on faults in these complex deforming zones (e.g. central Garlock fault, Eastern California Shear Zone, Big Bend San Andreas), in part reflecting the substantial epistemic uncertainty in GPS rate estimates for these faults. Our analysis suggests new GPS measurements and InSAR imaging that could refine slip rate estimates on a number of faults. However, in some cases GPS slip rate uncertainties are endemic and cannot be rectified by even higher station density or greater measurement precision. The difficulty arises because interseismic deformation is due to aseismic slip or localized ductile shearing on the down-dip extensions of faults that are locked (not slipping) in the seismogenic upper crust, smearing out the geodetically measured strain over a scale length of several times the locking depth of each fault (10-20 km). Where faults are closely spaced and slip at comparable rates, velocity gradients are quasi-uniform and the effects of individual faults cannot be distinguished. Better geologic slip rate constraints could ameliorate this non-uniqueness, but only under the assumption that geologic and GPS rates should agree.

  3. The geometry of the active strike-slip El Tigre Fault, Precordillera of San Juan, Central-Western Argentina: integrating resistivity surveys with structural and geomorphological data

    Science.gov (United States)

    Fazzito, Sabrina Y.; Cortés, José M.; Rapalini, Augusto E.; Terrizzano, Carla M.

    2013-07-01

    The geometry and related geomorphological features of the right-lateral strike-slip El Tigre Fault, one of the main morphostructural discontinuities in the Central-Western Precordillera of Argentina, were investigated. Achievements of this survey include: recognition of structural and geometrical discontinuities along the fault trace, identification and classification of landforms associated with local transpressional and transtensional sectors, observation of significant changes in the fault strike and detection of right and left bends of different wavelength. In the Central Segment of the El Tigre Fault, 2D electrical resistivity tomography surveys were carried out across the fault zone. The resistivity imaging permitted to infer the orientation of the main fault surface, the presence of blind fault branches along the fault zone, tectonic tilting of the Quaternary sedimentary cover, subsurface structure of pressure ridges and depth to the water table. Based on this information, it is possible to characterize the El Tigre Fault also as an important hydro-geological barrier. Our survey shows that the main fault surface changes along different segments from a high-angle to a subvertical setting whilst the vertical-slip component is either reverse or normal, depending on the local transpressive or transtensive regime induced by major bends along the trace. These local variations are expressed as sections of a few kilometres in length with relatively homogeneous behaviour and frequently separated by oblique or transversal structures.

  4. Investigation of intraplate seismicity near the sites of the 2012 major strike-slip earthquakes in the eastern Indian Ocean through a passive-source OBS experiment

    Science.gov (United States)

    Guo, L.; Lin, J.; Yang, H.

    2017-12-01

    The 11 April 2012 Mw8.6 earthquake off the coast of Sumatra in the eastern Indian Ocean was the largest strike-slip earthquake ever recorded. The 2012 mainshock and its aftershock sequences were associated with complex slip partitioning and earthquake interactions of an oblique convergent system, in a new plate boundary zone between the Indian and Australian plates. The detail processes of the earthquake interactions and correlation with seafloor geological structure, however, are still poorly known. During March-April 2017, an array of broadband OBS (ocean bottom seismometer) were deployed, for the first time, near the epicenter region of the 2012 earthquake sequence. During post-expedition data processing, we identified 70 global earthquakes from the National Earthquake Information Center (NEIC) catalog that occurred during our OBS deployment period. We then picked P and S waves in the seismic records and analyzed their arrival times. We further identified and analyzed multiple local earthquakes and examined their relationship to the observed seafloor structure (fracture zones, seafloor faults, etc.) and the state of stresses in this region of the eastern Indian Ocean. The ongoing analyses of the data obtained from this unique seismic experiment are expected to provide important constraints on the large-scale intraplate deformation in this part of the eastern Indian Ocean.

  5. Intraplate earthquake swarm in Belo Jardim, NE Brazil: reactivation of a major Neoproterozoic shear zone (Pernambuco Lineament)

    Science.gov (United States)

    Lopes, Afonso E. V.; Assumpção, Marcelo; do Nascimento, Aderson F.; Ferreira, Joaquim Mendes; Menezes, Eduardo A. S.; Barbosa, José Roberto

    2010-03-01

    Intraplate earthquakes in stable continental areas have been explained basically by reactivation of pre-existing zones of weakness, stress concentration, or both. Zones of weakness are usually identified as sites of the last major orogeny, provinces of recent alkaline intrusions, or stretched crust in ancient rifts. However, it is difficult to identify specific zones of weakness and intraplate fault zones are not always easily correlated with known geological features. Although Northeastern Brazil is one of the most seismically active areas in the country (magnitudes 5 roughly every 5 yr), with hypocentral depths shallower than ~10 km and seismic zones as long as 30-40 km, no clear relationship with the known surface geology can be usually established with confidence, and a clear identification of zones of weakness has not yet been possible. Here we present the first clear case of seismic activity occurring as reactivation of an old structure in Brazil: the Pernambuco Lineament, a major Neoproterozoic shear zone. The 2004 earthquake swarm of Belo Jardim (magnitudes up to 3.1) and the recurrent activities in the nearby towns of São Caetano and Caruaru (magnitudes up to 4.0 and 3.8), show that the Pernambuco Lineament is a weak zone. A local seismic network showed that the Belo Jardim swarm of 2004 November occurred by normal faulting on a North dipping, E-W oriented fault plane in close agreement with the E-W trending structures within the Pernambuco Lineament. The Belo Jardim activity was concentrated in a 1.5 km (E-W) by 2 km (downdip) fault area, and average depth of 4.5 km. The nearby Caruaru activity occurs as both strike-slip and normal faulting, also consistent with local structures of the Pernambuco Lineament. The focal mechanisms of Belo Jardim, Caruaru and S. Caetano, indicate E-W compressional and N-S extensional principal stresses. The NS extension of this stress field is larger than that predicted by numerical models such as those of Coblentz

  6. Review on symmetric structures in ductile shear zones

    Science.gov (United States)

    Mukherjee, Soumyajit

    2017-07-01

    Symmetric structures in ductile shear zones range widely in shapes and geneses. Matrix rheology, its flow pattern, its competency contrast with the clast, degree of slip of the clast, shear intensity and its variation across shear zone and deformation temperature, and degree of confinement of clast in shear zones affects (independently) the degree of symmetry of objects. Kinematic vorticity number is one of the parameters that govern tail geometry across clasts. For example, symmetric and nearly straight tails develop if the clast-matrix system underwent dominantly a pure shear/compression. Prolonged deformation and concomitant recrystallization can significantly change the degree of symmetry of clasts. Angular relation between two shear zones or between a shear zone and anisotropy determines fundamentally the degree of symmetry of lozenges. Symmetry of boudinaged clasts too depends on competency contrast between the matrix and clast in some cases, and on the degrees of slip of inter-boudin surfaces and pure shear. Parasitic folds and post-tectonic veins are usually symmetric.

  7. Influence of fault trend, fault bends, and fault convergence on shallow structure, geomorphology, and hazards, Hosgri strike-slip fault, offshore central California

    Science.gov (United States)

    Johnson, S. Y.; Watt, J. T.; Hartwell, S. R.

    2012-12-01

    We mapped a ~94-km-long portion of the right-lateral Hosgri Fault Zone from Point Sal to Piedras Blancas in offshore central California using high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. The database includes 121 seismic profiles across the fault zone and is perhaps the most comprehensive reported survey of the shallow structure of an active strike-slip fault. These data document the location, length, and near-surface continuity of multiple fault strands, highlight fault-zone heterogeneity, and demonstrate the importance of fault trend, fault bends, and fault convergences in the development of shallow structure and tectonic geomorphology. The Hosgri Fault Zone is continuous through the study area passing through a broad arc in which fault trend changes from about 338° to 328° from south to north. The southern ~40 km of the fault zone in this area is more extensional, resulting in accommodation space that is filled by deltaic sediments of the Santa Maria River. The central ~24 km of the fault zone is characterized by oblique convergence of the Hosgri Fault Zone with the more northwest-trending Los Osos and Shoreline Faults. Convergence between these faults has resulted in the formation of local restraining and releasing fault bends, transpressive uplifts, and transtensional basins of varying size and morphology. We present a hypothesis that links development of a paired fault bend to indenting and bulging of the Hosgri Fault by a strong crustal block translated to the northwest along the Shoreline Fault. Two diverging Hosgri Fault strands bounding a central uplifted block characterize the northern ~30 km of the Hosgri Fault in this area. The eastern Hosgri strand passes through releasing and restraining bends; the releasing bend is the primary control on development of an elongate, asymmetric, "Lazy Z" sedimentary basin. The western strand of the Hosgri Fault Zone passes through a significant restraining bend and

  8. Strain localization in the middle- to upper continental crust: examples from the Patos and Pernambuco shear zones (Borborema Province, NE Brazil)

    Science.gov (United States)

    Viegas, G.; Archanjo, C. J.; Hollanda, M. H.; Vauchez, A. R.

    2014-12-01

    The accommodation of deformation in the Earth's lithosphere typically results in a heterogeneous distribution of strain in the continental crust, which is a function of effective pressure, temperature and strain rate at different structural levels. In Northeast Brazil, the Borborema Province is characterized by an interconnected, crustal-scale shear zone system associated with a widespread granitic plutonism. Two of the most prominent structures of this system, the Patos and Pernambuco shear zones, are characterized by ~ 600 km long E-W striking mylonite belts in which strain localization processes are observed either in association with partial melting in the Patos strike-slip fault, or as zones of overprinting brittle-ductile deformation in the Pernambuco shear zone. Deformation mechanisms are distinct across the Patos shear zone, mainly marked by crystalline plasticity and diffusion creep in the high-temperature northern border, magmatic flow in the central region and dislocation creep coupled with microfracturing in the southern sector. The Espinho Branco migmatite (~ 565 Ma) acts as a weak rheological layer that accumulates strain in the northern portion of the fault. Alternatively, the absence of partial melting and the dominant cataclastic/plastic flow regime lead to grain-size sensitive strain localization at the southern border. The Pernambuco shear zone was nucleated at the vicinities of two granitoid batholiths at c.a. 588 Ma. Low-temperature mylonites adjacent to the batholiths show several microstructures indicating coeval activity of brittle-ductile deformation. Recent zircon U-Pb (SHRIMP) data on these mylonites yielded mean ages of ~ 539 Ma, suggesting successive events of thermal input and shearing within the structure. These features suggest that strain localization processes exert an important control on the rheology of the continental lithosphere; the accommodation of deformation in the middle crust is mainly attained by the presence of weak

  9. Three-dimensional shuffling of horses in a strike-slip duplex: an example from the Lambertville sill, New Jersey

    Science.gov (United States)

    Laney, Stephen E.; Gates, Alexander E.

    1996-06-01

    Detailed analysis of a dextral strike-slip duplex within the relatively isotropic rocks of the Lambertville sill, New Jersey indicates that horses have experienced vertical, horizontal and oblique movements resulting from extrusional shuffling within a restraining bend. This is the first documentation of the three-dimensional movement of horses within a strike-slip duplex. Deformation within the duplex shows a complex system of early synthetic fractures and reverse faults followed by antithetic fractures which dissect previously continuous slab-shaped horses into diamond-shaped lenses. Most faults are oblique slip. Antithetic fault movements and clockwise rigid rotation of horses dominate the south half of the duplex and synthetic movements and counterclockwise rotations dominate the north half. Slickenline plunges on curved horse-bounding fault surfaces within the duplex range from nearly horizontal to 40° resulting in both lateral movements (middle) to normal movements (tails) on a single horse. Curved slickensides commonly have opposite senses of movement on either side of individual horses indicating relative emergence or submergence. Such a geometry could also result from a group of horses moving in the same oblique direction but at different rates. These complex extrusional-type movements were observed in both cross-sectional and plan views. The net result of the movements is a contraction or flattening of the duplex normal to the bounding faults. The horses shifted to accommodate this flattening as overall displacement was transferred between the bounding faults along curved internal faults.

  10. Structural fabrics, mineralization and Lamaride kinematics of the Idaho Springs-Ralston shear zone, Colorado mineral belt and central Front Range uplift

    Science.gov (United States)

    Caine, Jonathan S.; Nelson, E.P.; Beach, S.T.; Layer, P.W.

    2006-01-01

    The Idaho Springs and Central City mining districts form the central portion of a structurally controlled hydrothermal precious- and base-metal vein system in the Front Range of the northeast-trending Colorado Mineral Belt. Three new 40Ar/39Ar plateau ages on hydrothermal sericite indicate the veins formed during the Laramide orogeny between 65.4??1.5 - 61.9??1.3 Ma. We compile structural geologic data from surface geological maps, subsurface mine maps, and theses for analysis using modern graphical methods and integration into models of formation of economic mineral deposits. Structural data sets, produced in the 1950s and 1960s by the U.S. Geological Survey, are compiled for fabric elements, including metamorphic foliations, fold axial trends, major brittle fault zones, quartz and precious- and base-metal veins and fault veins, Tertiary dikes, and joints. These fabric elements are plotted on equal-area projections and analyzed for mean fabric orientations. Strike-slip fault-vein sets are mostly parallel or sub-parallel, and not conjugate as interpreted by previous work; late-stage, normal-slip fault veins possibly show a pattern indicative of triaxial strain. Fault-slip kinematic analysis was used to model the trend of the Laramide maximum horizontal stress axis, or compression direction, and to determine compatibility of opening and shear motions within a single stress field. The combined-model maximum compression direction for all strike slip fault veins is ???068??, which is consistent with published Laramide compression directions of ???064?? (mean of 23 regional models) and ???072?? for the Front Range uplift. The orientations of fabric elements were analyzed for mechanical and kinematic compatibility with opening, and thus permeability enhancement, in the modeled regional east-northeast, Laramide compression direction. The fabric orientation analysis and paleostress modeling show that structural permeability during mineralization was enhanced along pre

  11. Coexistence and transition between shear zones in slow granular flows.

    Science.gov (United States)

    Moosavi, Robabeh; Shaebani, M Reza; Maleki, Maniya; Török, János; Wolf, Dietrich E; Losert, Wolfgang

    2013-10-04

    We report experiments on slow granular flows in a split-bottom Couette cell that show novel strain localization features. Nontrivial flow profiles have been observed which are shown to be the consequence of simultaneous formation of shear zones in the bulk and at the boundaries. The fluctuating band model based on a minimization principle can be fitted to the experiments over a large variation of morphology and filling height with one single fit parameter, the relative friction coefficient μ(rel) between wall and bulk. The possibility of multiple shear zone formation is controlled by μ(rel). Moreover, we observe that the symmetry of an initial state, with coexisting shear zones at both side walls, breaks spontaneously below a threshold value of the shear velocity. A dynamical transition between two asymmetric flow states happens over a characteristic time scale which depends on the shear strength.

  12. deposit, Singhbhum shear zone, eastern India

    Indian Academy of Sciences (India)

    Textural and compositional data of pyrites suggest that the hydrothermal fluid responsible for pre-/early-shearing mineralization evolved from Co-rich to Ni-rich and the late-/post-shearing fluid was largely depleted in minor elements. Sulphur isotope compositions of pyrite mostly furnish positive values ranging between ...

  13. Quartz and feldspar rheology at mid-crustal conditions: the example of the Pernambuco shear zone (NE Brazil)

    Science.gov (United States)

    Ferreira Viegas, Luís Gustavo; Menegon, Luca; Archanjo, Carlos; Vauchez, Alain

    2015-04-01

    Rheological models that predict the strength of the middle- to upper continental crust are mainly based on the behaviour of the two most common silicate minerals, feldspar and quartz. At natural pressure-temperature conditions typical of the middle crust, quartz is expected to be mechanically weaker than feldspars if deformation is accommodated by crystal plasticity. Dislocation creep in quartz localizes in recrystallized layers while feldspar forms stronger porphyroclasts. However, the presence of mineral reactions may promote a drastic change in feldspar rheology, causing marked grain size reduction and weakening due to activation of diffusion creep. Under such conditions, the feldspar-derived reaction products represent the mechanically weak rheological phase that accommodates most of the bulk strain while quartz deforms via dislocation creep. The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at upper-greenschist/amphibolite facies conditions, thus representing a preserved section of the middle continental crust. Initially coarse (> 50 µm) grained feldspar crystals are intensively fractured and reduced to an ultrafine-grained mixture consisting of fractured albite and K-feldspar grains (~ 5-8 µm in size) localized in C' oriented shear bands. Detailed microstructural observations and EBSD analysis do not show any evidence of intracrystalline plasticity in feldspars and/or uid-enhanced reaction weakening. Quartz occurs either as thick (~ 1mm) monomineralic bands or as thin ribbons dispersed in the feldspathic mixture. The microstructure and recrystallized grain size (~ 20 µm) are similar in both the thick monomineralic band and in the thin ribbons. Elongated quartz grains form [0001] axis maxima around Y, while recrystallized grains tend to scatter their c-axes between Y and Z in a girdle-like pattern in both the monomineralic band and in the thin ribbons embedded in the

  14. Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    Science.gov (United States)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-03-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse-grained (> 50 µm) feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains ( and rhomb slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the quartz monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 µm vs. 5 µm respectively). The fine-grained feldspar mixture has a weak crystallographic-preferred orientation interpreted as the result of shear zone parallel-oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Once C' shear bands were generated and underwent viscous deformation at constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate 1 order of magnitude faster than the monophase quartz monomineralic veins, as evidenced by applying experimentally and theoretically calibrated flow laws for dislocation creep in quartz and diffusion creep in feldspar. Overall, our data set indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase feldspathic material localized much of the strain. Extensive grain-size reduction and weakening of feldspars is attained in the East Pernambuco mylonites mainly via fracturing which would trigger a switch to diffusion creep and strain localization without a prominent role of metamorphic reactions.

  15. Brittle grain size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

    Science.gov (United States)

    Viegas, Gustavo; Menegon, Luca; Archanjo, Carlos

    2016-04-01

    The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse (> 50 μm) grained feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains ( and rhomb slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 μm vs 5 μm, respectively).The fine-grained feldspar mixture has a weak crystallographic preferred orientation interpreted as the result of oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Assuming that the C' shear bands deformed under constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate one order of magnitude faster than the monophase quartz ribbons. Overall, our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystalline plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the feldspathic material localized much of the strain. Extensive grain-size reduction and weakening of feldspars is attained in the East Pernambuco shear zone mainly via fracturing under relatively fluid-absent conditions which would trigger a switch to diffusion creep and further strain localization without a prominent role of metamorphic reactions.

  16. Stress near geometrically complex strike-slip faults - Application to the San Andreas fault at Cajon Pass, southern California

    Science.gov (United States)

    Saucier, Francois; Humphreys, Eugene; Weldon, Ray, II

    1992-01-01

    A model is presented to rationalize the state of stress near a geometrically complex major strike-slip fault. Slip on such a fault creates residual stresses that, with the occurrence of several slip events, can dominate the stress field near the fault. The model is applied to the San Andreas fault near Cajon Pass. The results are consistent with the geological features, seismicity, the existence of left-lateral stress on the Cleghorn fault, and the in situ stress orientation in the scientific well, found to be sinistral when resolved on a plane parallel to the San Andreas fault. It is suggested that the creation of residual stresses caused by slip on a wiggle San Andreas fault is the dominating process there.

  17. Analogue Modeling of Oblique Convergent Strike-Slip Faulting and Application to The Seram Island, Eastern Indonesia

    Directory of Open Access Journals (Sweden)

    Benyamin Sapiie

    2014-12-01

    Full Text Available DOI:10.17014/ijog.v1i3.189Sandbox experiment is one of the types of analogue modeling in geological sciences in which the main purpose is simulating deformation style and structural evolution of the sedimentary basin.  Sandbox modeling is one of the effective ways in conducting physically modeling and evaluates complex deformation of sedimentary rocks. The main purpose of this paper is to evaluate structural geometry and deformation history of oblique convergent deformation using of integrated technique of analogue sandbox modeling applying to deformation of Seram Fold-Thrust-Belt (SFTB in the Seram Island, Eastern Indonesia. Oblique convergent strike-slip deformation has notoriously generated area with structural complex geometry and pattern resulted from role of various local parameters that control stress distributions. Therefore, a special technique is needed for understanding and solving such problem in particular to relate 3D fault geometry and its evolution. The result of four case (Case 1 to 4 modeling setting indicated that two of modeling variables clearly affected in our sandbox modeling results; these are lithological variation (mainly stratigraphy of Seram Island and pre-existing basement fault geometry (basement configuration. Lithological variation was mainly affected in the total number of faults development.  On the other hand, pre-existing basement fault geometry was highly influenced in the end results particularly fault style and pattern as demonstrated in Case 4 modeling.  In addition, this study concluded that deformation in the Seram Island is clearly best described using oblique convergent strike-slip (transpression stress system.

  18. Quantifying the Variation in Shear Zone Character with Depth: a Case Study from the Simplon Shear Zone, Central Alps

    Science.gov (United States)

    Cawood, T. K.; Platt, J. P.

    2017-12-01

    A widely-accepted model for the rheology of crustal-scale shear zones states that they comprise distributed strain at depth, in wide, high-temperature shear zones, which narrow to more localized, high-strain zones at lower temperature and shallower crustal levels. We test and quantify this model by investigating how the width, stress, temperature and deformation mechanisms change with depth in the Simplon Shear Zone (SSZ). The SSZ marks a major tectonic boundary in the central Alps, where normal-sense motion and rapid exhumation of the footwall have preserved evidence of older, deeper deformation in rocks progressively further into the currently-exposed footwall. As such, microstructures further from the brittle fault (which represents the most localized, most recently-active part of the SSZ) represent earlier, higher- temperature deformation from deeper crustal levels, while rocks closer to the fault have been overprinted by successively later, cooler deformation at shallower depths. This study uses field mapping and microstructural studies to identify zones representing deformation at various crustal levels, and characterize each in terms of zone width (representing width of the shear zone at that time and depth) and dominant deformation mechanism. In addition, quartz- (by Electron Backscatter Diffraction, EBSD) and feldspar grain size (measured optically) piezometry are used to calculate the flow stress for each zone, while the Ti-in-quartz thermometer (TitaniQ) is used to calculate the corresponding temperature of deformation. We document the presence of a broad zone in which quartz is recrystallized by the Grain Boundary Migration (GBM) mechanism and feldspar by Subgrain Rotation (SGR), which represents the broad, deep zone of deformation occurring at relatively high temperatures and low stresses. In map view, this transitions to successively narrower zones, respectively characterized by quartz SGR and feldspar Bulge Nucleation (BLG); quartz BLG and brittle

  19. Characteristics of the Late Quaternary right-lateral strike-slip movement of Bolokenu-Aqikekuduk fault in northern Tianshan Mountains, NW China

    Directory of Open Access Journals (Sweden)

    Jun Shen

    2011-10-01

    A typical strain partitioning style in the compression area has developed between the intermontane Bo-A fault and the piedmont thrust structures of Northern Tianshan Mountains, under the effect of oblique compression, as indicated by the piedmont thrust structure and the strike-slip fault in the mountains.

  20. A Physical Analog Model of Strike-Slip Faulting for Model-Based Inquiry in the Classroom

    Science.gov (United States)

    Curren, I. S.; Glesener, G.

    2013-12-01

    Geoscience educators often use qualitative physical analog models to demonstrate natural processes; while these are effective teaching tools, they often neglect the fundamental scientific practices that make up the core of scientific work. Physical analog models with dynamic properties that can be manipulated and measured quantitatively in real-time, on the other hand, can give students the opportunity to explore, observe and empirically test their own ideas and hypotheses about the relevant target concepts within a classroom setting. Providing classroom content for inquiry, such as a hands-on physical analog model, which fosters students' production and refinement of their mental models in participatory and discursive activities have been argued by many education researchers to help students build a deeper understanding of science and scientific reasoning. We present a physical analog model that was originally developed by UCLA's Modeling and Educational Demonstrations Laboratory (MEDL) for the purpose of engaging students in the study of elastic rebound on a strike-slip fault; it was later modified to accommodate research of complex tectonic processes associated with strike-slip faulting, which are currently debated by scientists in both the geology and geophysics disciplines. During experimentation, it became clear that this new design could be used as a relevant resource for inquiry from which students would be able to make and discuss real-time empirical measurements and observations to help them infer causal accounts of theoretical and/or unobservable dynamic processes within the Earth's crust. In our poster session, we will: 1) demonstrate the physical analog model; 2) describe various real-time data collection tools, as well as quantitative methods students can use to process their data; and 3) describe the surficial, structural and relational similarities between the physical analog model and the target concepts intended for students to explore in the

  1. Slip rate and slip magnitudes of past earthquakes along the Bogd left-lateral strike-slip fault (Mongolia)

    Science.gov (United States)

    Prentice, Carol S.; Rizza, M.; Ritz, J.F.; Baucher, R.; Vassallo, R.; Mahan, S.

    2011-01-01

    We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans—particularly well preserved in the arid environment of the Gobi region—allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is∼1 mm yr–1 along the WIB and EIB segments and∼0.5 mm yr–1 along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault. Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at Mw 7.78–7.95. Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of∼2500

  2. Inelastic deformations of fault and shear zones in granitic rock

    International Nuclear Information System (INIS)

    Wilder, D.G.

    1986-02-01

    Deformations during heating and cooling of three drifts in granitic rock were influenced by the presence of faults and shear zones. Thermal deformations were significantly larger in sheared and faulted zones than where the rock was jointed, but neither sheared nor faulted. Furthermore, thermal deformations in faulted or sheared rock were not significantly recovered during subsequent cooling, thus a permanent deformation remained. This inelastic response is in contrast with elastic behavior identified in unfaulted and unsheared rock segments. A companion paper indicates that deformations in unsheared or unfaulted rock were effectively modeled as an elastic response. We conclude that permanent deformations occurred in fractures with crushed minerals and fracture filling or gouge materials. Potential mechanisms for this permanent deformation are asperity readjustments during thermal deformations, micro-shearing, asperity crushing and crushing of the secondary fracture filling minerals. Additionally, modulus differences in sheared or faulted rock as compared to more intact rock would result in greater deformations in response to the same thermal loads

  3. Interactions between strike-slip earthquakes and the subduction interface near the Mendocino Triple Junction

    Science.gov (United States)

    Gong, Jianhua; McGuire, Jeffrey J.

    2018-01-01

    The interactions between the North American, Pacific, and Gorda plates at the Mendocino Triple Junction (MTJ) create one of the most seismically active regions in North America. The earthquakes rupture all three plate boundaries but also include considerable intraplate seismicity reflecting the strong internal deformation of the Gorda plate. Understanding the stress levels that drive these ruptures and estimating the locking state of the subduction interface are especially important topics for regional earthquake hazard assessment. However owing to the lack of offshore seismic and geodetic instruments, the rupture process of only a few large earthquakes near the MTJ have been studied in detail and the locking state of the subduction interface is not well constrained. In this paper, first, we use the second moments inversion method to study the rupture process of the January 28, 2015 Mw 5.7 earthquake on the Mendocino transform fault that was unusually well recorded by both onshore and offshore strong motion instruments. We estimate the rupture dimension to be approximately 6 km by 3 km corresponding to a stress drop of ∼4 MPa for a crack model. Next we investigate the frictional state of the subduction interface by simulating the afterslip that would be expected there as a result of the stress changes from the 2015 earthquake and a 2010 Mw 6.5 intraplate earthquake within the subducted Gorda plate. We simulate afterslip scenarios for a range of depths of the downdip end of the locked zone defined as the transition to velocity strengthening friction and calculate the corresponding surface deformation expected at onshore GPS monuments. We can rule out a very shallow downdip limit owing to the lack of a detectable signal at onshore GPS stations following the 2010 earthquake. Our simulations indicate that the locking depth on the slab surface is at least 14 km, which suggests that the next M8 earthquake rupture will likely reach the coastline and strong shaking

  4. Shear Zone-Hosted Base Metal Mineralization near Abraha ...

    African Journals Online (AJOL)

    Tadesse

    S, NE-SW trending shear zones; hydrothermal quartz (±calcite) veins of different generations; malachite stains .... consists of only metasedimentary rocks of argillite and carbonate composition but predominantly argillaceous. The rock types present are slate, phyllite, graphitic schist and metalimestone. The. Group is further ...

  5. Shear Zone-Hosted Base Metal Mineralization near Abraha ...

    African Journals Online (AJOL)

    Low-grade basement rocks of Neoproterozoic age with well developed shear zones and posttectonic granitic intrusives from Hawzien area of northern Ethiopia were studied for field characteristics, mineralogy, textures, alteration assemblages and geochemistry to explore their potential for base metal mineralization.

  6. Geometry and subsidence history of the Dead Sea basin: A case for fluid-induced mid-crustal shear zone?

    Science.gov (United States)

    ten Brink, Uri S.; Flores, C.H.

    2012-01-01

    Pull-apart basins are narrow zones of crustal extension bounded by strike-slip faults that can serve as analogs to the early stages of crustal rifting. We use seismic tomography, 2-D ray tracing, gravity modeling, and subsidence analysis to study crustal extension of the Dead Sea basin (DSB), a large and long-lived pull-apart basin along the Dead Sea transform (DST). The basin gradually shallows southward for 50 km from the only significant transverse normal fault. Stratigraphic relationships there indicate basin elongation with time. The basin is deepest (8-8.5 km) and widest (???15 km) under the Lisan about 40 km north of the transverse fault. Farther north, basin depth is ambiguous, but is 3 km deep immediately north of the lake. The underlying pre-basin sedimentary layer thickens gradually from 2 to 3 km under the southern edge of the DSB to 3-4 km under the northern end of the lake and 5-6 km farther north. Crystalline basement is ???11 km deep under the deepest part of the basin. The upper crust under the basin has lower P wave velocity than in the surrounding regions, which is interpreted to reflect elevated pore fluids there. Within data resolution, the lower crust below ???18 km and the Moho are not affected by basin development. The subsidence rate was several hundreds of m/m.y. since the development of the DST ???17 Ma, similar to other basins along the DST, but subsidence rate has accelerated by an order of magnitude during the Pleistocene, which allowed the accumulation of 4 km of sediment. We propose that the rapid subsidence and perhaps elongation of the DSB are due to the development of inter-connected mid-crustal ductile shear zones caused by alteration of feldspar to muscovite in the presence of pore fluids. This alteration resulted in a significant strength decrease and viscous creep. We propose a similar cause to the enigmatic rapid subsidence of the North Sea at the onset the North Atlantic mantle plume. Thus, we propose that aqueous fluid flux

  7. Shear-controlled evolution of the Red Sea: pull apart model

    Science.gov (United States)

    Makris, J.; Rihm, R.

    1991-11-01

    Results of seismic and other geophysical investigations suggest that strike-slip processes controlled the break-up of the Arabian plate from Africa and initiated the Red Sea Rift. Early oceanisation was facilitated by nucleation of pull apart basins and massive intrusives. The evolution of the Red Sea has gone through different stages. It was a zone of structural weakness already during the Pan-African orogeny approximately 600 Ma. A major reactivation, however, that gradually led to the present-day configuration was initiated during the late Oligocene with intense magmatic activity and the development of a continental rift. Wrench faulting played a key role in the early evolution of the Red Sea, as it shaped most of its western flank as a sharp plate boundary and resulted in the generation and rapid oceanisation of linearly arranged pull apart basins. Spatial distribution of these basins reflects the geometry of the strike-slip zone, which was controlled by pre-existing fault systems like the Najd Shear System, the Central African Fault Zone or the Onib-Hamisana and Baraka suture zones. Strike-slip motion along the latter zones of weakness influenced mainly the Egyptian and Sudanese coastal areas. Arabia was therefore separated from Africa by oceanisation in those regions, where pull apart basins developed. They were still connected in the in-between segments by stretched continental crust. With Arabia as the "moving" and Africa as the "stable" plate the eastern Red Sea flank was formed by pure shear through stretching, thinning and diffuse extension. As a consequence, the eastern and western flanks of the Red Sea are asymmetrical. The acceleration of the movement of Arabia in early/middle Miocene could no longer be accommodated by the opening in the Gulf of Suez and consequently the Dead Sea strike-slip fault developed approximately 14 Ma ago. Since plate motion was still oblique to the major structural trends, the pull apart evolution on the western flank

  8. Strike-slip fault Kinematics and mechanics at the seismic cycle time-scale : Results from new analogue model experiments.

    Science.gov (United States)

    Caniven, Yannick; Dominguez, Stéphane; Soliva, Roger; Cattin, Rodolphe; Peyret, Michel; Chéry, Jean; Romano, Christian

    2013-04-01

    The average seismic cycle duration extends from hundred to a few thousands years but geodetic measurements, including trilateration, GPS, Insar and seismological data extend over less than one century. This short time observation scale renders difficult, then, to constrain the role of key parameters such as fault friction and geometry, crust rheology, stress and strain rate that control the kinematics and mechanics of active faults. To solve this time scale issue, we have developed a new experimental set-up that reproduces scaled micro-earthquakes and several hundreds of seismic cycles along a strike-slip fault. The model is constituted by two polyurethane foam plates laterally in contact, lying on a basal silicone layer, which simulate the mechanical behaviour of an elastoplastic upper crust over a ductile lower crust, respectively. To simulate the boundary conditions of a strike-slip fault, a computerized motoreductor system moves the two compartments on an opposite sens and at a constant very low velocity (a few µm/s). The model spatial and temporal scaling, deduces from analog material physical and mechanical parameters, implies that 1 cm in the model represents 2-3 km in the nature and 1 s is equivalent to 5-15 years. Surface-horizontal strain field is quantified by sub-pixel correlation of digital camera pictures recorded every 16 µm of displacement. For each experience about 2000 horizontal-velocity field measurements are recorded. The analysis of model-interseismic and coseismic surface displacements and their comparison to seismogenic natural faults demonstrate that our analog model reproduces correctly both near and far-field surface strains. To compare the experiences, we have developed several algorithms that allow studying the main spatial and temporal evolution of the physical parameters and surface deformation processes that characterise the seismic cycle (magnitudes, stress, strain, friction coefficients, interseismic locking depth, recurrence

  9. Dynamic response to strike-slip tectonic control on the deposition and evolution of the Baranof Fan, Gulf of Alaska

    Science.gov (United States)

    Walton, Maureen A. L.; Gulick, Sean P. S.; Reece, Robert S.; Barth, Ginger A.; Christeson, Gail L.; VanAvendonk, Harm J.

    2014-01-01

    The Baranof Fan is one of three large deep-sea fans in the Gulf of Alaska, and is a key component in understanding large-scale erosion and sedimentation patterns for southeast Alaska and western Canada. We integrate new and existing seismic reflection profiles to provide new constraints on the Baranof Fan area, geometry, volume, and channel development. We estimate the fan’s area and total sediment volume to be ∼323,000 km2 and ∼301,000 km3, respectively, making it among the largest deep-sea fans in the world. We show that the Baranof Fan consists of channel-levee deposits from at least three distinct aggradational channel systems: the currently active Horizon and Mukluk channels, and the waning system we call the Baranof channel. The oldest sedimentary deposits are in the northern fan, and the youngest deposits at the fan’s southern extent; in addition, the channels seem to avulse southward consistently through time. We suggest that Baranof Fan sediment is sourced from the Coast Mountains in southeastern Alaska, transported offshore most recently via fjord to glacial sea valley conduits. Because of the translation of the Pacific plate northwest past sediment sources on the North American plate along the Queen Charlotte strike-slip fault, we suggest that new channel formation, channel beheadings, and southward-migrating channel avulsions have been influenced by regional tectonics. Using a simplified tectonic reconstruction assuming a constant Pacific plate motion of 4.4 cm/yr, we estimate that Baranof Fan deposition initiated ca. 7 Ma.

  10. A viscoplastic shear-zone model for episodic slow slip events in oceanic subduction zones

    Science.gov (United States)

    Yin, A.; Meng, L.

    2016-12-01

    Episodic slow slip events occur widely along oceanic subduction zones at the brittle-ductile transition depths ( 20-50 km). Although efforts have been devoted to unravel their mechanical origins, it remains unclear about the physical controls on the wide range of their recurrence intervals and slip durations. In this study we present a simple mechanical model that attempts to account for the observed temporal evolution of slow slip events. In our model we assume that slow slip events occur in a viscoplastic shear zone (i.e., Bingham material), which has an upper static and a lower dynamic plastic yield strength. We further assume that the hanging wall deformation is approximated as an elastic spring. We envision the shear zone to be initially locked during forward/landward motion but is subsequently unlocked when the elastic and gravity-induced stress exceeds the static yield strength of the shear zone. This leads to backward/trenchward motion damped by viscous shear-zone deformation. As the elastic spring progressively loosens, the hanging wall velocity evolves with time and the viscous shear stress eventually reaches the dynamic yield strength. This is followed by the termination of the trenchward motion when the elastic stress is balanced by the dynamic yield strength of the shear zone and the gravity. In order to account for the zig-saw slip-history pattern of typical repeated slow slip events, we assume that the shear zone progressively strengthens after each slow slip cycle, possibly caused by dilatancy as commonly assumed or by progressive fault healing through solution-transport mechanisms. We quantify our conceptual model by obtaining simple analytical solutions. Our model results suggest that the duration of the landward motion increases with the down-dip length and the static yield strength of the shear zone, but decreases with the ambient loading velocity and the elastic modulus of the hanging wall. The duration of the backward/trenchward motion depends

  11. Hematite (U-Th)/He thermochronometry constrains intraplate strike-slip faulting on the Kuh-e-Faghan Fault, central Iran

    Science.gov (United States)

    Calzolari, Gabriele; Rossetti, Federico; Ault, Alexis K.; Lucci, Federico; Olivetti, Valerio; Nozaem, Reza

    2018-03-01

    The Kuh-e-Faghan strike-slip fault system (KFF), located to the northern edge of the Lut Block in central Iran, developed through a Neogene-Quaternary pulsed history of eastward fault propagation and fault-related exhumation. This system is a consequence of the residual stresses transmitted from the Arabia-Eurasia convergent plate boundary. Here we integrate structural and textural analysis with new and previously published apatite fission-track (AFT) and apatite (U-Th)/He (apatite He) results, chlorite thermomentry, and hematite (U-Th)/He data from hematite-coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late Miocene-Pliocene burial and exhumation associated with the propagation of the KFF. Twenty-nine hematite (U-Th)/He (hematite He) dates from three striated hematite coated slip surfaces from the KFF fault core and damage zone yield individual dates from 12-2 Ma. Petrographic analysis and chlorite thermometry of a polyphase, fossil fluid system in the KFF fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal (T = 239 ± 10 °C) fluids and hematite formation. Hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics, no evidence of hematite comminution and similar hematite He closure temperatures ( 60-85 °C) in each sample. Integration of these results with thermal history modeling of AFT and apatite He data shows that KFF activity in the late Miocene is characterized by an early stage of fault nucleation, fluid circulation, hematite mineralization, and eastward propagation not associated with vertical movement that lasted from 12 to 7 Ma. Hematite He, AFT, and apatite He data track a second phase of fault system activity involving fault-related exhumation initiating at 7 Ma and continuing until present time. Our new data

  12. The Sorong Fault Zone, Indonesia: Mapping a Fault Zone Offshore

    Science.gov (United States)

    Melia, S.; Hall, R.

    2017-12-01

    The Sorong Fault Zone is a left-lateral strike-slip fault zone in eastern Indonesia, extending westwards from the Bird's Head peninsula of West Papua towards Sulawesi. It is the result of interactions between the Pacific, Caroline, Philippine Sea, and Australian Plates and much of it is offshore. Previous research on the fault zone has been limited by the low resolution of available data offshore, leading to debates over the extent, location, and timing of movements, and the tectonic evolution of eastern Indonesia. Different studies have shown it north of the Sula Islands, truncated south of Halmahera, continuing to Sulawesi, or splaying into a horsetail fan of smaller faults. Recently acquired high resolution multibeam bathymetry of the seafloor (with a resolution of 15-25 meters), and 2D seismic lines, provide the opportunity to trace the fault offshore. The position of different strands can be identified. On land, SRTM topography shows that in the northern Bird's Head the fault zone is characterised by closely spaced E-W trending faults. NW of the Bird's Head offshore there is a fold and thrust belt which terminates some strands. To the west of the Bird's Head offshore the fault zone diverges into multiple strands trending ENE-WSW. Regions of Riedel shearing are evident west of the Bird's Head, indicating sinistral strike-slip motion. Further west, the ENE-WSW trending faults turn to an E-W trend and there are at least three fault zones situated immediately south of Halmahera, north of the Sula Islands, and between the islands of Sanana and Mangole where the fault system terminates in horsetail strands. South of the Sula islands some former normal faults at the continent-ocean boundary with the North Banda Sea are being reactivated as strike-slip faults. The fault zone does not currently reach Sulawesi. The new fault map differs from previous interpretations concerning the location, age and significance of different parts of the Sorong Fault Zone. Kinematic

  13. Discrete shear-transformation-zone plasticity modeling of notched bars

    Science.gov (United States)

    Kondori, Babak; Amine Benzerga, A.; Needleman, Alan

    2018-02-01

    Plane strain tension analyses of un-notched and notched bars are carried out using discrete shear transformation zone plasticity. In this framework, the carriers of plastic deformation are shear transformation zones (STZs) which are modeled as Eshelby inclusions. Superposition is used to represent a boundary value problem solution in terms of discretely modeled Eshelby inclusions, given analytically for an infinite elastic medium, and an image solution that enforces the prescribed boundary conditions. The image problem is a standard linear elastic boundary value problem that is solved by the finite element method. Potential STZ activation sites are randomly distributed in the bars and constitutive relations are specified for their evolution. Results are presented for un-notched bars, for bars with blunt notches and for bars with sharp notches. The computed stress-strain curves are serrated with the magnitude of the associated stress-drops depending on bar size, notch acuity and STZ evolution. Cooperative deformation bands (shear bands) emerge upon straining and, in some cases, high stress levels occur within the bands. Effects of specimen geometry and size on the stress-strain curves are explored. Depending on STZ kinetics, notch strengthening, notch insensitivity or notch weakening are obtained. The analyses provide a rationale for some conflicting findings regarding notch effects on the mechanical response of metallic glasses.

  14. The Effective Rheology of Natural Subduction Shear Zones: Insights from Numerical Simple Shear Experiments

    Science.gov (United States)

    Ioannidi, Paraskevi Io; Le Pourhiet, Laetitia; Moreno, Marcos; Agard, Philippe; Oncken, Onno; Angiboust, Samuel

    2017-04-01

    Determination of the subduction interface rheological parameters is an interesting aspect of geodynamics since it can help better understand the physical nature of plate locking and its relation to surface deformation patterns observed at different time scales (GPS displacements during the seismic cycle). Since direct rheological measurements are not possible, unfortunately, we herein try to determine the effective rheological parameters of a subduction interface using finite element modelling. We use the open source finite element code pTatin to create 2D models, starting with a homogeneous medium representing shearing at the subduction interface. We tested several boundary conditions trying to find the one that can best mimic simple shear experiments performed on rock samples. After examining different parameters including the shearing velocity, the temperature and the viscosity, we added complexity to the geometry by including a second phase. This complexity arose from field observations, where composite shear zone outcrops often characterize the subduction interface. Stronger crustal blocks embedded within a sedimentary and/or serpentinized matrix have been reported for several exhumed subduction zones. We implemented a simplified model to simulate simple shearing of a two-phase medium in order to quantify the effect of heterogeneous rheology on stress and strain localization. Preliminary results show different strength in the models depending on the block-to-matrix ratio. In order to test our methodology, we first use clast-in-matrix geometries from thin sections taken through lab experiments. In a second stage, we upscale the method to outcrop scale clast-in-matrix geometries. By sampling at different depths along exhumed former subduction interfaces, we expect to be able to provide effective friction of a natural interface. In a next step, these effective frictions will be used as input into seismic cycle deformation models in an attempt to assess the

  15. Influence of the Eastern California Shear Zone on deposition of the Mio-Pliocene Bouse Formation: Insights from the Cibola area, Arizona

    Science.gov (United States)

    Dorsey, Rebecca J.; O'Connell, Brennan; Homan, Mindy B.; Bennett, Scott E. K.

    2017-01-01

    The Eastern California Shear Zone (ECSZ) is a wide zone of late Cenozoic strike-slip faults and related diffuse deformation that currently accommodates ~20–25% of relative Pacific–North America plate motion in the lower Colorado River region (Fig. 1A; Dokka and Travis, 1990; Miller et al., 2001; Guest et al., 2007; Mahan et al., 2009). The ECSZ is kinematically linked southward to dextral faults in the northern Gulf of California (Bennett et al., 2016a), and it may have initiated ca. 8 Ma when major strike-slip faults developed in the northern Gulf and Salton Trough region (Bennett et al., 2016b; Darin et al., 2016; Woodburne, 2017). Thus deformation related to the ECSZ occurred in the lower Colorado River region during deposition of the Bouse Formation, which is commonly bracketed between 6.0 and 4.8 Ma (House et al., 2008; Sarna-Wojcicki et al., 2011; Spencer et al., 2013) and may be as old as 6–7 Ma in the south (McDougall and Miranda Martínez, 2014, 2016). Post-4.5 Ma broad sagging is recognized along the lower Colorado River (Howard et al., 2015), but the possibility that faults of the ECSZ influenced local to regional subsidence patterns during deposition of the Bouse Formation has received little attention to date (e.g., Homan, 2014; O’Connell et al., 2016). The Bouse Formation is a widespread sequence of late Miocene to early Pliocene deposits exposed discontinuously along the lower Colorado River corridor (Fig. 1A). In the southern Blythe basin it consists of three regionally correlative members: (1) Basal Carbonate, consisting of supratidal and intertidal mud-flat marls, intertidal and shallow subtidal bioclastic grainstone and conglomerate, and subtidal marl; (2) Siliciclastic member, consisting of Colorado River-derived green claystone, red mudstone and siltstone, and cross-bedded river channel sandstone; and (3) Upper Bioclastic member fossiliferous sandy calcarenite, coarse pebbly grainstone, and calcareous-matrix conglomerate (Homan, 2014

  16. The importance of strain localisation in shear zones

    Science.gov (United States)

    Bons, Paul D.; Finch, Melanie; Gomez-Rivas, Enrique; Griera, Albert; Llorens, Maria-Gema; Steinbach, Florian; Weikusat, Ilka

    2016-04-01

    The occurrence of various types of shear bands (C, C', C'') in shear zones indicate that heterogeneity of strain is common in strongly deformed rocks. However, the importance of strain localisation is difficult to ascertain if suitable strain markers are lacking, which is usually the case. Numerical modelling with the finite-element method has so far not given much insight in the development of shear bands. We suggest that this is not only because the modelled strains are often not high enough, but also because this technique (that usually assumes isotropic material properties within elements) does not properly incorporate mineral deformation behaviour. We simulated high-strain, simple-shear deformation in single- and polyphase materials with a full-field theory (FFT) model coupled to the Elle modelling platform (www.elle.ws; Lebensohn 2001; Bons et al. 2008). The FFT-approach simulates visco-plastic deformation by dislocation glide, taking into account the different available slip systems and their critical resolved shear stresses in relations to the applied stresses. Griera et al. (2011; 2013) have shown that this approach is particularly well suited for strongly anisotropic minerals, such as mica and ice Ih (Llorens 2015). We modelled single- and polyphase composites of minerals with different anisotropies and strengths, roughly equivalent to minerals such as ice Ih, mica, quartz and feldspar. Single-phase polycrystalline aggregates show distinct heterogeneity of strain rate, especially in case of ice Ih, which is mechanically close to mica (see also Griera et al. 2015). Finite strain distributions are heterogeneous as well, but the patterns may differ from that of the strain rate distribution. Dynamic recrystallisation, however, usually masks any strain and strain rate localisation (Llorens 2015). In case of polyphase aggregates, equivalent to e.g. a granite, we observe extensive localisation in both syn- and antithetic shear bands. The antithetic shear bands

  17. Focused seismicity triggered by flank instability on Kīlauea's Southwest Rift Zone

    Science.gov (United States)

    Judson, Josiah; Thelen, Weston A.; Greenfield, Tim; White, Robert S.

    2018-03-01

    Swarms of earthquakes at the head of the Southwest Rift Zone on Kīlauea Volcano, Hawai´i, reveal an interaction of normal and strike-slip faulting associated with movement of Kīlauea's south flank. A relocated subset of earthquakes between January 2012 and August 2014 are highly focused in space and time at depths that are coincident with the south caldera magma reservoir beneath the southern margin of Kīlauea Caldera. Newly calculated focal mechanisms are dominantly dextral shear with a north-south preferred fault orientation. Two earthquakes within this focused area of seismicity have normal faulting mechanisms, indicating two mechanisms of failure in very close proximity (10's of meters to 100 m). We suggest a model where opening along the Southwest Rift Zone caused by seaward motion of the south flank permits injection of magma and subsequent freezing of a plug, which then fails in a right-lateral strike-slip sense, consistent with the direction of movement of the south flank. The seismicity is concentrated in an area where a constriction occurs between a normal fault and the deeper magma transport system into the Southwest Rift Zone. Although in many ways the Southwest Rift Zone appears analogous to the more active East Rift Zone, the localization of the largest seismicity (>M2.5) within the swarms to a small volume necessitates a different model than has been proposed to explain the lineament outlined by earthquakes along the East Rift Zone.

  18. DISCRETE DEFORMATION WAVE DYNAMICS IN SHEAR ZONES: PHYSICAL MODELLING RESULTS

    Directory of Open Access Journals (Sweden)

    S. A. Bornyakov

    2016-01-01

    Full Text Available Observations of earthquake migration along active fault zones [Richter, 1958; Mogi, 1968] and related theoretical concepts [Elsasser, 1969] have laid the foundation for studying the problem of slow deformation waves in the lithosphere. Despite the fact that this problem has been under study for several decades and discussed in numerous publications, convincing evidence for the existence of deformation waves is still lacking. One of the causes is that comprehensive field studies to register such waves by special tools and equipment, which require sufficient organizational and technical resources, have not been conducted yet.The authors attempted at finding a solution to this problem by physical simulation of a major shear zone in an elastic-viscous-plastic model of the lithosphere. The experiment setup is shown in Figure 1 (A. The model material and boundary conditions were specified in accordance with the similarity criteria (described in detail in [Sherman, 1984; Sherman et al., 1991; Bornyakov et al., 2014]. The montmorillonite clay-and-water paste was placed evenly on two stamps of the installation and subject to deformation as the active stamp (1 moved relative to the passive stamp (2 at a constant speed. The upper model surface was covered with fine sand in order to get high-contrast photos. Photos of an emerging shear zone were taken every second by a Basler acA2000-50gm digital camera. Figure 1 (B shows an optical image of a fragment of the shear zone. The photos were processed by the digital image correlation method described in [Sutton et al., 2009]. This method estimates the distribution of components of displacement vectors and strain tensors on the model surface and their evolution over time [Panteleev et al., 2014, 2015].Strain fields and displacements recorded in the optical images of the model surface were estimated in a rectangular box (220.00×72.17 mm shown by a dot-and-dash line in Fig. 1, A. To ensure a sufficient level of

  19. Onshore-offshore seismic reflection profiling across the southern margin of the Sea of Japan: back-arc opening, shortening and active strike-slip deformation

    Science.gov (United States)

    Sato, Hiroshi; Ishiyama, Tatsuya; Kato, Naoko; Toda, Shigeru; Kawasaki, Shinji; Fujiwara, Akira; Tanaka, Yasuhisa; Abe, Susumu

    2017-04-01

    Pliocene to early Pleistocene along the limited fault system. The change in the direction of the motion of PHS at 1 Ma produced major change in stress regime from NS compression to EW compression in the back-arc. Following the change of stress regime, former reverse faults reactivated as strike-slip fault. Reuse of pre-existing faults are common, and crustal deformation concentrates relatively narrow zone in the back-arc failed rifts. Two-months after from our survey, Mw 6.2 Tottoriken-chubu earthquake occurred just beneath the onshore part of the seismic line. The source fault corresponds to the boundary of abrupt change in P-wave velocity, however there were no surface ruptures and distinctive geologic faults. The bottom of seismogenic layer corresponds to TWT 4.5 sec., which is almost the top horizon of reflective middle crust.

  20. Mechanics of evenly spaced strike-slip faults and its implications for the formation of tiger-stripe fractures on Saturn's moon Enceladus

    Science.gov (United States)

    Yin, An; Zuza, Andrew V.; Pappalardo, Robert T.

    2016-03-01

    We present the first mechanical analysis based on realistic rheology and boundary conditions on the formation of evenly spaced strike-slip faults. Two quantitative models employing the stress-shadow concept, widely used for explaining extensional-joint spacing, are proposed in this study: (1) an empirically based stress-rise-function model that simulates the brittle-deformation process during the formation of evenly spaced parallel strike-slip faults, and (2) an elastic plate model that relates fault spacing to the thickness of the fault-hosting elastic medium. When applying the models for the initiation and development of the tiger-stripe fractures (TSF) in the South Polar Terrain (SPT) of Enceladus, the mutually consistent solutions of the two models, as constrained by the mean spacing of the TSF at ∼35 km, requires that the brittle ice-shell thickness be ∼30 km, the elastic thickness be ∼0.7 km, and the cohesive strength of the SPT ice shell be ∼30 kPa. However, if the brittle and elastic models are decoupled and if the ice-shell cohesive strength is on the order of ∼1 MPa, the brittle ice shell would be on the order of ∼10 km.

  1. The tsunami-like sea level disturbance in Crotone harbor, Italy, after the Mw6.5 strike-slip earthquake of 17 November 2015 in Lefkada Isl., Ionian Sea, Greece

    Science.gov (United States)

    Novikova, Tatyana; Annunziato, Alessandro; Charalampakis, Marinos; Romano, Fabrizio; Volpe, Manuela; Tonini, Roberto; Gerardinger, Andrea; Papadopoulos, Gerassimos A.

    2016-04-01

    On 17 November 2015 an Mw6.5 earthquake ruptured offshore Lefkada Isl. in Ionian Sea, Greece, causing two human victims, minor damage and several ground failures including coastal landslides. Fault plane solutions released by CMT/Harvard, NOA and other institutes have indicated that the faulting style was strike-slip right-lateral, which is quite typical for the area, as for example, the Mw6.3 event that occurred on August 14, 2003, in exactly the same fault zone. In spite of the very low tsunami potential commonly associated to this faulting mechanism, a tsunami-like sea level change was recorded after the earthquake by one tide-gauge in the Crotone harbor, Italy. Preliminary tsunami numerical simulations were performed to reproduce the observed signal. The spectral analysis of the synthetic mareograms close to the entrance of the harbor shows the presence of some peaks that could justify the relation between the natural port resonance and the observed wave amplification. Of particular interest is the coupling between the tsunami energy and the natural modes of basin oscillation enhancing tsunami wave amplitude in harbors through resonance, as shown in some historical events in the Mediterranean Sea and elsewhere. This research is a contribution to the EU-FP7 tsunami research project ASTARTE (Assessment, Strategy And Risk Reduction for Tsunamis in Europe), grant agreement no: 603839, 2013-10-30.

  2. Microstructural and rheological evolution of calcite mylonites during shear zone thinning: Constraints from the Mount Irene shear zone, Fiordland, New Zealand

    Science.gov (United States)

    Negrini, Marianne; Smith, Steven A. F.; Scott, James M.; Tarling, Matthew S.

    2018-01-01

    Layers of calc-mylonite in the Mount Irene shear zone, Fiordland, New Zealand, show substantial variations in thickness due to deflection of the shear zone boundaries around wall rock asperities. In relatively thick parts (c. 2.6 m) of the shear zone, calcite porphyroclasts are internally strained, contain abundant subgrain boundaries and have a strong shape preferred orientation (SPO) and crystallographic preferred orientation (CPO), suggesting that deformation occurred mainly by dislocation creep involving subgrain-rotation recrystallization. In relatively thin parts (c. 1.5 m) of the shear zone, aggregates of fine-grained recrystallized calcite surrounding flattened porphyroclasts have a weak SPO and CPO, and contain polygonal calcite grains with low degrees of internal misorientation. The recrystallized aggregates also contain microstructures (e.g. grain quadruple junctions, randomized misorientation axes) similar to those reported for neighbor-switching processes during grain-boundary sliding. Comparison of subgrain sizes in the porphyroclasts to published grain-size differential-stress relationships indicates that stresses and strain rates were substantially higher in relatively thin parts of the shear zone. The primary microstructural response to higher stresses and strain rates was an increase in the amount of recrystallization to produce aggregates that deformed by grain-boundary sliding. However, even after the development of interconnected networks of recrystallized grains, dislocation creep by subgrain-rotation recrystallization continued to occur within porphyroclasts. This behavior suggests that the bulk rheology of shear zones undergoing thinning and thickening can be controlled by concomitant grain-size insensitive and grain-size sensitive mechanisms. Overall, our observations show that shear zone thickness variations at constant P-T can result in highly variable stresses and strain rates, which in turn modifies microstructure, deformation mechanism

  3. The last interglacial period at Guantanamo Bay, Cuba and an estimate of late Quaternary tectonic uplift rate in a strike-slip regime

    Science.gov (United States)

    Schweig, E. S.; Muhs, D. R.; Simmons, K. R.; Halley, R. B.

    2015-12-01

    Guantanamo Bay, Cuba is an area dominated by a strike-slip tectonic regime and is therefore expected to have very low Quaternary uplift rates. We tested this hypothesis by study of an unusually well preserved emergent reef terrace around the bay. Up to 12 m of unaltered, growth-position reef corals are exposed at about 40 sections examined around ˜40 km of coastline. Maximum reef elevations in the protected, inner part of the bay are ˜11-12 m, whereas outer-coast shoreline angles of wave-cut benches are as high as ˜14 m. Fifty uranium-series analyses of unrecrystallized corals from six localities yield ages ranging from ˜134 ka to ˜115 ka, when adjusted for small biases due to slightly elevated initial 234U/238U values. Thus, ages of corals correlate this reef to the peak of the last interglacial period, marine isotope stage (MIS) 5.5. Previously, we dated the Key Largo Limestone to the same high-sea stand in the tectonically stable Florida Keys. Estimates of paleo-sea level during MIS 5.5 in the Florida Keys are ~6.6 to 8.3 m above present. Assuming a similar paleo-sea level in Cuba, this yields a long-term tectonic uplift rate of 0.04-0.06 m/ka over the past ~120 ka. This estimate supports the hypothesis that the tectonic uplift rate should be low in this strike-slip regime. Nevertheless, on the southeast coast of Cuba, east of our study area, we have observed flights of multiple marine terraces, suggesting either (1) a higher uplift rate or (2) an unusually well-preserved record of pre-MIS 5.5 terraces not observed at Guantanamo Bay.

  4. Uraninite in the uranium deposits of Singhbhum Shear Zone, Bihar

    International Nuclear Information System (INIS)

    Krishna Rao, N.; Rao, G.V.U.

    1980-01-01

    Uraninite is the main uranium mineral in the uranium deposits of Singhbhum Shear Zone, Bihar. The uraninite from different deposits have compositions varying between UOsub(2.30) to UOsub(2.44) which is typical of vein uraninites. They contain 2 , but have appreciable rare earths (approximately equal to 5%). They also contain 12-15% PbO, which is all radiogenic. Among the rare earths the heavy lanthanides predominate. In addition uraninite from Narwapahar shows an enrichment in Eu. The unit cell edge of uraninite from different deposits varies between 5.420 A and 5.453 A. The uraninite from the copper deposits of Rakha and Surda, and Narwapahar have decidedly higher cell edge (5.45 A) than those from Bhatin and Jaduguda (5.42 A). On annealing at 1000deg C in an inert atmosphere the cell edge decreased to a near constant value of 5.428 A, the contraction varying between 0.01 A to 0.03 A. D.T.A. and T.G.A. curves of Narwapahar and Bhatin uraninite indicate that these differ considerably from those of pure UO 2 . There are also significant differences between the two. These differences are attributed to crystallinity and degree of disorder in the uraninite lattice. The variations in the composition, cell edge, annealing and oxidation characteristics of uraninite from different uranium deposits reflect different temperature conditions during their formation. (author)

  5. The spin zone: Transient mid-crust permeability caused by coseismic brecciation

    Science.gov (United States)

    Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Bate, Charlotte E.; Shulman, Deborah

    2016-06-01

    Pore fluids migrating through the deep section of continental strike-slip fault zones have been invoked to explain such phenomena as tectonic tremor, stress transfer across the brittle-ductile transition, and short timescales of co-seismic healing. In this contribution, we describe a coseismic mechanism for forming transient vertical fluid conduits within dilational jogs in strike-slip faults. We present field observations of breccias that formed coseismically at dilational stepovers in the dextral Pofadder Shear Zone, a ∼ 1 Ga exhumed continental strike-slip fault in South Africa and Namibia. These breccias are interpreted to have formed when tensile fractures emanating from rupture tips intersected mylonitic foliation parallel to the rupture surface, which then failed, disaggregating the rock. We used quartz textures in the mylonites determined by electron backscatter diffraction to uniquely compare the orientation of each clast to the neighboring wall rock and constrain finite clast rotation within breccia bodies. Comparison of two- and three-dimensional rotation patterns show that clast trajectories are highly scattered when decoupled from wall rock, suggesting that Pofadder breccias were not formed by gradual plucking of clasts during slip. The dilational breccia bodies have sub-vertical geometries and high porosities relative to the host mylonites. We infer that the opening of these breccias may have created instantaneous, temporary vertical pathways for fluid draining through the brittle-plastic transition. These pathways healed post-seismically by cementation or ductile creep along the fault. The connection of many adjacent and overprinting breccia bodies through time provides a mechanism for fluid transport on a 10 s of km scale though the middle crust.

  6. Thermomechanics of an extensional shear zone, Raft River metamorphic core complex, NW Utah

    Science.gov (United States)

    Gottardi, Raphaël; Teyssier, Christian

    2013-08-01

    A detailed structural and microstructural analysis of the Miocene Raft River detachment shear zone (NW Utah) provides insight into the thermomechanical evolution of the continental crust during extension associated with the exhumation of metamorphic core complexes. Combined microstructural, electron backscattered diffraction, strain, and vorticity analysis of the very well exposed quartzite mylonite show an increase in intensity of the rock fabrics from west to east, along the transport direction, compatible with observed finite strain markers and a model of ``necking'' of the shear zone. Microstructural evidence (quartz microstructures and deformation lamellae) suggests that the detachment shear zone evolved at its peak strength, close to the dislocation creep/exponential creep transition, where meteoric fluids played an important role on strain hardening, embrittlement, and eventually seismic failure. Empirically calibrated paleopiezometers based on quartz recrystallized grain size and deformation lamellae spacing show very similar results, indicate that the shear zone developed under stress ranging from 40 MPa to 60 MPa. Using a quartzite dislocation creep flow law we further estimate that the detachment shear zone quartzite mylonite developed at a strain rates between 10-12 and 10-14 s-1. We suggest that a compressed geothermal gradient across this detachment, which was produced by a combination of ductile shearing, heat advection, and cooling by meteoric fluids, may have triggered mechanical instabilities and strongly influenced the rheology of the detachment shear zone.

  7. Interfacial stresses in strengthened beam with shear cohesive zone ...

    Indian Academy of Sciences (India)

    2016-08-26

    Aug 26, 2016 ... This paper presents an analytical solution, based on Smith and Teng's equations, for interfacial shear and normal stresses in reinforced concrete (RC) beams strengthened with a fibre reinforced polymer (FRP) plate. However, the shear stress–strain relationship is considered to be bilinear curve.

  8. Areas of Active Tectonic Uplift Are Sensitive to Small Changes in Fold Orientations within a Broad Zone of Left-lateral Transpression and Shearing, Dominican Republic and Haiti (Hispaniola)

    Science.gov (United States)

    Ambrosius, I.; Mann, P.

    2014-12-01

    Previous GPS studies have shown that the island of Hispaniola is a 250 km-wide zone of active, east-west, left-lateral shearing along two major strike-slip zones: the Septentrional-Oriente fault zone through the northern part of the island and the Enriquillo-Plantain Garden fault zone (EPGFZ) through the southern part of the island. The total interplate rate distributed on both faults is 21 mm/yr. Using a high-resolution DEM, we constructed fluvial channel profiles across transpression-related folds of late Miocene to recent age in the area of central and southern Dominican Republic and Haiti to determine controls of areas of relatively high, moderate, and slow uplift inferred from fluvial channel profiles. Fold axes in this area extend for 50-150 km and exhibit two different trends: 1) folds that occupy the area of the Sierra de Neiba-Chaine des Matheux north of the Enriquillo-Cul-de-Sac Valley and EPGFZ and folds that occupy the area of the Sierra de Bahoruco-Massif de la Selle all exhibit more east-west fold axes trending 110; 2) folds that occupy the area northwest of the EPGFZ in the western Chaine des Matheux and Sierra de Neiba all exhibit fold axes with more northwest trends of 125. River channel profiles show that the second group of more northwesterly-trending fold axes show relatively higher rates of tectonic uplift based on their convex-upward river profiles. Our interpretation for regional variations in river profiles and inferred uplift is that uplift is more pronounced on fold axes trending 15 degrees more to the northwest because their axes are more oblique to the interplate direction of east-west shearing. Longterm uplift rates previously measured from a stairstep of late Quaternary coral terraces at the plunging nose of the westernmost Chaine des Matheux have been previously shown to be occurring at a rate of 0.19 mm/yr. Onland exposures of Holocene corals are found only on one locality within the southern area of folds 30 km west of the epicenter

  9. Extensional and compressional regime driven left-lateral shear in southwestern Anatolia (eastern Mediterranean): The Burdur-Fethiye Shear Zone

    Science.gov (United States)

    Elitez, İrem; Yaltırak, Cenk; Aktuğ, Bahadır

    2016-10-01

    The tectonic framework of the eastern Mediterranean presented in this paper is based on an active subduction and small underwater hills/mountains on the oceanic crust moving toward the north. The Hellenic Arc, the Anaximander Mountains, the Rhodes and Finike basins, the compressional southern regions of the Western Taurides, and the extensional western Anatolian graben are the main interrelated tectonic structures that are shaped by the complex tectonic regimes. There are still heated debates regarding the structural properties and tectonic evolution of the southwestern Anatolia. GPS velocities and focal mechanisms of earthquakes demonstrate the absence of a single transform fault across the Burdur-Fethiye region; however, hundreds of small faults showing normal and left-lateral oblique slip indicate the presence of a regionally extensive shear zone in southwestern Turkey, which plays an important role in the eastern Mediterranean tectonics. The 300-km-long, 75-90-km-wide NE-SW-trending Burdur-Fethiye Shear Zone developed during the formation of Aegean back-arc extensional system and the thrusting of Western Taurides. Today, the left-lateral differential motion across the Burdur-Fethiye Shear Zone varies from 3 to 4 mm/yr in the north to 8-10 mm/yr in the south. This finding could be attributed to the fact that while the subduction of the African Plate is relatively fast beneath the western Anatolia at the Hellenic Trench, it is slow or locked beneath the Western Taurides. Therefore, the GPS vectors and their distributions on land indicate remarkable velocity differences and enable us to determine the left-lateral shear zone located between the extensional and compressional blocks. Furthermore, this active tectonic regime creates differences in topography. This study also demonstrates how deep structures, such as the continuation of the subduction transform edge propagator (STEP) fault between the Hellenic and Cyprus arcs in the continental area, can come into play

  10. Shear zone nucleation and deformation transient: effect of heterogeneities and loading conditions in experimentally deformed calcite

    Science.gov (United States)

    Morales, L. F. G.; Rybacki, E.; Dresen, G. H.; Kilian, R.

    2015-12-01

    In the Earth's middle to lower crust, strain is frequently localized along ductile shear zones, which commonly nucleate at structural and material heterogeneities. To investigate shear zone nucleation and development due to heterogeneities, we performed constant strain-rate (CSR) and constant stress (CS) simple shear (torsion) deformation experiments on Carrara marble samples containing weak (limestone) inclusions. The experiments were conducted in a Paterson-type gas deformation apparatus at 900 °C temperature and 400 MPa confining pressure and maximum bulk shear strains of 3. Peak shear stress was about 20 MPa for all the samples, followed by smooth weakening and steady state behavior. The strain is predominantly localized in the host marble within the process zone in front of the inclusion, defined by a zone of intense grain size reduction due to dynamic recrystallization. In CS tests a narrow shear zone developed in front of the inclusion, whereas in CSR experiments the deformation is more heterogeneously distributed, up to g=3.. In the later, secondary foliations oblique to the process zone and alternating thin, high-strain layers are common. In samples deformed at the same shear strain (g=1), the average recrystallized grain size in the process zone is similar for CS and CSR conditions. Crystallographic preferred orientation (CPO) measurements shows that different grain sizes have slightly different CPO patterns. CPO strength varies for different grain sizes, with a CPO strength peak between 40-50 μm, decreasing progressively within smaller grain size, but with secondary peaks for different coarse-grained sizes. Our observations suggest that the initial formation and transient deformation of shear zones is strongly affected by loading conditions.

  11. Effect of tree roots on a shear zone: modeling reinforced shear stress.

    Science.gov (United States)

    Kazutoki Abe; Robert R. Ziemer

    1991-01-01

    Tree roots provide important soil reinforcement that impoves the stability of hillslopes. After trees are cut and roots begin to decay, the frequency of slope failures can increase. To more fully understand the mechanics of how tree roots reinforce soil, fine sandy soil containing pine roots was placed in a large shear box in horizontal layers and sheared across a...

  12. Tibet- Himalayan Analogs of Pan-African Shear Zones : Implications for Neoproterozoic Tectonics

    Science.gov (United States)

    Attoh, K.; Brown, L. D.

    2009-12-01

    Large-scale shear zones are distinct features of Tibet-Himalayan orogen and the Pan-African Trans-Saharan belt. Prominent examples in the Pan-African-belt extend for ~2500 km from the Sahara to the Gulf of Guinea and are characterized by right-slip movements. The NS shear zones, such as 4°50’-Kandi shear zone (KSZ) are complemented by NE-SW shear zones that preserve a record of sinistral movements and are represented by the Central Cameroon shear zone (CCSZ) in the eastern part of the Pan-African domain. The West African shear zones project into similar structures in the Borborema Province of northeast Brazil. In addition, the Pan-African belt preserves structures and rock assemblages that indicate subduction-collision tectonics We propose that structures of Tibet-Himalayan collisional orogen are instructive analogs of the Pan-African structures where: (i) the Pan-African front corresponds to the Main Himalayan thrust and it’s splays; (ii) the main Pan-African suture zone is analogous to the Indus-Tsangpo suture in the Tibet-Himalayan belt; (iii) the 4°50’-KSZ corresponds to Karakoram and it’s linkages with Jiali fault system and (iv) left-slip CCSZ and related shear zones are analogs of Altyn Tagh and Kumlun faults and their splays. This suggests the operation of escape-type tectonics in the Neoproterozoic belt of West-Africa and predicts the nature of the deep structures in the Cenozoic Tibet-Himalayan orogen.

  13. Cenozoic structural inversion from transtension to transpression in Yingxiong Range, western Qaidam Basin: New insights into strike-slip superimposition controlled by Altyn Tagh and Eastern Kunlun Faults

    Science.gov (United States)

    Cheng, Xiang; Zhang, Daowei; Jolivet, Marc; Yu, Xiangjiang; Du, Wei; Liu, Runchao; Guo, Zhaojie

    2018-01-01

    A Cenozoic structural inversion event from transtension to transpression involving salt tectonics has been uncovered in the Yingxiong Range, the western Qaidam Basin. Seismic reflection data show that there are two common structural styles in the Yingxiong Range: (1) the positive flower structure; (2) the thrust-controlled fold at shallow depth and the positive inverted flower structure at deep levels, which are separated by a salt layer in the upper Xiaganchaigou Formation. The Yingxiong Range experienced a first stage of transtension in the Eocene, induced by the Altyn Tagh Fault, and a second stage of transpression from the early Miocene to present, jointly controlled by the Altyn Tagh and Eastern Kunlun Faults. The Eocene transtension produced numerous NW-striking right-stepping en-échelon transtensional normal faults or fractures in the Yingxiong Range. At the same time, evaporites and mudstone were deposited in the vicinity of these faults. In the early Miocene, the Eocene transtensional normal faults were reactivated in a reverse sense, and the thrust-controlled folds at shallow depth started to form simultaneously. With transpression enhanced in the late Cenozoic, positive flower structures directly formed in places without evaporites. The Cenozoic transtension to transpression inversion of the Yingxiong Range is the result of strike-slip superimposition controlled by the Altyn Tagh and Eastern Kunlun Faults in time and space.

  14. Structure of the la VELA Offshore Basin, Western Venezuela: AN Obliquely-Opening Rift Basin Within the South America-Caribbean Strike-Slip Plate Boundary

    Science.gov (United States)

    Blanco, J. M.; Mann, P.

    2015-12-01

    Bathymetric, gravity and magnetic maps show that the east-west trend of the Cretaceous Great Arc of the Caribbean in the Leeward Antilles islands is transected by an en echelon series of obliquely-sheared rift basins that show right-lateral offsets ranging from 20 to 40 km. The basins are 75-100 km in length and 20-30 km in width and are composed of sub-parallel, oblique slip normal faults that define deep, bathymetric channels that bound the larger islands of the Leeward Antilles including Aruba, Curacao and Bonaire. A single basin of similar orientation and structure, the Urumaco basin, is present to the southwest in the Gulf of Venezuela. We mapped structures and sedimentation in the La Vela rift basin using a 3D seismic data volume recorded down to 6 seconds TWT. The basin can be mapped from the Falcon coast where it is correlative with the right-lateral Adicora fault mapped onshore, and its submarine extension. To the southeast of the 3D survey area, previous workers have mapped a 70-km-wide zone of northeast-striking, oblique, right-lateral faults, some with apparent right-lateral offsets of the coastline. On seismic data, the faults vary in dip from 45 to 60 degrees and exhibit maximum vertical offsets of 600 m. The La Vela and other obliquely-opening rifts accommodate right-lateral shear with linkages to intervening, east-west-striking right-lateral faults like the Adicora. The zone of oblique rifts is restricted to the trend of the Great Arc of the Caribbean and may reflect the susceptiblity of this granitic basement to active shearing. The age of onset for the basins known from previous studies on the Leeward Antilles is early Miocene. As most of these faults occur offshore their potential to generate damaging earthquakes in the densely populated Leeward Antilles is not known.

  15. Structural analysis and magmatism characterization of the Major Gercino shear zone, Santa Catarina State, Brazil

    International Nuclear Information System (INIS)

    Passarelli, Claudia Regina

    1996-01-01

    This work describes the geometric and kinematic characteristics of the Major Gercino Shear Zone (MGSZ) in the Canelinha-Garcia area. This shear zone is one of the major lineaments that affect all southern Brazilian precambrian terrains. In Santa Catarina State, it separates, along its whole extension, the supracrustal rocks of the Brusque belt (northern part) from the Granitoid belt (southern). This zone is characterized by a regional NE trend and a dextral sense of movement where ductile-brittle structures predominate. The MGSZ is composed of two mylonitic belts separated by granitoid rocks probably associated to the development of the shear zone. Both shear zones show cataclastic to ultra mylonitic rocks, but mylonites and protomylonites conditions at high strain rate. The calc-alkaline granitoids present in the area can be grouped in two granitoid associations with meta to peraluminous affinities. The Rolador Granitoid Association is characterized by grayish porphyritic biotite-monzogranites and the Fernandes Granitoid Association by coarsed-grained to porphyritic pinkish amphibole-syenogranites. The U-Pb and Rb-Sr ages range from 670 to 590 Ma with the Sr 87 / Sr 86 initial ratios suggesting a crustal contribution in the generation of these rocks. The importance of the pure shear component is also emphasized by the results of the Fry method. Many z axes of the strain ellipses are at high angle to the shear foliation. Symmetric porphyroclasts also corroborate this hypothesis. The micaceous minerals formed during the shear development indicate K-Ar ages around 555 ± 15 Ma. Brittle reactivations of the shear zone have been placed by K-Ar in fine-fraction materials at Triassic time (215 ± 15 Ma.)

  16. New tectono-geochronological constraints on timing of shearing along the Ailao Shan-Red River shear zone: Implications for genesis of Ailao Shan gold mineralization

    Science.gov (United States)

    Liu, Junlai; Chen, Xiaoyu; Wu, Wenbin; Tang, Yuan; Tran, My-Dung; Nguyen, Quang-Luat; Zhang, Zhaochong; Zhao, Zhidan

    2015-05-01

    Several world class gold deposits are located along the Ailao Shan (ALS) belt in eastern Tibet, China. The genesis of gold mineralization along the belt, however, has been the subject of debates in the last decades, which highlights the importance of dating shearing, magmatism and mineralization along the Ailao Shan-Red River shear zone (ASRR). Through detailed field observations and microscopic analysis, a group of leucocratic intrusions from within and outside the shear zone along the ALS belt are investigated in the present paper. Pre-, syn- and post-shearing intrusions are grouped based on structural and microstructural analysis. LA-ICP-MS and SIMS dating of the intrusions revealed the existence of two age populations, a group of ages older than 30 Ma and the other younger than 28 Ma. The former are distributed both within and outside the shear zone, and the latter, in contrast, occur only within the shear zone. Our new results show that the ductile shearing along the ASRR shear zone initiated since ca. 30 Ma ago. The dating results place major constraints on timing of shearing along the ASRR shear zone and have profound implications on the genesis of gold mineralization along the ALS belt. The present study reveals that ductile shearing along the ASRR shear zone was resulted from extrusion of the Indochina block late during the Indian-Eurasian plate collision. Meanwhile, we conclude that the gold mineralization took place prior to the shearing, but in close relation to an early magmatism (>30 Ma) ascribed to post-collisional extension collapse involving mantle processes, early during the plate collision.

  17. Granitoïdes mylonitiques d'âge Viséen supérieur dans le massif de l'Argentera (Alpes occidentales, Italie) : indications sur l'âge et la cinématique de la zone de cisaillement Ferrière Mollières

    Science.gov (United States)

    Musumeci, Giovanni; Colombo, Fabrizio

    The Argentera Massif in the western Alps is made of up two medium-high-grade metamorphic complexes of Variscan age. They are separated by a regional-scale northwest-trending shear zone, the Ferrière-Mollières Line, which consists of low-grade mylonitic rocks. Muscovite-bearing mylonitic leucogranites crop out as subvertical northwest-trending intrusions, in the northern portion of the shear zone. A Rb/Sr muscovite-wr age of 327±3 Ma on foliated leucogranite gives a lower limit for the age of mylonitic deformation for which kinematic indicators indicate a dextral sense of shear. This strike-slip tectonics is compatible with the extensional regime that occurred during Carboniferous in the whole western Europe. To cite this article: G. Musumeci, F. Colombo, C. R. Geoscience 334 (2002) 213-220.

  18. Early lineations in a later shear zone: case study from the Eastern Ghats Belt, India

    Science.gov (United States)

    Bose, S.; Gupta, S.

    2016-12-01

    In polydeformed gneissic terranes, ductile shear zones may cut across rocks with older penetrative fabrics. Earlier lineations in later ductile shear zones need to be identified to avoid incorrect kinematic interpretation. To investigate the fate of early lineations during later ductile shearing, the Mahanadi Shear Zone (MSZ) from the Eastern Ghats Belt (EGB) in India is taken as a case study. The EGB is a Proterozoic granulite terrane correlated with Indo-Antarctica collision. The MSZ lies within the EGB, but is oriented almost perpendicular to the trend of the belt. The penetrative structural fabric in the EGB is NE-SW trending and dipping SE. However, a broad swing in structural trend from NE-SW to WNW-ESE can be detected near the MSZ from satellite imagery. In mylonitised rocks of the shear zone, a discrepancy between the shear zone lineation and inferred shear sense leads to uncertainty in kinematic interpretation of the shear zone. The EGB rock types include charnockites, quartzofeldspathic gneisses and garnet-sillimanite-bearing metapelitic gneisses (khondalites). Outside the MSZ, gneisses preserve an earlier, dominantly down-dip intersection lineation. Sillimanite needles in khondalites are aligned parallel to this lineation, while quartz and garnet are also annealed into the granulite facies fabric. In the vicinity of the shear zone, evidence of dextral non-coaxial shearing progressively increases but the lineation distribution is scattered. Quartz grains show strong undulose extinction caused by strain at lower temperatures, and crystallographic c-axis fabric analyses using EBSD indicate deformation by basal c-slip mechanism. Preferred alignment of the sillimanite needles is disrupted in khondalites within the MSZ because of partial rotation of the needles towards the sub-horizontal movement direction, with the extent of rotation of the needles being apparently controlled by grain size. Some sillimanite needles also appear to have undergone

  19. From 2012 HAITI-SIS Survey: thick-skin versus thin-skin tectonics partitioned along offshore strike-slip Faults-Haïti

    Science.gov (United States)

    Ellouz, N.; Leroy, S. D.; Momplaisir, R.; Mercier de Lepinay, B.

    2013-12-01

    The characterization of the deformation along large strike-slip fault-systems like transpressive boundaries between N. Caribbean/N America is a challenging topic, which requires a multi-scale approach. Thanks to Haiti-sis new data, the precise description of the fault segmentation pattern, the sedimentogical distribution, the uplift/subsidence rates, the along-fault and intra-basin fluids circulations, allows to actualize the evolution of the deformation history up to present-day . All the co-seismic surface to near-surface events, have to be also identified in order to integrate geophysical solutions for the earthquake, within the present-day geological and structural pattern. These two approaches, ranging from geological to instantaneous time-scales have been used during multi-tools Haiti-Sis oceanographic survey, allowing to document and image these different aspects at a large scale. The complex strike-slip North Caribbean boundary registered significative stress partitioning. Oblique convergence is expressed by along-strike evolution; from rifted segments (Cayman Through) to transpressive ones (Haiti, Dominican Rep.), to subduction (Porto Rico). In the Haiti-Sis survey, we acquired new offshore data surrounding the active fault areas, in the Gonâve Bay, the Jamaica Channel and along Southern Peninsula. Mapping the sea-floor, and HR seismic acquisition were our main objectives, in order to characterize the fault and fold architecture, with a new delineation of active segments. Offshore piston cores, have been used as representative of the modern basin sedimentation, and to document the catastrophic events (earthquakes, massive flood or sudden destabilization of the platform ) represented by turbiditic or mass-flow sequences, with the objective to track the time recurrence of seismic events by dating some of these catastrophic sediment deposition. At surface, the other markers of the fault activity are linked with along-fault permeability and fluid circulation

  20. Seismically-triggered soft-sediment deformation structures close to a major strike-slip fault system in the Eastern Alps (Hirlatz cave, Austria)

    Science.gov (United States)

    Salomon, Martina Lan; Grasemann, Bernhard; Plan, Lukas; Gier, Susanne; Schöpfer, Martin P. J.

    2018-05-01

    We investigate episodic soft-sediment deformation structures cross-cut by normal faults preserved in unlithified finely laminated calcite rich sediments in the Hirlatz cave in the Northern Calcareous Alps (Austria). These sediments comprise varve-like alternations of brighter carbonate/quartz rich layers, and darker clay mineral rich layers. The deformed sediments contain abundant millimeter to centimeter-scale soft-sediment structures (load casts, ball-and-pillow structures), sheet slumps (thrust faults and folds), erosive channels filled with slides and chaotic slumps. After deposition and soft-sediment deformation normal faults developed within the entire sedimentary succession, an event that probably correlates with an offset of c. 10 cm of the passage wall above the outcrop. Our major conclusions are: (i) The sediments have a glacial origin and were deposited in the Hirlatz cave under phreatic fluvio-lacustrine conditions. The deposition and the soft-sediment deformation occurred most likely during the last glaciation (i.e. around 25 ka ago); (ii) The liquefaction and formation of the soft-sediment structures in water-saturated stratified layers was triggered by episodic seismic events; (iii) The internally deformed sediments were later displaced by normal faults; (iv) A possible source for the seismic events is the active sinistral Salzach-Ennstal-Mariazeller-Puchberger (SEMP) strike-slip fault which is located about 10 km south of the outcrop and plays a major role in accommodating the extrusion of the Eastern Alps towards the Pannonian Basin. To our knowledge, the described structures are the first report of liquefaction and seismically induced soft-sediment deformations in Quaternary sediments in the Eastern Alps.

  1. 3D deformation in strike-slip systems: Analogue modelling and numerical restoration Deformación 3D en sistemas de rumbo: modelación analógica y restauración numérica

    Directory of Open Access Journals (Sweden)

    Daniel González

    2012-05-01

    Full Text Available Regional and local strike-slip systems in Chile are complex and pose interesting questions, such as the interaction between strike-slip and reverse faults, how they evolve, and the relationship between shortening, rotation and uplift. Within this context, we developed a new analytical method based on analogue and numerical modelling applied to 3D, pure and transtensional-transpressional strike-slip systems. Analogue modelling results indicate that in restraining stepovers of strike-slip fault systems, where antiformal pop-up structures are usually formed, pre-existent basement structures with a high angle to the main strike-slip fault will generate a higher rotation of blocks. However, when these structures are oriented at a high angle with respect to the main stress convergence vector, the rotation will be less and therefore a higher tendency to uplift will be produced. These results were applied to NW- and SE-striking basement faults oblique to N-S mega-thrust faults in central Chile (32°-35°S, for which we propose a simultaneous development based on the analogue model results. Moreover, we propose that strike-slip movement occurred on thrust faults in central Chile. Furthermore, we performed a numerical restoration of an analogue experiment which modeled a pure strike-slip system, and concluded that the restoration is very sensitive to shortening data as well as to rotational data. These results are extremely important for future numerical and regional analysis of strike-slip systems.Los sistemas de rumbo regionales y locales en Chile son complejos y plantean interesantes preguntas, tales como la interacción entre fallas de rumbo y fallas inversas, cómo evolucionan ellas, y la relación entre acortamiento, rotación y alzamiento. En este contexto, desarrollamos un nuevo método analítico basado en modelamiento analógico y numérico de sistemas de rumbo de cizalle puro y sistemas transpresionales-trantensionales en 3D. Los resultados del

  2. Understanding ductile-to-brittle transition of metallic glasses from shear transformation zone dilatation

    Directory of Open Access Journals (Sweden)

    M.Q. Jiang

    2015-08-01

    Full Text Available A theoretical model that takes into account the free-volume aided cooperative shearing of shear transformation zones (STZs is developed to quantitatively understand the ductile-to-brittle transition (DBT of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-type rearrangements to dilatational processes (termed tension transformation zones (TTZs.

  3. Strain and shape-fabric variations associated with ductile shear zones

    Science.gov (United States)

    Simpson, Carol

    The foliated and compositionally-banded granitic orthogneisses in the central core of the Maggia Nappe, a Lower Pennine basement nappe of the Central Swiss Alps, are shown to be the sheared equivalent of late-Hercynian age granitic intrusions. These ductile shear zones show mineral assemblages in amphibolite facies, are Alpine in age and form an anastomosing network enclosing remnant lozenge-shaped pods of relatively undeformed rock. The foliation developed within the shear zones concomitantly with a change in shape of quartz grain aggregates from initially equidimensional, through 'tear-drop' shapes, to ribbon-like aggregates. These shape changes occurred by intracrystalline glide together with intercrystalline slip on deformation-induced planar surfaces.

  4. The Suruli shear zone and regional scale folding pattern in Madurai ...

    Indian Academy of Sciences (India)

    The Suruli shear zone and regional scale folding pattern in. Madurai block of Southern Granulite Terrain, south India. V Srinivasan. 1,∗ and P Rajeshdurai. 2. 1. Geological Survey of India, E/5, Arera Colony, Bhopal 462 016, India. 2. Geological Survey of India, Jawaharlal Nehru Road, Guindy, Chennai 600 032, India. ∗.

  5. The discovery of a conjugate system of faults in the Wharton Basin intraplate deformation zone.

    Science.gov (United States)

    Singh, Satish C; Hananto, Nugroho; Qin, Yanfang; Leclerc, Frederique; Avianto, Praditya; Tapponnier, Paul E; Carton, Helene; Wei, Shengji; Nugroho, Adam B; Gemilang, Wishnu A; Sieh, Kerry; Barbot, Sylvain

    2017-01-01

    The deformation at well-defined, narrow plate boundaries depends on the relative plate motion, but how the deformation takes place within a distributed plate boundary zone remains a conundrum. This was confirmed by the seismological analyses of the 2012 great Wharton Basin earthquakes [moment magnitude ( M w ) 8.6], which suggested the rupture of several faults at high angles to one another. Using high-resolution bathymetry and seismic reflection data, we report the discovery of new N294°E-striking shear zones, oblique to the plate fabric. These shear zones are expressed by sets of normal faults striking at N335°E, defining the direction of the principal compressional stress in the region. Also, we have imaged left-lateral strike-slip faults along reactivated N7°E-oriented oceanic fracture zones. The shear zones and the reactivated fracture zones form a conjugate system of faults, which accommodate present-day intraplate deformation in the Wharton Basin.

  6. Vertical-axis rotations and deformation along the active strike-slip El Tigre Fault (Precordillera of San Juan, Argentina) assessed through palaeomagnetism and anisotropy of magnetic susceptibility

    Science.gov (United States)

    Fazzito, Sabrina Y.; Rapalini, Augusto E.; Cortés, José M.; Terrizzano, Carla M.

    2017-03-01

    Palaeomagnetic data from poorly consolidated to non-consolidated late Cenozoic sediments along the central segment of the active El Tigre Fault (Central-Western Precordillera of the San Juan Province, Argentina) demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical-axis rotations of variable magnitude. This deformation has affected in different amounts Miocene to late Pleistocene samples and indicates a complex kinematic pattern. Several inherited linear structures in the shear zone that are oblique to the El Tigre Fault may have acted as block boundary faults. Displacement along these faults may have resulted in a complex pattern of rotations. The maximum magnitude of rotation is a function of the age of the sediments sampled, with largest values corresponding to middle Miocene-lower Pliocene deposits and minimum values obtained from late Pleistocene deposits. The kinematic study is complemented by low-field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a N-S stretching direction, subparallel to the strike of the main fault.

  7. Effect of Different Loading Conditions on the Nucleation and Development of Shear Zones Around Material Heterogeneities

    Science.gov (United States)

    Rybacki, E.; Nardini, L.; Morales, L. F.; Dresen, G.

    2017-12-01

    Rock deformation at depths in the Earth's crust is often localized in high temperature shear zones, which occur in the field at different scales and in a variety of lithologies. The presence of material heterogeneities has long been recognized to be an important cause for shear zones evolution, but the mechanisms controlling initiation and development of localization are not fully understood, and the question of which loading conditions (constant stress or constant deformation rate) are most favourable is still open. To better understand the effect of boundary conditions on shear zone nucleation around heterogeneities, we performed a series of torsion experiments under constant twist rate (CTR) and constant torque (CT) conditions in a Paterson-type deformation apparatus. The sample assemblage consisted of copper-jacketed Carrara marble hollow cylinders with one weak inclusion of Solnhofen limestone. The CTR experiments were performed at maximum bulk strain rates of 1.8-1.9*10-4 s-1, yielding shear stresses of 19-20 MPa. CT tests were conducted at shear stresses between 18.4 and 19.8 MPa resulting in shear strain rates of 1-2*10-4 s-1. All experiments were run at 900 °C temperature and 400 MPa confining pressure. Maximum bulk shear strains (γ) were ca. 0.3 and 1. Strain localized within the host marble in front of the inclusion in an area termed process zone. Here grain size reduction is intense and local shear strain (estimated from markers on the jackets) is up to 8 times higher than the applied bulk strain, rapidly dropping to 2 times higher at larger distance from the inclusion. The evolution of key microstructural parameters such as average grain size and average grain orientation spread (GOS, a measure of lattice distortion) within the process zone, determined by electron backscatter diffraction analysis, differs significantly as a function of loading conditions. Both parameters indicate that, independent of bulk strain and distance from the inclusion, the

  8. Relating rheology to geometry in large-scale natural shear zones

    Science.gov (United States)

    Platt, John

    2016-04-01

    The geometry and width of the ductile roots of plate boundary scale faults are very poorly understood. Some field and geophysical data suggests widths of tens of km in the lower crust, possibly more in the upper mantle. Other observations suggest they are much narrower. Dip slip shear zones may flatten out and merge into zones of subhorizontal lower crustal or asthenospheric flow. The width of a ductile shear zone is simply related to relative velocity and strain rate. Strain rate is related to stress through the constitutive relationship. Can we constrain the stress, and do we understand the rheology of materials in ductile shear zones? A lot depends on how shear zones are initiated. If they are localized by pre-existing structures, width and/or rheology may be inherited, and we have too many variables. If shear zones are localized primarily by shear heating, initial shear stress has to be very high (> 1 GPa) to overcome conductive heat loss, and very large feedbacks (both positive and negative) make the system highly unstable. Microstructural weakening requires a minimum level of stress to cause deformation and damage in surrounding rock, thereby buffering the stress. Microstructural weakening leads to grain-size sensitive creep, for which we have constitutive laws, but these are complicated by phase mixing in polyphase materials, by viscous anisotropy, by hydration, and by changes in mineral assemblage. Here are some questions that need to be addressed. (1) If grain-size reduction by dynamic recrystallization results in a switch to grain-size sensitive creep (GSSC) in a stress-buffered shear zone, does dynamic recrystallization stop? Does grain growth set in? If grain-size is still controlled by dislocation processes, then the effective stress exponent for GSSC is 4-5, even though the dominant mechanism may be diffusion and/or grain-boundary sliding (GBS). (2) Is phase mixing in ultramylonites primarily a result of GBS + neighbour switching, creep cavitation and

  9. High-rate GPS results for the April 2012 Sumatra earthquake sequence, an unusual, complex, and very large intraplate strike-slip event

    Science.gov (United States)

    Hill, E. M.; Hermawan, I.; Lay, T.; Yue, H.; Banerjee, P.; Qiu, Q.; Macpherson, K. A.; Feng, L.; Tsang, L. L.; Lubis, A.; Tapponnier, P.; Sieh, K. E.

    2012-12-01

    The 11 April 2012 Mw 8.6 Sumatra earthquake was one of the largest strike-slip earthquakes ever recorded, and also one of the largest intraplate earthquakes. It was followed 2 hours later by another great earthquake, of Mw 8.2, in a similar location. The events occurred ~400 km from northern Sumatra, on the oceanic side of the Sunda megathrust. The event was recorded by high-rate GPS stations from our 50-station Sumatra GPS Array (SuGAr). We will present the coseismic displacements and constraints on slip obtained from this network. The location of the events is very interesting. Scientists have long been puzzled by the nature and location of the boundary between the Indian and Australian plates in the depths of the Indian Ocean. Because of the resistance provided by the collision of India with Tibet far to the north, the Indian plate is moving relatively northwards at about 1 cm/yr slower than the Australian plate; this difference in velocity causes strain between the Indian and Australian plates. These earthquakes provide important new evidence that this strain is reactivating a system of faults on the seafloor that were inherited from an older geological epoch, and bring up questions about why this deformation appears to be diffuse, rather than behaving as a proper plate boundary. The events also highlight a back-and-forth interaction between the intraplate faults and the Sunda megathrust; the 2004 megathrust event brought these earthquakes ahead in time, but these earthquakes will in turn have stressed the megathrust. Published seismological results have indicated great complexity in the rupture patterns for these events, with a cascading failure of multiple conjugate faults. Surprisingly, the majority of slip seems to have occurred on the WNW-trending, right-lateral faults, rather than the NNE-trending left-lateral faults that are prominent features of the seafloor. The seismological results also show that the ruptures are likely to have extended from the

  10. Crevasse Extent and Lateral Shearing of the McMurdo Shear Zone, Antarctica: Implications of Ice Shelf Stability

    Science.gov (United States)

    Kaluzienski, L. M.; Hamilton, G. S.; Koons, P. O.; Enderlin, E. M.; Arcone, S. A.; Borstad, C.; Walker, B.

    2016-12-01

    Antarctica's ice shelves modulate the flow of inland ice towards the ocean. Understanding the controls on ice-shelf stability is critical for predicting the future evolution of the ice sheet. For the western sector of the Ross Ice Shelf (RIS), a potentially important region of lateral resistance is the McMurdo Shear Zone (MSZ) just downstream of Minna Bluff. Here the fast-moving Ross Ice Shelf ( 450 m/yr) shears past the slower-moving McMurdo Ice Shelf ( 200 m/yr) creating a zone of intense crevassing. An analysis of several satellite image datasets including a high-resolution digital elevation model (DEM) extracted from stereo Worldview imagery suggests that many of these flow features originate as the RIS flows past Minna Bluff. Here we present a sensitivity analysis of RIS ice flow using the Ice Sheet System Model (ISSM) (Larour et al. 2012) and the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA). In this analysis we assess the sensitivity of model flow of RIS tributary glaciers to boundary condition perturbations within the Minna Bluff/MSZ region. Perturbations include ice shelf thickness variations as well as a scalar damage variable that quantifies the loss of load-bearing surface area due to ice shelf fracture. Field observations of surface flow and strain (GPS) and crevasse distribution and geometry (GPR)in the MSZ help constrain the model simulations. Initial results point to the importance of sub-ice shelf topography and its interaction with features such as Minna Bluff in determining stress distribution on the western RIS. Larour, E.; Seroussi, H.; Morlighem, M.; Rignot, E. 2012. Continental scale, high order, high spatial resolution, ice sheet modeling using the Ice Sheet System Model (ISSM), Journal of Geophysical Research

  11. Neoarchean ductile deformation in the Northeastern North China Craton: The Shuangshanzi ductile shear zone in Qinglong area, eastern Heibei, China

    Science.gov (United States)

    Liu, Boran; Neubauer, Franz; Liu, Junlai; Jin, Wei; Li, Weimin; Liang, Chenyue

    2017-04-01

    Archean granitic gneiss domes and greenstone belts are well-preserved in eastern NCC, one of the oldest Archean terrains in the world. The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei Province is located between an Archean granitic gneiss dome and a greenstone belt within an uplift in eastern NCC. Supracrustal rocks from the Neoarchean Shuangshanzi and Zhuzhangzi Groups were sheared, but some Archean granitic gneisses were also involved in the shearing along the eastern margin. In the southern part, the narrow NE-trending shear zone dips NW with dip angles of 40-60° and, in the northern part, the shear zone dips NWN with dip angles of 70-85°. Microstructural and EBSD fabric analyses suggest that the shear zone was developed at upper greenschist facies to lower amphibolite facies conditions with deformation temperatures of 400 to 550°C.LA-ICP-MS zircon U-Pb ages of mylonitized granitic rocks and undeformed quartz diorite cutting the shear zone suggest that the Shuangshanzi ductile shear zone was formed between 2550 Ma and 2452 Ma. Detailed kinematic studies of the shear zone show a clear sinistral shear sense with a slightly oblique-slip component in the northern part and a sinistral transtensional slip component in the southern part. It is therefore suggested that the shear zone was formed during the Anziling doming with respect to the down-slipping Neoarchean Shuangshanzi and Zhuzhangzi Groups. The difference in kinematics along the southern and the northern sections is interpreted to be caused by the doming with an uneven clockwise spiral rotation. The BIF-rich supracrustal rocks have higher density than their neighboring granitic gneisses, and therefore can easily sink to form synclines by sagduction processes. The sagduction is mainly triggered by gravitational inversion of high density supracrustal rocks with respect to relatively light granitic gneisses within the dome. As a result, the gneisses synchronously moved upward. A shear zone was

  12. Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone

    Science.gov (United States)

    Penney, Camilla; Tavakoli, Farokh; Saadat, Abdolreza; Nankali, Hamid Reza; Sedighi, Morteza; Khorrami, Fateme; Sobouti, Farhad; Rafi, Zahid; Copley, Alex; Jackson, James; Priestley, Keith

    2017-06-01

    We study the Makran subduction zone, along the southern coasts of Iran and Pakistan, to gain insights into the kinematics and dynamics of accretionary prism deformation. By combining techniques from seismology, geodesy and geomorphology, we are able to put constraints on the shape of the subduction interface and the style of strain across the prism. We also address the long-standing tectonic problem of how the right-lateral shear taken up by strike-slip faulting in the Sistan Suture Zone in eastern Iran is accommodated at the zone's southern end. We find that the subduction interface in the western Makran may be locked, accumulating elastic strain, and move in megathrust earthquakes. Such earthquakes, and associated tsunamis, present a significant hazard to populations around the Arabian Sea. The time-dependent strain within the accretionary prism, resulting from the megathrust earthquake cycle, may play an important role in the deformation of the Makran region. By considering the kinematics of the 2013 Balochistan and Minab earthquakes, we infer that the local gravitational and far-field compressive forces in the Makran accretionary prism are in balance. This force balance allows us to calculate the mean shear stress and effective coefficient of friction on the Makran megathrust, which we find to be 5-35 MPa and 0.01-0.03, respectively. These values are similar to those found in other subduction zones, showing that the abnormally high sediment thickness in the offshore Makran does not significantly reduce the shear stress on the megathrust.

  13. Structural setting and magnetic properties of pseudotachylyte in a deep crustal shear zone, western Canadian shield

    Science.gov (United States)

    Orlandini, O. F.; Mahan, K. H.; Brown, L. L.; Regan, S.; Williams, M. L.

    2012-12-01

    Seismic slip commonly produces pseudotachylytes, a glassy vein-filling substance that is typically interpreted as either a frictional melt or an ultra-triturated cataclasite. In either form, pseudotachylytes are commonly magnetite enriched, even in magnetite-free host rocks, and therefore are potentially useful as high fidelity recorders of natural magnetic fields at the time of slip in a wide array of lithologies. Pseudotachylytes generally have high magnetic susceptibility and thus should preserve the dominant field present as the material passes the Curie temperatures of magnetic minerals, primarily magnetite. Two potential sources have been proposed for the dominant magnetic field recorded: the earth's magnetic field at the time of slip or the temporary and orders of magnitude more intense field created by the presence of coseismic currents along the failure plane. Pseudotachylytes of the Cora Lake shear zone (CLsz) in the Athabasca Granulite Terrain, western Canadian shield, are consistently hosted in high strain ultramylonitic orthogneiss. Sinistral and extensional oblique-slip in the CLsz occurred at high-pressure granulite-grade conditions of ~1.0 GPa and >800°C and may have persisted to somewhat lower P-T conditions (~0.8 GPa, 700 °C) during ductile deformation. Pseudotachylyte-bearing slip surfaces have sinistral offset, matching the larger shear zone, and clasts of wall rock in the more brecciated veins display field evidence for ductile shear along the same plane prior to brittle failure. The presence of undeformed pseudotachylyte in kinematically compatible fracture arrays localized in ultramylonite indicates that brittle failure may have occurred in the waning stages of shear zone activity and at similar deep crustal conditions. Field-documented occurrences of pseudotachylyte include 2 cm-thick veins that run subparallel to mylonitic foliation and contain small flow-aligned clasts and large, heavily brecciated foliation-crosscutting zones up to

  14. Petrologic and chemical changes in ductile shear zones as a function of depth in the continental crust

    Science.gov (United States)

    Yang, Xin-Yue

    Petrologic and geochemical changes in ductile shear zones are important for understanding deformational and geochemical processes of the continental crust. This study examines three shear zones that formed under conditions varying from lower greenschist facies to upper amphibolite facies in order to document the petrologic and geochemical changes of deformed rocks at various metamorphic grades. The studied shear zones include two greenschist facies shear zones in the southern Appalachians and an upper amphibolite facies shear zone in southern Ontario. The mylonitic gneisses and mylonites in the Roses Mill shear zone of central Virginia are derived from a ferrodiorite protolith and characterized by a lower greenschist facies mineral assemblage. Both pressure solution and recrystallization were operative deformation mechanisms during mylonitization in this shear zone. Strain-driven dissolution and solution transfer played an important role in the mobilization of felsic components (Si, Al, K, Na, and Ca). During mylonitization, 17% to 32% bulk rock volume losses of mylonites are mainly attributed to removal of these mobile felsic components by a fluid phase. Mafic components (Fe, Mg, Ti, Mn and P) and trace elements, REE, Y, V and Sc, were immobile. At Rosman, North Carolina, the Brevard shear zone (BSZ) shows a deformational transition from the coarse-grained Henderson augen gneiss (HAG) to proto-mylonite, mylonite and ultra-mylonite. The mylonites contain a retrograde mineral assemblage as a product of fluid-assisted chemical breakdown of K-feldspar and biotite at higher greenschist facies conditions. Recrystallization and intra-crystalline plastic deformation are major deformation mechanisms in the BSZ. Fluid-assisted mylonitization in the BSZ led to 6% to 23% bulk volume losses in mylonites. During mylonitization, both major felsic and mafic elements and trace elements, Rb, Sr, Zr, V, Sc, and LREE were mobile; however, the HREEs were likely immobile. A shear zone

  15. Neoarchean ductile deformation of the Northeastern North China Craton: The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei, North China

    Science.gov (United States)

    Liu, Boran; Neubauer, Franz; Liu, Junlai; Jin, Wei; Li, Weimin; Liang, Chenyue

    2017-05-01

    Archean granitic gneiss domes and greenstone belts are well-preserved in eastern North China Craton (NCC), one of the oldest Archean terrains in the world. The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei Province is located between an Archean granitic gneiss dome and a greenstone belt within an uplift in eastern NCC. Supracrustal rocks from the Neoarchean Shuangshanzi and Zhuzhangzi Groups, and some Archean granitic gneisses were involved in the shearing along the eastern margin. In the southern part, the narrow NE-trending shear zone dips NW with dip angles of 40-60° and, in the northern part, the shear zone dips NWN with dip angles of 70-85°. Microstructural and EBSD fabric analyses suggest that the shear zone was developed at upper greenschist facies to lower amphibolite facies conditions with deformation temperatures of 400-550 °C. LA-ICP-MS zircon U-Pb dating of mylonitized granitic rocks and undeformed quartz diorite cutting the shear zone suggest that the Shuangshanzi ductile shear zone was formed between 2550 Ma and 2452 Ma. Detailed kinematic studies of the shear zone show a clear sinistral shear sense with a slightly oblique-slip component in the northern part and a sinistral transtensional slip component in the southern part. It is therefore suggested that the shear zone was formed during the Anziling doming with respect to the down-slipping Neoarchean Shuangshanzi and Zhuzhangzi Groups. The difference in kinematics along the southern and the northern sections is interpreted to be caused by the doming with an uneven clockwise spiral rotation. The BIF-rich supracrustal rocks have higher density than their neighboring granitic gneisses, and therefore can easily sink to form synclines by sagduction processes. The sagduction is mainly triggered by gravitational inversion of high density supracrustal rocks with respect to relatively light granitic gneisses within the dome. As a result, the gneisses synchronously moved upward. A shear zone

  16. Coseismic Dehydration and Amorphisation of Serpentinite in a Creeping Shear Zone

    Science.gov (United States)

    Tarling, M.; Smith, S. A. F.; Viti, C.; Rooney, J. S.; Gordon, K. C.

    2017-12-01

    Recent experiments show that coseismic heating in serpentinite-bearing faults can produce dehydration assemblages consisting of olivine + enstatite or talc, as well as amorphous material and melt. Identification of these coseismic products has not been made in natural serpentinite shear zones, possibly because the reaction products would be quickly altered or rehydrated to form serpentine. Magnetite-coated slip surfaces within the serpentinite mélange of the Livingstone Fault, New Zealand, contain microstructural and mineralogical evidence for coseismic dehydration and amorphization of serpentine due to frictional heating. The bulk serpentinite mélange has a scaly fabric that contains abundant evidence for pressure-solution creep. These fabrics are crosscut by multi-layered, magnetite-coated slip surfaces up to 1.5 mm thick that enclose numerous thin (products (nanocrystalline olivine, enstatite, amorphous silica) are restricted to a zone 500 um from the main slip surface, no products of dehydration or amorphisation are identifiable. Encapsulated within the magnetite layers and protected from subsequent hydration, the thin selvages of serpentinite provide the first evidence of highly localised dehydration and amorphisation of serpentinite in a natural shear zone. Interpreted in the context of recent experiments, our results suggest that 1) the slip surfaces experienced extreme dynamic weakening associated with coseismic dehydration and amorphisation and, 2) localized rupture and coseismic slip can propagate through serpentinite mélange deforming by bulk pressure-solution creep.

  17. Shear mixing in stellar radiative zones. I. Effect of thermal diffusion and chemical stratification

    Science.gov (United States)

    Prat, V.; Lignières, F.

    2014-06-01

    Context. Turbulent transport of chemical elements in radiative zones of stars is considered in current stellar evolution codes thanks to phenomenologically derived diffusion coefficients. Recent local numerical simulations suggest that the coefficient for radial turbulent diffusion due to radial differential rotation satisfies Dt ≃ 0.058κ/Ri, in qualitative agreement with the model of Zahn (1992, A&A, 265, 115). However, this model does not apply (i) when differential rotation is strong with respect to stable thermal stratification or (ii) when chemical stratification has a significant dynamical effect, a situation encountered at the outer boundary of nuclear-burning convective cores. Aims: We extend our numerical study to consider the effects of chemical stratification and of strong shear, and compare the results with prescriptions used in stellar evolution codes. Methods: We performed local, direct numerical simulations of stably stratified, homogeneous, sheared turbulence in the Boussinesq approximation. The regime of high thermal diffusivities, typical of stellar radiative zones, is reached thanks to the so-called small-Péclet-number approximation, which is an asymptotic development of the Boussinesq equations in this regime. The dependence of the diffusion coefficient on chemical stratification was explored in this approximation. Results: Maeder's extension of Zahn's model in the strong-shear regime (Maeder 1995, A&A, 299, 84) is not supported by our results, which are better described by a model found in the geophysical literature. As regards the effect of chemical stratification, our quantitative estimate of the diffusion coefficient as a function of the mean gradient of mean molecular weight leads to the formula Dt ≃ 0.45κ(0.12-Riμ) /Ri, which is compatible in the weak-shear regime with the model of Maeder & Meynet (1996, A&A, 313, 140) but not with Maeder's (1997, A&A, 321, 134).

  18. Quantifying Uncertainty in Inverse Models of Geologic Data from Shear Zones

    Science.gov (United States)

    Davis, J. R.; Titus, S.

    2016-12-01

    We use Bayesian Markov chain Monte Carlo simulation to quantify uncertainty in inverse models of geologic data. Although this approach can be applied to many tectonic settings, field areas, and mathematical models, we focus on transpressional shear zones. The underlying forward model, either kinematic or dynamic, produces a velocity field, which predicts the dikes, foliation-lineations, crystallographic preferred orientation (CPO), shape preferred orientation (SPO), and other geologic data that should arise in the shear zone. These predictions are compared to data using modern methods of geometric statistics, including the Watson (for lines such as dike poles), isotropic matrix Fisher (for orientations such as foliation-lineations and CPO), and multivariate normal (for log-ellipsoids such as SPO) distributions. The result of the comparison is a likelihood, which is a key ingredient in the Bayesian approach. The other key ingredient is a prior distribution, which reflects the geologist's knowledge of the parameters before seeing the data. For some parameters, such as shear zone strike and dip, we identify realistic informative priors. For other parameters, where the geologist has no prior knowledge, we identify useful uninformative priors.We investigate the performance of this approach through numerical experiments on synthetic data sets. A fundamental issue is that many models of deformation exhibit asymptotic behavior (e.g., flow apophyses, fabric attractors) or periodic behavior (e.g., SPO when the clasts are rigid), which causes the likelihood to be too uniform. Based on our experiments, we offer rules of thumb for how many data, of which types, are needed to constrain deformation.

  19. Indirect dating of deformation: a geochronological study from the Pan African Ajaj shear zone, Saudi Arabia.

    Science.gov (United States)

    Hassan, Mahmoud; Abu-Alam, Tamer; Stüwe, Kurt; Klötzli, Urs

    2013-04-01

    The metamorphic complexes of the Arabian-Nubian Shield were exhumed by different exhumation mechanisms (i.e. in extension or oblique transpression regime) during the Pan African activity of Najd Fault System - the largest pre-Mesozoic shear zone on Earth. The different exhumation mechanisms could be the consequence of (i) orientation of the complexes at slightly different angles with respect to the overall orientation of the principal stresses of the Najd Fault System, (ii) exhumation from different depths, or (iii) change of the stress regime through time. In order to test the third hypothesis, geochronological work will be applied on a representative suite of complexes across the Najd Fault System. In particular we focus on three complexes in the Arabian part of the shield named Qazaz, Hamadat and Wajh. In general, the metamorphic complexes of the Arabian part of the shield exhibit left-lateral transcurrent tectonism along the NW-SE Najd faults and right-lateral movement along conjugate NE-SW striking structures. The whole unit forms an anastomosing network of planar structures that demarcate large fish-shaped bodies of high grade metamorphics. The Hamadat complex is surrounded by a left-lateral greenshist facies WNW-ESE Ajaj shear zone. The complex consists of folds that are strongly pinched to the north and more open to the south marked by a well-developed parallel stretching sub-horizontal lineation. Granite intrusions along and across the Ajaj shear zone may allow testing the timing of the deformation. Deformed and non-deformed samples of these granites will be examined by age dating to determine the absolute timing of the metamorphism and the deformation for the complex. Some 20 samples are currently being prepared for zircon dating. Whilst no results are available at the time of writing of this abstract, they will be presented at EGU 2013.

  20. Shear wave splitting and crustal anisotropy in the Eastern Ladakh-Karakoram zone, northwest Himalaya

    Science.gov (United States)

    Paul, Arpita; Hazarika, Devajit; Wadhawan, Monika

    2017-06-01

    Seismic anisotropy of the crust beneath the eastern Ladakh-Karakoram zone has been studied by shear wave splitting analysis of S-waves of local earthquakes and P-to-S or Ps converted phases originated at the crust-mantle boundary. The splitting parameters (Φ and δt), derived from S-wave of local earthquakes with shallow focal depths, reveal complex nature of anisotropy with NW-SE and NE oriented Fast Polarization directions (FPD) in the upper ∼22 km of the crust. The observed anisotropy in the upper crust may be attributed to combined effects of existing tectonic features as well as regional tectonic stress. The maximum delay time of fast and slow waves in the upper crust is ∼0.3 s. The Ps splitting analysis shows more consistent FPDs compared to S-wave splitting. The FPDs are parallel or sub parallel to the Karakoram fault (KF) and other NW-SE trending tectonic features existing in the region. The strength of anisotropy estimated for the whole crust is higher (maximum delay time δt: 0.75 s) in comparison to the upper crust. This indicates that the dominant source of anisotropy in the trans-Himalayan crust is confined within the middle and lower crustal depths. The predominant NW-SE trending FPDs consistently observed in the upper crust as well as in the middle and lower crust near the KF zone support the fact that the KF is a crustal-scale fault which extends at least up to the lower crust. Dextral shearing of the KF creates shear fabric and preferential alignment of mineral grains along the strike of the fault, resulting in the observed FPDs. A Similar observation in the Indus Suture Zone (ISZ) also suggests crustal scale deformation owing to the India-Asia collision.

  1. Analysis of a high intensity shear zone between overlapping fiber ends in a polymer matrix composite

    DEFF Research Database (Denmark)

    Lindgreen, Britta

    2008-01-01

    The formation of high intensity shear zones in a glass fiber reinforced thermoplast is studied numerically. The thermoplast is characterized by a finite strain elastic-viscoplastic constitutive relation and the calculations are carried out using a dynamic finite element program where plane strain...... that develop as the highly deformed region approaches the limit resulting from network stiffening in the polymer. A simple analysis assuming periodicity is included in order to study the mechanical behaviour of the polymer matrix between fiber ends with long overlap....

  2. Internal shear layers and uniform momentum zones in a turbulent pipe flow

    Science.gov (United States)

    Gul, Melika; Elsinga, Gerrit E.; Westerweel, Jerry

    2017-11-01

    Turbulent pipe flow has previously been shown to contain large-scale nearly uniform momentum, which are separated by layers of significant shear. These internal layers are of interest, because they are associated with fluid transport between uniform momentum zones, hence with the growth of these large energy-containing motions. In this study, we compare two methods to detect and analyse the internal shear layers; the triple decomposition method (TDM) and the streamwise velocity histogram method. The assessment is based on time-resolved PIV measurements in the cross-section of the pipe spanning a range of Reynolds numbers (Reτ = 700-1178). The strong jumps in the conditionally averaged flow statistics across the layers detected by TDM are smeared out with the histogram method. Using the TDM method, some scaling analyses are performed for the layer thickness, and the velocity jump over the layer. It is found that the layer thickness becomes almost constant after 0.4R, and the streamwise velocity jump decreases from the wall region to the core of the pipe. With the histogram method, on the other hand, one distinct shear layer is distinguished from the distribution of all local peak velocities, which is corresponding to the 95% of the central velocity of the pipe.

  3. A hidden variable in shear transformation zone volume versus Poisson's ratio relation in metallic glasses

    Science.gov (United States)

    Kim, S. Y.; Oh, H. S.; Park, E. S.

    2017-10-01

    Herein, we elucidate a hidden variable in a shear transformation zone (STZ) volume (Ω) versus Poisson's ratio (ν) relation and clarify the correlation between STZ characteristics and the plasticity of metallic glasses (MGs). On the basis of cooperative shear model and atomic stress theories, we carefully formulate Ω as a function of molar volume (Vm) and ν. The twofold trend in Ω and ν is attributed to a relatively large variation of Vm as compared to that of ν as well as an inverse relation between Vm and ν. Indeed, the derived equation reveals that the number of atoms in an STZ instead of Ω is a microstructural characteristic which has a close relationship with plasticity since it reflects the preference of atomistic behaviors between cooperative shearing and the generation of volume strain fluctuation under stress. The results would deepen our understanding of the correlation between microscopic behaviors (STZ activation) and macroscopic properties (plasticity) in MGs and enable a quantitative approach in associating various STZ-related macroscopic behaviors with intrinsic properties of MGs.

  4. Late extensional shear zones and associated recumbent folds in the Alpujarride subduction complex, Betic Cordillera, southern Spain

    International Nuclear Information System (INIS)

    Orozco, M.; Alonso-Chaves, F.; Platt, J.

    2017-01-01

    The existence in the Alpujarride Complex (Betic Cordillera, southern Spain) of a relatively continuous extensional event (following crustal thickening) is based on detailed structural studies and is consistent with the P-T paths and geochronological data established for the Alpujarride rocks. According to our research, the Alpujarride Complex contains two large-scale shear zones accommodating early Miocene extension. The shear zones contain km-scale recumbent folds, some with sheath fold geometry, and megaboudinage structures, and are closely associated with detachment faults. Large-scale folds and boudins cause dome-like undulations in the detachments, which are inferred to overlap in time with the deformation in the shear zones. One shear zone in the eastern part of the orogen is top-N; the other, in the western part, is top-E. The change in the shear direction may represent a temporal evolution in the direction of shear, possibly related to a change in the subduction direction in space and time.

  5. Late extensional shear zones and associated recumbent folds in the Alpujarride subduction complex, Betic Cordillera, southern Spain

    Energy Technology Data Exchange (ETDEWEB)

    Orozco, M.; Alonso-Chaves, F.; Platt, J.

    2017-11-01

    The existence in the Alpujarride Complex (Betic Cordillera, southern Spain) of a relatively continuous extensional event (following crustal thickening) is based on detailed structural studies and is consistent with the P-T paths and geochronological data established for the Alpujarride rocks. According to our research, the Alpujarride Complex contains two large-scale shear zones accommodating early Miocene extension. The shear zones contain km-scale recumbent folds, some with sheath fold geometry, and megaboudinage structures, and are closely associated with detachment faults. Large-scale folds and boudins cause dome-like undulations in the detachments, which are inferred to overlap in time with the deformation in the shear zones. One shear zone in the eastern part of the orogen is top-N; the other, in the western part, is top-E. The change in the shear direction may represent a temporal evolution in the direction of shear, possibly related to a change in the subduction direction in space and time.

  6. Timing of strain localization in high-pressure low-temperature shear zones: The argon isotopic record

    Science.gov (United States)

    Laurent, Valentin; Scaillet, Stéphane; Jolivet, Laurent; Augier, Romain

    2017-04-01

    The complex interplay between rheology, temperature and deformation profoundly influences how crustal-scale shear zones form and then evolve across a deforming lithosphere. Understanding early exhumation processes in subduction zones requires quantitative age constraints on the timing of strain localization within high-pressure shear zones. Using both the in situ laser ablation and conventional step-heating 40Ar/39Ar dating (on phengite single grains and populations) methods, this study aims at quantifying the duration of ductile deformation and the timing of strain localization within HP-LT shear zones of the Cycladic Blueschist Unit (CBU, Greece). The rate of this progressive strain localization is unknown, and in general, poorly known in similar geological contexts. Critical to retrieve realistic estimates of rates of strain localization during exhumation, dense 40Ar/39Ar age transects were sampled along shear zones recently identified on Syros and Sifnos islands. There, field observations suggest that deformation progressively localized downward in the CBU during exhumation. In parallel, these shear zones are characterized by different degrees of retrogression from blueschist-facies to greenschist-facies P-T conditions overprinting eclogite-facies record throughout the CBU. Results show straightforward correlations between the degree of retrogression, the finite strain intensity and 40Ar/39Ar ages; the most ductilely deformed and retrograded rocks yielded the youngest 40Ar/39Ar ages. The possible effects of strain localization during exhumation on the record of the argon isotopic system in HP-LT shear zones are addressed. Our results show that strain has localized in shear zones over a 30 Ma long period and that individual shear zones evolve during 7-15 Ma. We also discuss these results at small-scale to see whether deformation and fluid circulations, channelled within shear bands, can homogenize chemical compositions and reset the 40Ar/39Ar isotopic record

  7. Middle Jurassic shear zones at Cap de Creus (eastern Pyrenees, Spain) : a record of pre-drift extension of the Piemonte–Ligurian Ocean?

    NARCIS (Netherlands)

    Vissers, Reinoud L. M.; Van Hinsbergen, Douwe J. J.; Wilkinson, Camilla M.; Ganerød, Morgan

    The Cap de Creus peninsula in NE Spain consists of greenschist- to amphibolite-facies metasediments and granitoid bodies of the Variscan Axial Zone of the Pyrenees, overprinted in the north by anastomosed greenschist-facies shear zones. Current tectonic interpretations ascribe these shear zones to

  8. Ankara Orogenic Phase, Its Age and Transition From Thrusting-dominated Paleotectonic Period to the Strike-slip Neotectonic Period, Ankara (Turkey)

    OpenAIRE

    DEVECİ, ALİ KOÇYİĞİT & ŞULE

    2008-01-01

    The Ankara section of the İzmir-Ankara-Erzincan Suture Zone (IAESZ) is characterized by two major groups of contractional structures, namely the Ankara forced folds-monoclines and the southward-verging foreland fold-imbricate thrust to reverse fault zone (AFITFZ). In the Ankara region, one of the areas where the various phases of deformation and related structures are particularly well-preserved and exposed is the Edige (Elmadağ) area, 48 km east-southeast of the city of Ankara. The youngest ...

  9. New active faults on Eurasian-Arabian collision zone: Tectonic activity of Özyurt and Gülsünler faults (Eastern Anatolian Plateau, Van-Turkey)

    Energy Technology Data Exchange (ETDEWEB)

    Dicle, S.; Üner, S.

    2017-11-01

    The Eastern Anatolian Plateau emerges from the continental collision between Arabian and Eurasian plates where intense seismicity related to the ongoing convergence characterizes the southern part of the plateau. Active deformation in this zone is shared by mainly thrust and strike-slip faults. The Özyurt thrust fault and the Gülsünler sinistral strike-slip fault are newly determined fault zones, located to the north of Van city centre. Different types of faults such as thrust, normal and strike-slip faults are observed on the quarry wall excavated in Quaternary lacustrine deposits at the intersection zone of these two faults. Kinematic analysis of fault-slip data has revealed coeval activities of transtensional and compressional structures for the Lake Van Basin. Seismological and geomorphological characteristics of these faults demonstrate the capability of devastating earthquakes for the area.

  10. New active faults on Eurasian-Arabian collision zone: Tectonic activity of Özyurt and Gülsünler faults (Eastern Anatolian Plateau, Van-Turkey)

    International Nuclear Information System (INIS)

    Dicle, S.; Üner, S.

    2017-01-01

    The Eastern Anatolian Plateau emerges from the continental collision between Arabian and Eurasian plates where intense seismicity related to the ongoing convergence characterizes the southern part of the plateau. Active deformation in this zone is shared by mainly thrust and strike-slip faults. The Özyurt thrust fault and the Gülsünler sinistral strike-slip fault are newly determined fault zones, located to the north of Van city centre. Different types of faults such as thrust, normal and strike-slip faults are observed on the quarry wall excavated in Quaternary lacustrine deposits at the intersection zone of these two faults. Kinematic analysis of fault-slip data has revealed coeval activities of transtensional and compressional structures for the Lake Van Basin. Seismological and geomorphological characteristics of these faults demonstrate the capability of devastating earthquakes for the area.

  11. Role of the Western Anatolia Shear Zone (WASZ) in Neotectonics Evolution of the Western Anatolia Extended Terrain, Turkey

    Science.gov (United States)

    Cemen, I.; Gogus, O. H.; Hancer, M.

    2013-12-01

    The Neotectonics period in western Anatolia Extended Terrain, Turkey (WAET) may have initiated in late Oligocene following the Eocene Alpine collision which produced the Izmir-Ankara suture zone. The Western Anatolia Shear Zone (WASZ) bounds the WAET to the east. The shear zone contains mostly normal faults in the vicinity of the Gulf of Gokova. However, its movement is mostly oblique slip from the vicinity of Tavas towards the Lake of Acigol where it makes a northward bend and possibly joins the Eskisehir fault zone to the north of the town of Afyon. The shear zone forms the southern and eastern margins of the Kale-Tavas, Denizli and Acigol basins. The shear zone is similar in its structural/tectonics setting to the Eastern California Shear zone (ECSZ) of the Basins and Ranges of North America Extended terrain which is also composed of many normal to oblique-slip faults and separates two extended terrains with different rates of extension. Western Anatolia experienced many devastating earthquakes within the last 2000 years. Many of the ancient Greek/Roman city states, including Ephesus, Troy, and Hierapolis were destroyed by large historical earthquakes. During the second half of the 20th century, the region experienced two major large earthquake giving normal fault focal mechanism solutions. They are the 1969, M=6.9 Alasehir and the 1970, M=7.1 Gediz earthquakes. These earthquakes had caused substantial damage and loss of life in the region. Therefore, a comprehensive understanding of the kinematics of the Cenozoic extensional tectonics and earthquake potential of the WASZ in the region, is very important, especially since the fault zone is very close to the major towns in eastern part of western Turkey, such as Mugla, Denizli, Sandikli, Dinar and Afyon.

  12. Characterizing fractures and shear zones in crystalline rock using seismic and GPR methods

    Science.gov (United States)

    Doetsch, Joseph; Jordi, Claudio; Laaksonlaita, Niko; Gischig, Valentin; Schmelzbach, Cedric; Maurer, Hansruedi

    2016-04-01

    Understanding the natural or artificially created hydraulic conductivity of a rock mass is critical for the successful exploitation of enhanced geothermal systems (EGS). The hydraulic response of fractured crystalline rock is largely governed by the spatial organization of permeable fractures. Defining the 3D geometry of these fractures and their connectivity is extremely challenging, because fractures can only be observed directly at their intersections with tunnels or boreholes. Borehole-based and tunnel-based ground-penetrating radar (GPR) and seismic measurements have the potential to image fractures and other heterogeneities between and around boreholes and tunnels, and to monitor subtle time-lapse changes in great detail. We present the analysis of data acquired in the Grimsel rock laboratory as part of the In-situ Stimulation and Circulation (ISC) experiment, in which a series of stimulation experiments have been and will be performed. The experiments in the granitic rock range from hydraulic fracturing to controlled fault-slip experiments. The aim is to obtain a better understanding of coupled seismo-hydro-mechanical processes associated with high-pressure fluid injections in crystalline rocks and their impact on permeability creation and enhancement. GPR and seismic data have been recorded to improve the geological model and characterize permeable fractures and shear zones. The acquired and processed data include reflection GPR profiles measured from tunnel walls, single-borehole GPR images, and borehole-to-borehole and tunnel-to-tunnel seismic and GPR tomograms. The reflection GPR data reveal the geometry of shear zones up to a distance of 30 m from the tunnels and boreholes, but the interpretation is complicated by the geometrical ambiguity around tunnels and boreholes and by spurious reflections from man-made structures such as boreholes. The GPR and seismic traveltime tomography results reveal brittle fractured rock between two ductile shear zones. The

  13. Geometry of the Gerede Segment, North Anatolian Fault Zone, Turkey

    Science.gov (United States)

    Caglayan, A.; ISIK, V.

    2012-12-01

    The North Anatolian Fault Zone (NAFZ) is an active dextral strike-slip fault zone in northern Turkey. The NAFZ is approximately 1200 km in length which extends from Karliova in the east and to reach as far as the Gulf of Saros in the west. The NAFZ becomes wider geometry from east to west which are characterized by 9 destructive earthquake of Ms>7 in the 20th century. An earthquake on 1944 February 1 (Ms 7,3) caused 180 km long surface rupture associated with 2-6.5 m of right-lateral slip between Bayramören in the east and Abant Lake in the west along the NAFZ, which is called the Gerede Segment. This study describes internal geometrical characteristics and deformation mechanism of faults with fault surfaces in the Gerede Segment. The faults along the segment variously cut across Mesozoic-Cenozoic basement rocks and Quaternary alluvium deposits. They juxtapose not only different units of basement but also basement rocks and alluvium. We select typical fault surface that have been formed the best exposures in limestone in different locality, which define exhumed main faults along the segment. These faults strike N70°-80°E and dip 50°-85°NW. Slickenlines on these fault surface plunge shallowly to the NE and/or SW. Fault surface include brittle kinematic indicators indicating right-lateral strike-slip displacements. Some typical Riedel shear fractures (R- and P-fractures) around the main faults also show dextral displacements. Along the main faults two main architectural elements including fault core and fault damage zone is typical. The fault damage zones of these faults are characterized by both fault-related fracturing and fluid-assisted deformation processes. Although breccia is common fault rock in fault zones, gouge and cataclasite are seen in variable exposures. We have defined crackle, mosaic and chaotic type breccias using clast-size and clast proportion. Rock fragments within breccias have occurred mm-cm scale from angular to rounded clast. Sub

  14. Significado tectónico y migración de fluidos hidrotermales en una red de fallas y vetas de un Dúplex de rumbo: un ejemplo del Sistema de Falla de Atacama Tectonic significance and hydrothermal fluid migration within a strike-slip duplex fault-vein network: an example from the Atacama Fault System

    Directory of Open Access Journals (Sweden)

    Viviana Olivares

    2010-07-01

    Full Text Available El Dúplex Caleta Coloso es una estructura de rumbo desarrollada durante la deformación frágil del Sistema de Falla de Atacama (SFA en el Cretácico Temprano. En su interior hay un sistema de vetas hidrotermales que documentan la naturaleza de la relación entre el transporte de fluidos y el desarrollo del dúplex. El sistema de vetas de orientación dominante NW se localiza en la roca de caja, adyacentes a las zonas de falla. Según su mineralogía dominante hay vetas de clorita, epidota-cuarzo y calcita-limonita, y según las relaciones de corte o su estructura interna, se definieron vetas tempranas (clorita, intermedias (epidota-cuarzo y tardías (calcita-limonitas. Algunas vetas muestran cristales perpendiculares u oblicuos a sus paredes (vetas de extensión y de extensión oblicua o fibras minerales orientadas paralelas a las estrías de las fallas (vetas-fallas. Estas últimas tienen indicadores cinemáticos compatibles con las fallas, evidenciando que fueron sincinemáticas con el desarrollo del dúplex. Según su microestructura, ellas se habrían formado en fracturas abiertas llenas de fluidos, bajo condiciones de presión inferior a la hidrostática, lo cual indicaría que la precipitación mineral ocurrió por caídas abruptas de la presión en una corteza somera (The Caleta Coloso Duplex is a brittle strike-slip structure developed along the Atacama Fault System during the Early Cretaceous. A hydrothermal vein system existing within the duplex documents the nature of the link between fluid transport and progressive structural development. The dominantly NW-striking vein system occurs near or at the damage zone of the duplex fault zones. Veins can be classified according to their composition and crosscutting relationships into early chlorite veins, intermediate epidotic-quartz veins and late calcite-limonite veins. Some of them exhibit minerals with their long axes oriented orthogonally or obliquely with respect to the vein walls

  15. Extension of Hellenic forearc shear zones in SW Turkey: the Pliocene-Quaternary deformation of the Eşen Çay Basin

    Science.gov (United States)

    ten Veen, Johan H.

    2004-03-01

    The Pliocene-Quaternary Eşen Çay Basin in southwestern Turkey has a key position in the southern Aegean to gain insight into both lateral and temporal changes in stresses exerted by plate convergence at the Hellenic-Cyprus arc junction. A tectonosedimentary study of the basin development in combination with a structural analysis helped to reveal internal basin deformation and adjacent basement kinematics in order to delineate 3D strain through time. In the Pliocene the basin originated as a fluviolacustrine basin situated in a depression related to a ramp-fold geometry in the Lycian nappe stack. During the late Pliocene, E-W extension caused the development of N-S normal faults, displacement along which caused the differentiation of the relief and deposition of local alluvial fan systems. The Pleistocene is also marked by widespread alluvial-fluvial sedimentation that is triggered by activity at 020° faults. This fault system resulted from WNW-ESE extension and caused disruption of the former basin floor by uplift and tilting of intrabasinal areas, which initiated development of new source areas for the fan sedimentation. The Holocene-Recent period is characterized by a complex combination of faults of which 070° sinistral strike-slip faults are the most important. Fault-slip analysis reveals that deformation occurred in transtension, explained by the addition of a sinistral shear component. This implies that stresses evolved from simple tensional to transtensional over the Pliocene-Quaternary period. The initial extension phase is explained by the kinematic effects of outward growth of the Hellenic forearc, comparable with observations from the island of Rhodes and the eastern Anaximander Mountains. The time-transgressive addition of a sinistral shear component was likely produced by the northeastward propagating transcurrent motions of forearc slivers sheared from the expanding forearc as has been previously inferred for Crete and Rhodes. The latter process

  16. Investigation of the Maule, Chile rupture zone using seismic attenuation tomography and shear wave splitting methods

    Science.gov (United States)

    Torpey, Megan Elizabeth

    The Maule, Chile 2010 Mw 8.8 earthquake afforded the opportunity to study the rupture zone (33°S-38°S) in detail using aftershocks recorded by the rapid-response IRIS CHAMP seismic network. We used measurements of differential S to P seismic attenuation to characterize the attenuation structure of the South American crust and upper mantle wedge. We implemented an evolving time window to determine Qs-1 values using a spectral ratio method and incorporated these measurements into a bounded linear inequality least squares inversion to solve for Qs -1 in a 3D volume. On a large-scale, we observe an east-dipping low attenuation feature, consistent with the location of the Nazca oceanic slab, and image progressively greater attenuation as we move towards the surface of our model. A dramatic feature in our model is a large, low-attenuation body in the same location where Hicks et al. (2014) resolved a high P wave velocity anomaly in their velocity tomography model. We calculated the shear wave splitting intensity of the Maule rupture zone by implementing the multichannel method of Chevrot (2000) which calculates the splitting intensity of teleseismic SK(K)S phases and splitting parameters, ϕ and deltat. The results we obtained show an overall fast direction with a strong component of trench parallel splitting and very few trench normal splits. The fast directions do not parallel the Nazca APM, but are instead dominated by splits rotated 40°-50° counter-clockwise from Nazca APM. Based on these data, we see little evidence for sub-slab entrained mantle flow and invoke the trench-parallel retrograde flow model as an explanation for our measurements. We developed an extended splitting intensity method to allow for use of the upgoing S phase from Maule aftershocks, utilizing the initial event polarization. For this local dataset, we observe three dominant fast directions oriented N20°W, N40°E, and N10°W-20°E and a subset of fast directions trending N60°-90°E which

  17. Structural evolution of Cenozoic basins in northeastern Tunisia, in response to sinistral strike-slip movement on the El Alia-Teboursouk Fault

    Science.gov (United States)

    Bejaoui, Hamida; Aïfa, Tahar; Melki, Fetheddine; Zargouni, Fouad

    2017-10-01

    This paper resolves the structural complexity of Cenozoic sedimentary basins in northeastern Tunisia. These basins trend NE-SW to ∼ E-W, and are bordered by old fracture networks. Detailed descriptions of the structural features in outcrop and in subsurface data suggest that the El Alia-Teboursouk Fault zone in the Bizerte area evolved through a series of tectonic events. Cross sections, lithostratigraphic correlations, and interpretation of seismic profiles through the basins show evidence for: (i) a Triassic until Jurassic-Early Cretaceous rifting phase that induced lateral variations of facies and strata thicknesses; (ii) a set of faults oriented NE-SW, NW-SE, N-S, and E-W that guided sediment accumulation in pull-apart basins, which were subject to compressive and transpressive deformation during Eocene (Lutetian-Priabonian), Miocene (Tortonian), and Pliocene-Quaternary; and (iii) NNW-SSE to NS contractional events that occurred during the Late Pliocene. Part of the latest phase has been the formation of different synsedimentary folded structures with significant subsidence inversion. Such events have been responsible for the reactivation of inherited faults, and the intrusion of Triassic evaporites, ensuring the role of a slip layer. The combined effects of the different paleoconstraints and halokinetic movements are at the origin of the evolution of these pull-apart basins. The subsurface data suggest that an important fault displacement occurred during the Mesozoic-Cenozoic. The patterns of sediment accumulation in the different basins reflect a high activity of deep ancient faults.

  18. Onshore-offshore evidence for periodic post-rift shear reversal along the Pernambuco Fracture Zone, NE Brazil

    Science.gov (United States)

    Balsamo, Fabrizio; Nestola, Yago; Storti, Fabrizio; Nogueira, Cézar; Bezerra, Hilario F. R.

    2014-05-01

    Oceanic facture zones are among the most evident bathymetric features of seafloors. They include transform faults that connect adjacent mid-ocean ridge segments and accommodate opposite spreading directions. According to the plate tectonics theory, only the latter are tectonically active. Recent onshore and offshore evidence in the Antarctic plate sector facing Australia suggest, conversely, that oceanic fracture zones can transfer shear into the plate interior. In this contribution we illustrate the results of a research project performed in the NE Brazilian passive margin, where the seismic activity is clustered along major crustal-scale, long-lived shear zones, thus resembling the Antarctic case. In particular, we performed a detailed study of the offshore pattern of seafloor age domains on both sides of the Pernambuco Fracture Zone (PFZ), which indicates non-uniform spreading rates on the two lithospheric lanes separated by the PFZ. The differential spreading rate, calculated in 8 age provinces from Upper Cretaceous to Present, varies between 1.3 and 8.8 mm/yr and periodically switched from right-lateral to left-lateral excess transform shear along the PFZ. Five major inversions were found, including a Tortonian inversion from right-lateral to left-lateral excess shear, consistently with structural data acquired in Miocene to Quaternary sediments along the PFZ. We discuss the impact of our findings in the current plate tectonic theory framework.

  19. The influence of the Precambrian Mughese Shear Zone structures on strain accommodation in the northern Malawi Rift

    Science.gov (United States)

    Dawson, Sam M.; Laó-Dávila, Daniel A.; Atekwana, Estella A.; Abdelsalam, Mohamed G.

    2018-01-01

    Precambrian shear zones have been recognized as regions that affect the propagation, segmentation, and location of continental rifts. However, it is still unclear how the orientation of these shear zones influence strain accommodation along the rifts. In this study, we investigated the influence of the Mughese Shear Zone (MSZ) on strain accommodation within the young magma-poor Malawi Rift, a seismically-active segment of the Western Branch of the East African Rift System. We used Shuttle Radar Topography Mission (SRTM) Digital Elevation Models (DEM), aeromagnetic data, and mapped mesoscopic-scale structures within the Precambrian MSZ and younger rocks in the Karonga area. We found that in the northern portion of the Karonga Fault Zone, a fault zone that accommodates the majority of extension in this region, one major fault is oriented 32°/59° SE and cuts across the Precambrian foliation that has an orientation of 301°/79° NE. South of the city of Karonga, the Precambrian foliation is sub-vertical and has a strike of 321°. Here, the Karonga fault splays from a main fault with a 2 km damage zone to several distinct E-and W-dipping faults over a 10 km zone that strike in the general direction of the foliation planes of the MSZ. Recent seismicity is distributed within this zone. The faults formed in reactivated foliation planes of the MSZ. The N-striking Karoo rift horsts and grabens and their associated rock formations might have also been reactivated in this area. These relationships suggest that within the northern Malawi Rift, extension was accommodated differently based on the nature and orientation of the pre-existing structures. The orientation of the Precambrian MSZ influences strain accommodation in the Karonga area and has important implications for seismic hazards. We conclude that the Karonga area is an important seismically active zone based on favorably-oriented and reactivated pre-existing structures.

  20. Excitation of tsunami by a pure strike-slip earthquake. ; Izu Oshima kinkai earthquake tsunami on Feb. 20, 1990. Yokozure danso jishin ni yoru tsunami no reiki. ; 1990 nen 2 gatsu 20 nichi Izu Oshima kinkai jishin tsunami

    Energy Technology Data Exchange (ETDEWEB)

    Abe, K. (Nippon Dental University, Tokyo (Japan). Niigata Junior College); Okada, M. (Meteorological Research Institute, Tsukuba (Japan))

    1993-06-24

    A numerical experiment was performed to reproduce the tsunami from the Izu-Oshima Kinkai Earthquake which occurred on February 20, 1990, using a tsunami excited by a pure strike-slip fault. An existence of a vertical fault with a length of 15 km and a width of 12 km was hypothesized in the south-north direction on the ocean bottom around the focal region. Then, a tsunami was assumed to have been excited when the fault was given a side-slip movement to create discrepancies of 1 m in the fault. Water level change for one hour after onset of the tsunami was calculated in one-second interval in each unit square with a side length of 1 km over an ocean area of 200 km from east to west and 150 km from north to south centering on the wave source. The results obtained from the calculation were harmonious with tsunami waveforms observed at five stations in the subject region and their spectral analytic results. Reproduced were the two predominant frequencies commonly observed at more than two stations, and difference in predominant cycles that appear according to azimuths of the observation points to the epicenter. These facts endorse the reasonability of the above hypothesis. 9 refs., 11 figs.

  1. Paleoseismology of the 1966 Varto Earthquake (Ms 6.8) and Structure of the Varto Fault Zone, Eastern Turkey

    Science.gov (United States)

    Isik, V.; Caglayan, A.; Saber, R.; Yesilyurt, N.

    2014-12-01

    Turkey is a region of active faulting and contains several strike-slip fault zones, which have generated both historical and recent large earthquakes. Two active fault zones in Turkey, the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault Zone (EAFZ), divide the area into the Anatolian micro-plate accommodating WSW-directed movement. The southeastern continuation of the NAFZ is often referred to the Varto Fault Zone (VFZ). The VFZ cuts mainly Pliocene volcano-sedimentary units and/or Quaternary deposits and is characterized by multiple fault strands and multiple, closely spaced, active seismogenic zones. Fault motions in the zone are primarily right-lateral, with a subordinate component of NNW-SSE shortening. Study area is Varto region in which indications of active faulting are very well preserved. We recognized three coseismic ruptures from five trench exposures. It is referred to these as events 1 (youngest) through 3 (oldest). The best evidence of event 3 comes from fault traces and its upward terminations. The major components of this fault are fault core and damage zone. The fault is not just one plane of discontinuity and bifurcates and creates additional slip surfaces, which propagate out of the plane of the original fault. Event 2 and event 1, referring to 1946 and 1966 earthquakes, are characterized primarily by discrete, regularly spaced normal faults with and 55-80 cm and 105-270 cm throws, respectively and geometry of growth strata. The VFZ in the study area include typical structures of strike-slip fault zone. It forms a number of parallel and slightly sub-parallel strands striking N50°-72°W including contractional and extensional brittle structures. Several meters to tens of meters wavelength active folds with ENE-WSW and WNW-ESE trending fold axis. These folds deform the Plio-Quaternary units and show classic asymmetry associated with both a south- and north-vergent fault propagation fold. Meso-scale normal faults are also well

  2. Development of Characterization Technology for Fault Zone Hydrology

    International Nuclear Information System (INIS)

    Karasaki, Kenzi; Onishi, Tiemi; Gasperikova, Erika; Goto, Junichi; Tsuchi, Hiroyuki; Miwa, Tadashi; Ueta, Keiichi; Kiho, Kenzo; Miyakawa, Kimio

    2010-01-01

    Several deep trenches were cut, and a number of geophysical surveys were conducted across the Wildcat Fault in the hills east of Berkeley, California. The Wildcat Fault is believed to be a strike-slip fault and a member of the Hayward Fault System, with over 10 km of displacement. So far, three boreholes of ∼ 150m deep have been core-drilled and borehole geophysical logs were conducted. The rocks are extensively sheared and fractured; gouges were observed at several depths and a thick cataclasitic zone was also observed. While confirming some earlier, published conclusions from shallow observations about Wildcat, some unexpected findings were encountered. Preliminary analysis indicates that Wildcat near the field site consists of multiple faults. The hydraulic test data suggest the dual properties of the hydrologic structure of the fault zone. A fourth borehole is planned to penetrate the main fault believed to lie in-between the holes. The main philosophy behind our approach for the hydrologic characterization of such a complex fractured system is to let the system take its own average and monitor a long term behavior instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to 'up-scale,' which is extremely tenuous.

  3. Rapid intraplate strain accumulation in the New Madrid seismic zone

    Science.gov (United States)

    Liu, Lanbo; Zoback, Mark D.; Segall, Paul

    1992-09-01

    Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes greater than 8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time. ubject Type="Secondary">Nature Conservation 36 36 6 6 6 2005 12 Springer Science+Business Media, Inc. 2005 373 10.1007/s00267-004-0373-6 6 Effects of Short- and Long-Term Disturbance Resulting from Military Maneuvers on Vegetation and Soils in a Mixed Prairie Area Research 849 861 2004 1 1 2005 10 7 Springer Science+Business Media, Inc. 2005

  4. Development of Characterization Technology for Fault Zone Hydrology

    Energy Technology Data Exchange (ETDEWEB)

    Karasaki, Kenzi; Onishi, Tiemi; Gasperikova, Erika; Goto, Junichi; Tsuchi, Hiroyuki; Miwa, Tadashi; Ueta, Keiichi; Kiho, Kenzo; MIyakawa, Kimio

    2010-08-06

    Several deep trenches were cut, and a number of geophysical surveys were conducted across the Wildcat Fault in the hills east of Berkeley, California. The Wildcat Fault is believed to be a strike-slip fault and a member of the Hayward Fault System, with over 10 km of displacement. So far, three boreholes of ~;; 150m deep have been core-drilled and borehole geophysical logs were conducted. The rocks are extensively sheared and fractured; gouges were observed at several depths and a thick cataclasitic zone was also observed. While confirming some earlier, published conclusions from shallow observations about Wildcat, some unexpected findings were encountered. Preliminary analysis indicates that Wildcat near the field site consists of multiple faults. The hydraulic test data suggest the dual properties of the hydrologic structure of the fault zone. A fourth borehole is planned to penetrate the main fault believed to lie in-between the holes. The main philosophy behind our approach for the hydrologic characterization of such a complex fractured system is to let the system take its own average and monitor a long term behavior instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to ?up-scale,? which is extremely tenuous.

  5. Kinematic and geochronological constraints on shear deformation in the Ferriere-Mollières shear zone (Argentera-Mercantour Massif, Western Alps): implications for the evolution of the Southern European Variscan Belt

    Science.gov (United States)

    Simonetti, Matteo; Carosi, Rodolfo; Montomoli, Chiara; Langone, Antonio; D'Addario, Enrico; Mammoliti, Elisa

    2018-02-01

    In the Western Alps, a steeply dipping km-scale shear zone (the Ferriere-Mollières shear zone) cross-cuts Variscan migmatites in the Argentera-Mercantour External Crystalline Massif. Structural analysis joined with kinematic vorticity and finite strain analyses allowed to recognize a high-temperature deformation associated with dextral transpression characterized by a variation in the percentage of pure shear and simple shear along a deformation gradient. U-Th-Pb dating of syn-kinematic monazites was performed on mylonites. The oldest 340 Ma ages were obtained in protomylonites, whereas ages of 320 Ma were found in mylonites from the core of the shear zone. These ages indicate that the Ferriere-Mollières shear zone is a still preserved Variscan shear zone. Ages of 320 Ma obtained in this work are in agreement with ages of the dextral transpressional shear zones occurring in the Maures-Tanneron Massif and Corsica-Sardinia. However, transpression in the Argentera-Mercantour Massif started earlier than in other sectors of the southern Variscan Belt. This is possibly caused by the curvature of the belt triggering the progressive migration of shear deformation. Our data allow a correlation between the Argentera-Mercantour Massif and other segments of the Southern European Variscan Belt, in particular with Maures-Tanneron Massif and Corsica-Sardinia, and contribute to fill a gap in the age of activity and in the kinematics of the flow of the system of dextral shear zones of the southern portion of the EVSZ.

  6. The lateral boundary of a metamorphic core complex: The Moutsounas shear zone on Naxos, Cyclades, Greece☆

    Science.gov (United States)

    Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai

    2013-01-01

    We describe the structure, microstructures, texture and paleopiezometry of quartz-rich phyllites and marbles along N-trending Moutsounas shear zone at the eastern margin of the Naxos metamorphic core complex (MCC). Fabrics consistently indicate a top-to-the-NNE non-coaxial shear and formed during the main stage of updoming and exhumation between ca. 14 and 11 Ma of the Naxos MCC. The main stage of exhumation postdates the deposition of overlying Miocene sedimentary successions and predates the overlying Upper Miocene/Pliocene conglomerates. Detailed microstructural and textural analysis reveals that the movement along the Moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher-temperature rocks. Paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20–77 MPa and a strain rate of 10−15–10−13 s−1 at 350 °C for quartz and ca. 300 °C for calcite. Chlorite geothermometry of the shear zone yields two temperature regimes, 300–360 °C, and 200–250 °C. The lower temperature group is interpreted to result from late-stage hydrothermal overprint. PMID:26523079

  7. Magnetic fabrics in characterization of magma emplacement and tectonic evolution of the Moyar Shear Zone, South India

    Directory of Open Access Journals (Sweden)

    P. Pratheesh

    2013-01-01

    Full Text Available The Moyar Shear Zone (MSZ of the South Indian granulite terrain hosts a prominent syenite pluton (∼560 Ma and associated NW-SE to NE-SW trending mafic dyke swarm (∼65 Ma and 95 Ma. Preliminary magnetic fabric studies in the mafic dykes, using Anisotropy of Magnetic Susceptibly (AMS studies at low-field, indicate successive emplacement and variable magma flow direction. Magnetic lineation and foliation in these dykes are identical to the mesoscopic fabrics in MSZ mylonites, indicating shear zone guided emplacement. Spatial distribution of magnetic lineation in the dykes suggests a common conduit from which the source magma has been migrated. The magnetic foliation trajectories have a sigmoidal shape to the north of the pluton and curve into the MSZ suggesting dextral sense of shear. Identical fabric conditions for magnetic fabrics in the syenite pluton and measured field fabrics in mylonite indicate syntectonic emplacement along the Proterozoic crustal scale dextral shear zone with repeated reactivation history.

  8. Quaternary layer anomalies around the Carlsberg Fault zone mapped with high-resolution shear-wave seismics south of Copenhagen

    DEFF Research Database (Denmark)

    Kammann, Janina; Hübscher, Christian; Nielsen, Lars

    The Carlsberg Fault zone is located in the N-S striking Höllviken Graben and traverses the city of Copenhagen. The fault zone is a NNW-SSE striking structure in direct vicinity to the transition zone of the Danish Basin and the Baltic Shield. Recent small earthquakes indicate activity in the area......, although none of the mapped earthquakes appear to have occurred on the Carlsberg Fault. We examined the fault evolution by a combination of very high resolution onshore shear-wave seismic data, one conventional onshore seismic profile and marine reflection seismic profiles. The chalk stratigraphy...... and the localization of the fault zone at depth was inferred from previous studies by other authors. We extrapolated the Jurassic and Triassic stratigraphy from the Pomeranian Bay to the area of investigation. The fault zone shows a flower structure in the Triassic as well as in Cretaceous sediments. The faulting...

  9. Modelling The Transport Of Solutes And Colloids In The Grimsel Migration Shear Zone

    Energy Technology Data Exchange (ETDEWEB)

    Kosakowski, G.; Smith, P

    2005-02-01

    This report describes modelling of the transport of solutes and colloids in an experimental system comprising an artificial dipole flow field in a water-conducting shear zone at Nagra's Grimsel Test Site (GTS) in the central Swiss Alps. The modelling work forms part of the Colloid and Radionuclide Retardation Project (CRR), which includes a series of field transport experiments and a supporting laboratory programme, as well as modelling studies. Four independent groups representing different organisations or research institutes have conducted the modelling, with each group employing its own modelling approach or approaches. Only the work conducted at the Paul Scherrer Institute (PSI) is described in the present report. The modelling approaches used in the present study may not be directly applicable to safety assessment problems and the direct implications of the results of this study for safety assessment are limited. It can, however, be said that the study has demonstrated the high degree of mobility of bentonite and other colloids in a system that is at least in some ways comparable to those of interest in safety assessment, and has shown that bentonite colloids can at least potentially affect the transport of some safety relevant radionuclides over longer temporal and spatial scales than those addressed here. (author)

  10. Simulations of a stretching bar using a plasticity model from the shear transformation zone theory

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris H.; Gibou, Frederic

    2010-06-05

    An Eulerian simulation is developed to study an elastoplastic model of amorphous materials that is based upon the shear transformation zone theory developed by Langer and coworkers. In this theory, plastic deformation is controlled by an effective temperature that measures the amount of configurational disorder in the material. The simulation is used to model ductile fracture in a stretching bar that initially contains a small notch, and the effects of many of the model parameters are examined. The simulation tracks the shape of the bar using the level set method. Within the bar, a finite difference discretization is employed that makes use of the essentially non-oscillatory (ENO) scheme. The system of equations is moderately stiff due to the presence of large elastic constants, and one of the key numerical challenges is to accurately track the level set and construct extrapolated field values for use in boundary conditions. A new approach to field extrapolation is discussed that is second order accurate and requires a constant amount of work per gridpoint.

  11. Metal contamination of agricultural soils in the copper mining areas of Singhbhum shear zone in India

    Science.gov (United States)

    Giri, Soma; Singh, Abhay Kumar; Mahato, Mukesh Kumar

    2017-06-01

    The study was intended to investigate the heavy metal contamination in the agricultural soils of the copper mining areas in Singhbhum shear zone, India. The total concentrations of the metals were determined by inductively coupled plasma-mass spectrometer (ICPMS). Pollution levels were assessed by calculating enrichment factor (EF), geo-accumulation index (I_geo), contamination factors (CF), pollution load index ( PLI), Nemerow index and ecological risk index (RI). The metal concentrations in the soil samples exceeded the average shale values for almost all the metals. Principal component analysis resulted in extraction of three factors explaining 82.6% of the data variability and indicated anthropogenic contribution of Cu, Ni, Co, Cr, Mn and Pb. The EF and I_geo values indicated very high contamination with respect to Cu followed by As and Zn in the agricultural soils. The values of PLI, RI and Nemerow index, which considered the overall effect of all the studied metals on the soils, revealed that 50% of the locations were highly polluted with respect to metals. The pollution levels varied with the proximity to the copper mining and processing units. Consequently, the results advocate the necessity of periodic monitoring of the agricultural soils of the area and development of proper management strategies to reduce the metal pollution.

  12. The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault

    Science.gov (United States)

    Thatcher, Wayne R.; Savage, James C.; Simpson, Robert W.

    2016-01-01

    Cluster analysis offers an agnostic way to organize and explore features of the current GPS velocity field without reference to geologic information or physical models using information only contained in the velocity field itself. We have used cluster analysis of the Southern California Global Positioning System (GPS) velocity field to determine the partitioning of Pacific-North America relative motion onto major regional faults. Our results indicate the large-scale kinematics of the region is best described with two boundaries of high velocity gradient, one centered on the Coachella section of the San Andreas Fault and the Eastern California Shear Zone and the other defined by the San Jacinto Fault south of Cajon Pass and the San Andreas Fault farther north. The ~120 km long strand of the San Andreas between Cajon Pass and Coachella Valley (often termed the San Bernardino and San Gorgonio sections) is thus currently of secondary importance and carries lesser amounts of slip over most or all of its length. We show these first order results are present in maps of the smoothed GPS velocity field itself. They are also generally consistent with currently available, loosely bounded geologic and geodetic fault slip rate estimates that alone do not provide useful constraints on the large-scale partitioning we show here. Our analysis does not preclude the existence of smaller blocks and more block boundaries in Southern California. However, attempts to identify smaller blocks along and adjacent to the San Gorgonio section were not successful.

  13. Middle cretaceous crustal anatexis associated to contractional deformation on Eden's shear zone

    International Nuclear Information System (INIS)

    Calderon, M.; Herve, F; Godoy, E.; Suarez, M; Watters, W.A

    2001-01-01

    The Puerto Eden's igneous and metamorphic complex (PEIMC) is composed by amphibolite facies schists, melanocratic and leucocratic diatexites (with biotite in schlieren structure), and orthomylonites intruded by schlieren bearing porphyritic biotite monzogranite, tabular garnet - tourmaline and white mica - garnet leucogranites, pegmatitic felsic dikes, andesitic dikes, and biotite hornblende granodiorites belonging to the South Patagonian Batholith (SPB). This locality represent the westernmost outcrop of the Eastern Andean Metamorphic Complex (EAMC), situated at 49 o 8min. 20.seg S - 74 o 23min.20seg. W, on the eastern margin of the SPB. A common relationship exists in convergent orogenic belts between a shear zone system, high-grade metamorphic rocks, and granites, which suggests a feedback relationship between crustal anatexis and contractional deformation that helps granite extraction and focusses granite ascent (Solar et al, 1998). The aim of this study is to constraint the temporal relationship between the magmatic and deformational evolution in Puerto Eden, associated to one or more events of crustal anatexis recorded. This work is based on geochemistry and K-Ar radiometric age data set previously presented as part of first author's MSc thesis related to the petrogenesis of PEIMC (au)

  14. Strain Localization in Crustal-scale Shear Zones and Argon Isotopic Record: Insights from Natural Fossilized Subduction Zones (Cycladic Blueschist Unit, Greece)

    Science.gov (United States)

    Laurent, V.; Scaillet, S.; Jolivet, L.; Augier, R.

    2016-12-01

    Retrieving realistic estimates of strain rates accumulated along major lithospheric structures is critical to understand the rheological behaviour of the lithosphere. We use the 40Ar/39Ar dating technique to obtain dense age transects along strain gradients at various scales across HP-LT shear zones from the Cycladic Blueschist Unit (CBU) to quantify rates of strain localization in a former subduction zone. This HP-LT metamorphic unit was exhumed through a continuum of extensional top-to-the east shearing, all the way from the depth of the eclogite- to greenschist-facies P-T conditions. During exhumation, deformation progressively localized downward in the CBU, along several large-scale ductile shear zones. The rate of this progressive strain localization is unknown, and in general, poorly known in similar geological contexts. White micas along these strain gradients were then dated with the 40Ar/39Ar method through various techniques (laser step heating on phengite single grain and population, and in situ laser ablation). We discuss the significance of obtained ages in terms of crystallization vs. cooling ages and use the crystallization ages for P-T-t paths. We compare our results with previous low-resolution studies on the examples of Alpine Corsica and the Betic Cordillera suggesting that strain localization at km-scale results into age gradients with a correlation between the most deformed samples and the youngest 40Ar/39Ar ages, leading to estimates of strain localization rates. We also discuss these results at small-scale to see whether deformation and fluid circulation, channelled within shear bands, can homogenize compositions and reset the 40Ar/39Ar isotopic record both in phengites within shear bands and the close-by foliation. This study brings new perspective on the process of strain localization through the dating of structures along strain gradients, especially on possible variation of rates of localisation through the entire exhumation history.

  15. An integrated study of aerospace data for uranium exploration in the Magajhi-Kotapali shear zone, Surguja district, Madhya Pradesh, India

    International Nuclear Information System (INIS)

    Chaturvedi, A.K.; Kak, S.N.

    1993-01-01

    Lower Proterozoic granite gneiss and associated cataclastic rocks of Surguja crystalline complex record uranium mineralisation along the WNW-ESE trending Magajhi-Kotapali shear zone. Extension of the shear zone and cross faults trending NE-SW were established using enhanced satellite data. On integrating it with aeroradiometric data, it has been found that uranium mineralisation is shear controlled and occur around the zone of intersection between the WNW-ESE trending shear and the NE-SW faults. The study has narrowed down the target area for detailed ground investigations and finally resulted in locating promising areas such as Chathila Pahar, Haskepi, Jarhakhar-Semarkhar, and Tilti forest with good extensions along the shear zone. (author). 18 refs., 5 figs

  16. Strain Variation in Accretionary Prisms Across Space and Time: Insights from the Makran Subduction Zone

    Science.gov (United States)

    Penney, C.; Tavakoli, F.; Saadat, A.; Nankali, H. R.; Sedighi, M.; Khorrami, F.; Sobouti, F.; Rafi, Z.; Copley, A.; Jackson, J. A.; Priestley, K. F.

    2017-12-01

    The Makran is one of the world's least-studied subduction zones. In particular, little is known about the accumulation and accommodation of strain in the onshore part of the subduction zone, which parallels the coasts of southern Iran and Pakistan. The deformation of the Makran accretionary prism results from both its subduction zone setting and N-S right-lateral shear between central Iran and Afghanistan. North of the Makran, this shear is accommodated by a series of right-lateral faults which offset the rocks of the Sistan Suture Zone, an abandoned accretionary prism. However, these right-lateral faults are not observed south of 27°N, and no major N-S faults cut the E-W trending structures of the Makran. How this right-lateral motion is accommodated at the southern end of the Sistan Suture Zone is a long-standing tectonic question. By combining results from geomorphology, GPS, seismology and modelling we conclude that right-lateral motion is transferred across the depression north of the accretionary prism to the region of right-lateral shear at the western end of the accretionary prism. This requires the Jaz Murian depression to be bounded by normal faults, consistent with the basin geomorphology. However, GPS data show compression across the margins of the basin, and no shallow normal-faulting earthquakes have been observed in the region. We therefore suggest that the behaviour of these faults may be time-dependent and controlled by the megathrust seismic cycle, as has been suggested elsewhere (e.g. Chile). Recent strike-slip earthquakes, including the 2013 Balochistan earthquake, have clustered at the prism's lateral edges, showing the importance of spatial, as well as temporal, variations in strain. These earthquakes have reactivated thrust faults in the Makran accretionary prism, showing that the style of strain within accretionary prisms can vary on multiple timescales and allowing us to calculate the coefficient of friction on the underlying megathrust.

  17. Crustal structure in high deformation zones: Insights from gravimetric and magnetometric studies in the Guacha Corral shear zone (Eastern Sierras Pampeanas, Argentina)

    Science.gov (United States)

    Radice, Stefania; Lince Klinger, Federico; Maffini, M. Natalia; Pinotti, Lucio P.; Demartis, Manuel; D´Eramo, Fernando J.; Giménez, Mario; Coniglio, Jorge E.

    2018-03-01

    The Guacha Corral shear zone (GCSZ) is represented by mylonites that were developed under amphibolites facies conditions from migmatitic protoliths. In this contribution, geophysical, petrological and structural data were combined to determine the 3D geometry of the GCSZ. New gravimetric, magnetometric and structural studies, along an E-W profile, were integrated with existing magnetotelluric and seismological data from a representative regional database of the Eastern Sierras Pampeanas. The zonation of different fabrics across the GCSZ suggests that the pre-existing heterogeneities of the protoliths played a key role in governing the degree of metamorphism of different regions. The low gravity anomalies observed in the GCSZ suggest a transitional boundary zone between the migmatitic and mylonitic domains, where highly deformed shear bands are interspersed with undeformed rocks, presenting gradual contacts. The mylonites in this shear zone show a considerably reduced density when compared to the migmatite protoliths. The density of the rocks gradually increases with depth until it reaches that of the protolith. These changes in the gravity values in response to density changes allowed us to infer a listric geometry at depth of the GCSZ. Low gravity anomalies in the profiles, in regions where high density rocks (migmatites) outcrop at the surface, modeled as buried granitic plutons.

  18. New insights into the distribution and evolution of the Cenozoic Tan-Lu Fault Zone in the Liaohe sub-basin of the Bohai Bay Basin, eastern China

    Science.gov (United States)

    Huang, Lei; Liu, Chi-yang; Xu, Chang-gui; Wu, Kui; Wang, Guang-yuan; Jia, Nan

    2018-01-01

    As the largest strike-slip fault system in eastern China, the northeast-trending Tan-Lu Fault Zone (TLFZ) is a significant tectonic element contributing to the Mesozoic-Cenozoic regional geologic evolution of eastern Asia, as well as to the formation of ore deposits and oilfields. Because of the paucity of data, its distribution and evolutionary history in the offshore Liaohe sub-basin of the northern Bohai Bay Basin (BBB) are still poorly understood. Investigations of the strike-slip fault system in the western portion of the offshore Liaohe sub-basin via new seismic data provide us with new insights into the characteristics of the Cenozoic TLFZ. Results of this study show that Cenozoic dextral strike-slip faults occurred near the center of the Liaoxi graben in the offshore Liaohe sub-basin; these strike-slip faults connect with their counterparts to the north, the western part of the onshore Liaohe sub-basin, and have similar characteristics to those in other areas of the BBB in terms of kinematics, evolutionary history, and distribution; consequently, these faults are considered as the western branch of the TLFZ. All strike-slip faults within the Liaoxi graben merge at depth with a central subvertical basement fault induced by the reactivation of a pre-existing strike-slip basement fault, the pre-Cenozoic TLFZ. Data suggest that the TLFZ across the whole Liaohe sub-basin comprises two branches and that the Cenozoic distribution of this system was inherited from the pre-Cenozoic TLFZ. This characteristic distribution might be possessed by the whole TLFZ, thus the new understandings about the distribution and evolutionary model of the TLFZ in this study can be inferred in many research fields along the whole fault zone, such as regional geology, ore deposits, petroleum exploration and earthquake hazard.

  19. Field Observations and Modeling Results of the McMurdo Shear Zone, Antarctica: Implications on Shear Margin Dynamics and Long- Term Viability of the South Pole Traverse

    Science.gov (United States)

    Kaluzienski, L. M.; Koons, P. O.; Enderlin, E. M.; Courville, Z.; Campbell, S. W.; Arcone, S.; Jordan, M.; Ray, L.

    2017-12-01

    Antarctica's ice shelves modulate the flow of inland ice towards the ocean. Understanding the controls on ice-shelf stability are critical to predicting the future evolution of the Antarctic Ice Sheet. For the Ross Ice Shelf (RIS), an important region of lateral resistance is the McMurdo Shear Zone (MSZ), a 5-10 km wide strip of heavily crevassed ice. On a yearly basis the United States Antarctic Program (USAP) mitigates crevasse hazards along the South Pole Traverse (SPoT) route that crosses this region. However, as ice advects northward past the lateral buttress of White Island into a region of greater flow divergence, intensified crevassing has been observed which will continue to place a substantial burden on safety mitigation efforts. The route has advected down-glacier towards this complex region since 2002 so the USAP currently has plans to relocate the shear zone crossing upstream in the near future. Our work aims to assess the feasibility of moving the route to several potential locations based on results from an integrated project incorporating detailed field-based observations of crevasse distributions and orientation from ground-penetrating radar (GPR), GPS and remote sensing observations of the flow and stress field within the MSZ, and finite element numerical modeling of local and regional kinematics within the region. In addition, we assess plausible dynamic forcings both upstream and downstream of the MSZ that could influence shear zone stability. These include changes in mass flux across the grounding lines of tributary glaciers such as the observed increase in ice discharge from of Byrd Glacier (Stearns et al., 2008) as well as changes at the MIS front due to recent intensified rift propagation (Banwel et al., 2017). Results from this work will increase our understanding of ice shelf shear margin dynamics and provide a firm basis for predicting the long-term behavior of the MSZ and viability of the SPoT. Stearns, Leigh A., Benjamin E. Smith, and

  20. Neoproterozoic Evolution and Najd‒Related Transpressive Shear Deformations Along Nugrus Shear Zone, South Eastern Desert, Egypt (Implications from Field‒Structural Data and AMS‒Technique)

    Science.gov (United States)

    Hagag, W.; Moustafa, R.; Hamimi, Z.

    2018-01-01

    The tectonometamorphic evolution of Nugrus Shear Zone (NSZ) in the south Eastern Desert of Egypt was reevaluated through an integrated study including field-structural work and magnetofabric analysis using Anisotropy of Magnetic Susceptibility (AMS) technique, complemented by detailed microstructural investigation. Several lines of evidence indicate that the Neoproterozoic juvenile crust within this high strain zone suffered an impressive tectonic event of left-lateral transpressional regime, transposed the majority of the earlier formed structures into a NNW to NW-directed wrench corridor depicts the northwestern extension of the Najd Shear System (NSS) along the Eastern Desert of Egypt. The core of the southern Hafafit dome underwent a high metamorphic event ( M 1) developed during the end of the main collisional orogeny in the Arabian-Nubian Shield (ANS). The subsequent M 2 metamorphic event was retrogressive and depicts the tectonic evolution and exhumation of the Nugrus-Hafafit area including the Hafafit gneissic domes, during the origination of the left-lateral transpressive wrench corridor of the NSS. The early tectonic fabric within the NSZ and associated highly deformed rocks was successfully detected by the integration of AMS-technique and microstructural observations. Such fabric grain was checked through a field-structural work. The outcomes of the present contribution advocate a complex tectonic evolution with successive and overlapped deformation events for the NSZ.

  1. The role of chemical processes and brittle deformation during shear zone formation and its potential geophysical implications

    Science.gov (United States)

    Goncalves, Philippe; Leydier, Thomas; Mahan, Kevin; Albaric, Julie; Trap, Pierre; Marquer, Didier

    2017-04-01

    Ductile shear zones in the middle and lower continental crust are the locus of interactions between mechanical and chemical processes. Chemical processes encompass metamorphic reactions, fluid-rock interactions, fluid flow and chemical mass-transfer. Studying these processes at the grain scale, and even the atom scale, on exposed inactive shear zones can give insights into large-scale geodynamics phenomena (e.g. crustal growth and mountain building through the reconstruction of P-T-t-D-Ɛ evolutionary paths. However, other major issues in earth sciences can be tackled through these studies as well. For instance, the mechanism of fluid flow and mass transfer in the deep crust where permeability should be small and transient is still largely debated. Studying exhumed inactive shear zones can also help to interpret several new geophysical observations like (1) the origin of tremor and very low frequency earthquakes observed in the ductile middle and lower crust, (2) mechanisms for generating slow slip events and (3) the physical origin of puzzling crustal anisotropy observed in major active crustal shear zones. In this contribution, we present a collection of data (deformation, petrology, geochemistry, microtexture) obtained on various shear zones from the Alps that were active within the viscous regime (T > 450°C). Our observations show that the development of a shear zone, from its nucleation to its growth and propagation, is not only governed by ductile deformation coeval with reactions but also involves brittle deformation. Although brittle deformation is a very short-lived phenomenon, our petrological and textural observations show that brittle failure is also associated with fluid flow, mass transfer, metasomatic reactions and recrystallization. We speculate that the fluids and the associated mineralogical changes involved during this brittle failure in the ductile crust might play a role in earthquake / tremor triggering below the brittle - ductile transition

  2. Paleoearthquakes on the Anninghe and Zemuhe fault along the southeastern margin of the Tibetan Plateau and implications for fault rupture behavior at fault bends on strike-slip faults

    Science.gov (United States)

    Wang, Hu; Ran, Yongkang; Chen, Lichun; Li, Yanbao

    2017-11-01

    Fault bends can serve as fault segment boundaries and are used in seismic hazard assessment. Recent studies addressing whether rupture propagation would be arrested at such structural complexities have commonly focused on computational modeling. However, multi-cycle paleoseismic rupture observations through fault bends have seldom been reported. In this study, we used trenching and radiocarbon dating to reveal paleoseismic rupture histories on the southern segment of the Anninghe fault (ANHF) along the southeastern margin of the Tibetan Plateau to explore multi-cycle surface rupture behavior at an extensional fault bend (with an angle of about 30°) at Xichang between the ANHF and Zemuhe fault (ZMHF). Specifically, nine trenches were opened in a fault depression at Maoheshan site and five paleoseismic events were identified. These have been named E1 through E5 respectively corresponding to events at 1400-935 BCE, 420-875 CE, 830-1360 CE, 1295-1715 CE, and 1790 CE-Present. After comparison with the historical records of earthquakes around Xichang and previous paleoseismic results, we suggest that the five seismic events are constrained at: 1365 BCE-935 BCE, 814 CE, 950 CE- 1145 CE, 1536 CE and 1850 CE, respectively. The average recurrence interval of earthquakes along the southern segment of the ANHF is about 700-800 yr. Furthermore, the evidence indicates that surface-faulting events along the southern segment of the ANHF appear to be unevenly spaced in time. Moreover, based on comparisons of seismic events along the ANHF and ZMHF, we find that two fault segments simultaneous ruptured during the 814 CE and 1850 CE earthquakes, event E3 and the 1536 CE earthquake ruptured the ANHF but not rupture the ZMHF. We suggest that the Xichang fault bend is not a persistent fault boundary, indicating that extensional fault bends with an angle of about 30° may not effectively terminate seismic ruptures on strike-slip faults.

  3. New Insights into Old Events: Improving Estimates of the Spatial Heterogeneity and Distribution of Co-Seismic Slip with Depth for Several Large Magnitude Strike-Slip Earthquakes using Geodetic Observations of the Near-Field Deformation.

    Science.gov (United States)

    Milliner, C. W. D.; Burgmann, R.; Wang, T.

    2016-12-01

    Finite-fault inversions of geodetic data to estimate co-seismic slip at depth, provide important information for faulting mechanics, understanding the behavior of the rupture process and constraints for dynamic rupture simulations. However, incorporating measurement of the near-field surface deformation has typically been difficult, due to decorrelation of the InSAR phase caused by complex ground deformation, and the difficulty of measuring diffuse, `off-fault' deformation in geologic field surveys. Such a lack of near-field data has been found to artificially generate deficits of shallow slip, by (a) overestimating slip at larger depths (3-8 km) by up to 30% [Xu et al. 2016], and (b) limiting the size of near-surface patches, with coarser meshes found to underestimate shallow slip [Huang et al. 2015], in turn distorting the spatial variation of slip across the rupture plane. Here we will present new results of kinematic slip inversions for the 1999 Mw 7.1 Hector Mine, 1999 Mw 7.6 Izmit and 2015 Mw 7.2 Tajikistan earthquakes using GPS data, SAR interferograms with refined phase unwrapping using SNAPHU, new SAR azimuth offsets, and optical image correlation results that can provide important near-field constraints of surface motion. Improved slip distributions for these large strike-slip earthquakes, which span a range of structural maturities, will allow us to assess whether more mature, `smoother' faults exhibit smoother slip distributions as predicted by quasi-static [Dieterich and Smith, 2009] and dynamic numerical rupture simulations [Dunham et al. 2011], and whether deficits of shallow slip are robust features. Understanding whether ruptures exhibit a deficit of shallow slip, and how the spatial heterogeneity of slip may vary between different fault systems holds significance for understanding how strain is released throughout the seismic cycle, generating realistic synthetic simulations of earthquake ruptures and the expected amount of ground shaking.

  4. Shear transformation zone activation during deformation in bulk metallic glasses characterized using a new indentation creep technique

    Science.gov (United States)

    J.B. Puthoff; H.B. Cao; Joseph E. Jakes; P.M. Voyles; D.S. Stone

    2009-01-01

    We have developed a novel type of nanoindentation creep experiment, called broadband nanoindentation creep (BNC), and used it to characterize the thermal activation of shear transformation zones (STZs) in three BMGs in the Zr-Cu-Al system. Using BNC, material hardness can be determined across a wide range of strain rates (10–4 to 10 s–...

  5. Metamorphic history of garnet-rich gneiss at Ktiš in the Lhenice shear zone, Moldanubian Zone of the southern Bohemian Massif, inferred from inclusions and compositional zoning of garnet

    Czech Academy of Sciences Publication Activity Database

    Kobayashi, T.; Hirajima, T.; Kawakami, T.; Svojtka, Martin

    2011-01-01

    Roč. 124, 1/2 (2011), s. 46-65 ISSN 0024-4937 Institutional research plan: CEZ:AV0Z30130516 Keywords : Bohemian Massif * Lhenice shear zone * garnet * P-T path * partial melting Subject RIV: DB - Geology ; Mineralogy Impact factor: 3.246, year: 2011

  6. Fethiye-Burdur Fault Zone (SW Turkey): a myth?

    Science.gov (United States)

    Kaymakci, Nuretdin; Langereis, Cornelis; Özkaptan, Murat; Özacar, Arda A.; Gülyüz, Erhan; Uzel, Bora; Sözbilir, Hasan

    2017-04-01

    Fethiye Burdur Fault Zone (FBFZ) is first proposed by Dumont et al. (1979) as a sinistral strike-slip fault zone as the NE continuation of Pliny-Strabo trench in to the Anatolian Block. The fault zone supposed to accommodate at least 100 km sinistral displacement between the Menderes Massif and the Beydaǧları platform during the exhumation of the Menderes Massif, mainly during the late Miocene. Based on GPS velocities Barka and Reilinger (1997) proposed that the fault zone is still active and accommodates sinistral displacement. In order to test the presence and to unravel its kinematics we have conducted a rigorous paleomagnetic study containing more than 3000 paleomagnetic samples collected from 88 locations and 11700 fault slip data collected from 198 locations distributed evenly all over SW Anatolia spanning from Middle Miocene to Late Pliocene. The obtained rotation senses and amounts indicate slight (around 20°) counter-clockwise rotations distributed uniformly almost whole SW Anatolia and there is no change in the rotation senses and amounts on either side of the FBFZ implying no differential rotation within the zone. Additionally, the slickenside pitches and constructed paleostress configurations, along the so called FBFZ and also within the 300 km diameter of the proposed fault zone, indicated that almost all the faults, oriented parallel to subparallel to the zone, are normal in character. The fault slip measurements are also consistent with earthquake focal mechanisms suggesting active extension in the region. We have not encountered any significant strike-slip motion in the region to support presence and transcurrent nature of the FBFZ. On the contrary, the region is dominated by extensional deformation and strike-slip components are observed only on the NW-SE striking faults which are transfer faults that accommodated extension and normal motion. Therefore, we claim that the sinistral Fethiye Burdur Fault (Zone) is a myth and there is no tangible

  7. Preliminary report of the uranium favorability of shear zones in the crystalline rocks of the southern Appalachians

    International Nuclear Information System (INIS)

    Penley, H.M.; Schot, E.H.; Sewell, J.M.

    1978-11-01

    Three sheared areas in the crystalline Piedmont and Blue Ridge provinces, from which uranium occurrences or anomalous radioactivity have been reported, were studied to determine their favorability for uranium mineralization. The study, which involved a literature review, geologic reconnaissance, ground radiometric surveys, and sampling of rock outcrops for petrographic and chemical analyses, indicates that more-detailed investigations of these and similar areas are warranted. In each area, surface leaching and deep residual cover make it difficult to assess the potential for uranium mineralization on the basis of results from chemical analyses for U 3 O 8 and the radiometric surveys. Although anomalous radioactivity and anomalous chemical uranium values were noted in only a few rock exposures and samples from the shear zones, the potential for uranium mineralization at depth could be much greater than indicated by these surface data. The study indicates that shear zones within Precambiran granitic basement complexes (such as the Wilson Creek Gneiss of western North Carolina, the Cranberry Gneiss of eastern Tennessee, and the Toxaway Gneiss of western South Carolina) are favorable as hosts for uranium and may contain subsurface deposits. Mylonitized graphitic schists immediately north of the Towaliga fault in Alabama and Georgia may be favorable host rocks for uranium

  8. Episodic reactivation of a Late Precambrian mylonite zone on the Gondwanan Margin of the Appalachians, southern Newfoundland

    Science.gov (United States)

    O'Brien, B. H.; O'Brien, S. J.; Dunning, G. R.; Tucker, R. D.

    1993-08-01

    The Grand Bruit Fault Zone of southern Newfoundland is a fundamental structure within Late Precambrian basement on the Gondwanan margin of the Appalachian orogen. Within the fault zone, a sequence of structures documents changes in the sense of ductile displacement from (1) reverse dip slip, to (2) dextral strike slip, to (3) sinistral oblique slip, and, finally, to (4) dextral lateral offsets. Fault movements along this structure were punctuated by emplacement of a variety of plutons and minor intrusions which, when precisely dated, allow these movements to be bracketed at between 571 Ma and 564 Ma, 497 Ma and 427 Ma, 424 Ma and 420 Ma, and 421 Ma and 387 Ma, respectively. The tectonic evolution of the Gondwanan inlier of southern Newfoundland is mirrored, in large part, by the record of mylonite development within the Grand Bruit Fault Zone. These tectonic events are attributable to well-constrained, regional orogenic events of both the Pan-African and Appalachian cycles. Newly formed shear zones in the fault zone reactivate parts of much older faults of similar regional orientation and are, in some cases, kinematically indistinguishable from the ancestral structures. Integration of precise geochronological data with the sequence of overprinted fault structures demonstrates that, although the role of progressive deformation in shear zone development was important, the observed disposition of structures and rock units is primarily a function of polyorogenic accretion. As a multiple-reactivated structural lineament in a Gondwanan basement inlier, the fault zone exerted fundamental control over the tectonic development of the leading edge of the convergent southeast margin of the orogen.

  9. Analogue modelling of strike-slip fault propagation across a rheological/morphological crustal anisotropy: implications for the morphotectonic evolution of the Gloria Fault - Tore Madeira Rise area in NE Atlantic.

    Science.gov (United States)

    Tomás, Ricardo; Rosas, Filipe M.; Duarte, João C.; Terrinha, Pedro; Kullberg, Maria C.; Almeida, Jaime; Barata, Frederico; Carvalho, Bruno; Almeida, Pedro

    2015-04-01

    The Gloria Fault (GF) marks the E-W dextral transcurrent plate boundary between Eurasia and Africa in NE Atlantic, displaying complying high magnitude (historical and instrumental) seismic activity (e.g. M=7.1 in 1939 and M=8.4 in 1941, Bufforn et al., 1988), and cutting across a NNE-SSW 1000 km long bathymetric ridge: the so called Tore-Madeira Rise - TMR (rising in average 3km above the abyssal plain). The precise origin and tectono-magmatic evolution of the TMR is still not fully understood, although reported wide-angle refraction data points to a rheological configuration comprising an isostatically compensated thickened oceanic crust, possibly formed during a period of high accretion in the Mid-Atlantic Ridge (Pierce and Barton, 1991). Widespread evidence for volcanic activity has also been recognized, spanning from late Cretaceous to Present (Geldmacher et al. 2006, Merle et al. 2009), noticeably with the most recent volcanism (~500 Ky) occurring as tectonically aligned volcanic plugs, distributed along the E-W tectonic trend of the GF-related structures. To better understand the complex interference at play in this key area between the tectonic structures (essentially determined by the Gloria Fault system), the present and past magmatic activity and the resulting seafloor morphology, a series of dynamically scaled analogue modelling experiments have been conceived and carried out. The main focus of this experimental work was to decipher the potential influence of a rheological vs. morphological anisotropy (accounting for the TMR) on the lateral propagation of a major right-lateral strike-slip fault (representing the GF). The preliminary comparison of the obtained experimental results with the natural morphotectonic pattern in the study area reveals, not only a strong tectonic control of the ongoing volcanism, manifested by the observed preferred directions of aligned volcanic plugs, but also a so far unsuspected deflection/distributed pattern of several

  10. Structural analysis of the Hasan-Robat marbles as traces of folded basement in the Sanandaj-Sirjan Zone, Iran

    Science.gov (United States)

    Nadimi, Alireza

    2015-11-01

    Cherty marbles of Hasan-Robat area, northwest of Isfahan, in the Sanandaj-Sirjan Zone of Iran preserves evidences of multiple deformational events. The Sanandaj-Sirjan Zone is the inner crystalline zone of the Zagros Orogen, which has been highly deformed and exhumed during continental collision between the Arabian Plate and Central Iran. The Hasan-Robat area is an example of the exposed Precambrian-Paleozoic basement rocks that stretched along two NW-SE-trending faults and located in the inner part of the HasanRobat positive flower strcuture. The Hasan-Robat marbles record a complex shortening and shearing history. This lead to the development of disharmonic ptygmatic folds with vertical to sub-vertical axes and some interference patterns of folding that may have been created from deformations during the Pan-African Orogeny and later phases. Based on this research, tectonic evolution of the Hasan-Robat area is interpreted as the product of three major geotectonic events that have been started after Precambrian to Quaternary: (1) old deformation phases (2) contractional movements and (3) strike-slip movements. Different sets and distributions of joints, faults and folds are confirmed with effect of several deformational stages of the area and formation of the flower structure.

  11. The effects of lower crustal strength and preexisting midcrustal shear zones on the formation of continental core complexes and low-angle normal faults

    KAUST Repository

    Wu, Guangliang

    2016-08-22

    To investigate the formation of core complexes and low-angle normal faults, we devise thermomechanical simulations on a simplified wedge-like orogenic hinterland that has initial topography, Moho relief, and a preexisting midcrustal shear zone that can accommodate shear at very low angles (<20°). We mainly vary the strength of the lower crust and the frictional strength of the preexisting midcrustal shear zone. We find that the strength of the lower crust and the existence and strength of a preexisting shear zone significantly affect the formation and evolution of core complexes. With increasing lower crustal strength, we recognize varying extensional features with decreasing exhumation rate: these are characterized by bivergent metamorphic massifs, classic Cordilleran metamorphic core complexes, multiple consecutive core complexes (or boudinage structures), and a flexural core complex underlined by a large subsurface low-angle detachment fault with a small convex curvature. Topographic loading and mantle buoyancy forces, together with divergent boundaries, drive a regional lower crustal flow that leads to the exhumation of the lower crust where intensive upper crustal faulting induces strong unloading. The detachment fault is a decoupling zone that accommodates large displacement and accumulates sustained shear strain at very low angle between upper and lower crust. Though the regional stress is largely Andersonian, we find non-Andersonian stress in regions adjacent to the preexisting shear zone and those with high topographic gradient. Our new models provide a view that is generally consistent with geological and geophysical observations on how core complexes form and evolve.

  12. Two-stage structural development of a Paleozoic auriferous shear zone at the Globe-Progress deposit, Reefton, New Zealand

    International Nuclear Information System (INIS)

    Milham, L.; Craw, D.

    2009-01-01

    The Globe-Progress gold deposit at Reefton is hosted in a curvilinear mineralised zone that cuts Paleozoic Greenland Group basement metagreywackes. Two discrete phases of mineralisation have resulted in the formation of five different ore types along the shear. An initial phase of mineralisation formed hydrothermal quartz veins and associated Au, As, and S enrichment, with low-grade mineralised host rock. These quartz veins and mineralised host rocks form the outer regions of the mineralised zone. A second hydrothermal phase introduced Sb, Au, As, and S during brittle shear deformation focused on the pre-existing mineralised rocks. This deformation and mineralisation resulted in the formation of metre-scale cataclasite ore and quartz breccia from mineralised host rock and hydrothermal quartz veins, respectively. Cataclasite was derived from argillite layers in the host rock, from which Na, Fe, and Mg have been leached during mineralisation; Al, Ti, and Cr have been conserved; and there has been minor enrichment in Sr, Pb, Zn, and Cu. No quartz was added to the cataclasite or quartz breccia during mineralisation, but some quartz recrystallisation occurred locally, and quartz clasts were physically incorporated into the cataclasite during deformation. The presence of euhedral sulfides in the cataclasite (40% of total sulfides), late-stage undeformed stibnite veins infilling breccia (1-5 cm 3 scale), and undeformed free gold in quartz breccia, imply that the second phase of mineralisation persisted both during and after cataclasis and brecciation. Antimony deposition is greatest in the central cataclasite, up to 6 wt%, and locally in the quartz breccia where stibnite veins are present. Concentrations of Sb decrease with distance from the shear zone. The second, Sb-rich phase of mineralisation in the Globe-Progress deposit resembles similar Sb-rich overprints in the correlative Victorian goldfield of Australia. (author). 38 refs., 10 figs., 1 tab.

  13. Structural analysis and magmatism characterization of the Major Gercino shear zone, Santa Catarina State, Brazil; Analise estrutural e caracterizacao do magmatismo da zona de cisalhamento Major Gercino, SC

    Energy Technology Data Exchange (ETDEWEB)

    Passarelli, Claudia Regina

    1996-12-31

    This work describes the geometric and kinematic characteristics of the Major Gercino Shear Zone (MGSZ) in the Canelinha-Garcia area. This shear zone is one of the major lineaments that affect all southern Brazilian precambrian terrains. In Santa Catarina State, it separates, along its whole extension, the supracrustal rocks of the Brusque belt (northern part) from the Granitoid belt (southern). This zone is characterized by a regional NE trend and a dextral sense of movement where ductile-brittle structures predominate. The MGSZ is composed of two mylonitic belts separated by granitoid rocks probably associated to the development of the shear zone. Both shear zones show cataclastic to ultra mylonitic rocks, but mylonites and protomylonites conditions at high strain rate. The calc-alkaline granitoids present in the area can be grouped in two granitoid associations with meta to peraluminous affinities. The Rolador Granitoid Association is characterized by grayish porphyritic biotite-monzogranites and the Fernandes Granitoid Association by coarsed-grained to porphyritic pinkish amphibole-syenogranites. The U-Pb and Rb-Sr ages range from 670 to 590 Ma with the Sr{sup 87} / Sr{sup 86} initial ratios suggesting a crustal contribution in the generation of these rocks. The importance of the pure shear component is also emphasized by the results of the Fry method. Many z axes of the strain ellipses are at high angle to the shear foliation. Symmetric porphyroclasts also corroborate this hypothesis. The micaceous minerals formed during the shear development indicate K-Ar ages around 555 {+-} 15 Ma. Brittle reactivations of the shear zone have been placed by K-Ar in fine-fraction materials at Triassic time (215 {+-} 15 Ma.) 220 refs., 107 figs., 18 tabs., 4 maps

  14. Structural control and origin of volcanism in the Taupo volcanic zone, New Zealand

    Science.gov (United States)

    Cole, J. W.

    1990-08-01

    Taupor volcanic zone (TVZ) is the currently active volcanic arc and back-arc basin of the Taupo-Hikurangi arc-trench system, North Island, New Zealand. The volcanic arc is best developed at the southern (Tongariro volcanic centre) end of the TVZ, while on the eastern side of the TVZ it is represented mainly by dacite volcanoes, and in the Bay of Plenty andesite/dacite volcanoes occur on either side of the Whakatane graben. The back-arc basin is best developed in the central part of the TVZ and comprises bimodal rhyolite and high-alumina basalt volcanism. Widespread ignimbrite eruptions have occurred from this area in the past 0.6 Ma. Normal faults occur in both arc and back-arc basin. They are generally steeply dipping (>40°) and strike between 040° and 080°. In the back-arc basin, fault zones are en echelon and have the same trend as alignments of rhyolite domes and basalt vents. Open fissures have formed during historic earthquakes along some of the faults, and geodetic measurements on the north side of Lake Taupo suggest extension of 14±4 mm/year. In the Bay of Plenty and ML=6.3 earthquake occurred on 2 March 1987. Modelling of known structure in the area together with data derived from this earthquake suggests block faulting with faults dipping 45°±10° NW and a similar dip is suggested by seismic profiling of faults offshore of the Bay of Plenty where extension is estimated to be 5±2 mm/year. To the east of the TVZ, the North Island shear belt (NISB) is a zone of reverse-dextral, strike-slip faults, the surface expression of which terminates at the eastern end of the TVZ. On the opposite side of the TVZ in the offshore western Bay of Plenty and on line with the NISB is the Mayor Island fault belt. If the two fault belts were once continuous, as seems likely, strike-slip faults probably extend through the basement of the TVZ. When extension associated with the arc and back-arc basin is combined with these strike-slip faults, the resulting transtension

  15. Micro tectonic milonitas analysis in the extreme south of the Sarandi del Yi shear zone: Kinematics and deformation conditions

    International Nuclear Information System (INIS)

    Oyhantçabal, P; Suarez, I; Seluchi, N; Martinez, X.

    2010-01-01

    The Shear Zone divides Sarandi del Yi Craton River Plate in Piedra Alta and Nico Perez land . The southern end of this zone extends to north - south from the vicinity of the town of Minas to Punta Solis. The predominant lithology of the study area consists of a granitic mylonite with abundant muscovite and biotite. Structural data of foliation , stretching lineation and kinematic indicators were surveyed .Petrographic analysis shows that quartz is presented as ribbons polycrystalline product subgrain rotation recrystallization and grain boundary migration . Feldspar porphyroclasts are partially recrystallized in developing type structures c ore and mantle . Kinematic indicators such as sigma porphyroclasts , mica fish and oblique foliation defined consistently sinistral sense . The presence of stable and mirmequitas in the plane of biotite foliation along the microstructures described in quartz and feldspar , can be inferred temperature conditions between 450 ° C and 550° C during deformation

  16. Granite emplacement at the termination of a major Variscan transcurrent shear zone: The late collisional Viseu batholith

    Science.gov (United States)

    Valle Aguado, B.; Azevedo, M. R.; Nolan, J.; Medina, J.; Costa, M. M.; Corfu, F.; Martínez Catalán, J. R.

    2017-05-01

    A major event of plutonic activity occurred all across the Central Iberian Zone of the Iberian Variscan Belt at the end of Late Paleozoic Variscan collisional tectonism. The present study focuses on the western sector of the Viseu late-post-tectonic batholith (central Portugal), a large composite intrusion comprising three main plutonic units: (a) small bodies of mafic to intermediate composition preferentially concentrated along the northern border, (b) a wide ring of coarse porphyritic biotite monzogranite (Cota-Viseu granite) and (c) a more evolved medium porphyritic, biotite-muscovite monzogranite occupying the central part of the intrusion (Alcafache granite). The compositional zonation pattern of the whole batholith and the complex mixing/mingling relationships between the voluminous Cota-Viseu porphyritic granite and the mafic/intermediate rocks suggest that these melts were withdrawn from a lower crustal source region undergoing partial melting, invasion by mantle-derived mafic magmas, mixing and fractional crystallization. New CA-ID-TIMS U-Pb zircon ages indicate that pluton assembly via multipulse injection of successive magma batches took place between 299.4 ± 0.4 Ma and 296.0 ± 0.6 Ma. A detailed anisotropy of magnetic susceptibility (AMS) survey suggests that pluton emplacement occurred at the extensional termination of a regional-scale, ENE-WSW trending, sinistral D3 shear zone - the Juzbado-Penalva Shear Zone (JPSZ). A dilational opening model involving the development of "en-échelon" tensional gashes at the extensional termination of the fault, followed by progressive opening and widening of north-south trending fractures, provided the space into which the successive magma batches arriving from below were emplaced. Vertical inflation was accommodated by depression of the pluton floor. The proposed model is consistent with the asymmetric wedge-shaped geometry of the intrusion (steep root zone on the northern side, discordant subvertical walls and

  17. A hidden variable in shear transformation zone volume versus Poisson’s ratio relation in metallic glasses

    Directory of Open Access Journals (Sweden)

    S. Y. Kim

    2017-10-01

    Full Text Available Herein, we elucidate a hidden variable in a shear transformation zone (STZ volume (Ω versus Poisson’s ratio (ν relation and clarify the correlation between STZ characteristics and the plasticity of metallic glasses (MGs. On the basis of cooperative shear model and atomic stress theories, we carefully formulate Ω as a function of molar volume (Vm and ν. The twofold trend in Ω and ν is attributed to a relatively large variation of Vm as compared to that of ν as well as an inverse relation between Vm and ν. Indeed, the derived equation reveals that the number of atoms in an STZ instead of Ω is a microstructural characteristic which has a close relationship with plasticity since it reflects the preference of atomistic behaviors between cooperative shearing and the generation of volume strain fluctuation under stress. The results would deepen our understanding of the correlation between microscopic behaviors (STZ activation and macroscopic properties (plasticity in MGs and enable a quantitative approach in associating various STZ-related macroscopic behaviors with intrinsic properties of MGs.

  18. The Main Shear Zone in Sør Rondane: A key feature for reconstructing the geodynamic evolution of East Antarctica

    Science.gov (United States)

    Ruppel, Antonia; Läufer, Andreas; Lisker, Frank; Jacobs, Joachim; Elburg, Marlina; Damaske, Detlef; Lucka, Nicole

    2013-04-01

    Structural investigations were carried out along the Main Shear Zone (MSZ) of western Sør Rondane (22°-25°E, 71.5°-72.5°S) to gain new information about the position of the East-/West-Gondwana suture and the ancient plate tectonic configuration during Gondwana amalgamation. The WSW-ENE striking MSZ divides south-western Sør Rondane in a northern amphibolite-facies terrane and a southern tonalite-trondhjemite-granodiorite (TTG) terrane. The structure can be traced over a distance of ca. 100 km and reaches several hundred meters in width. It is characterized by a right-lateral sense of movement and marked by a transpressional and also transtensional regime. Ductilely deformed granitoids (ca. 560 Ma: SHRIMP U-Pb of zircon) and ductile - brittle structures, which evolved in a transitional ductile to brittle regime in an undeformed syenite (ca. 499-459 Ma, Ar-Ar mica), provide a late Proterozoic/ early Paleozoic time limit for the activity of the shear zone (Shiraishi et al., 2008; Shiraishi et al., 1997). Documentation of ductile and brittle deformation allows reconstructing up to eight deformation stages. Cross-cutting relationships of structural features mapped in the field complemented by published kinematic data reveal the following relative age succession: [i] Dn+1 - formation of the main foliation during peak metamorphism, [ii] Dn+2 - isoclinal, intrafolial folding of the main foliation, mostly foliation-parallel mylonitic shear zones (1-2 meter thick), [iii] Dn+3 - formation of tight to closed folds, [iv] Dn+4 - formation of relatively upright, large-scale open folds, [v] Dn+5 - granitoid intrusion (e.g. Vengen granite), [vi] Dn+6 - dextral shearing between amphibolite and TTG terranes, formation of the MSZ, [vii] Dn+7 - intrusion of late- to post-tectonic granitoids, first stage of brittle deformation (late shearing along MSZ), intrusion of post-kinematic mafic dykes, [viii] Dn+8 - second stage of brittle deformation including formation of conjugate fault

  19. Plate interior polyphase fault systems and sedimentary basin evolution: A case study of the East Gobi Basin and East Gobi Fault Zone, southeastern Mongolia

    Science.gov (United States)

    Heumann, Matthew J.; Johnson, Cari L.; Webb, Laura E.

    2018-01-01

    Structural interpretation of 2-D seismic reflection data and subsurface-outcrop correlations reveal six distinct phases of deformation recorded in the Paleozoic basement rocks and Mesozoic-Cenozoic basin fill of the East Gobi Basin (EGB), southeastern Mongolia. These phases include arc accretion and arc-continent collision in late Paleozoic time, Late Triassic sinistral shear-zone development, Early Jurassic fold and thrust belt style shortening, Middle Jurassic-Lower Cretaceous extension and rift basin development, middle Cretaceous shortening with basin inversion and regional unconformity development, and Late Cretaceous-Oligocene thermal subsidence with renewed Paleogene left-lateral strike slip faulting across the fault zone. The five post-amalgamation deformation phases are localized along the East Gobi Fault Zone, suggesting that preexisting structures and boundary conditions exert fundamental controls on the long term evolution of intracontinental basins such as the EGB. Subsurface geophysical data and outcrop correlations demonstrate that the main subbasins of the EGB contain major differences in basement metamorphic and structural fabrics, basin fill patterns, and distinct Mesozoic-Cenozoic fault generations. Potential causes related to far-field boundary conditions and other driving factors are suggested for each of the major deformation phases.

  20. Formation of Lithospheric Shear Zones: Effect of Temperature on Two-Phase Grain Damage

    Science.gov (United States)

    Mulyukova, E.; Bercovici, D.

    2016-12-01

    Shear localization in the lithosphere is an important element of the planetary scale dynamics. Being a characteristic feature of the tectonic plate boundaries, as is geologically evidenced by the presence of small grain mylonites and ultramylonites, understanding shear localization can shed light on the initiation and evolution of plate tectonics. Shear localization in the ductile portion of the lithosphere can arise when its constituting polycrystalline material deforms by diffusion creep, which has a grain size sensitive viscosity, in combination with the Zener pinning, which reduces grain size and impedes grain growth. We explore the deformation conditions under which these self-weakening effects take place, and, in particular, the effect of temperature on these conditions. In the presented model, the lithosphere-like polycrystalline material is deformed in a two-dimensional simple shear set-up by applying a constant stress or strain rate at the boundaries. The mineral grains evolve to a stable size, which is obtained when the rate of coarsening by normal grain growth and the rate of grain size reduction by damage are in balance. The rates of these microstructural transformations are dictated by the applied rate of mechanical work and temperature. The temperature-dependence enters through its influence on the diffusion and dislocation creep compliances, as well as the coarsening coefficient for grain growth, and the value of the damage partitioning fraction, which is the fraction of deformational work that goes into creating new surface energy. We demonstrate that the increase of temperature with depth can lead to a significant change in the microstructure and influence the degree of localization in the ductile portion of the lithosphere. Within the framework of the two-phase grain damage model, we present the theoretical constraints on the temperature-dependent material properties that can best explain the field observations of mylonites and ultramylonites.

  1. Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD

    Science.gov (United States)

    Morrow, Carolyn A.; Lockner, David A.; Hickman, Stephen H.

    2015-01-01

    The San Andreas Fault Observatory at Depth (SAFOD) scientific drillhole near Parkfield, California crosses the San Andreas Fault at a depth of 2.7 km. Downhole measurements and analysis of core retrieved from Phase 3 drilling reveal two narrow, actively deforming zones of smectite-clay gouge within a roughly 200 m-wide fault damage zone of sandstones, siltstones and mudstones. Here we report electrical resistivity and permeability measurements on core samples from all of these structural units at effective confining pressures up to 120 MPa. Electrical resistivity (~10 ohm-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were one to two orders of magnitude lower than the surrounding damage zone material, consistent with broader-scale observations from the downhole resistivity and seismic velocity logs. The higher porosity of the clay gouge, 2 to 8 times greater than that in the damage zone rocks, along with surface conduction were the principal factors contributing to the observed low resistivities. The high percentage of fine-grained clay in the deforming zones also greatly reduced permeability to values low enough to create a barrier to fluid flow across the fault. Together, resistivity and permeability data can be used to assess the hydrogeologic characteristics of the fault, key to understanding fault structure and strength. The low resistivities and strength measurements of the SAFOD core are consistent with observations of low resistivity clays that are often found in the principal slip zones of other active faults making resistivity logs a valuable tool for identifying these zones.

  2. Integrated geophysical and geological modelling: insights in the 3D structure and kinematics of the Hercynian Suture Zone in the Champtoceaux area (Brittany, France)

    Science.gov (United States)

    Martelet, G.; Calcagno, Ph.; Gumiaux, C.; Truffert, C.; Bitri, A.; Gapais, D.; Brun, J. P.

    2003-04-01

    Using the Editeur Géologique, a software specifically developed for the purpose of 3D geological modelling by the French Geological Survey (BRGM), we model a segment of the Hercynian suture zone of western Europe, in Champtoceaux area (Brittany, western France). The area shows exposures of strongly deformed eclogite-bearing gneisses and micaschists. These units were stacked during collision and exhumed during late Devonian to early Carboniferous times. Regional-scale dextral simple shear accompanied strike-slip movements along the SASZ (South Armorican Shear Zone). It produced a km-scale antiformal structure in the Champtoceaux metamorphic units with a steeply-dipping axial plane and a steeply eastward-plunging axis. Interpretation of the recent Armor2 seismic profile shows that the well-recognized north-dipping early lithological structuration is cross-cut by Carboniferous south-dipping inverse tectonics of crustal extension. In order to precise and extend in 3D the structures interpreted in the seismic profile, we model seven radial gravity profiles throughout Champtoceaux periclinal termination, based on data from the French gravity database. Direct 2D modelling is performed at a crustal scale, based on seismic constraints and geological field observations, as well as density measurements on samples or in drill holes. Input in the Editeur Géologique, the consistency of cross-sections, digitized geological map and structural information (foliation dips) is first checked. From the surface to the Moho, available spatialised 2D information is then interpolated in the whole 3D space using adapted geostatistical analysis. Finally, taking into account densities associated to each modelled geological body, the computation of the 3D gravity effect of the model is compared to the measured Bouguer anomaly, which insures that all complex 3D gravity effects are well taken into account. Results emphasise the usefulness of integrated geological and geophysical 3D modelling

  3. Superimposed basin formation during Neogene-Quaternary extensional tectonics in SW-Anatolia (Turkey): Insights from the kinematics of the Dinar Fault Zone

    Science.gov (United States)

    Alçiçek, M. Cihat; Brogi, Andrea; Capezzuoli, Enrico; Liotta, Domenico; Meccheri, Marco

    2013-11-01

    In the extensional province of SW-Anatolia, the cross-cutting relationship between the NW- and NE-oriented Neogene and Quaternary basins is an ongoing debate in the understanding of the tectonic evolution of this area. In order to contribute to this issue, we carried out a structural and kinematic study along the seismogenic NW-trending Dinar Fault Zone (DFZ). This structure was initially controlled by the sedimentary and tectonic evolution of the NE-oriented Neogene Baklan, Acıgöl and Burdur basins and, later, by the NW-oriented Quaternary Dinar Basin. On the basis of > 1000 structural and kinematic data, in conjunction with basin stratigraphy, the DFZ can be divided into three almost parallel and continuous bands, that are: (a) the Hangingwall where Quaternary sediments are deformed by normal faults with mechanical striations; (b) the Inner Zone, corresponding to the present Dinar fault scarp, where NW-trending normal faults with mechanical striations are dominant, and (c) the Outer Zone, located in the footwall of the structure comprising the area between the fault scarp and undeformed bedrock, where faults exhibit variable orientation and kinematics, from strike-slip to normal dip-slip. These kinematics are mainly indicated by calcite shear veins and superimposed mechanical striations, respectively. This suggests that the DFZ changed kinematics over time, i.e., the DFZ initiated as dominant dextral strike-slip to oblique-slip fault system and continued with a dominant normal movement. Therefore, we hypothesize that the NW-trending DFZ was initially a transfer zone during the late Miocene-Pliocene, coeval to the sedimentary and structural evolution of the NE-trending Baklan, Acigöl and Burdur basins. During the Quaternary the DFZ, representing an already weakened crustal sector, played the role of a normal fault system providing the accommodation space for the Quaternary Dinar Basin. Hydrothermal circulation and volcanism at NE-/NW-trending faults

  4. Crustal-scale shear zones recording 400 m.y. of tectonic activity in the North Caribou greenstone belt, western Superior Province of Canada

    Science.gov (United States)

    Kalbfleisch, Netasha

    A series of crustal-scale shear zones demarcates the northern and eastern margins of the North Caribou greenstone belt (NCGB), proximal to a Mesoarchean terrane boundary in the core of the western Superior Province of Canada. The dominant deformation produced a pervasive steeply dipping fabric that trends broadly parallel to the doubly arcuate shape of the belt and was responsible for tight folding the banded iron formation host to Goldcorp's prolific gold deposit at Musselwhite mine. The shear zones in the North Caribou greenstone belt are of particular interest because of their ability to channel hydrothermal fluids with the potential to bear ore and cause alteration of the middle to shallow crust. Shear zones are commonly reactivated during subsequent tectonism, but exhibit a consistent and dominant dextral shear sense across the belt; fabric-forming micas and chlorite are generally Mg-rich. Although garnets samples from within the shear zones are dominantly almandine, they possess variable geochemical trends (HREEs of >2 orders of magnitude) and can be syn-, intra-, or post-tectonic in origin. In situ geochronological analysis of zircon (U-Pb) and monazite (total-Pb) in high strain rocks in and around the NCGB, interpreted in light of in situ geochemical analysis of garnet and fabric-forming micas and chlorite, reveals four relatively discrete events that span 400 million years. Metamorphism of the mid-crust was coeval with magmatism during docking of the Island Lake domain at c. 2.86 Ga and subsequent terrane accretion at the north and south margins of the North Caribou Superterrane from c. 2.75 to 2.71 Ga. Transpressive shear at c. 2.60 to 2.56 Ga and late re-activation of shear zones at c. 2.44 Ga produced a steeply-dipping pervasive fabric, and channeled fluids for late crystallization of garnet and monazite recorded in the Markop Lake deformation zone. These observations implicate a horizontal tectonic model similar to the modern eastern Pacific plate

  5. Thrusting and transpressional shearing in the Pan-African nappe southwest El-Sibai core complex, Central Eastern Desert, Egypt

    Science.gov (United States)

    El-Wahed, Mohamed A. Abd.

    2008-01-01

    The Wadi El-Shush area in the Central Eastern Desert (CED) of Egypt is occupied by the Sibai core complex and its surrounding Pan-African nappe complex. The sequence of metamorphic and structural events in the Sibai core complex and the enveloping Pan-African nappe can be summarized as follows: (1) high temperature metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks, (2) between 740 and 660 Ma, oblique island arc accretion resulted in Pan-African nappe emplacement and the intrusion of syn-tectonic gneissic tonalite at about 680 ± 10 Ma. The NNW-SSE shortening associated with oblique island arc accretion produced low angle NNW-directed thrusts and open folds in volcaniclastic metasediments, schists and isolated serpentinite masses (Pan-African nappe) and created NNE-trending recumbent folds in syn-tectonic granites. The NNW-SSE shortening has produced imbricate structures and thrust duplexes in the Pan-African nappe, (3) NE-ward thrusting which deformed the Pan-African nappe into SW-dipping imbricate slices. The ENE-WSW compression event has created NE-directed thrusts, folded the NNW-directed thrusts and produced NW-trending major and minor folds in the Pan-African nappe. Prograde metamorphism (480-525 °C at 2-4.5 kbar) was synchronous with thrusting events, (4) retrograde metamorphism during sinistral shearing along NNW- to NW-striking strike-slip shear zones (660-580 Ma), marking the external boundaries of the Sibai core complex and related to the Najd Fault System. Sinistral shearing has produced steeply dipping mylonitic foliation and open plunging folds in the NNW- and NE-ward thrust planes. Presence of retrograde metamorphism supports the slow exhumation of Sibai core complex under brittle-ductile low temperature conditions. Arc-accretion caused thrusting, imbrication and crustal thickening, whereas gravitational collapse of a compressed and thickened lithosphere initiated the sinistral movement

  6. Nanoindentation study on the characteristic of shear transformation zone in a Pd-based bulk metallic glass during serrated flow

    Science.gov (United States)

    Liao, G. K.; Long, Z. L.; Zhao, M. S. Z.; Peng, L.; Chai, W.; Ping, Z. H.

    2018-04-01

    This paper presents the research on the evolution of shear transformation zone (STZ) in a Pd-based bulk metallic glass (BMG) during serrated flow under nanoindentation. A novel method of estimating the STZ volume through statistical analysis of the serrated flow behavior was proposed for the first time. Based on the proposed method, the STZ volume of the studied BMG at various peak loads have been systematically investigated. The results indicate that the measured STZ volumes are in good agreement with that documented in literature, and the STZ size exhibits an increasing trend during indentation. Moreover, the correlation between the serrated flow dynamics and the STZ activation has also been evaluated. It is found that the STZ activation can promote the formation of self-organized critical (SOC) state during serrated flow.

  7. Double layer anisotropy beneath the New Madrid seismic zone and adjacent areas: insights from teleseismic shear wave splitting

    Directory of Open Access Journals (Sweden)

    Moikwathai Dax Moidaki

    2014-02-01

    Full Text Available A total of 93 well-defined PKS, 54 SKKS, and 126 SKS shear-wave splitting parameters are determined at 25 broadband seismic stations in an approximately 1000 by 1000 km2 area centered at the New Madrid seismic zone (NMSZ in order to test the existence of two anisotropic layers and to map the direction and strength of mantle fabrics. The individual splitting parameters suggest a significant and systematic spatial and azimuthal variation in the splitting parameters. The azimuthal variations at most stations can be explained as the results of present SW ward asthenospheric flow and NNE trending lithospheric fabrics formed during past orogenic events. In the NMSZ, rift-parallel fast directions (potentially related to a long-rift flow and rift-orthogonal fast directions from small-scale mantle convection are not observed. In addition, reduction in splitting times as a result of vertical asthenospheric flow is not observed.

  8. Representation and Management of the Knowledge of Brittle Deformation in Shear Zones Using Microstructural Data From the SAFOD Core Samples

    Science.gov (United States)

    Babaie, H. A.; Broda, C. M.; Kumar, A.; Hadizadeh, J.

    2010-12-01

    Web access to data that represent knowledge acquired by investigators studying the microstructures in the core samples of the SAFOD (San Andreas Observatory at Depth) project can help scientists efficiently integrate and share knowledge, query the data, and update the knowledge base on the Web. To achieve this, we have used OWL (Web Ontology Language) to build the brittle deformation ontology for the microstructures observed in the SAFOD core samples, by explicitly formalizing the knowledge about deformational processes, geological objects undergoing deformation, and the underlying mechanical and environmental conditions in brittle shear zones. The developed Web-based ‘SAFOD Brittle Microstructure and Mechanics Knowledge base’ (SAFOD BM2KB), which instantiates this ontology and is available at http://codd.cs.gsu.edu:9999/safod/index.jsp, will host and serve data that pertains to spatial objects, such as microstructure, gouge, fault, and SEM image, acquired by the SAFOD investigators through the studies of the SAFOD core samples. Deformation in shear zones involves complex brittle and ductile processes that alter, create, and/or destroy a wide variety of one- to three-dimensional, multi-scale spatial entities such as rocks and their constituent minerals and structure. These processes occur through a series of sub-processes that happen in different time intervals, and affect the spatial objects at granular to regional scales within shear zones. The processes bring about qualitative change to the spatial entities over time intervals that start and end with events. Processes, such as mylonitization and cataclastic flow, change the spatial location, distribution, dimension, size, shape, and orientation of some objects through translation, rotation and strain. These processes may also result in newly formed entities, such as a new mineral, gouge, vein, or fault, during one or more phases of deformation. Deformation processes may also destroy entities, such as a

  9. Structural geology of the French Peak accommodation zone, Nevada Test Site, southwestern Nevada

    International Nuclear Information System (INIS)

    Hudson, M.R.

    1997-01-01

    The French Peak accommodation zone (FPAZ) forms an east-trending bedrock structural high in the Nevada Test Site region of southwestern Nevada that formed during Cenozoic Basin and Range extension. The zone separates areas of opposing directions of tilt and downthrow on faults in the Yucca Flat and Frenchman Flat areas. Paleomagnetic data show that rocks within the accommodation zone adjacent to Yucca Flat were not strongly affected by vertical-axis rotation and thus that the transverse strikes of fault and strata formed near their present orientation. Both normal- and oblique strike-slip faulting in the FPAZ largely occurred under a normal-fault stress regime, with least principal stress oriented west-northwest. The normal and sinistral faults in the Puddle Peka segment transfers extension between the Plutonium Valley normal fault zone and the Cane Spring sinistral fault. Recognition of sinistral shear across the Puddle Peak segment allows the Frenchman Flat basin to be interpreted as an asymmetric pull-apart basin developed between the FPAZ and a zone of east-northeast-striking faults to the south that include the Rock Valley fault. The FPAZ has the potential to influence ground-water flow in the region in several ways. Fracture density and thus probably fracture conductivity is high within the FPAZ due to the abundant fault splays present. Moreover,, fractures oriented transversely to the general southward flow of ground water through Yucca Flat area are significant and have potential to laterally divert ground water. Finally, the FPAZ forms a faulted structural high whose northern and southern flanks may permit intermixing of ground waters from different aquifer levels, namely the lower carbonate, welded tuff, and alluvial aquifers. 42 refs

  10. Deformation Microstructures of the Yugu Peridotites in the Gyeonggi Massif, Korea: Implications for Olivine Fabric Transition in Mantle Shear Zones

    Science.gov (United States)

    Jung, H.; Park, M.

    2017-12-01

    Large-scale emplaced peridotite bodies may provide insights into plastic deformation process and tectonic evolution in the mantle shear zone. Due to the complexity of deformation microstructures and processes in natural mantle rocks, the evolution of pre-existing olivine fabrics is still not well understood. In this study, we examine well-preserved transitional characteristics of microstructures and olivine fabrics developed in a mantle shear zone from the Yugu peridotite body, the Gyeonggi Massif, Korean Peninsula. The Yugu peridotite body predominantly comprises spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We classified highly deformed peridotites into four textural types based on their microstructural characteristics: proto-mylonite; proto-mylonite to mylonite transition; mylonite; and ultra-mylonite. Olivine fabrics changed from A-type (proto-mylonite) via D-type (mylonite) to E-type (ultra-mylonite). Olivine fabric transition is interpreted as occurring under hydrous conditions at low temperature and high strain, because of characteristics such as Ti-clinohumite defects (and serpentine) and fluid inclusion trails in olivine, and a hydrous mineral (pargasite) in the matrix, especially in the ultra-mylonitic peridotites. Even though the ultra-mylonitic peridotites contained extremely small (24-30 μm) olivine neoblasts, the olivine fabrics showed a distinct (E-type) pattern rather than a random one. Analysis of the lattice preferred orientation strength, dislocation microstructures, recrystallized grain-size, and deformation mechanism maps of olivine suggest that the proto-mylonitic, mylonitic, and ultra-mylonitic peridotites were deformed by dislocation creep (A-type), DisGBS (D-type), and combination of dislocation and diffusion creep (E-type), respectively.

  11. Geochemistry of the granitoids from the Central Surguja Shear Zone, India: geological evolution and implications on uranium mineralization and exploration

    International Nuclear Information System (INIS)

    Saxena, V.P.; Murugan, C.; Sabot, H.K.; Krishnamurthy, P.

    1992-01-01

    Numerous stock-like bodies of grey granites (up to 15 km 2 across) and sheet-like bodies of pink granite (1 km to 15 km long and 0.2-0.5 km thick) have intruded along the cores of anticlines of the Central Surguja Shear Zone(CSSZ), during the Satpura Orogeny (Middle Proterozoic). Major, minor, and trace element data, critical elemental ratios, and Qz-Or-Ab normative mineralogical data indicate that the granitic melt was derived from palingenesis of crustal rocks. The pink granites represent melts equilibrated under very low pressure in a hydrous system, apparently influenced by fractionation and differentiation. The grey granites represent hydrous melts derived under pressure of about 5 kb. The pink granites are the youngest intrusives and show distinct enrichment of Rb(235-407 ppm), Y(33-356 ppm), Zr(120-533 ppm), Nb(16-161 ppm), and U(10-141 ppm). In general, the granites show high Rb/Sr and Ba/Sr, and low Ba/Rb ratios pointing to their evolved nature. Uranium mineralization at a number of places, such as at Jajawal, Dhabi, Dumhat, Pakni, and others is hosted by grey and pink granites, quartzo-feldspathic cataclasite, and chlorite-biotite schist, within the Central Surguja Shear Zone. Discriminant diagrams to infer palaeotectonic regimes using Rb, Nb, and Y indicate a within plate environment for the granites, notably for the pink types. Besides structurally controlled vein-type uranium mineralization, sedimentary rocks of the Gondwana Supergroup enveloping the Surguja Crystalline Complex (SCC) may also hold potential for sedimentary-type uranium mineralization in conducive locales. (author). 22 refs., 16 figs., 3 tabs

  12. Geodynamic hazard and risk assessments for sites close or in tectonic zones with shear movements

    Czech Academy of Sciences Publication Activity Database

    Schenk, Vladimír; Schenková, Zdeňka; Jechumtálová, Zuzana

    2007-01-01

    Roč. 51, č. 7 (2007), s. 1113-1117 ISSN 0943-0105 R&D Projects: GA MŠk LN00A005; GA MŠk(CZ) LC506; GA MŠk 1P05ME781; GA ČR GA205/97/0679; GA ČR GA205/01/0480; GA ČR GA205/05/2287; GA AV ČR 1QS300460551 Institutional research plan: CEZ:AV0Z30460519; CEZ:AV0Z30120515 Keywords : geodynamic hazard and risk * tectonic shear movements * urban and territorial planning Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.722, year: 2007

  13. The Sundance fault: A newly recognized shear zone at Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Spengler, R.W.; Braun, C.A.; Martin, L.G.; Weisenberg, C.W.

    1994-01-01

    Ongoing detailed mapping at a scale of 1:240 of structural features within the potential repository area indicates the presence of several previously unrecognized structural features. Minor north-trending west-side-down faults occur east and west of the Ghost Dance fault and suggest a total width of the Ghost Dance fault system of nearly 366 m (1200 ft). A zone of near-vertical N30 degrees-40 degrees W-trending faults, at least 274 m (900 ft) wide, has been identified in the northern part of our study area and may traverse across the potential repository area. On the basis of a preliminary analysis of available data, we propose to name this zone the open-quotes Sundance fault systemclose quotes and the dominant structure, occurring near the middle of the zone, the open-quotes Sundance faultclose quotes. Some field relations suggest left-stepping deflections of north-trending faults along a pre-existing northwest-trending structural fabric. Other field observations suggest that the open-quotes Sundance fault systemclose quotes offsets the Ghost Dance fault system in an apparent right lateral sense by at least 52 m (170 ft). Additional detailed field studies are needed to better understand structural complexities at Yucca Mountain

  14. The Sundance fault: A newly recognized shear zone at Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Spengler, R.W.; Braun, C.A.; Martin, L.G.; Weisenberg, C.W.

    1994-01-01

    Ongoing detailed mapping at a scale of 1:240 of structural features within the potential repository area indicates the presence of several previously unrecognized structural features. Minor north-trending west-side-down faults occur east and west of the Ghost Dance fault and suggest a total width of the Ghost Dance fault system of nearly 366 m (1200 ft). A zone of near-vertical N30 degrees - 40 degrees W - trending faults, at least 274 m (900 ft) wide, has been identified in the northern part of our study area and may traverse across the proposed repository area. On the basis of a preliminary analysis of available data, we propose to name this zone the ''Sundance fault system'' and the dominant structure, occurring near the middle of the zone, the ''Sundance fault.'' Some field relations suggest left-stepping deflections of north-trending faults along a preexisting northwest-trending structural fabric. Other field observations suggest that the ''Sundance fault system'' offsets the Ghost Dance fault system in an apparent right lateral sense by at least 52 m (170 ft). Additional detailed field studies, however, are needed to better understand structural complexities at Yucca Mountain

  15. Longitudinal dispersion in natural channels: 2. The roles of shear flow dispersion and dead zones in the River Severn, U.K.

    Directory of Open Access Journals (Sweden)

    P. M. Davis

    2000-01-01

    Full Text Available The classical one-dimensional advection-diffusion equation (ADE gives an inadequate description of tracer cloud evolution in the River Severn, U.K. A solute transport model incorporating the effects of tracer storage in dead zones is presented in which the channel is conceived as being divided into two parallel regions. The bulk flow region occurs in the central part. Its longitudinal dispersive properties are described by the ADE. Adjacent to this, an additional cross-sectional area is defined in which tracer can be stored temporarily in regions of slowly moving water called dead zones. Exchange between the two regions follows a first order rate equation. Applying the model to the River Severn shows that a dispersing cloud’s evolution occurs in two distinct stages with a rapid transitional phase. Initially, shear-dispersion is dominant while the tracer particles mix fully over the bulk flow. Once this has occurred, dead zone storage accounts well for the non-Fickian evolution of the cloud. After the transitional phase the dead zone storage mechanism clearly dominates over shear-dispersion. Overall, the combined shear flow dispersion – dead zone model (D-DZM provides a much better, physically consistent description of the tracer cloud’s evolution than the simple classical ADE approach can do alone. Keywords: Channels; dispersion; dead zones; tracers; River Severn

  16. Preservation of Permian allanite within an Alpine eclogite facies shear zone at Mt Mucrone, Italy: Mechanical and chemical behaviour of allanite during mylonitization

    DEFF Research Database (Denmark)

    Cenki-Tok, Benedicte; Oliot, E.; Berger, Alfons

    2011-01-01

    This study addresses the mechanical and cehmical behavior of allanite during shear zone formation under high-pressure metamorphism. Understanding physico-chemical processes related to the retention or resetting of Pb isotopes in allanite during geological processes is essential for robust petroch...

  17. Age and nature of eclogites in the Huwan shear zone, and the multi-stage evolution of the Qinling-Dabie-Sulu orogen, central China

    NARCIS (Netherlands)

    Wu, Y.B.; Hanchar, J.H.; Gao, S.; Sylvester, P.J.; Tubrett, M.; Qiu, H.N.; Wijbrans, J.R.; Brouwer, F.M.; Yang, S.H.; Yang, Q.J.; Liu, Y.S.

    2009-01-01

    In situ LA-ICPMS U-Pb, trace element, and Hf isotope data in zircon demonstrate a Carboniferous age for eclogite-facies metamorphism in Siluro-Devonian protoliths in the Huwan shear zone, Dabie Mountains, Central China. This age contrasts with the more prevailing Triassic age for high- to ultrahigh

  18. Thermal evolution of the Sisters shear zone, southern New Zealand; Formation of the Great South Basin and onset of Pacific-Antarctic spreading

    Science.gov (United States)

    Kula, Joseph; Tulloch, Andy J.; Spell, Terry L.; Wells, Michael L.; Zanetti, Kathleen A.

    2009-10-01

    The separation of Zealandia from West Antarctica was the final stage in the Cretaceous breakup of the Gondwana Pacific margin. Continental extension resulting in formation of the Great South Basin and thinning of the Campbell Plateau leading to development of the Pacific-Antarctic spreading ridge was partially accommodated along the Sisters shear zone. This east-northeast striking brittle-ductile structure exposed along the southeast coast of Stewart Island, New Zealand, is a greenschist facies extensional shear zone that separates a hanging wall of chloritic, brecciated granites, and undeformed conglomerate from a footwall of mylonitic Carboniferous and Early Cretaceous granites. This complex structure exhibits bivergent kinematics and can be subdivided into a northern and southern segment. The 40Ar/39Ar thermochronology indicates that cooling of the shear zone footwall began at ˜94 Ma with accelerated cooling over the interval ˜89-82 Ma. Structural and thermochronological data indicate a spatial and temporal link between the Sisters shear zone, initial sedimentation within the offshore Great South Basin, extension of the Campbell Plateau, and initiation of the Pacific-Antarctic spreading ridge.

  19. The TIPA shear zone (NW-Argentina): Evidence for early devonian movement verified by Sm-Nd dating of garnet and whole rock systems

    International Nuclear Information System (INIS)

    Hockenreiner, M.; Sollner, F.; Miller, H

    2001-01-01

    The Sierra de Copacabana (Catamarca province, NW Argentina) hosts in its northernmost part a large shear zone, which can be traced back to the north into the Sa. de Fiambala and to the south at least into the Sa. de Velasco. Timing of mylonitization is an important puzzle-piece in order to understand Paleozoic geotectonic processes on the western border of Gondwana (au)

  20. Quantification of Fault-Zone Plasticity Effects with Spontaneous Rupture Simulations

    Science.gov (United States)

    Roten, D.; Olsen, K. B.; Day, S. M.; Cui, Y.

    2017-09-01

    Previous studies have shown that plastic yielding in crustal rocks in the fault zone may impose a physical limit to extreme ground motions. We explore the effects of fault-zone non-linearity on peak ground velocities (PGVs) by simulating a suite of surface-rupturing strike-slip earthquakes in a medium governed by Drucker-Prager plasticity using the AWP-ODC finite-difference code. Our simulations cover magnitudes ranging from 6.5 to 8.0, three different rock strength models, and average stress drops of 3.5 and 7.0 MPa, with a maximum frequency of 1 Hz and a minimum shear-wave velocity of 500 m/s. Friction angles and cohesions in our rock models are based on strength criteria which are frequently used for fractured rock masses in civil and mining engineering. For an average stress drop of 3.5 MPa, plastic yielding reduces near-fault PGVs by 15-30% in pre-fractured, low strength rock, but less than 1% in massive, high-quality rock. These reductions are almost insensitive to magnitude. If the stress drop is doubled, plasticity reduces near-fault PGVs by 38-45% and 5-15% in rocks of low and high strength, respectively. Because non-linearity reduces slip rates and static slip near the surface, plasticity acts in addition to, and may partially be emulated by, a shallow velocity-strengthening layer. The effects of plasticity are exacerbated if a fault damage zone with reduced shear-wave velocities and reduced rock strength is present. In the linear case, fault-zone trapped waves result in higher near-surface peak slip rates and ground velocities compared to simulations without a low-velocity zone. These amplifications are balanced out by fault-zone plasticity if rocks in the damage zone exhibit low-to-moderate strength throughout the depth extent of the low-velocity zone (˜5 km). We also perform dynamic non-linear simulations of a high stress drop (8 MPa) M 7.8 earthquake rupturing the southern San Andreas fault along 250 km from Indio to Lake Hughes. Non-linearity in the

  1. A micro-kinematic framework for vorticity analysis in polyphase shear zones using integrated field, microstructural and crystallographic orientation-dispersion methods

    Science.gov (United States)

    Kruckenberg, S. C.; Michels, Z. D.; Parsons, M. M.

    2017-12-01

    We present results from integrated field, microstructural and textural analysis in the Burlington mylonite zone (BMZ) of eastern Massachusetts to establish a unified micro-kinematic framework for vorticity analysis in polyphase shear zones. Specifically, we define the vorticity-normal surface based on lattice-scale rotation axes calculated from electron backscatter diffraction data using orientation statistics. In doing so, we objectively identify a suitable reference frame for rigid grain methods of vorticity analysis that can be used in concert with textural studies to constrain field- to plate-scale deformation geometries without assumptions that may bias tectonic interpretations, such as relationships between kinematic axes and fabric forming elements or the nature of the deforming zone (e.g., monoclinic vs. triclinic shear zones). Rocks within the BMZ comprise a heterogeneous mix of quartzofeldspathic ± hornblende-bearing mylonitic gneisses and quartzites. Vorticity axes inferred from lattice rotations lie within the plane of mylonitic foliation perpendicular to lineation - a pattern consistent with monoclinic deformation geometries involving simple shear and/or wrench-dominated transpression. The kinematic vorticity number (Wk) is calculated using Rigid Grain Net analysis and ranges from 0.25-0.55, indicating dominant general shear. Using the calculated Wk values and the dominant geographic fabric orientation, we constrain the angle of paleotectonic convergence between the Nashoba and Avalon terranes to 56-75º with the convergence vector trending 142-160° and plunging 3-10°. Application of the quartz recrystallized grain size piezometer suggests differential stresses in the BMZ mylonites ranging from 44 to 92 MPa; quartz CPO patterns are consistent with deformation at greenschist- to amphibolite-facies conditions. We conclude that crustal strain localization in the BMZ involved a combination of pure and simple shear in a sinistral reverse transpressional

  2. Rb-Sr dating of strain-induced mineral growth in two ductile shear zones in the western gneiss region of Nord-Troendelag, Central Norway

    International Nuclear Information System (INIS)

    Piasecki, M.A.; Cliff, R.A.

    1988-01-01

    In the Bjugn district of the northern part of the Western Gneiss Region, Nord-Troendelag, a basement gneiss-cover nappe boundary is marked by a thick zone of ductile shearing. In this zone a layer-parallel mylonitic fabric with related new mineral growth overprints and retrogresses a previous fabric associated with a granulite facies mineral assemblage. Related minor shear belts contain abundant new minerals and vein systems, including pegmatites, believed to represent strain-induced products formed at the time of the shearing movements. Central parts of two large muscovite books from such a pegmatite yielded Rb-Sr, Early to Middle Devonian ages of 389±6 Ma and 386±6 Ma, interpreted as indicating the approximate time of pegmatite formation and of the shearing. Small, matrix-size muscovite and biotite grains from the host mylonite gave ages of 378±6 Ma and 365±5 Ma, respectively, supposed to relate to post-shearing uplift and cooling

  3. Quartz grainsize evolution during dynamic recrystallization across a natural shear zone boundary

    Science.gov (United States)

    Xia, Haoran; Platt, John P.

    2018-04-01

    Although it is widely accepted that grainsize reduction by dynamic recrystallization can lead to strain localization, the details of the grainsize evolution during dynamic recrystallization remain unclear. We investigated the bulge size and grainsizes of quartz at approximately the initiation and the completion stages of bulging recrystallization across the upper boundary of a 500 m thick mylonite zone above the Vincent fault in the San Gabriel Mountains, southern California. Within uncertainty, the average bulge size of quartz, 4.7 ± 1.5 μm, is the same as the recrystallized grainsize, 4.5 ± 1.5 μm, at the incipient stage of dynamic recrystallization, and also the same within uncertainties as the recrystallized grainsize when dynamic recrystallization is largely complete, 4.7 ± 1.3 μm. These observations indicate that the recrystallized grainsize is controlled by the nucleation process and does not change afterwards. It is also consistent with the experimental finding that the quartz recrystallized grainsize paleopiezometer is independent of temperature.

  4. Uraninite, Coffinite and Brannerite from Shear-Zone Hosted Uranium Deposits of the Bohemian Massif (Central European Variscan Belt

    Directory of Open Access Journals (Sweden)

    Miloš René

    2017-03-01

    Full Text Available New mineralogical data are presented for shear-zone hosted uranium mineralisation from selected uranium deposits that occur in the Bohemian Massif. The uranium mineralisation is in high-grade metamorphic rocks of the Moldanubian Zone and/or in granitic rocks of the Moldanubian batholith and Bor pluton as complex uraninite–coffinite and uraninite–coffinite–brannerite assemblages. For analysed coffinites and brannerites, anomalous enrichment of Y (up to 3.4 wt % Y2O3 and Zr (up to 13.8 wt % ZrO2 is significant. The microprobe data indicate that coffinites from the Rožná and Okrouhlá Radouň uranium deposits contain variable PbO (0–4.3 wt %, FeO (0–2.5 wt %, Al2O3 (0–3.5 wt %, P2O5 (0–1.8 wt %, and CaO (0.7–3.5 wt %. Brannerite is present in unaltered and altered grains with variable concentrations of U4+ (0–0.5 apfu, U6+ (0.06–0.49 apfu, Ti (0.90–2.63 apfu, Ca (0.09–0.41 apfu, and low concentrations of Al (0–0.19 apfu, Th (0–0.04 apfu, Y (0–0.08 apfu, Zr (0–0.13 apfu and REE (0–0.14 apfu.

  5. Core Description and Characteristics of Fault Zones from Hole-A of the Taiwan Chelungpu-Fault Drilling Project

    Directory of Open Access Journals (Sweden)

    En-Chao Yeh

    2007-01-01

    Full Text Available Taiwan Chelungpu-fault Drilling Project was conducted in drill site Dakeng, Taichung City of central western Taiwan during 2004 - 2005 principally to investigate the rupture mechanism in the northern segment of the Chi-Chi earthquake of 21 September 1999, and also to examine regional stratigraphy and tectonics. Core examination (500 - 1800 m of Hole-A gave profound results aiding in illustrating the lithologic column, deformation structure, and architectural pattern of fault zones along the borehole. Lithology column of Hole-A was identified downward as the Cholan Formation (500 - 1027 m, Chinshui Shale (1027 - 1268 m, Kueichulin Formation (1268 - 1712 m, and back to the Cholan Formation (1712 - 2003 m again. A dramatic change is observed regarding sedimentation age and deformation structure around 1712 m. Along the core, most bedding dips _ _ Around 1785 m, bedding dip jumps up to _ the bottom of borehole. Five structure groups of different orientations (dip direction/dip are observed throughout the core. Based on the orientation and sense of shear, they are categorized as thrust (105/30, left-lateral fault (015/30 - 80, right-lateral fault (195/30 - 80, normal fault (105/5 - 10, and backthrust (285/40 - 50. Ten fault zones have been recognized between 500 and 2003 m. We interpret the fault zone located at around 1111 m as being the most likely candidate for rupture deformation during Chi-Chi earthquake. The fault zone seated around 1712 m is recognized as the Sanyi fault zone which is 600 m beneath the Chelungpu fault zone. Ten fault zones including thrust faults, strike-slip faults and backthrust are classified as the Chelungpu Fault System (1500 m. According to the deformation textures within fault zones, the fault zones can be categorized as three types of deformation: distinct fracture deformation, clayey-gouge deformation, and soft-rock deformation. Fracture deformation is dominant within the Chelungpu Fault System and abother two

  6. Geochemical significance of neoproterozoic rasimalai alkali syenite emplaced along Dharmapuri shear zone in the Northern part of Tamil Nadu

    International Nuclear Information System (INIS)

    Thangavel, S.; Balasubramani, S.; Nagaraju, M.; Bhattacharya, D.; Zakaulla, Syed; Rai, A.K.

    2015-01-01

    The Rasimalai alkali syenite complex is emplaced within Peninsular Gneissic complex and spatially associated with NE-SW trending major Dharmapuri shear zone (DSZ) in the northern part of Tamil Nadu. It is surrounded by epidote hornblend egneiss, which is the fenetised product of Charnockite and occurs about 20 km NE of Alangayam in Vellore district. It is mainly comprised of medium to coarse grained grey syenite (albite and orthoclase) and medium to micro grained pink syenite (orthoclase, microcline and perthite) at places porphyritic in nature with hornblende, riebeckitc, aegirine and acmite as accessory minerals. Grey syenite is non radioactive and uranium mineralisation is associated with pink syenite (syngenetic and disseminated type) and quartz-barite veins (hydrothermal type). Hydrothermal activity is manifested in the form of pyrite, chalcopyrite, galena, barite, calcite and calcian-strontianite which occur in the form of disseminations, stringers, lumps, aggregates, veinlets and veins. Presence of high silica (63.14-75.43%) with high field strength elements (U, Th, Nb and Pb) and large ion lithophile elements (Rb, Sr, K, Ba) possibly indicates that Rasimalai alkali syenite is the product of crustal communication and partial melting of protracted emplacement of parental alkali basaltic magma

  7. C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit

    Science.gov (United States)

    Martz, Pierre; Cathelineau, Michel; Mercadier, Julien; Boiron, Marie-Christine; Jaguin, Justine; Tarantola, Alexandre; Demacon, Mickael; Gerbeaud, Olivier; Quirt, David; Doney, Amber; Ledru, Patrick

    2017-12-01

    Graphitic shear zones are spatially associated with unconformity-related uranium deposits that are located around the unconformity between the strata of the Paleo- to Mesoproterozoic Athabasca Basin (Saskatchewan, Canada) and its underlying Archean to Paleoproterozoic basement. The present study focuses on basement-hosted ductile-brittle graphitic shear zones near the Cigar Lake U deposit, one of the largest unconformity-related U deposits. The goal of the study is to decipher the pre-Athabasca Basin fluid migration history recorded within such structures and its potential role on the formation of such exceptional deposit. Dominantly C-O-H(-N) metamorphic fluids have been trapped in Fluid Inclusion Planes (FIPs) in magmatic quartz within ductile-brittle graphitic shear zones active during retrograde metamorphism associated with the formation of the Wollaston-Mudjatik Transition Zone (WMTZ) between ca. 1805 and 1720 Ma. Such fluids show a compositional evolution along the retrograde path, from a dense and pure CO2 fluid during the earliest stages, through a lower density CO2 ± CH4-N2 (± H2O) fluid and, finally, to a very low density CH4-N2 fluid. Statistical study of the orientation, distribution, proportion, and chemical characterization of the FIPs shows that: i) CO2 (δ13CCO2 around - 9‰ PDB) from decarbonation reactions and/or partial water-metamorphic graphite equilibrium initially migrated regionally and pervasively under lithostatic conditions at about 500 to 800 °C and 150 to 300 MPa. Such P-T conditions attest to a high geothermal gradient of around 60 to 90 °C/km, probably related to rapid exhumation of the basement or a large-scale heat source. ii) Later brittle reactivation of the shear zone at around 450 °C and 25-50 MPa favored circulation of CO2-CH4-N2(± H2O) fluids in equilibrium with metamorphic graphite (δ13CCO2 around - 14‰) under hydrostatic conditions and only within the shear zones. Cooling of these fluids and the water uptake linked

  8. Constraints on strain rate and fabric partitioning in ductilely deformed black quartzites (Badajoz-Córdoba Shear Zone, Iberian Massif)

    Science.gov (United States)

    Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio

    2013-04-01

    The Badajoz-Córdoba Shear Zone is a is 30-40 km wide and 400 km long, NW-SE trending structure located at the boundary between the Ossa-Morena and Central-Iberian Zones of the Iberian Massif. Two elongated domains can be differentiated inside: the Obejo-Valsequillo domain to the NE and the Ductile Shear Belt (DSB) to the SW. The former exhibits Precambrian to Cambrian volcano-sedimentary rocks unconformably overlaying a Neoproterozoic basement formed by the "Serie Negra". The latter, 5-15 km wide, is composed mainly of metamorphic tectonites including the "Serie Negra" and other units located structurally under it. The petrofabric of "Serie Negra" black quartzites from the DSB is analyzed in this study with the Electron Back-Scattered Diffraction technique (EBSD). Black quartzites represent originally siliceous, chemical-biochemical shallow-water marine deposits, currently composed almost exclusively of quartz and graphite. Macroscopically they exhibit an outstanding planolinear tectonic fabric. Petrographically, coarse- and fine-grained dynamically recrystallized quartz bands alternate. The former contain quartz grains with irregular shapes, mica inclusions and "pinning" grain boundaries. Oriented mica grains and graphite particles constrain irregular quartz grain shapes. Quartz ribbons with chessboard microstructures also occur, indicating recrystallization under elevated temperatures coeval with extreme stretching. Fine-grained recrystallized quartz bands are dominated by quartz grains with straight boundaries, triple junctions, a scarcer evidence of bulging, and a higher concentration of dispersed, minute graphite grains. Quartz lattice-preferred orientation (LPO) patterns permit to identify two well-developed maxima for [c] axes: one close to the Y structural direction and the other one around Z, and -axes girdles normal to Y and Z. Although both [c] axis maxima appear in the coarse- and fine-grained bands, subsets can be isolated with grain cluster

  9. Stratigraphy, palynology and organic geochemistry of the Devonian-Mississippian metasedimentary Albergaria-a-Velha Unit (Porto-Tomar shear zone, W Portugal)

    Czech Academy of Sciences Publication Activity Database

    Machado, G.; Franců, E.; Vavrdová, Milada; Flores, D.; Fonseca, P. E.; Rocha, F.; Gama Pereira, L. C.; Gomes, A.; Fonseca, M.; Chaminé, H. I.

    2011-01-01

    Roč. 55, č. 2 (2011), s. 139-164 ISSN 1641-7291. [International Palynological Conference of the International Commission of the Paleozoic Microflora (CIMP). Warsaw-Kielce, 13.09.2010-19.09.2010] Institutional research plan: CEZ:AV0Z30130516 Keywords : Mississippian * Late Devonian * Ossa-Morena Zone * Porto-Tomar shear zone * palynology * organic geochemistry * turbidite systems * provenance * phytoplankton Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.844, year: 2011 http://gq.pgi.gov.pl/gq/article/viewFile/7606/pdf_4

  10. Slip rate of the Calico fault: Implications for geologic versus geodetic rate discrepancy in the Eastern California Shear Zone

    Science.gov (United States)

    Oskin, Michael; Perg, Lesley; Blumentritt, Dylan; Mukhopadhyay, Sujoy; Iriondo, Alexander

    2007-03-01

    Long-term (105 years) fault slip rates test the scale of discrepancy between infrequent paleoseismicity and relatively rapid geodetic rates of dextral shear in the Eastern California Shear Zone (ECSZ). The Calico fault is one of a family of dextral faults that traverse the Mojave Desert portion of the ECSZ. Its slip rate is determined from matching and dating incised Pleistocene alluvial fan deposits and surfaces displaced by fault slip. A high-resolution topographic base acquired via airborne laser swath mapping aids in identification and mapping of deformed geomorphic features. The oldest geomorphically preserved alluvial fan, unit B, is displaced 900 ± 200 m from its source at Sheep Springs Wash in the northern Rodman Mountains. This fan deposit contains the first preserved occurrence of basalt clasts derived from the Pipkin lava field and overlies Quaternary conglomerate deposits lacking these clasts. The 40Ar/39Ar dating of two flows from this field yields consistent ages of 770 ± 40 ka and 735 ± 9 ka. An age of 650 ± 100 ka is assigned to this fan deposit based on these ages and on the oldest cosmogenic 3He exposure date of 653 ± 20 ka on a basalt boulder from the surface of unit B. This assigned age and offset together yield a mid-Pleistocene to present average slip rate of 1.4 ± 0.4 mm/yr. A younger fan surface, unit K, records 100 ± 10 m of dextral displacement and preserves original depositional morphology of its surface. Granitic boulders and pavement samples from this surface yield an average age of 56.4 ± 7.7 ka after taking into account minimal cosmogenic inheritance of granitic clasts. The displaced and dated K fans yield a slip rate of 1.8 ± 0.3 mm/yr. Distributed deformation of the region surrounding the fault trace, if active, could increase the overall displacement rate to 2.1 ± 0.5 mm/yr. Acceleration of slip rate from an average of 1.4 mm/yr prior to ˜50 ka to 1.8 mm/yr since ˜50 ka is possible, though a single time-averaged slip

  11. crustal shear zone

    Indian Academy of Sciences (India)

    area of Delhi Fold Belt, Rajasthan, are characterised by foliation parallel alternate bands of amphibole- ... Kajalbas, the present study area (lat: 25. ◦. 38 ... (b). Stereographic plot showing the π girdle of calc-silicate foliation (n = 56) contoured at intervals of 3%, 6%, 12% and 24%. (in increasing shades of grey; max 27.78%).

  12. crustal shear zone

    Indian Academy of Sciences (India)

    significant mass transfer of rock-forming elements. (Fyfe et al. 1978 ... flow of these elements may control the metamor- phic reactions which in ..... Planet. Sci. Lett. 236 524–541. Etheridge M A, Wall V J and Vernon R H 1983 The role of the fluid phase during regional metamorphism and deformation; J. Metamorph. Geol.

  13. Preliminary results on the tectonic activity of the Ovacık Fault (Malatya-Ovacık Fault Zone, Turkey): Implications of the morphometric analyses

    Science.gov (United States)

    Yazıcı, Müge; Zabci, Cengiz; Sançar, Taylan; Sunal, Gürsel; Natalin, Boris A.

    2016-04-01

    The Anatolian 'plate' is being extruded westward relative to the Eurasia along two major tectonic structures, the North Anatolian and the East Anatolian shear zones, respectively making its northern and eastern boundaries. Although the main deformation is localized along these two structures, there is remarkable intra-plate deformation within Anatolia, especially which are characterized by NE-striking sinistral and NW-striking dextral strike-slip faults (Şengör et al. 1985). The Malatya-Ovacık Fault Zone (MOFZ) and its northeastern member, the Ovacık Fault (OF), is a one of the NE-striking sinistral strike slip faults in the central 'ova' neotectonic province of Anatolia, located close to its eastern boundary. Although this fault zone is claimed to be an inactive structure in some studies, the recent GPS measurements (Aktuǧ et al., 2013) and microseismic activity (AFAD, 2013) strongly suggest the opposite. In order to understand rates and patterns of vertical ground motions along the OF, we studied the certain morphometric analyses such as hypsometric curves and integrals, longitudinal channel profiles, and asymmetry of drainage basins. The Karasu (Euphrates) and Munzur rivers form the main drainage systems of the study area. We extracted all drainage network from SRTM-based Digital Elevation Model with 30 m ground pixel resolution and totally identified 40 sub-drainage basins, which are inhomogeneously distributed to the north and to the south of the OF. Most of these basins show strong asymmetry, which are mainly tilted to SW. The asymmetry relatively decreases from NE to SW in general. The only exception is at the margins of the Ovacık Basin (OB), where almost the highest asymmetry values were calculated. On the other hand, the characteristics of hypsometric curves and the calculated hypsometric integrals do not show the similar systematic spatial pattern. The hypsometric curves with convex-shaped geometry, naturally indicating relatively young morphology

  14. Reply to discussion by M. C. Alçiçek et al. on ;Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey;, Journal of African Earth Sciences, 118, 137-148, by R. Aksoy and S. Aksarı

    Science.gov (United States)

    Aksoy, Rahmi; Aksarı, Süleyman

    2017-10-01

    In their discussion on the Aksoy and Aksarı (2016) article, Alçiçek et al. (2017) claim that our stratigraphic interpretation, age assignment for the rock units and kinematic analysis depended on incorrect data. They also claim that there is no evidence for a NE-trending fault zone (Fethiye-Burdur Fault Zone) from Fethiye to Burdur with left-lateral strike-slip movement. Our opposing views on the above-mentioned issues are given below.

  15. Microstructures and magnetic fabrics of the Ngaoundéré granite pluton (Cameroon): Implications to the late-Pan-African evolution of Central Cameroon Shear Zone

    Science.gov (United States)

    Dawaï, Daouda; Tchameni, Rigobert; Bascou, Jérome; Awe Wangmene, Salomon; Fosso Tchunte, Périclex Martial; Bouchez, Jean-Luc

    2017-05-01

    The Ngaoundéré granite pluton, in Central-North Cameroon, located near the Central Cameroon Shear zone (CCSZ), and previously studied for its petrography and geochemistry, is characterized by the absence of macroscopic markers of deformation. In this study, we report microstructures and magnetic fabrics (AMS) of this pluton and discuss the relationship with the Pan-African evolution of the CCSZ. The pluton consists of a porphyritic Hbl-Bt-monzogranite at its rim and a porphyritic biotite-granite at its core, a petrographic distribution denoting a normal zoning pattern, i.e. more silicic toward the centre. As expected, magnetic susceptibilities values also exhibit a zoning pattern in agreement with petrographic zonation. Thermomagnetic data indicate that this pluton is dominantly ferromagnetic in behaviour. As indicated by its microstructures, the pluton has suffered a continuum of deformation from the magmatic state to the high temperature solid-state during magma crystallization and solidification. The magnetic foliations dominantly strike NE-SW and dip moderately to steeply and the lineations mostly plunge shallowly to the NE or SW, roughly parallel to NE-to ENE-trending Central Cameroun Shear Zone (CCSZ). The foliation poles define a girdle pattern with a zone axis (52°/11°) rather close to the best line of the lineations (44°/21°). These fabrics correlate with the structures of the country rocks ascribed by several workers to a regional transpression. Toward the margins of the pluton, particularly the northern one, the lineations tend to rotate from NE to N in azimuth. This change is interpreted as due to strain partitioning, simple shearing with NE-SW extension being relayed by compression toward the northern pluton border. This new magnetic fabric study suggests that the Ngaoundéré pluton (poorly dated at c. 575 Ma) was emplaced during the late stages of the CCSZ dextral transpressive movement. It also provides some more constraints on the correlation

  16. Bauxite to eclogite: Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam

    Science.gov (United States)

    Nakano, Nobuhiko; Osanai, Yasuhito; Nam, Nguyen Van; Tri, Tran Van

    2018-03-01

    We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure-temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3-50.9 wt%), TiO2, and total Fe2O3, and poor in SiO2 (7.9-24.1 wt%), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00 ± 0.06, 1.07 ± 0.04, 1.09 ± 0.03, 0.29 ± 0.07, and 1.15 ± 0.05 g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism ( 2.5 GPa at 650 °C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U-Pb ages from 265 to 36 Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257 ± 8 Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia

  17. The nature of the Ailao Shan-Red River (ASRR) shear zone: Constraints from structural, microstructural and fabric analyses of metamorphic rocks from the Diancang Shan, Ailao Shan and Day Nui Con Voi massifs

    Science.gov (United States)

    Liu, Junlai; Tang, Yuan; Tran, My-Dung; Cao, Shuyun; Zhao, Li; Zhang, Zhaochong; Zhao, Zhidan; Chen, Wen

    2012-03-01

    The structural geology, timing of shearing, and tectonic implications of the ASRR shear zone, one of the most striking lineaments in Southeast Asia, have been the topics of extensive studies over the past few decades. The Xuelong Shan (XLS), Diancang Shan (DCS), Ailao Shan (ALS) and Day Nui Con Voi (DNCV) metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution. Our field structural analysis, detailed microstructural and fabric analysis, as well as the quartz, sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during Cenozoic tectonic evolution in the shear zone. Among the contrasting structural and microstructural associations in the shear zone, D2 structures, which were formed at the brittle to ductile transition during large-scale left-lateral shearing in the second deformation episode, predominate over the structural styles of the other two deformation episodes. Discrete micro-shear zones with intensive grain size reduction compose the characteristic structural style of D2 deformation. In addition, several types of folds (early shearing folds, F21, and late-shearing folds, F22) were formed in the sheared rocks, including discrete to distributed mylonitic foliation, stretching lineation and shear fabrics (e.g., mica fish, domino structures, as well as sigma and delta fabrics). A sequence of microstructures from syn-kinematic magmatic flow, high-temperature solid-state deformation, to brittle-ductile shearing is well-preserved in the syn-kinematic leucocratic intrusions. Deformation structures from the first episode (D1) are characterized by F1 folds and distributed foliations (S1) in rocks due to pure shearing at high temperatures. They are preserved in weakly sheared (D2) rocks along the eastern margin of the ALS belt or in certain low-strain tectonic enclaves within the shear zone. Furthermore, semi

  18. Static and dynamic experimental study of strengthened reinforced short concrete corbel by using carbon fabrics, crack path in shear zone

    Directory of Open Access Journals (Sweden)

    I. Ivanova

    2015-10-01

    Full Text Available The paper presents an experimental analysis of tracking the path of the cracks and crack growth in strengthened or repair reinforced concrete short corbels bonded by carbon fiber fabrics under static and dynamic loads. The reinforced short concrete corbel is a used precast element, for industrial buildings and structures. In fact, their functioning interestingly unconventional is compared to classical beam type elements. Then the effects of bending and shearing are combined in this case. The horizontal reinforced steel is localized to resist to tensile strength induced in bending top and a transversal strength-absorbing contribution. The introduction of carbon fiber composite in the field of Civil Engineering allows to strengthen or repair reinforced concrete structures using adhesive. So the carbon fiber material has many advantages as its low weight, flexibility, easier handling and also interesting physicochemical properties. However maintenance of civil engineering works is to protect them by ensuring better sealing or limiting corrosion. Then strengthening is to repair structures by using bonding technique to compensate their rigidity loss and limit the cracking. This allows to improve their performance and durability. Bonding of composite material in tensile zone of corbel retrieves most tensile stress and allows the structure to extend their load-bearing capacity. The local behavior of the structure is measured by means of the extensometer technique based on electrical strain gauges. This technique allowed to measure strains of steel, carbon fiber fabrics and concrete. The results of this investigation showed that strengthened reinforced concrete corbel bonded by carbon fiber fabrics can improve the ultimate load to twice and stiffens less than a third. The ultimate load, strain and displacement of the specimen are compared to reference experimental model of monotonic and cyclic applied loads. The success of strengthening depends strongly

  19. SPECIALIZED MAPPING OF CRUSTAL FAULT ZONES. PART 1: BASIC THEORETICAL CONCEPTS AND PRINCIPLES

    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky

    2014-01-01

    Full Text Available Long-term studies of shear zones have included collection of data on fractures showing no indication of displacement which are termed as 'blank' fractures. A method aimed at mapping fault structures and stress fields has been developed on the basis of results of paragenetic analysis of measurements of abundant fractures. The method is termed as 'specialized mapping', firstly, due to its specific structural goal so that to distinguish it from the conventional geological mapping of regions in nature, and, secondly, because of the specific procedure applied to refer to fractures as references to decipher fault-block patterns of natural regions. In Part 1, basic theoretical concepts and principles of specialized mapping are described. Part 2 is being prepared for publication in one of the next issues of the journal; it will cover stages of the proposed method and describe some of the cases of its application.In terms of general organizational principles, specialized mapping is similar to other methods based on structural paragenetic analysis and differs from such methods in types of paragenesises viewed as references to reveal crustal fault zones. Such paragenesises result from stage-by-stage faulting (Fig 2 and Fig. 7 during which stress fields of the 2nd order are regularly changeable within the shear zone. According to combined experimental and natural data, a complete paragenesis of fractures in the shear zone includes a major (1st order fault plane and fractures of other seven types, R, R’, n, n’, t, t’ and T (2nd order (Fig. 4 and Fig 8. At the fracture level, each of them corresponds to a paragenesis including three nearly perpendicular systems of early ruptures (Fig. 1, which are based on two classical patterns of conjugated fractures, one of which is consistent with the position of the fault plane (Fig. 3. Taking into account that strike-slip, reverse and normal faults are similar in terms of mechanics (i.e. they are formed due to

  20. Spatial evolution of Zagros collision zone in Kurdistan, NW Iran: constraints on Arabia-Eurasia oblique convergence

    Science.gov (United States)

    Sadeghi, Shahriar; Yassaghi, Ali

    2016-04-01

    Stratigraphy, detailed structural mapping and a crustal-scale cross section across the NW Zagros collision zone provide constraints on the spatial evolution of oblique convergence of the Arabian and Eurasian plates since the Late Cretaceous. The Zagros collision zone in NW Iran consists of the internal Sanandaj-Sirjan, Gaveh Rud and Ophiolite zones and the external Bisotoun, Radiolarite and High Zagros zones. The Main Zagros Thrust is the major structure of the Zagros suture zone. Two stages of oblique deformation are recognized in the external part of the NW Zagros in Iran. In the early stage, coexisting dextral strike-slip and reverse dominated domains in the Radiolarite zone developed in response to deformation partitioning due to oblique convergence. Dextral-reverse faults in the Bisotoun zone are also compatible with oblique convergence. In the late stage, deformation partitioning occurred during southeastward propagation of the Zagros orogeny towards its foreland resulting in synchronous development of orogen-parallel strike-slip and thrust faults. It is proposed that the first stage was related to Late Cretaceous oblique obduction, while the second stage resulted from Cenozoic collision. The Cenozoic orogen-parallel strike-slip component of Zagros oblique convergence is not confined to the Zagros suture zone (Main Recent Fault) but also occurred in the external part (Marekhil-Ravansar fault system). Thus, it is proposed that oblique convergence of Arabian and Eurasian plates in Zagros collision zone initiated with oblique obduction in the Late Cretaceous followed by oblique collision in the late Tertiary, consistent with global plate reconstructions.

  1. Infiltration of meteoric fluids in an extensional detachment shear zone (Kettle dome, WA, USA): How quartz dynamic recrystallization relates to fluid-rock interaction

    Science.gov (United States)

    Quilichini, Antoine; Siebenaller, Luc; Nachlas, William O.; Teyssier, Christian; Vennemann, Torsten W.; Heizler, Matthew T.; Mulch, Andreas

    2015-02-01

    We document the interplay between meteoric fluid flow and deformation processes in quartzite-dominated lithologies within a ductile shear zone in the footwall of a Cordilleran extensional fault (Kettle detachment system, Washington, USA). Across 150 m of shear zone section, hydrogen isotope ratios (δD) from synkinematic muscovite fish are constant (δD ˜ -130‰) and consistent with a meteoric fluid source. Quartz-muscovite oxygen isotope thermometry indicates equilibrium fractionation temperatures of ˜365 ± 30 °C in the lower part of the section, where grain-scale quartz deformation was dominated by grain boundary migration recrystallization. In the upper part of the section, muscovite shows increasing intragrain compositional zoning, and quartz microstructures reflect bulging recrystallization, solution-precipitation, and microcracking that developed during progressive cooling and exhumation. The preserved microstructural characteristics and hydrogen isotope fingerprints of meteoric fluids developed over a short time interval as indicated by consistent mica 40Ar/39Ar ages ranging between 51 and 50 Ma over the entire section. Pervasive fluid flow became increasingly channelized during detachment activity, leading to microstructural heterogeneity and large shifts in quartz δ18O values on a meter scale. Ductile deformation ended when brittle motion on the detachment fault rapidly exhumed the mylonitic footwall.

  2. Deformation characterization of a regional thrust zone in the northern Rif (Chefchaouen, Morocco)

    Science.gov (United States)

    Vitale, Stefano; Zaghloul, Mohamed Najib; Tramparulo, Francesco D.'Assisi; El Ouaragli, Bilal

    2014-07-01

    This paper provides the structural analysis of the Chefchaouen area in the northern Rif. Here the Dorsale Calcaire superposes, by means of an excellently exposed thrust fault, onto the Predorsalian succession in turn tectonically covering the Massylian Unit. Hanging wall carbonates of the Dorsale Calcaire Unit form a WSW-verging regional fold with several parasitic structures, deformed by late reverse faults in places indicating an ENE vergence. A 200 m thick shear zone characterizes the upper part of the Predorsalian succession, located at footwall of the Dorsale Calcaire Unit. Here the dominantly pelitic levels are highly deformed by (i) C‧ type shear bands indicating a mean WSW tectonic transport and (ii) conjugate extensional shear planes marking an extension both orthogonal and parallel to the shear direction. The Massylian Unit is characterized by a strain gradient increasing toward the tectonic contact with the overlying Predorsalian succession, where the dominantly pelitic levels are so highly deformed so as appearing as a broken formation. Such as the previous succession, conjugate extensional shear bands and normal faults indicate a horizontal extension parallel to the thrust front synchronous with the mainly WSW-directed overthrusting. The whole thrust sheet pile recorded a further shortening, characterized by a NW-SE direction, expressed by several reverse and thrust faults and related folds. Finally strike-slip and normal faults were the last deformation structures recorded in the analyzed rocks. A possible tectonic evolution for these successions is provided. In the late Burdigalian, the Dorsale Calcaire Unit tectonically covered the Predorsalian succession and together the Massylian Unit. The latter two successions were completely detached from their basement and accreted in the orogenic wedge within a general NE-SW shortening for the analyzed sector of the northern Rif. At lithosphere scale the thrust front migration was driven by roll back and

  3. Petrology and ⁴⁰Ar/3⁹Ar-chronology of metavolcanic rocks from the Northern Phyllite Zone (Southern Hunsrück and Taunus Mountains, Germany): insights into a late Variscan ductile shear zone.

    Science.gov (United States)

    Fladt, Matthias; Soder, Christian; Schwarz, Winfried; Trieloff, Mario

    2017-04-01

    The Northern Phyllite Zone (NPZ) is a low-grade mylonitic shear zone between the high-grade rocks of the Mid-German Crystalline Zone and the very low-grade rocks of the Rhenohercynian Zone of the Variscan orogen. The NPZ comprises low-grade metasedimentary and metavolcanic rocks. Basaltic, intermediate and rhyolitic metavolcanics from the Soonwald and the Southern Taunus Mountains show the following paragenesis: actinolite + chlorite + epidote + albite + phengite + titanite + quartz ± calcite ± stilpnomelane ± pumpellyite ± aegirine-augite; blue amphibole (winchite) + chlorite + phengite + stilpnomelane + albite + titanite + quartz + magnetite ± epidote ± hematite; quartz + albite + K-feldspar + phengite + chlorite + titanite ± stilpnomelane ± ilmenite ± magnetite ± hematite. Occasionally, relict magmatic phases are present. The foliation strikes SW-NE and dips 60-70° to the NW. Stretching lineations are subhorizontal. P-T-estimations were done on the basis of equilibrium assemblage modelling yielding peak metamorphic conditions of 300-350 °C and 6-6.5 kbar. Thus, burial depths of 20-22 km and a low geothermal gradient of 15-16 °C/km are inferred. ⁴⁰Ar/3⁹Ar-dating of stepwise heated phengite separates (100-200 µm) results in plateau ages of ˜320 Ma. Two of the examined separates show argon diffusive loss ⁴⁰Ar/3⁹Ar-age spectra, which yield a period of argon loss between 145 and 130 Ma. Diffusive argon loss is possibly related to widespread Jurassic-Cretaceous hydrothermal activity in SW Germany. We interpret the Northern Phyllite Zone as a sinistral shear zone documenting prolonged oblique convergence following the peak of the Variscan orogeny between 340-330 Ma until 320 Ma.

  4. Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments

    Science.gov (United States)

    Alonso-Henar, Jorge; Schreurs, Guido; Martinez-Díaz, José Jesús; Álvarez-Gómez, José Antonio; Villamor, Pilar

    2015-01-01

    The El Salvador Fault Zone (ESFZ) is an active, approximately 150 km long and 20 km wide, segmented, dextral strike-slip fault zone within the Central American Volcanic Arc striking N100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Structural field data and mapping suggest a phase of extension, at some stage during the evolution of the ESFZ. This phase would explain dip-slip movements on structures that are currently associated with the active, dominantly strike slip and that do not fit with the current tectonic regime. Field observations suggest trenchward migration of the arc. Such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the Cocos plate beneath the Chortis Block during the Miocene/Pliocene. We carried out 4-D analog model experiments to test whether an early phase of extension is required to form the present-day fault pattern in the ESFZ. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures. This extensional phase is followed by a strike-slip dominated regime, which results in intersegment areas with local transtension and segments with almost pure strike-slip motion. The results of our experiments combined with field data along the Central American Volcanic Arc indicate that the slab rollback intensity beneath the Chortis Block is greater in Nicaragua and decreases westward to Guatemala.

  5. In-situ tracer tests and models developed to understand flow paths in a shear zone at the Grimsel Test Site, Switzerland

    Science.gov (United States)

    Blechschmidt, I.; Martin, A. J.

    2012-12-01

    The Grimsel Test Site (www.grimsel.com) is an international underground research laboratory excavated at a depth of 450m below the surface in the crystalline Aare Massif of southern Switzerland in 1984. It is operated and owned by the National Cooperative for the Disposal of Radioactive Waste of Switzerland (NAGRA) which is the organization responsible for managing and researching the geological disposal of all types of radioactive wastes originating in Switzerland. One experiment, the Colloid Formation and Migration test (CFM*), is an ongoing in-situ migration test started in 2004 to study colloid facilitated transport behavior of radionuclides through a shear zone. The importance of colloid transport in the context of a radioactive waste repository is that it provides a mechanism for potentially enhancing the advective transport of radionuclides. The montmorillonite clays that are planned to be used as an engineered barrier around the radioactive waste in many repository concepts may be a source of such colloids under specific hydraulic and/or chemical boundary conditions. The CFM project includes an integrated programme of field testing, laboratory studies and modelling/interpretation. The field tests are performed in a shear zone where the natural outflow has been controlled by a tunnel packer system and flow is monitored with an array of boreholes drilled for CFM and previous experiments at the site. The flow field is controlled by a low-rate extraction from a surface packer. The controlled low-rate extraction creates a region of low hydraulic gradients and fluid velocity within the shear zone, suitable for study under repository-relevant or other geo-resource relevant conditions. Here we present a summary of the migration tracer tests carried out so far to understand the hydraulic properties and transport characteristics of the shear zone using both stable and radioactive (Na-22, Cs-137, Ba-133, Th-232, Np-237, Am-243, Pu-242) tracers as well as colloids, and

  6. An exceptionally long paleoseismic record of a slow-moving fault: The Alhama de Murcia fault (Eastern Betic shear zone, Spain)

    DEFF Research Database (Denmark)

    Ortuño, María.; Masana, Eulalia.; García-Meléndez, Eduardo.

    2012-01-01

    for the southern tip of the Alhama de Murcia fault (Eastern Betic shear zone), which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity. At its tip, the fault divides into a splay with two main faults bounding the Góñar fault system. At this area...... and the application of an improved protocol for the infrared stimulated luminescence (IRSL) dating of K-feldspar allowed us to constrain a paleoseismic record as old as 325 ka. We identified a minimum of six possible paleo of Mw = 6–7 and a maximum mean recurrence interval of 29 k.y. This provides compelling evidence...

  7. Three Types of Flower Structures in a Divergent-Wrench Fault Zone

    Science.gov (United States)

    Huang, Lei; Liu, Chi-yang

    2017-12-01

    Flower structures are typical features of wrench fault zones. In conventional studies, two distinct kinds of flower structures have been identified based on differences in their internal structural architecture: (1) negative flower structures characterized by synforms and normal separations and (2) positive flower structures characterized by antiforms and reverse separations. In addition to negative and positive flower structures, in this study, a third kind of flower structure was identified in a divergent-wrench fault zone, a hybrid characterized by both antiforms and normal separations. Negative flower structures widely occur in divergent-wrench fault zones, and their presence indicates the combined effects of extensional and strike-slip motion. In contrast, positive and hybrid flower structures occur only in fault restraining bends and step overs. A hybrid flower structure can be considered as product of a kind of structural deformation typical of divergent-wrench zones; it is the result of the combined effects of extensional, compressional, and strike-slip strains under a locally appropriate compressional environment. The strain situation in it represents the transition stage that in between positive and negative flower structures. Kinematic and dynamic characteristics of the hybrid flower structures indicate the salient features of structural deformation in restraining bends and step overs along divergent-wrench faults, including the coexistence of three kinds of strains (i.e., compression, extension, and strike-slip) and synchronous presence of compressional (i.e., typical fault-bend fold) and extensional (normal faults) deformation in the same place. Hybrid flower structures are also favorable for the accumulation of hydrocarbons because of their special structural configuration in divergent-wrench fault zones.

  8. Preliminary Interpretation of a Radionuclide and Colloid Tracer Test in a Granodiorite Shear Zone at the Grimsel Test Site, Switzerland

    Energy Technology Data Exchange (ETDEWEB)

    Reimus, Paul W. [Los Alamos National Laboratory

    2012-08-30

    In February and March 2012, a tracer test involving the injection of a radionuclide-colloid cocktail was conducted in the MI shear zone at the Grimsel Test Site, Switzerland, as part of the Colloids Formation and Migration (CFM) project. The colloids were derived from FEBEX bentonite, which is mined in Spain and is being considered as a potential waste package backfill in a Spanish nuclear waste repository. The tracer test, designated test 12-02 (second test in 2012), involved the injection of the tracer cocktail into borehole CFM 06.002i2 and extraction from the Pinkel surface packer at the main access tunnel wall approximately 6.1 m from the injection interval. The test configuration is depicted in Figure 1. This configuration has been used in several conservative tracer tests and two colloid-homologue tracer tests since 2007, and it is will be employed in an upcoming test involving the emplacement of a radionuclide-doped bentonite plug into CFM 06.002i2 to evaluate the swelling and erosion of the bentonite and the transport of bentonite colloids and radionuclides from the source to the extraction point at the tunnel wall. Interpretive analyses of several of the previous tracer tests, from 09-01 through 12-02 were provided in two previous Used Fuel Disposition Program milestone reports (Arnold et al., 2011; Kersting et al., 2012). However, only the data for the conservative tracer Amino-G Acid was previously analyzed from test 12-02 because the other tracer data from this test were not available at the time. This report documents the first attempt to quantitatively analyze the radionuclide and colloid breakthrough curves from CFM test 12-02. This report was originally intended to also include an experimental assessment of colloid-facilitated transport of uranium by bentonite colloids in the Grimsel system, but this assessment was not conducted because it was reported by German collaborators at the Karlsruhe Institute of Technology (KIT) that neither uranium nor

  9. Metamorphic and Ar/Ar geochronology constraints on the Alakeci shear zone: Implications for the extensional exhumation history of the northern Kazdag Massif, NW Turkey

    International Nuclear Information System (INIS)

    Bonev, N; Beccaletto, L; Robyr, M; Monie, P

    2008-01-01

    The Kazdag Massif exposes a metamorphic dome in the Biga Peninsula of northwest Turkey. An extensional origin has been proposed for the dome, limited on both flanks by detachments and/or shear zones. The northern flank is bounded by the extensional Alakeci Shear Zone (ASZ), whose P-T-t path is still poorly known. We therefore focus on its metamorphic conditions and related temporal history to precise its tectono-metamorphic evolution. The local tectonostratigraphy in structurally ascending order comprises: (i) the high-grade metamorphic core rocks of the Kazdag Massif (gneisses and micaschists intercalated with amphibolites and marbles); (ii) the two kilometer-thick ASZ; (iii) the overlaying unmetamorphosed pre-Cenomanian accretionary Cetmi melange; and (iv) Neogene sedimentary and volcanic cover rocks. ASZ mylonites were derived from both the core rocks and the melange lithologies. From the north to the south the mylonitic fabrics in the ASZ depict a top-to-the N-NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdag Massif. The northward transition from ductile to brittle-ductile regime through the ASZ shows that the deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium within the mylonitic gneisses and schists contains Qtz + Fs + Ms + Bt + Grt ± St ± Sill, with late retrogressive chlorite after biotite and garnet. Four samples of ASZ rocks yielded pressures between 6.9-5.7 kbar and temperatures between 706-587 deg. C. Three samples from the mylonitic rocks supplied in situ isochron 36 Ar/ 40 Ar mica ages between 31.2-24.2 Ma, which we interpret to date the cooling of the mylonites following the P-T decrease across the ASZ. The metamorphic and structural results support the extensional character of the ASZ, and sketch transition from

  10. A new chronostratigraphy (40Ar-39Ar and U-Pb Dating) for the Middle Section of the Burdur-Fethiye Shear Zone, SW Turkey

    Science.gov (United States)

    Elitez, İrem; Yaltırak, Cenk; Sunal, Gürsel

    2017-04-01

    There are few basins containing younger rocks along the Burdur-Fethiye Shear Zone, such as the Burdur, Tefenni, Eşen and Acı göl basins. The middle section of the Burdur-Fethiye Shear Zone, where Neogene sediments predominate, includes three modern basins: the Acı payam, Çameli and Gölhisar basins. All these basins represent portions of larger carbonate lakes. A considerable number of studies suggested controversial Neogene stratigraphy of these basins and environs. In most cases, the local river and alluvial fan deposits were mapped together with the lacustrine sediments. According to most studies, the lacustrine deposits are of Pliocene age, except in small areas north and east of Acı payam Basin. Our field observations revealed two distinct young sedimentary sequences that unconformably overlies the pre-Neogene basement in the middle section of the Burdur-Fethiye Shear Zone. The first sequence begins with meandering- and braided-river sediments, which transition upward into lacustrine sediments. The uppermost part of the lacustrine sediments consists mostly of red-wine-coloured claystones and silty carbonates including caliche. This sequence is overlain by alluvial fan conglomerates, mudstones and claystones. In the northern part of Acı payam Basin at elevations of ˜1500-1600 m, the lamproites cut or overlie both fluvial conglomerates and lacustrine marls, claystones and limestones. In addition, a tuff level was found in the lacustrine sediments south-west of Çameli Basin. We provide new geochronological data from these volcanic rocks. Zircon U-Pb results from tuff level yielded age of 6.933±0.041 Ma. The lamproites are dated at 5.06±1.44, 5.69±2.34, 6.08±0.48, 6.43±0.29, 6.94±0.35, 6.98±0.31 and 6.88±0.22 Ma by 39Ar/40Ar dating method. Consequently, a Messinian age is suggested for the uppermost part of the river deposits. Field relations show that the lacustrine sediments are upper Miocene-lower Pliocene in age and the widespread exposures of

  11. Deformation assisted by fluids in quartz veins of shear zones: an example from Iron Formations of Quadrilátero Ferrífero, Brazil.

    Science.gov (United States)

    Barbosa, Paola; Lagoeiro, Leonardo

    2013-04-01

    The evidences of fluid activity in rocks are well recognized. In many cases, the fluid is responsible to remobilize many elements (e.g. Au, Mn, Si) that may be transported over a long distance and precipitated as new minerals in regions of low stress of the rock. In many deformed rocks, the origin of a large number of structures (veins, pressure shadows, dissolved grain boundaries, etc) may be correlated to the fluid activity. However, the fluids are important not only during the crack-and-seal process but also after the sealing ceases. As an example of how the fluids are responsible to rearrange the structure of the rock, we studied many quartz veins of one iron-formation from Brazil. The rocks were collected in Quadrilátero Ferrífero (QF), Brazil, that is one of the most important metalogenetic provinces in the world. It is assumed the existence of a deformational and metamorphic gradient in the rocks of QF, increasing the occurrence of penetrative structures from southwest to northeast. However, the effects of the local shear zones in the deformation pattern of QF may not be neglected. Shear zones are generally recognized as structures that accommodate deformation, eventually with intense fluid percolation. It is indubitable that there is a relationship between the fluid activity and the deformation accommodation in shear zones. So, to investigate how the fluid activity can affect the mechanisms of accommodation of deformation in rocks of shear zones from QF, we characterized the crystallographic preferred orientation (CPO) of some quartz vein by EBSD (electron backscattering diffraction). All the samples came from the same outcrop and from the same dextral shear zone, localized in the low-deformation region of QF, under greenschist metamorphic conditions. The samples were oriented according to the XYZ reference system, with X parallel to the foliation and Z normal to the XY plane. The veins are quartz-rich layers parallel to the rock foliation. They do not

  12. Evidences of Shear Deformations and Faulting on Comet 67P/ Churyumov-Gerasimenko: a Driving Force for the Mechanical Erosion of the Nucleus?

    Science.gov (United States)

    Matonti, C.; Auger, A. T.; Groussin, O.; Jorda, L.; Attree, N.; Viseur, S.; El Maarry, M. R.

    2016-12-01

    Fractures and faults are widespread and pervasive in Earth crustal and sedimentary rocks. They result from deviatoric stresses applied on brittle materials. In various contexts, their geometry often allows one to infer the direction and sometimes the magnitude of the stress that led to their formation. The Rosetta spacecraft has orbited comet 67P for two years and has acquired images of the nucleus surface with an unprecedented spatial resolution, down to 20 cm/px. These data open the way for entirely new geological interpretations of the structures observed at the surface of cometary nuclei. In this work, we focus on the structural interpretations of the meter to hectometer scale lineaments observed on the surface from the OSIRIS-NAC images. To improve interpretations, we performed the digitalization of lineaments in selected zones. In brittle material regions (essentially Atum and Khonsu), we observed structures that nicely match fault splay, duplexes blocks and anastomosing or "en-échelon" patterns. Such structures strongly suggest the occurrence of sheared zones and "strike-slip fault" arrays, which are observed here for the first time at the surface of a comet nucleus. Despite the large differences in the gravity magnitude and nucleus material strength compared to Earth, the observation of such structures seems to confirm comparable gravity to strength ratio between 67P and the Earth (Groussin et al., 2015). Most of these shear structures are sub-parallel and located inside or near the nucleus neck regions (Hapi, Sobek and Wosret), which is consistent with an increased relative shear stress at the boundary of the two lobes (Hirabayashi et al., 2016). These results emphasize mechanisms that may have important implications on the nucleus strength estimation and how it is eroded. Indeed, considering the fault propagation laws along with multiple angles views of structures, the observed faults likely propagate inside the nucleus over several tenths to hundreds of

  13. The integrated analyses of digital field mapping techniques and traditional field methods: implications from the Burdur-Fethiye Shear Zone, SW Turkey as a case-study

    Science.gov (United States)

    Elitez, İrem; Yaltırak, Cenk; Zabcı, Cengiz; Şahin, Murat

    2015-04-01

    The precise geological mapping is one of the most important issues in geological studies. Documenting the spatial distribution of geological bodies and their contacts play a crucial role on interpreting the tectonic evolution of any region. Although the traditional field techniques are still accepted to be the most fundamental tools in construction of geological maps, we suggest that the integration of digital technologies to the classical methods significantly increases the resolution and the quality of such products. We simply follow the following steps in integration of the digital data with the traditional field observations. First, we create the digital elevation model (DEM) of the region of interest by interpolating the digital contours of 1:25000 scale topographic maps to 10 m of ground pixel resolution. The non-commercial Google Earth satellite imagery and geological maps of previous studies are draped over the interpolated DEMs in the second stage. The integration of all spatial data is done by using the market leading GIS software, ESRI ArcGIS. We make the preliminary interpretation of major structures as tectonic lineaments and stratigraphic contacts. These preliminary maps are controlled and precisely coordinated during the field studies by using mobile tablets and/or phablets with GPS receivers. The same devices are also used in measuring and recording the geologic structures of the study region. Finally, all digitally collected measurements and observations are added to the GIS database and we finalise our geological map with all available information. We applied this integrated method to map the Burdur-Fethiye Shear Zone (BFSZ) in the southwest Turkey. The BFSZ is an active sinistral 60-to-90 km-wide shear zone, which prolongs about 300 km-long between Suhut-Cay in the northeast and Köyceğiz Lake-Kalkan in the southwest on land. The numerous studies suggest contradictory models not only about the evolution but also about the fault geometry of this

  14. Spatial evolution of Zagros collision zone in Kurdistan - NW Iran, constraints for Arabia-Eurasia oblique convergence

    Science.gov (United States)

    Sadeghi, S.; Yassaghi, A.

    2015-09-01

    Stratigraphy, detailed structural mapping and crustal scale cross section of the NW Zagros collision zone evolved during convergence of the Arabian and Eurasian plates were conducted to constrain the spatial evolution of the belt oblique convergence since Late Cretaceous. Zagros orogeny in NW Iran consists of the Sanandaj-Sirjan, Gaveh Rud and ophiolite zones as internal, and Bisotoun, Radiolarite and High Zagros zones as external parts. The Main Zagros Thrust is known as major structures of the Zagros suture zone. Two stages of deformation are recognized in the external parts of Zagros. In the early stage, presence of dextrally deformed domains beside the reversely deformed domains in the Radiolarite zone as well as dextral-reverse faults in both Bisotoun and Radiolarite zones demonstrates partitioning of the dextral transpression. In the late stage, southeastward propagation of the Zagros orogeny towards its foreland resulted in synchronous development of orogen-parallel strike-slip and pure thrust faults. It is proposed that the first stage related to the late Cretaceous oblique obduction, and the second stage is resulted from Cenozoic collision. Cenozoic orogen-parallel strike-slip component of Zagros oblique faulting is not confined to the Zagros suture zone (Main Recent) but also occurred in the more external part (Marekhil-Ravansar fault system). Thus, it is proposed that oblique convergence of Arabia-Eurasia plates occurred in Zagros collision zone since the Late Cretaceous.

  15. Strike slip faulting inferred from offsetting of drainages: Lower ...

    Indian Academy of Sciences (India)

    (a) Geological map of a part of lower Narmada valley showing disposition of active faults and structures (Agarwal. 1986). Red dotted box represents the area of figure 1(b). (b) Digital Elevation Model (DEM) of the part of Narmada valley showing various tectonic geomorphic features like fault scarp, palaeobank, linear valley ...

  16. Strike slip faulting inferred from offsetting of drainages: Lower ...

    Indian Academy of Sciences (India)

    The evolution of fault scarps, deformed rivers, marine terraces and the morphology of the moun- tain fronts have been studied for understanding neotectonic evolution of an area (Morisawa and. Hack 1985; Merritts and Hesterberg 1994; Keller and Printer 1996). Tricart (1974) discussed long- term effects of faulting and ...

  17. Strike slip faulting inferred from offsetting of drainages: Lower ...

    Indian Academy of Sciences (India)

    The detailed analysis of landforms,drainages and geology of the area between the rivers Amaravati and Karjan was carried out in order to understand the tectonic history of the lower Narmada basin. Movement along the various faults in the area was studied on the basis of the drainage offsetting. Horizontal offsetting of ...

  18. Complex fragmentation and silicification structures in fault zones: quartz crystallization and repeated fragmentation in the Rusey fault zone (Cornwall/UK)

    Science.gov (United States)

    Yilmaz, Tim I.; Blenkinsop, Tom; Duschl, Florian; Kruhl, Jörn H.

    2015-04-01

    Silicified fault rocks typically show structures resulting from various stages of fragmentation and quartz crystallization. Both processes interact episodically and result in complex structures on various scales, which require a wide spectrum of analysis tools. Based on field and microstructural data, the spatial-temporal connection between deformation, quartz crystallization and fluid and material flow along the Rusey fault zone was investigated. The fault can be examined in detail in three dimensions on the north Cornwall coast, UK. It occurs within Carboniferous sandstones, siltstones, mudstones and slates of the Culm basin, and is likely to have had a long history. The fault rocks described here formed during the younger events, possibly due to Tertiary strike-slip reactivation. Frequent fragmentation, flow and crystallization events and their interaction led to various generations of complex-structured quartz units, among them quartz-mantled and partly silicified wall-rock fragments, microcrystalline quartz masses of different compositions and structures, and quartz vein patterns of various ages. Lobate boundaries of quartz masses indicate viscous flow. Fragments are separated by quartz infill, which contains cm-sized open pores, in which quartz crystals have pyramidal terminations. Based on frequent occurrence of feathery textures and the infill geometry, quartz crystallization from chalcedony appears likely, and an origin from silica gel is discussed. Fragmentation structures are generally fractal. This allows differentiation between various processes, such as corrosive wear, wear abrasion and hydraulic brecciation. Material transport along the brittle shear zone, and displacement of the wall-rocks, were at least partly governed by flow of mobile fluid-quartz-particle suspensions. The complex meso- to microstructures were generated by repeated processes of fragmentation, quartz precipitation and grain growth. In general, the brittle Rusey fault zone

  19. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Pseudotachylytes, as well as the country rock, bear the evidence of conjugate strike slip shearing along NNE–SSW and NW–SE directions, suggesting an N–S compression. The Gangavalli Shear Zone represents the NNE–SSW fault of the conjugate system along which a right lateral shear has produced seismic slip motion ...

  20. Quartz preferred orientation in naturally deformed mylonitic rocks (Montalto shear zone-Italy): a comparison of results by different techniques, their advantages and limitations

    Science.gov (United States)

    Fazio, Eugenio; Punturo, Rosalda; Cirrincione, Rosolino; Kern, Hartmut; Pezzino, Antonino; Wenk, Hans-Rudolf; Goswami, Shalini; Mamtani, Manish A.

    2017-10-01

    In the geologic record, the quartz c-axis patterns are widely adopted in the investigation of crystallographic preferred orientations (CPO) of naturally deformed rocks. To this aim, in the present work, four different methods for measuring quartz c-axis orientations in naturally sheared rocks were applied and compared: the classical universal stage technique, the computer-integrated polarization microscopy method (CIP), the time-of-flight (TOF) neutron diffraction analysis , and the electron backscatter diffraction (EBSD). Microstructural analysis and CPO patterns of quartz, together with the ones obtained for feldspars and micas in mylonitic granitoid rocks, have been then considered to solve structural and geological questions related to the Montalto crustal scale shear zone (Calabria, southern Italy). Results obtained by applying the different techniques are discussed, and the advantages as well as limitations of each method are highlighted. Importantly, our findings suggest that patterns obtained by means of different techniques are quite similar. In particular, for such mylonites, a subsimple shear (40% simple shear vs 60% pure shear) by shape analysis of porphyroclasts was inferred. A general tendency of an asymmetric c-maximum near to the Z direction (normal to foliation) suggesting dominant basal slip, consistent with fabric patterns related to dynamically recrystallization under greenschist facies, is recognized. Rhombohedral slip was likely active as documented by pole figures of positive and negative rhombs (TOF), which reveal also potential mechanical Dauphiné twinning. Results showed that the most complete CPO characterization on deformed rocks is given by the TOF (from which also other quartz crystallographic axes can be obtained as well as various mineral phases may be investigated). However, this use is restricted by the fact that (a) there are very few TOF facilities around the world and (b) there is loss of any domainal reference, since TOF is a

  1. Evolution of Brasiliano-age granitoid types in a shear-zone environment, Umarizal-Caraubas region, Rio Grande do Norte, northeast Brazil

    Science.gov (United States)

    Galindo, A. C.; Dall'Agnol, R.; McReath, I.; Lafon, J. M.; Teixeira, N.

    1995-01-01

    A sequence of Brasiliano-age granitoid types is exposed in a small area near the cities of Umarizal and Caraúbas in Rio Grande do Norte State, Northeast Brazil. Porphyritic K-alkali-calcic monzogranite is an important facies of the oldest Caraúbas intrusion (RbSr whole rock isochron age of ca. 630 Ma), which suffered solid-state deformation due to movements on a major NE-trending shear zone. The intrusion of the Prado and part of the Quixaba bodies was probably controlled by the shear zone. These two bodies include mafic/intermediate rocks, some of which contain two pyroxenes, and have hybrid, partly alkaline and partly shoshonitic geochemical characteristics. Rock types and ages are similar to those of some Pan-African occurrences in southwestern Nigeria. The Tourão body, intruded at ca. 590 Ma, presents preferred mineral orientations which are probably largely magmatic, since little evidence is found for widespread solid-state deformation. On the other hand, its intrusion may have been facilitated by the presence of the shear-zone faults. The rocks form a monomodal felsic K-alkali-calcic suite. With the exception of the Quixaba body, all these earlier granitoids are magmatic epidote- and magnetite-bearing porphyritic monzogranites with trace element geochemical characteristics of modern syn-collisional granites. The latest intrusion at ca. 545 Ma is mainly represented by potassic quartz syenites and related rocks, some of which contain fayalite or ferrohypersthene. These rocks possess neither well developed mineral orientations of magmatic origin nor signs of solid-state deformation. They are mineralogically similar to, but younger than some of the "bauchites" of central Nigeria. Geochemical signatures are comparable with those of modern within-plate granites. All granitoids present high ( 87Sr/ 86Sr)i ratios which range from 0.708 to 0.712, and increase with decreasing age. Such ratios are compatible with important or dominant crustal contributions. On the

  2. Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

    Science.gov (United States)

    Gaidzik, Krzysztof; Ramírez-Herrera, Maria Teresa; Kostoglodov, Vladimir

    2016-10-01

    This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named "La Venta Fault" shows evidence of recent activity, corroborated also by GPS measurements (4-5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995

  3. Uraninite, coffinite and brannerite from shear-zone hosted uranium deposits of the Bohemian Massif (Central European Variscan belt)

    Czech Academy of Sciences Publication Activity Database

    René, Miloš; Dolníček, Z.

    2017-01-01

    Roč. 7, č. 4 (2017), č. článku 50. ISSN 2075-163X Institutional support: RVO:67985891 Keywords : uranium deposits * mineralogy * uraninite * coffinite * brannerite * Moldanubian Zone * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 2.088, year: 2016 http://www.mdpi.com/2075-163X/7/4/50

  4. Unexpected earthquake hazard revealed by Holocene rupture on the Kenchreai Fault (central Greece): Implications for weak sub-fault shear zones

    Science.gov (United States)

    Copley, Alex; Grützner, Christoph; Howell, Andy; Jackson, James; Penney, Camilla; Wimpenny, Sam

    2018-03-01

    High-resolution elevation models, palaeoseismic trenching, and Quaternary dating demonstrate that the Kenchreai Fault in the eastern Gulf of Corinth (Greece) has ruptured in the Holocene. Along with the adjacent Pisia and Heraion Faults (which ruptured in 1981), our results indicate the presence of closely-spaced and parallel normal faults that are simultaneously active, but at different rates. Such a configuration allows us to address one of the major questions in understanding the earthquake cycle, specifically what controls the distribution of interseismic strain accumulation? Our results imply that the interseismic loading and subsequent earthquakes on these faults are governed by weak shear zones in the underlying ductile crust. In addition, the identification of significant earthquake slip on a fault that does not dominate the late Quaternary geomorphology or vertical coastal motions in the region provides an important lesson in earthquake hazard assessment.

  5. Kinematics and significance of a poly-deformed crustal-scale shear zone in central to south-eastern Madagascar: the Itremo-Ikalamavony thrust

    Science.gov (United States)

    Giese, Jörg; Schreurs, Guido; Berger, Alfons; Herwegh, Marco

    2017-09-01

    Across the crystalline basement of Madagascar, late Archaean rocks of the Antananarivo Block are tectonically overlain by Proterozoic, predominantly metasedimentary units of the Ikalamavony and Itremo Groups of the Southwest Madagascar Block. The generally west-dipping tectonic contact can be traced for more than 750 km from NW to SE and is referred to here as the Itremo-Ikalamavony thrust. The basal units of the SW Madagascar Block comprise metasedimentary quartzites with the potential to preserve a multistage deformation history in their microstructures. Previous studies suggest contrasting structural evolutions for this contact, including eastward thrusting, top-to-the-west directed extension and right-lateral strike-slip deformation during the late Neoproterozoic/Ediacaran. In this study, we integrate remote sensing analyses, structural and petrological fieldwork, as well as microstructural investigations of predominantly quartz mylonites from the central southern segment of the contact between Ankaramena and Maropaika. In this area, two major phases of ductile deformation under high-grade metamorphic conditions occurred in latest Neoproterozoic/early Phanerozoic times. A first (Andreaba) phase produces a penetrative foliation, which is parallel to the contact between the two blocks and contemporaneous with widespread magmatism. A second (Ihosy) phase of deformation folds Andreaba-related structures. The investigated (micro-)structures indicate that (a) juxtaposition of both blocks possibly already occurred prior to the Andreaba phase, (b) (re-)activation with top-to-the-east thrusting took place during the latest stages of the Andreaba phase, (c) the Ihosy phase resulted in regional-scale open folding of the tectonic contact and (d) reactivation of parts of the contact took place at distinctively lower temperatures post-dating the major ductile deformations.

  6. Imaging the concealed section of the Whakatane fault below Whakatane city, New Zealand, with a shear wave land streamer system

    Science.gov (United States)

    Polom, Ulrich; Mueller, Christof; Krawczyk, CharLotte M.

    2016-04-01

    The Mw 7.1 Darfield Earthquake in September 2010 ruptured the surface along the Greendale Fault that was not known prior to the earthquake. The subsequent Mw 6.3 Christchurch earthquake in February 2011 demonstrated that concealed active faults have a significant risk potential for urban infrastructure and human life in New Zealand if they are located beneath or close to such areas. Mapping exposures and analysis of active faults incorporated into the National Seismic Hazard Model (NSHM) suggests that several thousands of these active structures are yet to be identified and have the potential to generate moderate to large magnitude earthquakes (i.e. magnitudes >5). Geological mapping suggests that active faults pass beneath, or within many urban areas in New Zealand, including Auckland, Blenheim, Christchurch, Hastings/Napier, Nelson, Rotorua, Taupo, Wellington, and Whakatane. Since no established methodology for routinely locating and assessing the earthquake hazard posed by concealed active faults is available, the principal objective of the presented study was to evaluate the usefulness of high-resolution shear wave seismic reflection profiling using a land streamer to locate buried faults in urban areas of New Zealand. During the survey carried out in the city of Whakatane in February 2015, the method was first tested over a well known surface outcrop of the Edgecumbe Fault 30 km south-west of Whakatane city. This allowed further to investigate the principle shear wave propagation characteristics in the unknown sediments, consisting mainly of effusive rock material of the Taupo volcanic zone mixed with marine transgression units. Subsequently the survey was continued within Whakatane city using night operation time slots to reduce the urban noise. In total, 11 profiles of 5.7 km length in high data quality were acquired, which clearly show concealed rupture structures of obviously different age in the shallow sediments down to 100 m depth. Subject to depth

  7. Temporal stress changes associated with the 2008 May 29 MW 6 earthquake doublet in the western South Iceland Seismic Zone

    Science.gov (United States)

    Hensch, Martin; Lund, Björn; Árnadóttir, Thóra; Brandsdóttir, Bryndís

    2016-01-01

    On 2008 May 29, two magnitude MW ˜ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001-2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 ± 10° (95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8-10 MPa, the pre-event shear stress is estimated to 16-20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime-from normal faulting to strike-slip faulting-was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.

  8. Do the eclogites of the Variscan Malpica-Tuy shear zone in NW Spain point to continental subduction?

    Science.gov (United States)

    Li, Botao; Massonne, Hans-Joachim

    2014-05-01

    High-pressure (HP: P > 10 kbar) rocks such as eclogite typically occur in suture zones of collided continental plates in Phanerozoic times. In case of an extended area at the surface of a denuded orogen with HP and even ultrahigh pressure (UHP) metamorphic rocks, they are often interpreted as the result of continental subduction. We have tested this idea for the HP-UHP area of the Malpica-Tuy zone of the Variscan orogen, which was formed by the collision of Gondwana and Laurussia. For the test, we have initially studied an eclogite and its surrounding gneiss of this zone in detail. The eclogite contains the assemblage garnet, omphacite, amphibole, rutile, ilmenite, clinozoisite/epidote, quartz, and phengite with Si-contents as high as 3.45 per formula unit (pfu) in inner portions and 3.27-3.35 pfu in rims. Garnet exhibits chemical zonation with Gro25Alm55Pyr15Spe5, Gro29Alm57Pyr13Spe1, and Gro23Alm56Pyr20Spe1 as inner core, mantle, and outermost rim compositions, respectively. The gneiss is a former medium-grained granite now composed of quartz, plagioclase, K-feldspar, biotite, phengite, garnet, clinozoisite/epidote, titanite, apatite and ilmenite. Phengite shows Si contents between 3.40 (core) and 3.00 (rim) pfu. Garnet is chemically zoned with Gro69.6Alm27Pyr0.4Spe3, Gro65.5Alm32.5Pyr0.5Spe1.5, Gro65.7Alm31.7Pyr0.6Spe2, and Gro56.6Alm41.6Pyr1.2Spe0.6 as core, mantle, rim and outermost rim compositions, respectively. P-T pseudosections were calculated with the PERPLEX computer program in the system Na2O-K2O-CaO-FeO-O2-MnO-MgO-Al2O3-SiO2-TiO2-H2O for the bulk-rock compositions of the studied eclogite and gneiss. These pseudosections were contoured by isopleths of various parameters such as molar fractions of garnet components. Based on this contouring a P-T path was derived that starts at HP conditions for both lithologies. Garnet began to form at 22 kbar and 565°C in the eclogite. Subsequently, the temperatures increased to 585°C and the pressure decreased to

  9. Characterizing a large shear-zone with seismic and magnetotelluric methods: The case of the Dead Sea Transform

    Science.gov (United States)

    Maercklin, N.; Bedrosian, P.A.; Haberland, C.; Ritter, O.; Ryberg, T.; Weber, M.; Weckmann, U.

    2005-01-01

    Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a ???10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1-4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others. Copyright 2005 by the American Geophysical Union.

  10. Scissoring Fault Rupture Properties along the Median Tectonic Line Fault Zone, Southwest Japan

    Science.gov (United States)

    Ikeda, M.; Nishizaka, N.; Onishi, K.; Sakamoto, J.; Takahashi, K.

    2017-12-01

    The Median Tectonic Line fault zone (hereinafter MTLFZ) is the longest and most active fault zone in Japan. The MTLFZ is a 400-km-long trench parallel right-lateral strike-slip fault accommodating lateral slip components of the Philippine Sea plate oblique subduction beneath the Eurasian plate [Fitch, 1972; Yeats, 1996]. Complex fault geometry evolves along the MTLFZ. The geomorphic and geological characteristics show a remarkable change through the MTLFZ. Extensional step-overs and pull-apart basins and a pop-up structure develop in western and eastern parts of the MTLFZ, respectively. It is like a "scissoring fault properties". We can point out two main factors to form scissoring fault properties along the MTLFZ. One is a regional stress condition, and another is a preexisting fault. The direction of σ1 anticlockwise rotate from N170°E [Famin et al., 2014] in the eastern Shikoku to Kinki areas and N100°E [Research Group for Crustral Stress in Western Japan, 1980] in central Shikoku to N85°E [Onishi et al., 2016] in western Shikoku. According to the rotation of principal stress directions, the western and eastern parts of the MTLFZ are to be a transtension and compression regime, respectively. The MTLFZ formed as a terrain boundary at Cretaceous, and has evolved with a long active history. The fault style has changed variously, such as left-lateral, thrust, normal and right-lateral. Under the structural condition of a preexisting fault being, the rupture does not completely conform to Anderson's theory for a newly formed fault, as the theory would require either purely dip-slip motion on the 45° dipping fault or strike-slip motion on a vertical fault. The fault rupture of the 2013 Barochistan earthquake in Pakistan is a rare example of large strike-slip reactivation on a relatively low angle dipping fault (thrust fault), though many strike-slip faults have vertical plane generally [Avouac et al., 2014]. In this presentation, we, firstly, show deep subsurface

  11. SPECIALIZED MAPPING OF CRUSTAL FAULT ZONES. PART 2: MAIN STAGES AND PROSPECTS

    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky

    2015-01-01

    the basis analysis of the scatter of joint systems, shearing angles and other relevant information. Group II.3: construction of a circle diagram for the specified mapping site with local fault poles (Fig. 8, Б, identification of conjugated systems and dynamic settings of their formation (Fig. 2, plotting the information onto the schematic map of the location under study, and marking the transregional fault zones (Fig. 7, В–К with observation sites showing similar settings and paragenesises of local faults. Group II.4: comparison between diagrams of fault poles of local ranks with reference patterns selected according to the availability of conjugated pairs of fractures (Fig. 9, Б–Г; based on the above comparison, decision making on potential formation of a paragenesis of local faults in the strike-slip, normal and reserve/thrust fault zones (Fig. 9, Д–Ж, and delineation of boundaries of such zones in the schematic map by connecting the observation sites with similar solutions (Fig. 7, Л–Н.Stage III is aimed at interpreting and includes comprehensive analyses of mapping results and priori information, construction of a final scheme of the fault zones showing their subordination by ranks (Fig. 7, О and schemes of fault zones for various structure formation stages, showing types of faults and specific features of their internal patterns, i.e. definition of the peripheral sub-zone, sub-zones of fractures of the 2nd order and, if established, the sub-zone of the major fault (Fig. 7, Л–Н.Prospects of the special mapping method can be highlighted upon its comparison with the conventional structural methods applied in studies of faults. On the one side, the method requires time-consuming mass mea­surements and special processing of 'dumb' joints; on the other side, it provides for analyses of abundant jointing data, ensures a high level of detail in mapping of patterns of fault zones, reveals rank subordination of faults and helps to determine other

  12. Ductile shear zones can induce hydraulically over-pressured fractures in deep hot-dry rock reservoirs: a new target for geothermal exploration?

    Science.gov (United States)

    Schrank, C. E.; Karrech, A.; Regenauer-Lieb, K.

    2014-12-01

    It is notoriously difficult to create and maintain permeability in deep hot-dry rock (HDR) geothermal reservoirs with engineering strategies. However, we predict that long-lived, slowly deforming HDR reservoirs likely contain hydraulically conductive, over-pressured fracture systems, provided that (a) the underlying lower crust and/or mantle are not entirely depleted of fluids and (b) the fracture system has not been drained into highly permeable overlying rocks. Such fracture systems could be targeted for the extraction of geothermal energy. Our prediction hinges on the notion that polycrystalline creep through matter transfer by a liquid phase (dissolution-precipitation creep) is a widespread mechanism for extracting fluids from the lower crust and mantle. Such processes - where creep cavities form during the slow, high-temperature deformation of crystalline solids, e.g., ceramics, metals, and rocks - entail the formation of (intergranular) fluid-assisted creep fractures. They constitute micron-scale voids formed along grain boundaries due to incompatibilities arising from diffusion or dislocation creep. Field and laboratory evidence suggest that the process leading to creep fractures may generate a dynamic permeability in the ductile crust, thus extracting fluids from this domain. We employed an elasto-visco-plastic material model that simulates creep fractures with continuum damage mechanics to model the slow contraction of high-heat-producing granites overlain by sedimentary rocks in 2D. The models suggest that deformation always leads to the initiation of a horizontal creep-damage front in the lower crust. This front propagates upwards towards the brittle-ductile transition (BDT) during protracted deformation where it collapses into highly damaged brittle-ductile shear zones. If the BDT is sufficiently shallow or finite strain sufficiently large, these shear zones trigger brittle faults emerging from their tips, which connect to the sub-horizontal damage

  13. Geotechnical studies at Jaduguda uranium mine for optimisation of stopping and support parameters in molybdenite shear zone

    International Nuclear Information System (INIS)

    Ghosh, A.K.; Sinha, A.; Prasad, L.; Prasad, M.; Raju, N.M.

    1991-01-01

    In recent years, a few geotechnical studies have been conducted by the Central Mining Research Station, Dhanbad, at Jaduguda mine to improve ground control system and to optimise stopping parameters in the wide orebody zone at deeper levels and thus to add to productivity and recovery of these mines ensuring adequate safety. The replacement of mechanical point-anchored rock-bolts by full column cement grouted bolts, installed as per the designed pattern, has improved the ground condition, decreased the consumption of timber supports by around 70%, curtailed the support installation time and reduced the support cost to a remarkable extent even at the most problematic sites of Jaduguda mine. The analysis of stress development observations in the slope pillars of this mine reveals that the size of the slope pillars may be reduced by 20% in width which means an extra recovery of about 75 to 100 tonnes of ore per pillar per slice. In this paper, the authors have presented a brief account of their studies at this mine in the last four years. (author). 10 refs., 10 tabs., 9 figs

  14. Shear machines

    International Nuclear Information System (INIS)

    Astill, M.; Sunderland, A.; Waine, M.G.

    1980-01-01

    A shear machine for irradiated nuclear fuel elements has a replaceable shear assembly comprising a fuel element support block, a shear blade support and a clamp assembly which hold the fuel element to be sheared in contact with the support block. A first clamp member contacts the fuel element remote from the shear blade and a second clamp member contacts the fuel element adjacent the shear blade and is advanced towards the support block during shearing to compensate for any compression of the fuel element caused by the shear blade (U.K.)

  15. Age of blastomilonites of the Yenisei regional shear zone as evidence of the Vendian accretionary-collision events at the western margin of the Siberian Craton

    Science.gov (United States)

    Likhanov, I. I.; Reverdatto, V. V.; Zinov'ev, S. V.; Nozhkin, A. D.

    2013-05-01

    The age of the latest impulse of dynamometamorphic structural-compositional transformations (603-615 Ma) was established from the 40Ar-39Ar age of micas from balstomilonites of the Garevka metamorphic complex of the Yenisei Ridge confined to the Priyenisei shear zone. The age of these tectonic-thermal events marks the final stage of the Neoproterozoic evolution of the Yenisei Ridge related to the accretion of the Isakovka terrane to the western margin of the Siberian Craton. These results are in agreement with the age of metamorphic rocks of northwestern Prisayany, which are incorporated into the Sayany-Yenisei accretionary belt along with Yenisei Ridge. The conformable data on two regions indicate a global Vendian accretionary-collision event, which led to the formation of the Sayany-Yenisei accretionary belt, lateral thickening of the continental crust to the southwestern margin of the Siberian Craton, and its subsequent tectonic reworking. The synchronous Vendian orogenesis and consequence of the tectonic-thermal events along the periphery of the large Precambrian cratons of the Baltic and Siberia confirm their close spatial relation about 800 Ma ago, which agrees with contemporary paleomagnetic reconstructions.

  16. On some aspects of the stratigraphy, depositional environment and its bearing on uranium mineralisation in parts of the Singhbhum shear zone, Bihar

    International Nuclear Information System (INIS)

    Virnave, S.N.; Mukhopadhyay, T.K.; Krishnabadri, N.S.R.

    1994-01-01

    A review of the geology and controls of uranium mineralisation in the Singhbhum Shear Zone between Narwapahar (Lat. 22deg44'N; Long. 86deg15'E) in the west, to Ghatsila (Lat. 22deg25'N; Long. 86deg20'E) in the southeast and up to Dalmas in the north is presented in the light of new data based on facies analysis and palaeo-current studies on the conglomerate and associated meta-sediments in the area. Synthesis and integration of geologic data have led to the following conclusions: a) The facies variation and its distribution pattern in the area demonstrate fluviatile conditions of deposition with upward fining and thinning sequences b) The sedimentary sequence shows progressive younging towards north without any obvious break or juxta-position of the older over the younger. c) The nature of Jaduguda sedimentary facies assemblage is indicative of a fluvial fan with conglomerate gray-wacke-arenite assemblage representing proximal fan facies. On the basis of facies model, the area north of Subarnarekha river represents a meandering fluvial pattern. d) Uranium mineralisation is distinctly stratabound with characteristic facies association. (author). 13 refs., 11 figs., 3 tabs

  17. Recycling and utilisation of industrial solid waste: an explorative study on gold deposit tailings of ductile shear zone type in China.

    Science.gov (United States)

    Liu, Rui; Huang, Fei; Du, Runxiang; Zhao, Chunming; Li, Yongli; Yu, Haoran

    2015-06-01

    Tailings are solid waste arising from mineral processing. This type of waste can cause severe damage to the environment during stockpiling as a result of the leaching of something harmful into the ecosystem. Gold deposit of ductile shear zone type is an important type of gold deposit, and the recycling of its tailings has been challenging researchers for a long time. In this article, the characteristics of this type of tailings were systematically studied by using modern technical means. Considering the characteristics of the tailings, clay was selected to make up for the shortcomings of the tailings and improve their performance. Water and raw materials were mixed to produce green bodies, which are subsequently sintered into ceramic bodies at 980 °C~1020 °C (sintering temperature). The results showed that some new kinds of mineral phases, such as mullite, anorthite and orthoclase, appear in ceramic bodies. Furthermore, the ceramic bodies have a surface hardness of 5 to 6 (Mohs scale), and their water absorption and modulus of rupture can meet some technical requirements of ceramic materials described in ISO 13006-2012 and GB 5001-1985. These gold mine tailings can be made into ceramic tiles, domestic ceramic bodies, and other kinds of ceramic bodies for commercial and industrial purposes after further improvements. © The Author(s) 2015.

  18. Two-stage rifting of Zealandia-Australia-Antarctica: Evidence from 40Ar/39Ar thermochronometry of the Sisters shear zone, Stewart Island, New Zealand

    Science.gov (United States)

    Kula, Joseph; Tulloch, Andy; Spell, Terry L.; Wells, Michael L.

    2007-05-01

    The Sisters shear zone is a newly discovered Late Cretaceous detachment fault system exposed for 40 km along the southeast coast of Stewart Island, southernmost New Zealand. Footwall rocks consist of variably deformed ca. 310 and 105 Ma granites that range from undeformed to protomylonite, mylonite, and ultramylonite. The hanging wall includes non-marine conglomerate and brittley deformed granite. K-feldspar thermochronometry of the footwall indicates moderately rapid cooling (20 30 C°/m.y.) due to tectonic denudation over the interval ca. 89 82 Ma. Return to slow cooling at 82 Ma coincides with the age of the oldest seafloor adjacent to the Campbell Plateau and reflects the mechanical transition from continental extension to lithospheric rupture and formation of the Pacific-Antarctic Ridge. Our findings support a two-stage rift model for continental breakup of this part of the Gondwana margin. Stage one (ca. 101 88 Ma) is the northward propagation of continental extension and the Tasman Ridge as recorded in mylonite dredged from the Ross Sea and the Paparoa core complex. Stage two (ca. 89 82 Ma) is extension between the Campbell Plateau and West Antarctica leading to formation of the Pacific-Antarctic Ridge.

  19. On thrusting, regional unconformities and exhumation of high-grade greenstones in Neoarchean orogens. The case of the Waroonga Shear Zone, Yilgarn Craton

    Science.gov (United States)

    Zibra, I.; Korhonen, F. J.; Peternell, M.; Weinberg, R. F.; Romano, S. S.; Braga, R.; De Paoli, M. C.; Roberts, M.

    2017-08-01

    During the Neoarchean, the dominant tectonic style progressively changed from an episodic-overturn/stagnant-lid regime to modern-style plate tectonics. The Neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts. The case study presented here provides insights into how such transition in tectonic style occurred, a matter that is generally controversial. We present structural and metamorphic data from the c. 2660 Ma Waroonga Shear Zone (WSZ) in the Neoarchean Yilgarn orogen (Western Australia). The WSZ contains a syntectonic pluton and older, high-grade greenstones. The tectonic fabric in the pluton developed during melt-present thrusting, followed by syn-cooling wrench-dominated transpression. Mafic greenstones preserve three metamorphic assemblages. The M1 assemblage (Grt-Cpx-Qtz) records peak P-T conditions of 12 ± 1 kbar and 800 ± 50 °C, followed by isothermal decompression to 9 kbar (M2). These anhydrous assemblages might predate the WSZ. Greenstones then underwent decompression at c. 2660 Ma (3-4 kbar; 600-650 °C), defined by the amphibole-rich M3 assemblage, synkinematic with the tectonic fabric in the WSZ. We show that shearing along the WSZ exhumed these greenstones by at least 10 km, inducing major uplift and erosion. Archean accretionary orogens developed on weak lithosphere, where deformation suppressed crustal thickening, orogenic relief and synorogenic exhumation of orogenic roots. However, our study indicates a genetic link between (i) strain localization along contractional structures, inducing large-scale uplift; (ii) exhumation of high-grade greenstones; (iii) development of inverse metamorphic gradients; (iv) establishment of a regional unconformity, with clastic sediments fed by the uplifted terrane; (v) incorporation of portions of the newly-formed orogenic basins into the footwall of the WSZ. These features imply that the Yilgarn orogenic lithosphere at c. 2660 Ma was stiff enough to allow

  20. Controls on continental strain partitioning above an oblique subduction zone, Northern Andes

    Science.gov (United States)

    Schütt, Jorina M.; Whipp, David M., Jr.

    2016-04-01

    Strain partitioning is a common process at obliquely convergent plate margins dividing oblique convergence into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the subduction margin. In subduction zones, strain partitioning in the upper continental plate is mainly controlled by the shear forces acting on the plate interface and the strength of the continental crust. The plate interface forces are influenced by the subducting plate dip angle and the obliquity angle between the normal to the plate margin and the convergence velocity vector, and the crustal strength of the continent is strongly affected by the presence or absence of a volcanic arc, with the presence of the volcanic arcs being common at steep subduction zones. Along the ˜7000 km western margin of South America the convergence obliquity, subduction dip angles and presence of a volcanic arc all vary, but strain partitioning is only observed along parts of it. This raises the questions, to what extent do subduction zone characteristics control strain partitioning in the overriding continental plate, and which factors have the largest influence? We address these questions using lithospheric-scale 3D numerical geodynamic experiments to investigate the influence of subduction dip angle, convergence obliquity, and weaknesses in the crust owing to the volcanic arc on strain partitioning behavior. We base the model design on the Northern Volcanic Zone of the Andes (5° N - 2° S), characterized by steep subduction (˜ 35°), a convergence obliquity between 31° -45° and extensive arc volcanism, and where strain partitioning is observed. The numerical modelling software (DOUAR) solves the Stokes flow and heat transfer equations for a viscous-plastic creeping flow to calculate velocity fields, thermal evolution, rock uplift and strain rates in a 1600 km x 1600 km box with depth 160 km. Subduction geometry and material properties are based on a

  1. Tectonic blocks and suture zones of eastern Thailand: evidence from enhanced airborne geophysical analysis

    Directory of Open Access Journals (Sweden)

    Arak Sangsomphong

    2013-04-01

    Full Text Available Airborne geophysical data were used to analyze the complex structures of eastern Thailand. For visual interpretation, the magnetic data were enhanced by the analytical signal, and we used reduction to the pole (RTP and vertical derivative (VD grid methods, while the radiometric data were enhanced by false-colored composites and rectification. The main regional structure of this area trends roughly in northwest-southeast direction, with sinistral faulting movements. These are the result of compression tectonics (sigma_1 in an east-west direction that generated strike-slip movement during the pre Indian-Asian collision. These faults are cross-cut by the northeast-southwest-running sinistral fault and the northwest-southeast dextral fault, which occurred following the Indian-Asian collision, from the transpession sinistral shear in the northwest-southeast direction. Three distinct geophysical domains are discernible; the Northern, Central and Southern Domains. These three domains correspond very well with the established geotectonic units, as the Northern Domain with the Indochina block, the Central Domain with the Nakhonthai block, the Upper Southern Sub-domain with the Lampang-Chaing Rai block, and the Lower Southern Sub-domain with the Shan Thai block. The Indochina block is a single unit with moderate radiometric intensities and a high magnetic signature. The direction of the east-west lineament pattern is underlain by Mesozoic non-marine sedimentary rock, with mafic igneous bodies beneath this. The Nakhonthai block has a strong magnetic signature and a very weak radiometric intensity, with Late Paleozoic-Early Mesozoic volcanic rock and mélange zones that are largely covered by Cenozoic sediments. The boundaries of this block are the southern extension of the Mae Ping Faults and are oriented in the northwest-southeast direction. The Lampang-Chaing Rai and Shan Thai blocks, with very weak to moderate magnetic signatures and moderate to very

  2. Constraining the thermal and tectonic evolution of a greenschist facies shear zone on Syros, Greece by using stable isotopes and mineral chemistry.

    Science.gov (United States)

    Cisneros, M.; Barnes, J.; Behr, W. M.

    2016-12-01

    Retrograde metamorphic rocks are key to understanding the exhumation history of high-pressure/low-temperature terranes. The Cycladic Blueschist Unit of Syros, Greece experienced peak metamorphic conditions of 15 kbar and 500 °C at 50 Ma and was subsequently exhumed to the shallow-crust ( 1-3 km) by 15 Ma; however, the processes associated with exhumation from mantle depths to the mid-crust remain poorly understood. We present structural, microstructural, and geochemical analyses of greenschist facies metamafic rocks exposed on Lotos beach in Syros that help to constrain the early exhumation history of these rocks. The outcrop preserves two main fabrics: 1) an early transposition foliation (Ss) defined by tight, isoclinal folds with shallow hingelines, and 2) upright open folds with a steep axial-planar cleavage (Sc). Ss is associated with viscous deformation and alignment of both amphibole and epidote into the foliation plane, whereas Sc is associated with semi-brittle deformation, amphibole overgrowths, and boudinage in elongate epidote (ep). Amphiboles display a progressive evolution from Na-to-Ca-rich end-members and exhibit continuous crystallization throughout Ss and Sc, as evidenced by new amphibole growth and overgrowths oriented parallel to foliation. Cal-qtz precipitates in ep boudin necks and chl + cal pseudomorphs after actinolite represent the last stage of lower greenschist facies metamorphism. These results indicate that foliation-forming deformation initiated prior-to or during blueschist facies and continued through lowermost greenschist facies. Oxygen isotope thermometry indicates that qtz-cal pairs equilibrated at 187 °C. Carbon and oxygen isotope values of fluids in equilibrium with qtz-cal pairs (δ18O and δ13C ≈ 0 ‰) indicate a seawater-derived fluid source. Preliminary results suggest this shear zone experienced cooling during decompression, followed by interaction with fluids transferred along a low-angle detachment.

  3. Phylogeography of Beck's Desert Scorpion, Paruroctonus becki, reveals Pliocene diversification in the Eastern California Shear Zone and postglacial expansion in the Great Basin Desert.

    Science.gov (United States)

    Graham, Matthew R; Jaeger, Jef R; Prendini, Lorenzo; Riddle, Brett R

    2013-12-01

    The distribution of Beck's Desert Scorpion, Paruroctonus becki (Gertsch and Allred, 1965), spans the 'warm' Mojave Desert and the western portion of the 'cold' Great Basin Desert. We used genetic analyses and species distribution modeling to test whether P. becki persisted in the Great Basin Desert during the Last Glacial Maximum (LGM), or colonized the area as glacial conditions retreated and the climate warmed. Phylogenetic and network analyses of mitochondrial cytochrome c oxidase 1 (cox1), 16S rDNA, and nuclear internal transcribed spacer (ITS-2) DNA sequences uncovered five geographically-structured groups in P. becki with varying degrees of statistical support. Molecular clock estimates and the geographical arrangement of three of the groups suggested that Pliocene geological events in the tectonically dynamic Eastern California Shear Zone may have driven diversification by vicariance. Diversification was estimated to have continued through the Pleistocene, during which a group endemic to the western Great Basin diverged from a related group in the eastern Mojave Desert and western Colorado Plateau. Demographic and network analyses suggested that P. becki underwent a recent expansion in the Great Basin. According to a landscape interpolation of genetic distances, this expansion appears to have occurred from the northwest, implying that P. becki may have persisted in part of the Great Basin during the LGM. This prediction is supported by species distribution models which suggest that climate was unsuitable throughout most of the Great Basin during the LGM, but that small patches of suitable climate may have remained in areas of the Lahontan Trough. Published by Elsevier Inc.

  4. Influence of micaceous impurity on dynamically recrystallized quartz c-axis fabric in L- S tectonites from the Singhbhum Shear Zone and its footwall, Eastern India

    Science.gov (United States)

    Joy, S.; Saha, D.

    1998-11-01

    When temperature and strain rate remain constant the quartz c-axis fabric in deformed pure quartz aggregates, is largely dependent on deformation kinematics. Asymmetry of the fabric, e.g. in type-I asymmetric crossed girdle pattern in natural quartz tectonites, simulated fabric or experimentally deformed quartz aggregates is generally related to sense of vorticity for a non-coaxial flow. Natural quartz tectonites, however, often contain micaceous impurities. Measurement on a sample of 59 quartz tectonites with mesoscopic L- S fabric and representing low {T}/{T m}, deformation under non-coaxial flow, from the Singhbhum Shear Zone and Dhanjori quartzites. Eastern India provides the basic data to quantitatively assess the influence of mica on (i) asymmetry of quartx c-axis fabric and (ii) degree of crystallographic preferred orientation, i.e. fabric intensity, taking c-axes of dynamically recrystallized quartz grains as a fabric element. A fabric intensity parameter (κ) is defined as the ratio of the greatest eigenvalue to the least eigenvalue of the orientation tensor matrix corresponding to c-axis orientations in each measured specimen. The modal percent of mica (μ) in the sample varies from 2 to 35; that of recrystallized quartz grains (ν), as opposed to relict clasts. from 45 to 98. The asymmetry of the fabrics in the above sample, measured either as the Am statistic or as the angle between the central segment of the fabric skeleton and direction of mineral elongation lineation is independent of mica content. Correlation-regression analysis of the variables κ, μ, and ν. demonstrate a negative correlation between micaceous impurity and the fabric intensity parameter. The regression equation is of the form κ = 0.13 ν1.11μ-0.617.

  5. Did the Malaysian Main Range record a weak hot Mega Shear?

    Science.gov (United States)

    Sautter, Benjamin; Pubellier, Manuel

    2015-04-01

    The Main Range of Peninsular Malaysia is a batholith that extends over more than 500km from Malacca in the South to the Thailand border in the North. It results from the subduction/accretion history of the western margin of Sunda Plate by Late Triassic times. We present a structural analysis based on geomorphology, field observations and geochronological data. While most of the basement fabrics are characterized by N-S structures such as granitic plutons, sutures, and folds, a prominent oblique deformation occurred by the End of the Mesozoics synchronous with a widespread thermal anomaly (eg Tioman, Stong, Gunung Jerai, Khanom, Krabi plutons). Morphostructures and drainage anomalies from Digital Elevation Model (SRTM and ASTER), allow us to highlight 2 major groups of penetrative faults in the Central Range Batholith: early NW-SE (5km spaced faults some of which are identified as thrust faults) cross-cut and offset by NNE-SSW dextral normal faults. The regularly spaced NW-SE faults bend toward the flanks of the Batholith and tend to parallel both the Bentong Raub Suture Zone to the East and the strike slip Bok Bak Fault to the West, thus giving the overall fault network the aspect of a large C/S band. Hence, a ductile/brittle behavior can be proposed for the sigmoid faults in the core of the Batholith, whereas the NNE faults are clearly brittle, more linear and are found on the smaller outlying plutons. Radiogenic crystallization ages are homogenous at 190±20Ma (U-Pb Zircon, Tc>1000°C and K-Ar Muscovite, Tc350°C) whereas Zircon fission tracks(Tc=250°C) show specific spatial zoning of the data distribution with ages at 100±10Ma for the outlying plutons and ages at 70±10Ma for the Main Range. We propose a structural mechanism according to which the Main Range would be the ductile core of a Mega-Shear Zone exhumed via transpressive tectonics by the end of Mesozoic Times. A first stage between 100 and 70Ma (Upper Cretaceous) of dextral transpression affected

  6. Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone, Russia)

    Science.gov (United States)

    Smekalin, Oleg P.; Shchetnikov, Alexander A.; White, Dustin

    2013-01-01

    The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780-3440 years.

  7. Sub-crustal earthquakes within the Australia-Pacific plate boundary zone beneath the Southern Alps, New Zealand

    Science.gov (United States)

    Boese, C. M.; Stern, T. A.; Townend, J.; Bourguignon, S.; Sheehan, A.; Smith, E. G. C.

    2013-08-01

    Sub-crustal earthquakes have been observed sporadically for ∼40 years in the central South Island of New Zealand. We report on 20 events recorded between December 2008 and February 2012 near the Alpine Fault in the continental collision zone between the Australian and Pacific plates. A subset of 18 events at depths of 47-74 km occurs south of Mt. Cook and together with recently reported tremor locations indicates along-strike variations in deformation behaviour along the plate boundary. The sub-crustal earthquakes south of Mt. Cook increase in depth, frequency and size southwards towards the Puysegur subduction zone. Focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike-slip and reverse faulting solutions. Stress inversion analysis of the focal mechanisms yields a stress field favouring oblique-reverse faulting. We interpret the geographic and vertical distributions of these sub-crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of New Zealand in the Eocene and was overridden when dextral strike-slip motion initiated on the Alpine Fault. We infer that sub-crustal earthquakes occur along the leading edge of this structure, which is attached to the continental Australian crust.

  8. Late Cretaceous evolution of the northern Sistan suture zone ...

    Indian Academy of Sciences (India)

    Demartis et al. 2011) and Africa (Ferre et al. 1995;. Cecys and Benn 2007; Vegas et al. 2008). ..... pressional and dextral strike-slip movement at least in the later episodes of intrusion, when magma was cooling. .... Internal fabric and strike-slip emplacement of the Pan-. African granite of Solli Hills, northern Nigeria; Tectonics.

  9. Coseismic conjugate faulting structures produced by the 2016 Mw 7.1 Kumamoto earthquake, Japan

    Science.gov (United States)

    Lin, Aiming; Chiba, Tatsuro

    2017-06-01

    Field investigations and analyses of airborne LiDAR data reveal that the 2016 Mw7.1 Kumamoto earthquake produced a ∼40-km-long surface rupture zone with a typical conjugate Riedel shearing fault structure along the pre-existing right-lateral strike-slip Hinagu-Futagawa Fault Zone (HFFZ). The conjugate Riedel shearing structure comprises two sets of coseismic shear fault zones that are oriented to NE-SW to ENE-WSW and WNW-ESE to E-W. The NE-SW to ENE-WSW-trending shear fault zone is characterized by R Riedel shear structures with right-lateral strike-slip displacement of up to 2.5 m, including left-stepping en echelon cracks (T-shear) and mole tracks (P-shear). In contrast, the WNW-ESE to E-W-trending shear fault zone is dominated by R‧ Riedel shear structures with left-lateral displacement of up to 1.3 m, including right-stepping en echelon tension cracks (T) and mole tracks (P), which are concentrated in a zone of strike-slip faults of HFFZ under the present E-W compressive stress in the study area, associated with the ongoing penetration of the Philippine Sea Plate into the Eurasian Plate.

  10. Continuous shear - a method for studying material elements passing a stationary shear plane

    DEFF Research Database (Denmark)

    Lindegren, Maria; Wiwe, Birgitte; Wanheim, Tarras

    2003-01-01

    Traditionally, material response to shear deformation has been studied with methods where the shear is gradually increasing from zero to the final value over a certain fixed deformation zone, e.g. in the well-known torsion test of a tube with a defined shear zone established by a machined...... circumferential groove. Normally shear in metal forming processes is of another nature, namely where the material elements move through a stationary shear zone, often of small width. In this paper a method enabling the simulation of this situation is presented. A tool for continuous shear has beeen manufactured...... and tested with AlMgSil and copper. The sheared material has thereafter been tested n plane strain compression with different orientation concerning the angle between the shear plane and the compression direction....

  11. A Tensile Origin for Pulverized Fault Zone Rock

    Science.gov (United States)

    St Julien, R. C.; Griffith, W. A.; Ghaffari, H. O.

    2017-12-01

    The origin of highly fragmented, but lightly strained rocks distributed asymmetrically across major strike slip faults has been enigmatic since their first recognition, yet the explanation has major implications for earthquake physics. These so called "pulverized" rocks are found up to 100m away from the principal slip zone of the San Andreas fault and other strike slip faults around the world. Experiments suggest that rock pulverization occurs at strain rates on the order of 102 s-1, pointing to a coseismic origin; however, strain rates during sub-Rayleigh earthquake rupture propagation 100m from faults is expected to be at least two orders of magnitude smaller than this, leading some to suggest that pulverization occurs during supershear earthquake rupture. Numerical solutions suggest that states of isotropic tension occur in more compliant sides of the fault, and at distances as great as 100m from the fault, as a sub-Rayleigh rupture propagates. We develop a novel modification to the Split-Hopkinson Pressure Bar apparatus wherein an axial compressive pulse produces isotropic radial tension in a disk-shaped rock specimen. We show that under isotropic tension, fragmentation of Westerly Granite occurs at strain rates on the order of 100 s-1, and fragment size scales inversely with strain rate in close agreement with energy-based fragmentation models. Similar experiments on thermally pre-treated Westerly granite specimens demonstrate how pre-existing damage can further reduce strain rates and tensile stresses required for intense fragmentation. Our results solve the strain rate-distance scaling problem between laboratory and field observations of pulverized rocks and also explains the asymmetric distribution of fault rocks. Furthermore, this implies long-term preferred earthquake rupture directivity along major faults where pulverized rocks are found.

  12. 3D geodynamic models for the development of opposing continental subduction zones: The Hindu Kush-Pamir example

    Science.gov (United States)

    Liao, Jie; Gerya, Taras; Thielmann, Marcel; Webb, A. Alexander G.; Kufner, Sofia-Katerina; Yin, An

    2017-12-01

    The development of opposing continental subduction zones remains scantly explored in three dimensions. The Hindu Kush-Pamir orogenic system at the western end of the Himalayan orogen provides a rare example of continental collision linked to two opposing intra-continental subduction zones. The subducted plates feature a peculiar 3D geometry consisting of two distinct lithospheric fragments with different polarities, subduction angles and slab-curvatures beneath the Hindu Kush and Pamir, respectively. Using 3D geodynamic modeling, we simulate possible development of two opposing continental subduction zones to understand the dynamic evolution of the Hindu Kush-Pamir orogenic system. Our geodynamic model reproduces the major tectonic elements observed: (1) the deeper subduction depth, the steeper dip angle and the southward offset of the Hindu Kush subduction zone relative to the Pamir naturally occur if convergence direction of the subducting Indian plate and dip-direction of the Hindu Kush subduction zone match. (2) The formation of the highly asymmetrically curved Pamir region and the south-dipping subduction is promoted by the initial geometry of the indenting Indian lithosphere together with the existence of a major strike-slip fault on the eastern margin of the Pamir region. (3) Subduction of only the lower continental crust during continental collision can occur if the coupling between upper and lower crusts is weak enough to allow a separation of these two components, and that (4) the subduction of mainly lower crust then facilitates that conditions for intermediate-depth seismicity can be reached. (5) The secondary tectonic features modeled here such as strike-slip-fault growth, north-northwest striking extension zone, and lateral flow of the thickened ductile upper crust are comparable to the current tectonics of the region. (6) Model results are further compared to the potentially similar orogenic system, i.e., the Alpine orogen, in terms of the curved

  13. Hidden Earthquake Potential in Plate Boundary Transition Zones

    Science.gov (United States)

    Furlong, Kevin P.; Herman, Matthew; Govers, Rob

    2017-04-01

    the Pacific plate (without a triple junction). Here, the short-term, earthquake-cycle signal recorded by GPS shows a reduction in plate motion-directed displacements, which has been interpreted to reflect reduced coupling along the southernmost segment. However, this signal records both the subduction interface coupling effects related to the megathrust earthquake cycle and the shear deformation produced by the extensive right-lateral shear of the Marlborough Fault system (MFS). This superposition of deformation signals combine to mask a strongly coupled interface. The relevance of this effect is seen in the recent (November 2016) Kaikoura earthquake ,which appears to have both ruptured the megathrust interface and produced strike slip displacements on upper-plate crustal faults. These effects seen at these locations and elsewhere may cause misinterpretations of short-term deformation signals in terms of the longer term tectonic behavior of the plate boundary, missing a significant component of the earthquake potential.

  14. Cenozoic high-K alkaline magmatism and associated Cu-Mo-Au mineralization in the Jinping-Fan Si Pan region, southeastern Ailao Shan-Red River shear zone, southwestern China-northwestern Vietnam

    Science.gov (United States)

    Tran, My Dung; Liu, Junlai; Nguyen, Quang Luat; Chen, Yue; Tang, Yuan; Song, Zhijie; Zhang, Zhaochong; Zhao, Zhidan

    2014-01-01

    The Jinping-Fan Si Pan (JFP) Cenozoic magmatic and Cu-Mo-Au metallogenic belt in the southeastern part of the Ailao Shan shear zone host the Tongchang, Chang‧an, Habo, and Chinh Sang Cu-Mo-Au deposits. These deposits form an integrated epithermal-porphyry regional mineralization system associated with 40-32 Ma high-K alkaline magmatism. The magmatic rocks in the belt have relatively low TiO2 (<0.73 wt%), P2O5 (<0.29 wt%), and FeO* (<4.99 wt%), and high Na2O (2.86-4.75 wt%) and K2O (4.01-7.98 wt%). They also have high contents of incompatible trace elements, and are enriched in LILE (Rb, Ba, K, Sr) and LREE. They have marked Nb, Ta, Ti and P depletion in primitive mantle-normalized spidergrams, and plot close to the EMII mantle field in the Sr-Nd isotopic diagram. These characteristics are similar to those of the Eocene high-K alkaline rocks along the northern Ailao Shan belt, eastern Tibet plateau. The sulfur and lead isotope analyses of sulfide minerals from both the ores and related magmatic rocks confirm the involvement of a magmatic ore fluid. The Cenozoic alkaline intrusions and Cu-Mo-Au mineralization in the JFP were formed prior to the initiation of left-lateral shearing along the Ailao Shan shear zone. The magmas appear to have been derived from enriched mantle, possibly with mixing of materials from the buried Tethyan oceanic lithosphere, and/or crust.

  15. Structure and LA-ICP-MS zircon U-Pb dating of syntectonic plutons emplaced in the Pan-African Banyo-Tcholliré shear zone (central north Cameroon)

    Science.gov (United States)

    Nomo, Emmanuel Negue; Tchameni, Rigobert; Vanderhaeghe, Olivier; Sun, Fenguye; Barbey, Pierre; Tekoum, Léontine; Tchunte, Periclex Martial Fosso; Eglinger, Aurélien; Fouotsa, Nicaise Alliance Saha

    2017-07-01

    The Tcholliré massif, in central north Cameroon, consists of elongated granite plutons that crop out along the Pan-African Tcholliré-Banyo shear zone (TBSZ), a potential suture zone within the Central Africa Orogenic Belt. New structural and geochronological data on these granites constrain the tectonic regime and timing of the TBSZ. The plutons consist of syntectonic granites and granodiorite containing dioritic mafic enclaves. They show an S2 sub-vertical foliation, that trends NE-SW to ENE-WSW. The related L2 lineation is subhorizontal to shallowly plunging to the SW or NE. Kinematic indicators such as asymmetric folds, sigmoidal-shape boudins, shear bands, imbricated feldspar phenocrysts along antithetic fractures point to a sinistral sense of shear. Microstructural analysis shows that structures are acquired from the submagmatic to the low temperature solid state suggesting progressive deformation of the magma during its emplacement, crystallization and cooling. U-Pb zircon dating on this massif yields emplacement ages of 719 ± 12 Ma for the biotite-amphibole granite and muscovite granite, 652.2 ± 5.4 Ma for the biotite-granite and 632 ± 13 Ma for the leucogranite. These geochronological data show in addition, Palaeoproterozoic inherited ages of 1631 ± 30 Ma on the leucogranites of this massif, and point to a Palaeoproterozoic contribution in their genesis. The range of ages (ca. 87 Ma) points to the timing of syntectonic emplacement of felsic magmas coeval with sinistral transpression along the TBSZ during the Pan-African orogeny. These results show that the TBSZ has recorded prolonged deformation associated with crustal magmatism between the Palaeoproterozoic Adamawa-Yadé domain to the southeast and the Sinassi-Mayo Kebbi Neoproterozoic magmatic arc to the Northwest.

  16. Integrating GIS-based geologic mapping, LiDAR-based lineament analysis and site specific rock slope data to delineate a zone of existing and potential rock slope instability located along the grandfather mountain window-Linville Falls shear zone contact, Southern Appalachian Mountains, Watauga County, North Carolina

    Science.gov (United States)

    Gillon, K.A.; Wooten, R.M.; Latham, R.L.; Witt, A.W.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.

    2009-01-01

    Landslide hazard maps of Watauga County identify >2200 landslides, model debris flow susceptibility, and evaluate a 14km x 0.5km zone of existing and potential rock slope instability (ZEPRSI) near the Town of Boone. The ZEPRSI encompasses west-northwest trending (WNWT) topographic ridges where 14 active/past-active rock/weathered rock slides occur mainly in rocks of the Grandfather Mountain Window (GMW). The north side of this ridgeline is the GMW / Linville Falls Fault (LFF) contact. Sheared rocks of the Linville Falls Shear Zone (LFSZ) occur along the ridge and locally in the valley north of the contact. The valley is underlain principally by layered granitic gneiss comprising the Linville Falls/Beech Mountain/Stone Mountain Thrust Sheet. The integration of ArcGIS??? - format digital geologic and lineament mapping on a 6m LiDAR (Light Detecting and Ranging) digital elevation model (DEM) base, and kinematic analyses of site specific rock slope data (e.g., presence and degree of ductile and brittle deformation fabrics, rock type, rock weathering state) indicate: WNWT lineaments are expressions of a regionally extensive zone of fractures and faults; and ZEPRSI rock slope failures concentrate along excavated, north-facing LFF/LFSZ slopes where brittle fabrics overprint older metamorphic foliations, and other fractures create side and back release surfaces. Copyright 2009 ARMA, American Rock Mechanics Association.

  17. Pan-African deformations in the basement of the Negele area, southern Ethiopia

    Science.gov (United States)

    Yihunie, Tadesse

    2002-03-01

    Polydeformed and metamorphosed Neoproterozoic rocks of the East African Orogen in the Negele area constituted three lithostructurally distinct and thrust-bounded terranes. These are, from west to east, the Kenticha, Alghe and Bulbul terranes. The Kenticha and Bulbul terranes are metavolcano-sedimentary and ultramafic sequences, representing parts of the Arabian-Nubian Shield (ANS), which are welded to the central Alghe gneissic terrane of the Mozambique Belt affinity along N-S-trending sheared thrust contacts. Structural data suggest that the Negele basement had evolved through three phases of deformation. During D1 (folding) deformation, north-south upright and inclined folds with north-trending axes were developed. East and west-verging thrusts, right-lateral shearing along the north-oriented Kenticha and Bulbul thrust contacts and related structural elements were developed during D2 (thrusting) deformation. The pervasive D1 event is interpreted to have occurred at 620-610 Ma and the D2 event ended prior to 554 Ma. Right-lateral strike-slips along thrust contacts are interpreted to have been initiated during late D2. During D3, left-lateral strike-slip along the Wadera Shear Zone and respective strike-slip movements along conjugate set of shear zones were developed in the Alghe terrane, and are interpreted to have occurred later than 557 Ma. The structural data suggest that eastward thrusting of the Kenticha and westward tectonic transport of the Bulbul sequences over the Alghe gneissic terrane of the Mozambique Belt, during D2, were accompanied by right-lateral strike-slip displacements along thrust contacts. Right-lateral strike-slip movements along the Kenticha thrust contact, further suggest northward movement of the Kenticha sequence during the Pan-African orogeny in the Neoproterozoic. Left-lateral strike-slip along the orogen-parallel NNE-SSW Wadera Shear Zone and strike-slip movements along a conjugate set of shear zones completed final terrane

  18. The polyphased tectonic evolution of the Anegada Passage in the northern Lesser Antilles subduction zone

    Science.gov (United States)

    Laurencin, M.; Marcaillou, B.; Graindorge, D.; Klingelhoefer, F.; Lallemand, S.; Laigle, M.; Lebrun, J.-F.

    2017-05-01

    The influence of the highly oblique plate convergence at the northern Lesser Antilles onto the margin strain partitioning and deformation pattern, although frequently invoked, has never been clearly imaged. The Anegada Passage is a set of basins and deep valleys, regularly related to the southern boundary of the Puerto Rico-Virgin Islands (PRVI) microplate. Despite the publications of various tectonic models mostly based on bathymetric data, the tectonic origin and deformation of this Passage remains unconstrained in the absence of deep structure imaging. During cruises Antithesis 1 and 3 (2013-2016), we recorded the first deep multichannel seismic images and new multibeam data in the northern Lesser Antilles margin segment in order to shed a new light on the structure and tectonic pattern of the Anegada Passage. We image the northeastern extent of the Anegada Passage, from the Sombrero Basin to the Lesser Antilles margin front. Our results reveal that this northeastern segment is an EW trending left-stepping en échelon strike-slip system that consists of the Sombrero and Malliwana pull-apart basins, the Malliwana and Anguilla left-lateral faults, and the NE-SW compressional restraining bend at the Malliwana Hill. Reviewing the structure of the Anegada Passage, from the south of Puerto Rico to the Lesser Antilles margin front, reveals a polyphased tectonic history. The Anegada Passage is formed by a NW-SE extension, possibly related to the rotation or escape of PRVI block due to collision of the Bahamas Bank. Currently, it is deformed by an active WNW-ESE strike-slip deformation associated to the shear component of the strain partitioning resulting from the subduction obliquity.

  19. Fault Zone Architecture and Mineralogy: Implications in Fluid Flow and Permeability in Crustal Scale Fault Zones in the Southern Andes.

    Science.gov (United States)

    Roquer, T.; Terrón, E.; Perez-Flores, P.; Arancibia, G.; Cembrano, J. M.

    2014-12-01

    Fluid flow in the upper crust is controlled by the permeability and interconnection of fractures in the fault zones. The permeability within the fault zone is determined by its activity, architecture and, in particular, by the mineralogy of the core and the damage zone. Whereas the permeability structure of a fault zone can be defined by the volume proportion of the core with respect to the damage zone, the relationship between the mineralogy and permeability along fault zones still remains obscure. This work examines structural and mineralogical data to show the relationship between the mineral composition of the fault zone with its permeability in the Liquiñe-Ofqui Fault System (LOFS) and the Arc-oblique Long-lived Fault Systems (ALFS), Southern Chile. The LOFS is an active ca. 1200 km long strike-slip Cenozoic intra-arc structure that strikes NNE in its master traces and NE in its subsidiary traces, with dextral and dextral-normal movement mostly developed in the last 6 My. Although the LOFS and the ALFS cross-cut each other, the ALFS is an apparently older basement fault system where seismic and field evidences record sinistral, sinistral-normal and sinistral-reverse movements. One 22-m-long NE transect was mapped orthogonal to a segment of the ALFS, where host rocks are Miocene andesitic rocks. Structural and XRD sampling were conducted in the core and damage zone. Structural mapping shows a multiple core, NW-striking fault zone with foliated gouge and an asymmetric damage zone, where the hanging wall has significantly higher mesoscopic fracture density than the footwall. The hanging wall is characterized by NW-striking, steeply dipping veins. Preliminary XRD results indicate the presence of homogenously distributed Ca-rich zeolite (mainly laumontite) in the core and the veins of the damage zone, which could indicate that the core acted as a conduit for low-temperature (ca. 220°C) fluids.

  20. Re-Os, Sm-Nd, U-Pb, and stepwise lead leaching isotope systematics in shear-zone hosted gold mineralization: genetic tracing and age constraints of crustal hydrothermal activity

    Science.gov (United States)

    Frei, R.; Nägler, Th. F.; Schönberg, R.; Kramers, J. D.

    1998-06-01

    A combined Re-Os, Sm-Nd, U-Pb, and stepwise Pb leaching (PbSL) isotope study of hydrothermal (Mo-W)-bearing minerals and base metal sulfides from two adjacent shear zone hosted gold deposits (RAN, Kimberley) in the Harare-Shamva greenstone belt (Zimbabwe) constrain the timing of the mineralizing events to two periods. During an initial Late Archean event (2.60 Ga) a first molybdenite-scheelite bearing paragenesis was deposited in both shear zone systems, followed by a local reactivation of the shear systems during an Early Proterozoic (1.96 Ga) tectono-thermal overprint, during which base metal sulfides and most of the gold was (re-)deposited. While PbSL has revealed an open-system behavior of the U-Pb systematics in molybdenite and wolframite from the RAN mine, initial Archean Re-Os ages are still preserved implying that this system in these minerals was more resistant to the overprint. A similar retentivity could be shown for the Sm-Nd system in scheelite and powellite associated with the above ore minerals. Re-Os isotopic data from the Proterozoic mineralization in the Kimberley mine point to a recent gain of Re, most pronouncedly affecting Fe-rich sulfides such as pyrrhotite. A significant Re-loss in powellitic scheelite (an alteration phase of molybdenite-bearing scheelite), coupled with a marked loss of U in W-Mo ore minerals, complements the observation of a major Re uptake in Fe-sulfides during oxidizing conditions in a weathering environment. Pyrrhotite under these conditions behaves as an efficient Re-sink. Lead isotope signatures from PbSL residues of molybdenite, powellite, and quartz indicate a continental crustal source and/or contamination for the mineralizing fluid by interaction of the fluids with older sedimentary material as represented by the direct host country rocks. Our investigation reveals the potential of the Re-Os isotopic system applied to crustal hydrothermal ore minerals for genetic tracing and dating purposes. The simplified chemical

  1. The Geomorphological Developments Along the East Anatolian Fault Zone, Turkey

    Science.gov (United States)

    Saber, R.; Caglayan, A.; Isik, V.; Seyitoglu, G.

    2014-12-01

    The collision of Eurasia with Arabia has given rise to intracontinental shortening in SE Turkey and development of large scale fault zones. The East Anatolian Fault Zone (EAFZ), a major active fault zone over 700 km in length with NE-striking, defines the boundary zone between Eurasia plate and Anatolian micro-plate. Although the northeastern continuation of the zone merges into the North Anatolian Fault Zone at Karliova region, the southwestern continuation has been the subject of some debate. The zone is characterized by numerous, complex faults and segmented surface ruptures. It cuts and offsets several distinctive units in east and southeast Turkey. The portion of the EAFZ examined in this study extends from Celikhan to Turkoglu. Active fault strands in this portion of the EAFZ is termed the Erkenek and Golbasi segments. The zone is made of several NE-SW closely spaced strands cut across Mesozoic-to-Tertiary variable rock units and structures, indicating inception of strike-slip motion in Quaternary and characterized by a series of basins. Fault-related several morphological features have been mapped are within the study area, suggesting the left-lateral motion of fault strands along this part of the EAFZ. Offset streams, beheaded channels, pressure and shutter ridges, linear valleys and ridges and sag ponds are prominent morpho-tectonic features. Offset streams have been measured as few meters to hundreds of meters and show sinistral displacement along the fault zone. Fault scarps, several tens of metres high, are developed in fan deposits along the length of the fault strands. Forming the set of linear sag ponds in Golbasi reveals extentional activity of the EAFZ in this area. Motion of fault strands formed linear valleys and ridges parallel to the faults which is most remarkable features. Our geomorphic studies demonstrated the ongoing activity of the the EAFZ between Celikhan to Turkoglu regions.

  2. The Mid-Hungarian line: a zone of repeated tectonic inversions

    Science.gov (United States)

    Csontos, László; Nagymarosy, András

    1998-11-01

    The Mid-Hungarian line is a major tectonic feature of the Intra-Carpathian area separating two terranes of different origin and tectonic structure. Although this tectonic line was known from borehole records, it has not been described in seismic sections. The study presents interpreted seismic lines crossing the supposed trace of the Mid-Hungarian line. These seismic sections show north-dipping normal faults and thrust faults as well as cross-cutting young strike-slip faults. A complex tectonic history is deduced, including intra-Oligocene-Early Miocene thrusting, Middle Miocene extension, local Late Miocene inversion and Late Miocene-Pliocene normal faulting and left-lateral wrenching. In the light of our seismic study we think that the best candidate for the Mid-Hungarian line is a north-dipping detachment fault beneath large masses of Neogene volcanics. The auxiliary structures to the north seen on seismic sections suggest that it moved as a south-vergent thrust fault during the Palaeogene-Early Miocene which later was reactivated as a set of normal faults. The northern Alcapa unit overrode the southern Tisza-Dacia unit along this fault zone. The same relative positions are observed in the northern termination of the line. Other structures along the supposed trace of the line are north-dipping normal- or strike-slip faults which frequently were reactivated as smaller thrust faults during the late Neogene. Palaeogene-Early Miocene thrusting along the line might be the result of the opposite Tertiary rotations of the two major units, as suggested by palaeomagnetic measurements and earlier models.

  3. Integration of geophysical and geological data for delimitation of mineralized zones in Um Naggat area, Central Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Ibrahim Gaafar

    2015-06-01

    Interpretations of the aeromagnetic maps delineated four regional structural trends oriented due NNW, NW, ENE and E–W directions. They are identified as strike-slip faults, which coincide well with field observations, where NW-trending faults cut and displace right laterally ENE-trending older ones. The interaction between these two strike-slip fault systems confining the albite granite is easily identified on the regional data presenting longer wavelength anomalies, implying deep-seated structures. They could represent potential pathways for migration of enriched mineralized fluids. Geochemically, albite granites of peraluminous characteristics that had suffered extensive post-magmatic metasomatic reworking, resulted into development of (Zr, Hf, Nb, Ta, U, Th, Sn and albite-enriched and greisenized granite body of about 600 m thick, and more than 3 km in strike length. The albite granite is characterized by sharp increase in average rare metal content: Zr (830 ppm, Hf (51 ppm, Nb (340 ppm, Ta (44 ppm, and U (90 ppm. Thorite, uranothorite, uraninite and zircon are the main uranium-bearing minerals of magmatic origin within the enclosing granite. However, with respect to Zr, Nb, and Ta, the albitized granite can be categorized as rare metal granite. The integration of airborne geophysical (magnetic and γ-ray spectrometric, geological, geochemical and mineralogical data succeeded in assigning the albite granite of Um Naggat pluton as a mineralized zone. This zone is characterized by its high thorium and uranium of hydrothermal origin as indicated by its low Th/U ratio, with rare metals mineralization controlled by two main structural trends in the NW- and ENE-directions.

  4. Kinematics of Post-obduction Deformation of the Tertiary Ridge at Al-Khod Village (Muscat, Oman

    Directory of Open Access Journals (Sweden)

    Andreas Scharf

    2016-11-01

    Full Text Available Structural investigations in post-obductional Paleocene to Eocene limestones of the Tertiary Ridge reveal a ~1 km long WNW-ESE striking strike-slip fault system within the ridge, consisting of two main sub-parallel, strike-slip faults. Considering the geometry of the Harding Strain Ellipse, the orientation of structures between the two strike-slip faults (e.g., Riedel shears, folds, reverse faults point to left-lateral motion. The abundance of large-scale folds (up to 100 m in wave length and amplitude between the two strike-slip faults led us to the interpretation of transpressive conditions in a first approximation. Moreover, the Tertiary Ridge of the study area consists of three distinct structural domains. The faults of Domain A and C are oriented WNW-ESE, but the trend of the faults in the central Domain B differs by ~10°. The left-lateral strike-slip fault system exists only in Domain B. We propose that the direction of greatest stress during Miocene plate convergence (sigma 1 was oriented 032°/212°. Considering the trend of the strike-slip zone and the orientation of sigma 1, the left-lateral motion must have been transpressive. Sigma 1 is perpendicularly oriented to the domains A and C. Prior to the Miocene D2 compressional event the study area was affected by a D1 extensional event, related to the opening of the Red Sea and the Gulf of Aden or to gravity-driven normal faulting. The D2 compressional/transpressional structures of the Miocene are reactivating the D1 structures of the Oligocene.

  5. High tsunami risk at northern tip of Sumatra as a result of the activity of the Sumatra Fault Zone (SFZ) combined with coastal landslides

    Science.gov (United States)

    Haridhi, H. A.; Huang, B. S.; Wen, K. L.; Mirza, A.; Rizal, S.; Purnawan, S.; Fajri, I.; Klingelhoefer, F.; Liu, C. S.; Lee, C. S.; Wilson, C. R.

    2017-12-01

    The lesson learned from the 12 January 2010, Mw 7.0 Haiti earthquake has shown that an earthquake with strike-slip faulting can produce a significant tsunami. This occasion is rare since in the fact of the fault consist predominantly of lateral motion, which is rarely associated with significant uplift or tsunami generation. Yet, another hint from this event, that this earthquake was accompanied by a coastal landslide. Again, there were only few records of a submarine slides as a primary source that generate a tsunami. Hence, the Haiti Mw 7.0 earthquake was generated by these combined mechanisms, i.e. strike-slip faulting earthquake and coastal landslide. In reflecting this event, the Sumatra region exhibit almost identical situation, where the right lateral strike-slip faulting of Sumatra Fault Zone (SFZ) is located. In this study, we are focusing at the northern tip of SFZ at Aceh Province. The reason we focused our study at its northern tip is that, since the Sumatra-Andaman mega earthquake and tsunami on 26 December 2004, which occurred at the subduction zone, there were no records of significant earthquake along the SFZ, where at this location the SFZ is divided into two faults, i.e. Aceh and Seulimeum faults. This study aimed as a mitigation effort, if an earthquake happened at these faults, do we observe a similar result as that happened at Haiti or not. To do so, we access the high-resolution shallow bathymetry data that acquired through a Community-Based Bathymetric Survey (CBBS), examines five scanned Single Channel Seismic (SCS) reflections data, perform the slope stability analysis and that simulate the tsunami using Cornell Multi-grid Coupled Tsunami Model (COMCOT) model with a combined source of fault activity and submarine landslide. The result shows that, by these combined mechanisms, if the earthquake as large as 7 Mw or larger, it could produce a tsunami as high as 6 meters along the coast. The detailed shallow bathymetric and the slope stability

  6. Transverse zones controlling the structural evolution of the Zipaquira Anticline (Eastern Cordillera, Colombia): Regional implications

    Science.gov (United States)

    García, Helbert; Jiménez, Giovanny

    2016-08-01

    We report paleomagnetic, magnetic fabric and structural results from 21 sites collected in Cretaceous marine mudstones and Paleogene continental sandstones from the limbs, hinge and transverse zones of the Zipaquira Anticline (ZA). The ZA is an asymmetrical fold with one limb completely overturned by processes like gravity and salt tectonics, and marked by several axis curvatures. The ZA is controlled by at least two (2) transverse zones known as the Neusa and Zipaquira Transverse Zones (NTZ and ZTZ, respectively). Magnetic mineralogy methods were applied at different sites and the main carriers of the magnetic properties are paramagnetic components with some sites being controlled by hematite and magnetite. Magnetic fabric analysis shows rigid-body rotation for the back-limb in the ZA, while the forelimb is subjected to internal deformation. Structural and paleomagnetic data shows the influence of the NTZ and ZTZ in the evolution of the different structures like the ZA and the Zipaquira, Carupa, Rio Guandoque, Las Margaritas and Neusa faults, controlling several factors as vergence, extension, fold axis curvature and stratigraphic detatchment. Clockwise rotations unraveled a block segmentation following a discontinuos model caused by transverse zones and one site reported a counter clockwise rotation associated with a left-lateral strike slip component for transverse faults (e.g. the Neusa Fault). We propose that diverse transverse zones have been active since Paleogene times, playing an important role in the tectonic evolution of the Cundinamarca sub-basin and controlling the structural evolution of folds and faults with block segmentation and rotations.

  7. Shear-Wave Splitting and Crustal Anisotropy in the Shillong-Mikir Plateau of Northeast India

    Science.gov (United States)

    Bora, Dipok K.; Hazarika, Devajit; Paul, Arpita; Borah, Kajaljyoti; Borgohain, Jayanta Madhab

    2018-01-01

    Seismic anisotropy of crust beneath the Shillong-Mikir Plateau and the surrounding regions of northeast India have been investigated with the help of splitting analysis of S-wave of local earthquakes. We estimate a total 83 pairs of splitting parameters ( Φ and δt) from 67 local shallow focus earthquakes (depth ≤ 32 km) recorded by the 10 broadband seismological stations operated in the study region. The results show delay times ranging from 0.02 to 0.2 s, which correspond to anisotropy up to 4%, suggesting significant strength of anisotropy in the study region. Fast polarization direction ( Φ) in the Shillong Plateau shows mostly NW-SE trend in the western part and NE-SW trend in the northern part. Φs near Kopili fault (KF) follows NW-SE trend. Φ at most of the stations in the study region is consistent with the local stress orientation, suggesting that the anisotropy is mainly caused by preferentially aligned cracks responding to the stress field. On the other hand, anisotropy observed near the KF is due to aligned macroscopic fracture related to strike-slip movement in the fault zone.

  8. The dynamics of a shear band

    Science.gov (United States)

    Giarola, Diana; Capuani, Domenico; Bigoni, Davide

    2018-03-01

    A shear band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the shear band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which keeps into account the singularity at the shear band tips and permits the analysis of an incident wave impinging a shear band. It is shown that the presence of the shear band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the shear band tips, which promotes shear band growth. Moreover, the waves scattered by the shear band are shown to generate a fine texture of vibrations, parallel to the shear band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the shear band.

  9. Rupture Along 400 km of the Bering Fracture Zone in the Komandorsky Islands Earthquake (MW 7.8) of 17 July 2017

    Science.gov (United States)

    Lay, Thorne; Ye, Lingling; Bai, Yefei; Cheung, Kwok Fai; Kanamori, Hiroo; Freymueller, Jeffrey; Steblov, Grigory M.; Kogan, Mikhail G.

    2017-12-01

    The 17 July 2017 Komandorsky Islands MW 7.8 earthquake involved arc-parallel right-lateral patchy strike-slip faulting along 400 km of the Bering Fracture Zone (BFZ) in the westernmost Aleutian Islands back arc. The large size of the earthquake indicates that the BFZ serves regionally as the primary plate boundary extending from the Near Islands to Kamchatka, with the fore-arc Komandorsky Sliver translating rapidly parallel to the Aleutian Trench. The slip distribution is determined by analysis of seismic, tsunami, and geodetic observations. Fault displacements of 4 to 8.5 m, mostly in the upper 15 km, but with localized extension to 20 to 30 km depth along a 100 km long segment of the BFZ, are comparable to the possible slip deficit since the last major earthquakes in this region in 1849 and 1858, given an estimated 5.1 cm/yr rate between the Komandorsky Sliver and the Bering Plate.

  10. Late-orogenic extension and strike-slip deformation in the Neogene of southeastern Spain

    NARCIS (Netherlands)

    Meijninger, B.M.L.

    2006-01-01

    The Betic Cordillera of southern Spain form the western end of the Alpine orogen, which during the Neogene was affected by large-scale late-orogenic extension. Extension, however, occurred within a setting of continuous slow convergence of the African and European plates. During the Neogene,

  11. Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting

    Science.gov (United States)

    Green, Robert G.; White, Robert S.; Greenfield, Tim

    2014-01-01

    Along mid-ocean ridges the extending crust is segmented on length scales of 10-1,000km. Where rift segments are offset from one another, motion between segments is accommodated by transform faults that are oriented orthogonally to the main rift axis. Where segments overlap, non-transform offsets with a variety of geometries accommodate shear motions. Here we use micro-seismic data to analyse the geometries of faults at two overlapping rift segments exposed on land in north Iceland. Between the rift segments, we identify a series of faults that are aligned sub-parallel to the orientation of the main rift. These faults slip through left-lateral strike-slip motion. Yet, movement between the overlapping rift segments is through right-lateral motion. Together, these motions induce a clockwise rotation of the faults and intervening crustal blocks in a motion that is consistent with a bookshelf-faulting mechanism, named after its resemblance to a tilting row of books on a shelf. The faults probably reactivated existing crustal weaknesses, such as dyke intrusions, that were originally oriented parallel to the main rift and have since rotated about 15° clockwise. Reactivation of pre-existing, rift-parallel weaknesses contrasts with typical mid-ocean ridge transform faults and is an important illustration of a non-transform offset accommodating shear motion between overlapping rift segments.

  12. (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone

    Science.gov (United States)

    Moser, Amy C.; Evans, James P.; Ault, Alexis K.; Janecke, Susanne U.; Bradbury, Kelly K.

    2017-10-01

    The timing, tempo, and processes of punctuated deformation in strike-slip fault systems are challenging to resolve in the rock record. Faults in the Mecca Hills, adjacent to the southernmost San Andreas Fault, California, accommodate active deformation and exhumation in the Plio-Pleistocene sedimentary rocks and underlying crystalline basement. We document the spatiotemporal patterns of San Andreas Fault-related deformation as recorded in crystalline basement rocks of the Mecca Hills using fault microstructural observations, geochemical data, and hematite (n = 24) and apatite (n = 44) (U-Th)/He (hematite He, apatite He) thermochronometry data. Reproducible mean hematite He dates from minor hematite-coated fault surfaces in the Painted Canyon Fault damage zone range from ∼0.7-0.4 Ma and are younger than ∼1.2 Ma apatite He dates from adjacent crystalline basement host rock. These data reveal concomitant Pleistocene pulses of fault slip, fluid flow, and synkinematic hematite mineralization. Hematite textures, crystal morphology, and hematite He data patterns imply some damage zone deformation occurred via cyclic crack-seal and creep processes. Apatite He data from crystalline basement define distinct date-eU patterns and indicate cooling across discrete fault blocks in the Mecca Hills. Uniform ∼1.2 Ma apatite He dates regardless of eU are located exclusively between the Painted Canyon and Platform faults. Outside of this fault block, samples yield individual apatite He dates from ∼30-1 Ma that define a positive apatite He date-eU correlation. These patterns reveal focused exhumation away from the main trace of the San Andreas Fault at ∼1.2 Ma. Low-temperature thermochronometry of fault-related rocks provides an unprecedented window into the 105-106-yr record of San Andreas Fault-related deformation in the Mecca Hills and documents hematite deformation mechanisms that may be operative in other strike-slip faults world-wide.

  13. Petrogenesis and tectonic of the Urucum granitic suite, Rio Doce Valley (Minas Gerais - Brazil: an example of syn to late collisional peraluminous magmatism associated with high-angle transcurrent shear zone

    Directory of Open Access Journals (Sweden)

    Hermínio Arias Nalini Júnior

    Full Text Available The Urucum suite (582 ± 2 Ma, zircon U-Pb age, situated in the Mid-Rio Doce Valley, eastern part of Minas Gerais State, is characterized by elongated, NW-SE and N-S trending granitic massifs associated with the Conselho Peña-Resplendor high-angle shear zone. It corresponds to a syn to late collisional magmatism that presents dominant solid-state foliation. Four facies are distinguished within the Urucum suite: (i a porphyritic (Urucum; (ii a medium- to coarse nequigranular (Palmital; (iii a tourmaline-bearing; and (iv a pegmatitic facies. These facies are peraluminous, with alumina saturation index varying from 0.98 to 1.38. SiO2 contents vary from 70.7 to 73.7 wt%, with K2O values ranging from 3.5 to 5.7 wt%, Na2O from 1.9 to 4.4 wt%, MgO from 0.6 to 1.2 wt%, and CaO from 0.3 to 0.9%. Harker-type diagrams show rather continuous trends from the less-evolved Urucum facies to the more evolved tourmaline-bearing and pegmatitic facies. The behavior of several major oxides and trace elements (Fe2O3, MgO, MnO, CaO, TiO2, Al2O3, K2O, Rb and Ba reflects the role played by fractionation of ferromagnesian minerals, feldspars and accessory minerals. Initial Sr87/Sr86 ratios vary from 0.711 to 0.716, with εNd (580 Ma values between -7.4 to -8.2, and Sm-Nd TDM model ages ranging from 2290 to 1840 Ma.

  14. Assessment of Shear Strength in Silty Soils

    Directory of Open Access Journals (Sweden)

    Stefaniak Katarzyna

    2015-06-01

    Full Text Available The article presents a comparison of shear strength values in silty soils from the area of Poznań, determined based on selected Nkt values recommended in literature, with values of shear strength established on the basis of Nkt values recommended by the author. Analysed silty soils are characterized by the carbonate cementation zone, which made it possible to compare selected empirical coefficients both in normally consolidated and overconsolidated soils

  15. Hydromechanical heterogeneities of a mature fault zone: impacts on fluid flow.

    Science.gov (United States)

    Jeanne, Pierre; Guglielmi, Yves; Cappa, Frédéric

    2013-01-01

    In this paper, fluid flow is examined for a mature strike-slip fault zone with anisotropic permeability and internal heterogeneity. The hydraulic properties of the fault zone were first characterized in situ by microgeophysical (VP and σc ) and rock-quality measurements (Q-value) performed along a 50-m long profile perpendicular to the fault zone. Then, the local hydrogeological context of the fault was modified to conduct a water-injection test. The resulting fluid pressures and flow rates through the different fault-zone compartments were then analyzed with a two-phase fluid-flow numerical simulation. Fault hydraulic properties estimated from the injection test signals were compared to the properties estimated from the multiscale geological approach. We found that (1) the microgeophysical measurements that we made yield valuable information on the porosity and the specific storage coefficient within the fault zone and (2) the Q-value method highlights significant contrasts in permeability. Fault hydrodynamic behavior can be modeled by a permeability tensor rotation across the fault zone and by a storativity increase. The permeability tensor rotation is linked to the modification of the preexisting fracture properties and to the development of new fractures during the faulting process, whereas the storativity increase results from the development of micro- and macrofractures that lower the fault-zone stiffness and allows an increased extension of the pore space within the fault damage zone. Finally, heterogeneities internal to the fault zones create complex patterns of fluid flow that reflect the connections of paths with contrasting properties. © 2013, The Author(s). Ground Water © 2013, National Ground Water Association.

  16. Morphometric analysis of El Salvador Fault Zone. Implications to the tectonic evolution. Central America.

    Science.gov (United States)

    Alonso-Henar, Jorge; Jesús Martínez-Díaz, José; Álvarez-Gómez, José Antonio

    2013-04-01

    It is considered that the study of the recent topography development, and the use of geomorphological indexes are good tools for the quantification of the active tectonics. We have used quantitative geomorphology in order to improve our understanding of the recent activity and tectonic evolution of the El Salvador Fault Zone (ESFZ); an E-W oriented strike-slip fault zone that extends 150 km through El Salvador (Martínez-Díaz et al. 2004). Previous studies propose a transtensive tectonic regime at the Central America Volcanic Arc in El Salvador, which induces relative vertical motions on the faults within El Salvador Fault Zone (i.e. Álvarez-Gómez et al., 2008, Cáceres et al. 2005,). This relative vertical displacement can be quantified with the use of hypsometry as a geomorphological character. The morphometric analysis done contributes to a better understanding of the ESFZ. We have defined km scale tectonic block relative displacements that may be useful to constrain the strain distribution along the ESFZ, length of segments with homogeneous vertical movements and lateral relay of active structures. This study supports the hypothesis of a recent migration in the maximum shortening direction, and the accomodation of the current deformation through the reactivation of pre-existing structures inherited from a previous tectonic frame. A similar tectonic evolution as described Weinberg (1992) in Nicaragua, is interpreted from the results of this study.

  17. The strain-dependent spatial evolution of garnet in a high- P ductile shear zone from the Western Gneiss Region (Norway): a synchrotron X-ray microtomography study

    Energy Technology Data Exchange (ETDEWEB)

    Macente, A. [School of Geosciences, University of Edinburgh, The King' s Building James Hutton Road Edinburgh EH9 3FE UK; Fusseis, F. [School of Geosciences, University of Edinburgh, The King' s Building James Hutton Road Edinburgh EH9 3FE UK; Menegon, L. [School of Geography, Earth and Environmental Sciences, Faculty of Science and Engineering, Plymouth University, Fitzroy Drake Circus Plymouth Devon PL4 8AA UK; Xianghui, X. [Argonne National Laboratory, 9700 S. Cass Ave Building 431-B003 Argonne IL USA; John, T. [Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74-100 12249 Berlin Germany

    2017-03-27

    Reaction and deformation microfabrics provide key information to understand the thermodynamic and kinetic controls of tectono-metamorphic processes, however they are usually analysed in two dimensions, omitting important information regarding the third spatial dimension. We applied synchrotron-based X-ray microtomography to document the evolution of a pristine olivine gabbro into a deformed omphacite-garnet eclogite in four dimensions, where the 4th dimension is represented by the degree of strain. In the investigated samples, which cover a strain gradient into a shear zone from the Western Gneiss Region (Norway), we focused on the spatial transformation of garnet coronas into elongated clusters of garnets with increasing strain. Our microtomographic data allowed quantification of garnet volume, shape and spatial arrangement evolution with increasing strain. We combined microtomographic observations with light microscope- and backscatter electron images as well as electron microprobe- (EMPA) and electron backscatter diffraction (EBSD) analysis to correlate mineral composition and orientation data with the X-ray absorption signal of the same mineral grains. With increasing deformation, the garnet volume almost triples. In the low strain domain, garnets form a well interconnected large garnet aggregate that develops throughout the entire Page 1 of 52 sample. We also observed that garnet coronas in the gabbros never completely encapsulate olivine grains. In the most highly deformed eclogites, the oblate shapes of garnet clusters reflect a deformational origin of the microfabrics. We interpret the aligned garnet aggregates to direct synkinematic fluid flow and consequently influence the transport of dissolved chemical components. EBSD analyses reveal that garnet show a near-random crystal preferred orientation that testifies no evidence for crystal plasticity. There is, however evidence for minor fracturing, neo-nucleation and overgrowth. Microprobe chemical analysis

  18. MM98.21 Method for studying material element passing a stationary shear plane

    DEFF Research Database (Denmark)

    Lindegren, Maria; Wiwe, Birgitte; Christensen, Thomas

    1998-01-01

    Traditionally, material response to shear deformation has been studied with methods where the shear is gradually increasing from zero to the final value over a certain fixed deformation zone as e.g. in the well-known torsion test of tube with a defined shear zone established by a machined...... circumferential grove. Normally shear in metal forming processes are of another nature, namely where the material elements move through a stationary shear zone, often of small width. In this paper a method enabling the simulation of this situation is suggested....

  19. Impact of the slab dip change onto the deformation partitioning in the northern Lesser Antilles oblique subduction zone (Antigua-Virgin Islands)

    Science.gov (United States)

    Laurencin, Muriel; Marcaillou, Boris; Klingelhoefer, Frauke; Graindorge, David; Lebrun, Jean-Frédéric; Laigle, Mireille; Lallemand, Serge

    2017-04-01

    Marine geophysical cruises Antithesis (2013-2016) investigate the impact of the variations in interplate geometry onto margin tectonic deformation along the strongly oblique Lesser Antilles subduction zone. A striking features of this margin is the drastic increase in earthquake number from the quiet Barbuda-St Martin segment to the Virgin Islands platform. Wide-angle seismic data highlight a northward shallowing of the downgoing plate: in a 150 km distance from the deformation front, the slab dipping angle in the convergence direction decreases from 12° offshore of Antigua Island to 7° offshore of Virgin Islands. North-South wide-angle seismic line substantiates a drastic slab-dip change that likely causes this northward shallowing. This dip change is located beneath the southern tip of the Virgin Islands platform where the Anegada Passage entails the upper plate. Based on deep seismic lines and bathymetric data, the Anegada Passage is a 450 km long W-E trending set of pull-apart basins and strike-slip faults that extends from the Lesser Antilles accretionary prism to Puerto Rico. The newly observed sedimentary architecture within pull-apart Sombrero and Malliwana basins indicates a polyphased tectonic history. A past prominent NW-SE extensive to transtensive phase, possibly related to the Bahamas Bank collision, opened the Anegada Passage as previously published. Transpressive tectonic evidences indicate that these structures have been recently reactivated in an en-echelon sinistral strike-slip system. The interpreted strain ellipsoid is consistent with deformation partitioning. We propose that the slab northward shallowing increases the interplate coupling and the seismic activity beneath the Virgin Islands platform comparatively to the quiet Barbuda-St Martin segment. It is noteworthy that the major tectonic partitioning structure in the Lesser Antilles forearc is located above the slab dip change where the interplate seismic coupling increases.

  20. Development of Hydrologic Characterization Technology of Fault Zones

    Energy Technology Data Exchange (ETDEWEB)

    Karasaki, Kenzi; Onishi, Tiemi; Wu, Yu-Shu

    2008-03-31

    Through an extensive literature survey we find that there is very limited amount of work on fault zone hydrology, particularly in the field using borehole testing. The common elements of a fault include a core, and damage zones. The core usually acts as a barrier to the flow across it, whereas the damage zone controls the flow either parallel to the strike or dip of a fault. In most of cases the damage zone isthe one that is controlling the flow in the fault zone and the surroundings. The permeability of damage zone is in the range of two to three orders of magnitude higher than the protolith. The fault core can have permeability up to seven orders of magnitude lower than the damage zone. The fault types (normal, reverse, and strike-slip) by themselves do not appear to be a clear classifier of the hydrology of fault zones. However, there still remains a possibility that other additional geologic attributes and scaling relationships can be used to predict or bracket the range of hydrologic behavior of fault zones. AMT (Audio frequency Magneto Telluric) and seismic reflection techniques are often used to locate faults. Geochemical signatures and temperature distributions are often used to identify flow domains and/or directions. ALSM (Airborne Laser Swath Mapping) or LIDAR (Light Detection and Ranging) method may prove to be a powerful tool for identifying lineaments in place of the traditional photogrammetry. Nonetheless not much work has been done to characterize the hydrologic properties of faults by directly testing them using pump tests. There are some uncertainties involved in analyzing pressure transients of pump tests: both low permeability and high permeability faults exhibit similar pressure responses. A physically based conceptual and numerical model is presented for simulating fluid and heat flow and solute transport through fractured fault zones using a multiple-continuum medium approach. Data from the Horonobe URL site are analyzed to demonstrate the

  1. Development of Hydrologic Characterization Technology of Fault Zones

    International Nuclear Information System (INIS)

    Karasaki, Kenzi; Onishi, Tiemi; Wu, Yu-Shu

    2008-01-01

    Through an extensive literature survey we find that there is very limited amount of work on fault zone hydrology, particularly in the field using borehole testing. The common elements of a fault include a core, and damage zones. The core usually acts as a barrier to the flow across it, whereas the damage zone controls the flow either parallel to the strike or dip of a fault. In most of cases the damage zone is the one that is controlling the flow in the fault zone and the surroundings. The permeability of damage zone is in the range of two to three orders of magnitude higher than the protolith. The fault core can have permeability up to seven orders of magnitude lower than the damage zone. The fault types (normal, reverse, and strike-slip) by themselves do not appear to be a clear classifier of the hydrology of fault zones. However, there still remains a possibility that other additional geologic attributes and scaling relationships can be used to predict or bracket the range of hydrologic behavior of fault zones. AMT (Audio frequency Magneto Telluric) and seismic reflection techniques are often used to locate faults. Geochemical signatures and temperature distributions are often used to identify flow domains and/or directions. ALSM (Airborne Laser Swath Mapping) or LIDAR (Light Detection and Ranging) method may prove to be a powerful tool for identifying lineaments in place of the traditional photogrammetry. Nonetheless not much work has been done to characterize the hydrologic properties of faults by directly testing them using pump tests. There are some uncertainties involved in analyzing pressure transients of pump tests: both low permeability and high permeability faults exhibit similar pressure responses. A physically based conceptual and numerical model is presented for simulating fluid and heat flow and solute transport through fractured fault zones using a multiple-continuum medium approach. Data from the Horonobe URL site are analyzed to demonstrate the

  2. Active faults and related Late Quaternary deformation along the Northwestern Himalayan Frontal Zone, India

    Directory of Open Access Journals (Sweden)

    T. Nakata

    2003-06-01

    Full Text Available Numerous newly-identified traces of active faults in the Himalayan foothill zone along the HFF around Chandigarh, in Pinjore Dun, along the piedmont zone of the Lower Siwalik hill front and within the Lower Tertiary hill range reveal the pattern of thrust and strike-slip faulting, striking parallel to the principal structural trend (NNW-SSE of the orogenic belt. The active Chandigarh Fault, Pinjore Garden Fault and Barsar thrust have vertically dislocated, warped and backtilted fluvial and alluvial-fan surfaces made up of Late Pleistocene-Holocene sediments. West- and southwest-facing fault scarplets with heights ranging from 12 to 50 m along these faults suggest continued tectonic movement through Late Pleistocene to recent times. Gentle warping and backtilting of the terraces on the hanging wall sides of the faults indicate fault-bend folding. These active faults are the manifestation of north-dipping imbricated thrust faults branching out from the major fault systems like the Main Boundary Fault (MBF and Himalayan Frontal Fault (HFF, probably merging down northward into a décollement. The Taksal Fault, striking NNW-SSE, shows prominent right-lateral movement marked by lateral offset of streams and younger Quaternary terraces and occupies a narrow deep linear valley along the fault trace. Right stepping along this fault has resulted in formation of a small pull-apart basin. Fault scarplets facing ENE and WSW are the manifestation of dip-slip movement. This fault is an example of slip-partitioning between the strike-slip and thrust faults, suggesting ongoing oblique convergence of the Indian plate and northward migration of a tectonic sliver. Slip rate along the Taksal Fault has been calculated as 2.8 mm/yr. Preliminary trench investigation at the base of the Chandigarh Fault Scarp has revealed total displacement of 3.5 m along a low angle thrust fault with variable dip of 20° to 46° due northeast, possibly the result of one

  3. Three-dimensional characterization of microporosity and permeability in fault zones hosted in heterolithic succession

    Science.gov (United States)

    Riegel, H. B.; Zambrano, M.; Jablonska, D.; Emanuele, T.; Agosta, F.; Mattioni, L.; Rustichelli, A.

    2017-12-01

    The hydraulic properties of fault zones depend upon the individual contributions of the damage zone and the fault core. In the case of the damage zone, it is generally characterized by means of fracture analysis and modelling implementing multiple approaches, for instance the discrete fracture network model, the continuum model, and the channel network model. Conversely, the fault core is more difficult to characterize because it is normally composed of fine grain material generated by friction and wear. If the dimensions of the fault core allows it, the porosity and permeability are normally studied by means of laboratory analysis or in the other case by two dimensional microporosity analysis and in situ measurements of permeability (e.g. micro-permeameter). In this study, a combined approach consisting of fracture modeling, three-dimensional microporosity analysis, and computational fluid dynamics was applied to characterize the hydraulic properties of fault zones. The studied fault zones crosscut a well-cemented heterolithic succession (sandstone and mudstones) and may vary in terms of fault core thickness and composition, fracture properties, kinematics (normal or strike-slip), and displacement. These characteristics produce various splay and fault core behavior. The alternation of sandstone and mudstone layers is responsible for the concurrent occurrence of brittle (fractures) and ductile (clay smearing) deformation. When these alternating layers are faulted, they produce corresponding fault cores which act as conduits or barriers for fluid migration. When analyzing damage zones, accurate field and data acquisition and stochastic modeling was used to determine the hydraulic properties of the rock volume, in relation to the surrounding, undamaged host rock. In the fault cores, the three-dimensional pore network quantitative analysis based on X-ray microtomography images includes porosity, pore connectivity, and specific surface area. In addition, images were

  4. Test and Analysis of a New Ductile Shear Connection Design for RC Shear Walls

    DEFF Research Database (Denmark)

    Sørensen, Jesper Harrild; Hoang, Linh Cao; Olesen, John Forbes

    2017-01-01

    This paper presents a new and construction-friendly shear connection for assembly of precast reinforced concrete shear wall elements. In the proposed design, the precast elements have indented interfaces and are connected by a narrow zone grouted with mortar and reinforced with overlapping U......-bar loops. Contrary to the classical shear connections, the planes of the U-bar loops are here parallel to the plane of the wall elements. This feature enables a construction-friendly installation of the elements without the risk of rebars clashing. The core of mortar inside each U-bar loop is reinforced...

  5. Effects of shear coupling on shear properties of wood

    Science.gov (United States)

    Jen Y. Liu

    2000-01-01

    Under pure shear loading, an off-axis element of orthotropic material such as pure wood undergoes both shear and normal deformations. The ratio of the shear strain to a normal strain is defined as the shear coupling coefficient associated with the direction of the normal strain. The effects of shear coupling on shear properties of wood as predicted by the orthotropic...

  6. Subduction Zone Configuration of Central and Eastern Anatolia since the Late Cretaceous: Insights from Sedimentary Basins in the Neotethyan Suture Zone

    Science.gov (United States)

    Gürer, D.; Van Hinsbergen, D. J. J.; Matenco, L.; Corfu, F.; Langereis, C. G.; Ozkaptan, M.

    2015-12-01

    Subduction and accretion of continental and Neotethyan oceanic crustal fragments during Africa-Europe convergence since the Mesozoic formed the Anatolian fold-and-thrust belt. Sedimentary basins overlying key locations of the resulting fold-thrust belt that was metamorphosed to varying grades, may help to quantitatively kinematically restore the subduction evolution, and to identify timing, directions and amounts of post-accretionary extension, shortening and strike-slip faulting. The Upper Cretaceous - Oligocene Ulukışla basin straddles ophiolites, underlain by the HT-LP metamorphic Kırşehir Block (KB) to its north, and the HP-LT Bolkardağ/Afyon zone (BA) to its south. At its southern margin a series of small-offset faults consistent with latest Cretaceous-Paleocene N-S extension, was contemporaneous with (presumably extensional) exhumation of BA. Close to the contact with KB, a series of large-offset listric normal faults compatible with E-W extension offsets sediments and the base of newly dated Paleocene volcanics, showing E-W extension simultaneous with N-S extension in the south, prevailing until at least 56 Ma. Subsequently, N-S directed contraction led to E-W striking folds and thrusts and back-thrusting of the BA over the Ulukisla basin, probably in Oligocene time, and coeval left lateral strike-slip motion along the Ecemiş fault (EF) at the eastern basin margin. We explain the interplay between two Late Cretaceous-Paleocene extension directions to result from interplay between N-S and E-W striking subduction segments in central and eastern Anatolia, respectively. The latter can be followed farther east towards the Bitlis. In addition, absence of a Kirsehir block in eastern Anatolia led to a much longer duration of subduction below the Pontides, throughout the Paleogene and perhaps until as young as the Middle Miocene, with a suture below the Sivas basin that covers the contact between the KB, the Pontides and the Taurides. We restore an amount of

  7. The Two Subduction Zones of the Southern Caribbean: Lithosphere Tearing and Continental Margin Recycling in the East, Flat Slab Subduction and Laramide-Style Uplifts in the West

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Niu, F.; Schmitz, M.

    2015-12-01

    The southern Caribbean plate boundary is a complex strike-slip fault system bounded by oppositely vergent subduction zones, the Antilles subduction zone in the east, and a currently locked Caribbean-South American subduction zone in the west (Bilham and Mencin, 2013). Finite-frequency teleseismic P-wave tomography images both the Atlanic (ATL) and the Caribbean (CAR) plates subducting steeply in opposite directions to transition zone depths under northern South America. Ps receiver functions show a depressed 660 discontinuity and thickened transition zone associated with each subducting plate. In the east the oceanic (ATL) part of the South American (SA) plate subducts westward beneath the CAR, initiating the El Pilar-San Sebastian strike slip system, a subduction-transform edge propagator (STEP) fault (Govers and Wortel, 2005). The point at which the ATL tears away from SA as it descends into the mantle is evidenced by the Paria cluster seismicity at depths of 60-110 km (Russo et al, 1993). Body wave tomography and lithosphere-asthenosphere boundary (LAB) thickness determined from Sp and Ps receiver functions and Rayleigh waves suggest that the descending ATL also viscously removes the bottom third to half of the SA continental margin lithospheric mantle as it descends. This has left thinned continental lithosphere under northern SA in the wake of the eastward migrating Antilles subduction zone. The thinned lithosphere occupies ~70% of the length of the El Pilar-San Sebastian fault system, from ~64oW to ~69oW, and extends inland several hundred kilometers. In northwestern SA the CAR subducts east-southeast at low angle under northern Colombia and western Venezuela. The subducting CAR is at least 200 km wide, extending from northernmost Colombia as far south as the Bucaramanga nest seismicity. The CAR descends steeply under Lake Maracaibo and the Merida Andes. This flat slab is associated with three Neogene basement cored, Laramide-style uplifts: the Santa Marta

  8. Complex fragmentation and silicification structures in fault zones: quartz mineralization and repeated fragmentation along the Fountain Range Fault (Mt. Isa Inlier, Australia)

    Science.gov (United States)

    Seybold, Lina; Blenkinsop, Tom; Heuss, Soraya; Ord, Alison; Kruhl, Jörn H.

    2015-04-01

    In large-scale fault zones fracture networks are commonly generated by high volumes of pressurized fluids, followed by quartz precipitation. In this way large amounts of quartz are formed as microcrystalline masses and as complex vein systems, with partly highly different textures, as a result of different formation processes. Based on field and microstructural data and the quantification of vein patterns, the spatial and temporal connection between fragmentation, quartz crystallization and fluid and material flow along the Fountain Range Fault at Fountain Springs was investigated. Dextral strike-slip led to up to 25 km horizontal displacement along the fault. Due to various fragmentation and quartz formation processes, a ca. 100 m high, 80 - 100 m wide and km-long quartz ridge with numerous vein systems and variable microfabrics was formed. Locally, lenses of highly altered metamorphic wall-rocks occur in the quartz zone. Where exposed, the contact to wall rocks is sharp. Millimetre- to decimetre-thick quartz veins penetrate the wall-rocks only within metre distance from the contact. Several clearly distinguishable fine-grained reddish, brownish to dark and pigment-rich quartz masses form up to 50 m wide and up to several 100 m long steep lenses that build the major part of the silicified fault zone. A chronology can be established. Some of these lenses are oriented slightly oblique to the general trend of the quartz zone, in agreement with the supposed dextral strike slip along the fault. Numerous generations of typically µm-cm thick quartz veins transect the microcrystalline quartz masses and, locally, form anisotropic networks. In the quartz masses, angular fragments often composed of quartz with, again, internal fragmentation structures, indicate earlier fracturing and silicification events. Within the veins, quartz forms geodes, locally filled with fine-grained reddish quartz and palisade structures with feathery textures and fluid-inclusion zoning

  9. Structural analysis of cataclastic rock of active fault damage zones: An example from Nojima and Arima-Takatsuki fault zones (SW Japan)

    Science.gov (United States)

    Satsukawa, T.; Lin, A.

    2016-12-01

    Most of the large intraplate earthquakes which occur as slip on mature active faults induce serious damages, in spite of their relatively small magnitudes comparing to subduction-zone earthquakes. After 1995 Kobe Mw7.2 earthquake, a number of studies have been done to understand the structure, physical properties and dynamic phenomenon of active faults. However, the deformation mechanics and related earthquake generating mechanism in the intraplate active fault zone are still poorly understood. The detailed, multi-scalar structural analysis of faults and of fault rocks has to be the starting point for reconstructing the complex framework of brittle deformation. Here, we present two examples of active fault damage zones: Nojima fault and Arima-Takatsuki active fault zone in the southwest Japan. We perform field investigations, combined with meso-and micro-structural analyses of fault-related rocks, which provide the important information in reconstructing the long-term seismic faulting behavior and tectonic environment. Our study shows that in both sites, damage zone is observed in over 10m, which is composed by the host rocks, foliated and non-foliated cataclasites, fault gouge and fault breccia. The slickenside striations in Asano fault, the splay fault of Nojima fault, indicate a dextral movement sense with some normal components. Whereas, those of Arima-Takatsuki active fault shows a dextral strike-slip fault with minor vertical component. Fault gouges consist of brown-gray matrix of fine grains and composed by several layers from few millimeters to a few decimeters. It implies that slip is repeated during millions of years, as the high concentration and physical interconnectivity of fine-grained minerals in brittle fault rocks produce the fault's intrinsic weakness in the crust. Therefore, faults rarely express only on single, discrete deformation episode, but are the cumulative result of several superimposed slip events.

  10. Remarks on impact shearing

    Science.gov (United States)

    Klepaczko, J. R.

    1998-10-01

    A review is presented on recent progress in shear testing of materials at high and very high strain rates. Some experimental techniques are discussed which allow for materials testing in shear up to 10 6 ls. More detailed informations are provided on experimental techniques based on the Modified Double Shear specimen loaded by direct impact. This technique has been applied so far to test a variety of materials, including construction, armor and inoxidable steels, and also aluminum alloys. The double shear configuration has also been applied to test sheet metals, mostly used in the automotive industry, in a wide range of strain rates. Details of both techniques, including measuring systems and elastic wave propagation in tubes, are discussed. In addition, a new experimental configuration which can be applied for experimental studies of adiabatic shear propagation and high speed machining is discussed. The role of adiabatic heating at different rates of shearing is also discussed, including transition from pure isothermal to pure adiabatic deformation. It appears that the initial impact velocity is an important parameter in development of plastic localization. Finally, a new development is discussed in determination of the Critical Impact Velocity in shear. A comparison is shown between recent experimental findings and a simple analytic estimation. The CIV in shear is a certain mode of adiabatic failure which occurs at relatively high shear velocities of adjacent material layers. Numerical simulations support the existence of the CIV in shear which can be recognized to some extent as a material constant.

  11. Gas geochemistry of the hot spring in the Litang fault zone, Southeast Tibetan Plateau

    International Nuclear Information System (INIS)

    Zhou, Xiaocheng; Liu, Lei; Chen, Zhi; Cui, Yueju; Du, Jianguo

    2017-01-01

    The southeast Tibetan Plateau is a region with high level seismic activity and strong hydrothermal activity. Several large (7.5 > M > 7) historical earthquakes have occurred in the Litang fault zone (LFZ), eastern Tibetan Plateau since 1700. Litang Ms 5.1 earthquake occurred On Sept 23, 2016, indicating the reactivation of the LFZ. This study was undertaken to elucidate spatial-temporal variations of the hot spring gas geochemistry along the LFZ from Jun 2010 to April 2016. The chemical components, He, Ne and C isotropic ratios of bubbling gas samples taken from 18 hot springs along LFZ were investigated. Helium isotope ratios ( 3 He/ 4 He) measured in hot springs varied from 0.06 to 0.93 Ra (Ra = air 3 He/ 4 He = 1.39 × 10 −6 ), with mantle-derivd He up to 11.1% in the LFZ (assuming R/Ra = 8 for mantle) indicated the fault was a crustal-scale feature that acts as a conduit for deep fluid from the mantle. CO 2 concentrations of the majority of hot spring gas samples were ≥80 vol%, CO 2 / 3 He ratios varied from 1.4 to 929.5 × 10 10 , and δ 13 C CO2 values varied from −19.2‰ to −2.3‰ (vs. PDB). The proportions of mantle-derived CO 2 varied from 0 to 1.8%. Crustal marine limestone was the major contributor (>75%) to the carbon inventory of the majority of hot spring gas samples. Before Litang Ms 5.1 earthquake, the 3 He/ 4 He ratios obviously increased in the Heni spring from May 2013 to Apr 2016. The geographical distribution of the mantle-derivd He decreased from east to west along 30°N in the southeast Tibetan Plateau relative to a corresponding increase in the radiogenic component. The gas geochemical data suggested that the upwelling mantle fluids into the crust play an important role in seismic activity in the strike-slip faults along 30°N in the southeast Tibetan Plateau. - Highlights: • Gas geochemistry of hot springs along Litang fault, Southeast Tibetan Plateau were surveyed. • Mantle-derived He decreased from east to

  12. Shear Thinning in Xenon

    Science.gov (United States)

    Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

    2009-01-01

    We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

  13. Test and Analysis of a New Ductile Shear Connection Design for RC Shear Walls

    DEFF Research Database (Denmark)

    Sørensen, Jesper Harrild; Hoang, Linh Cao; Olesen, John Forbes

    2017-01-01

    This paper presents a new and construction-friendly shear connection for assembly of precast reinforced concrete shear wall elements. In the proposed design, the precast elements have indented interfaces and are connected by a narrow zone grouted with mortar and reinforced with overlapping U......-bar loops. Contrary to the classical shear connections, the planes of the U-bar loops are here parallel to the plane of the wall elements. This feature enables a construction-friendly installation of the elements without the risk of rebars clashing. The core of mortar inside each U-bar loop is reinforced...... with a transverse double T-headed bar to ensure transfer of tension between the overlapping U-bars. Push-off tests show that a significantly ductile load-displacement response can be obtained by the new solution as compared to the performance of the conventional keyed shear connection design. The influence...

  14. Collecting Deep Seismic Data in Densely Populated Vietnam

    Science.gov (United States)

    Harder, Steven; Dinh, Van-Toan

    2011-01-01

    The Red River shear zone (RRSZ) is a large-scale strike-slip feature, similar to California's San Andreas Fault system, that extends from Tibet to the South China Sea. Many believe that this fault system allowed Southeast Asia to extrude from Asia as the Indian subcontinent collided with the continent [e.g., Tapponnier et al., 1982]. However, others believe that the collision resulted in crustal thickening and that strike-slip faults helped to accommodate this thickening. There have been many studies of the tectonics and structural geology of the RRSZ both supporting the extrusion hypotheses [e.g., Leloup et al., 1995; Gilley et al., 2003] and challenging them [e.g., Wang and Burchfiel, 1997; Jolivet et al., 2001]. Unfortunately, there have been no crustal reflection or refraction seismic studies of the RRSZ's deep subsurface, data from which might reveal geologic structures indicative of either thickening or extrusion, helping to settle this debate.

  15. Enriquillo–Plantain Garden fault zone in Jamaica: paleoseismology and seismic hazard

    Science.gov (United States)

    Koehler, R.D.; Mann, P.; Prentice, Carol S.; Brown, L.; Benford, B.; Grandison-Wiggins, M.

    2013-01-01

    The countries of Jamaica, Haiti, and the Dominican Republic all straddle the Enriquillo–Plantain Garden fault zone ( EPGFZ), a major left-lateral, strike-slip fault system bounding the Caribbean and North American plates. Past large earthquakes that destroyed the capital cities of Kingston, Jamaica (1692, 1907), and Port-au-Prince, Haiti (1751, 1770), as well as the 2010 Haiti earthquake that killed more than 50,000 people, have heightened awareness of seismic hazards in the northern Caribbean. We present here new geomorphic and paleoseismic information bearing on the location and relative activity of the EPGFZ, which marks the plate boundary in Jamaica. Documentation of a river bank exposure and several trenches indicate that this fault is active and has the potential to cause major destructive earthquakes in Jamaica. The results suggest that the fault has not ruptured the surface in at least 500 yr and possibly as long as 28 ka. The long period of quiescence and subdued geomorphic expression of the EPGFZ indicates that it may only accommodate part of the ∼7–9 mm=yr plate deformation rate measured geodetically and that slip may be partitioned on other undocumented faults. Large uncertainties related to the neotectonic framework of Jamaica remain and more detailed fault characterization studies are necessary to accurately assess seismic hazards.

  16. Influence of mineralogy and microstructures on strain localization and fault zone architecture of the Alpine Fault, New Zealand

    Science.gov (United States)

    Ichiba, T.; Kaneki, S.; Hirono, T.; Oohashi, K.; Schuck, B.; Janssen, C.; Schleicher, A.; Toy, V.; Dresen, G.

    2017-12-01

    The Alpine Fault on New Zealand's South Island is an oblique, dextral strike-slip fault that accommodated the majority of displacement between the Pacific and the Australian Plates and presents the biggest seismic hazard in the region. Along its central segment, the hanging wall comprises greenschist and amphibolite facies Alpine Schists. Exhumation from 35 km depth, along a SE-dipping detachment, lead to mylonitization which was subsequently overprinted by brittle deformation and finally resulted in the fault's 1 km wide damage zone. The geomechanical behavior of a fault is affected by the internal structure of its fault zone. Consequently, studying processes controlling fault zone architecture allows assessing the seismic hazard of a fault. Here we present the results of a combined microstructural (SEM and TEM), mineralogical (XRD) and geochemical (XRF) investigation of outcrop samples originating from several locations along the Alpine Fault, the aim of which is to evaluate the influence of mineralogical composition, alteration and pre-existing fabric on strain localization and to identify the controls on the fault zone architecture, particularly the locus of brittle deformation in P, T and t space. Field observations reveal that the fault's principal slip zone (PSZ) is either a thin (govern strain localization. However, our preliminary results suggest that qualitative mineralogical composition has only minor impact on fault zone architecture. Quantities of individual mineral phases differ markedly between fault damage zone and fault core at specific sites, but the quantitative composition of identical structural units such as the fault core, is similar in all samples. This indicates that the degree of strain localization at the Alpine Fault might be controlled by small initial heterogeneities in texture and fabric or a combination of these, rather than in mineralogy. Further microstructural investigations are needed to test this hypothesis.

  17. Do microplates in subduction zones leave a geological record?

    Science.gov (United States)

    Stock, Joann M.; Lee, Jeffrey

    1994-12-01

    Active microplate boundaries in ocean-continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc. We discuss two modern cases. The first is the South Gorda-Juan de Fuca plate boundary in the Cascadia subduction zone, where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation. The second case is the Cocos-Rivera plate boundary in the Middle America trench, where the overlying Colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub-duction-related volcanism is spatially and geochemically complex. We apply these observations to boundaries of the Arguello, Monterey, Guadalupe, and Magdalena microplates, which existed in the subduction zone west of Baja California at various times from 20 to 12.5 Ma. The past positions of these boundaries relative to Baja California are constrained by global plate reconstructions, closure of the Gulf of California, and an estimate of extension in the Mexican Basin and Range province. Existing regional mapping and our additional reconnaissance mapping show that Paleocene to Eocene fluvial and marine sedimentary rocks south of Ensenada along the western Baja California peninsula and eastward to the mid-Miocene volcanic arc are undeformed. Limited available data reveal no major spatial or geochemical variations in the mid-Miocene volcanic arc that might correlate with the past positions of the microplate boundaries. Thus these microplate boundaries had little to no effect on the overriding continental plate. The nature of Guadalupe and Magdalena interactions with North America may have been closer to the South Gorda-Juan de Fuca example, with possible internal deformation of the microplates. The Monterey and Arguello microplates may have behaved like the modern Explorer plate, with largely strike-slip motion relative to North America during their last

  18. Architecture of buried reverse fault zone in the sedimentary basin: A case study from the Hong-Che Fault Zone of the Junggar Basin

    Science.gov (United States)

    Liu, Yin; Wu, Kongyou; Wang, Xi; Liu, Bo; Guo, Jianxun; Du, Yannan

    2017-12-01

    It is widely accepted that the faults can act as the conduits or the barrier for oil and gas migration. Years of studies suggested that the internal architecture of a fault zone is complicated and composed of distinct components with different physical features, which can highly influence the migration of oil and gas along the fault. The field observation is the most useful methods of observing the fault zone architecture, however, in the petroleum exploration, what should be concerned is the buried faults in the sedimentary basin. Meanwhile, most of the studies put more attention on the strike-slip or normal faults, but the architecture of the reverse faults attracts less attention. In order to solve these questions, the Hong-Che Fault Zone in the northwest margin of the Junggar Basin, Xinjiang Province, is chosen for an example. Combining with the seismic data, well logs and drill core data, we put forward a comprehensive method to recognize the internal architectures of buried faults. High-precision seismic data reflect that the fault zone shows up as a disturbed seismic reflection belt. Four types of well logs, which are sensitive to the fractures, and a comprehensive discriminated parameter, named fault zone index are used in identifying the fault zone architecture. Drill core provides a direct way to identify different components of the fault zone, the fault core is composed of breccia, gouge, and serpentinized or foliated fault rocks and the damage zone develops multiphase of fractures, which are usually cemented. Based on the recognition results, we found that there is an obvious positive relationship between the width of the fault zone and the displacement, and the power-law relationship also exists between the width of the fault core and damage zone. The width of the damage zone in the hanging wall is not apparently larger than that in the footwall in the reverse fault, showing different characteristics with the normal fault. This study provides a

  19. Reorientation of lineation in the Central Crystalline Zone, Munsiari ...

    Indian Academy of Sciences (India)

    During large scale ductile shear deformation, linear features of the rocks tend to be reoriented towards the direction of bulk shear. This is demonstrated in a crustal scale shear zone of the Himalaya, the. Main Central Thrust (MCT), typically exposed in the Munsiari–Milam area of eastern Kumaun Greater. Himalaya.

  20. What role did the Hikurangi subduction zone play in the M7.8 Kaikoura earthquake?

    Science.gov (United States)

    Wallace, L. M.; Hamling, I. J.; Kaneko, Y.; Fry, B.; Clark, K.; Bannister, S. C.; Ellis, S. M.; Francois-Holden, C.; Hreinsdottir, S.; Mueller, C.

    2017-12-01

    The 2016 M7.8 Kaikoura earthquake ruptured at least a dozen faults in the northern South Island of New Zealand, within the transition from the Hikurangi subduction zone (in the North Island) to the transpressive Alpine Fault (in the central South Island). The role that the southern end of the Hikurangi subduction zone played (or did not play) in the Kaikoura earthquake remains one of the most controversial aspects of this spectacularly complex earthquake. Investigations using near-field seismological and geodetic data suggest a dominantly crustal faulting source for the event, while studies relying on teleseismic data propose that a large portion of the moment release is due to rupture of the Hikurangi subduction interface beneath the northern South Island. InSAR and GPS data also show that a large amount of afterslip (up to 0.5 m) occurred on the subduction interface beneath the crustal faults that ruptured in the M7.8 earthquake, during the months following the earthquake. Modeling of GPS velocities for the 20 year period prior to the earthquake indicate that interseismic coupling was occurring on the Hikurangi subduction interface beneath the northern South Island, in a similar location to the suggested coseismic and postseismic slip on the subduction interface. We will integrate geodetic, seismological, tsunami, and geological observations in an attempt to balance the seemingly conflicting views from local and teleseismic data regarding the role that the southern Hikurangi subduction zone played in the earthquake. We will also discuss the broader implications of the observed coseismic and postseismic deformation for understanding the kinematics of the southern termination of the Hikurangi subduction zone, and its role in the transition from subduction to strike-slip in the central New Zealand region.

  1. Fractal properties and simulation of micro-seismicity for seismic hazard analysis: a comparison of North Anatolian and San Andreas Fault Zones

    Directory of Open Access Journals (Sweden)

    Naside Ozer

    2012-02-01

    Full Text Available We analyzed statistical properties of earthquakes in western Anatolia as well as the North Anatolian Fault Zone (NAFZ in terms of spatio-temporal variations of fractal dimensions, p- and b-values. During statistically homogeneous periods characterized by closer fractal dimension values, we propose that occurrence of relatively larger shocks (M >= 5.0 is unlikely. Decreases in seismic activity in such intervals result in spatial b-value distributions that are primarily stable. Fractal dimensions decrease with time in proportion to increasing seismicity. Conversely, no spatiotemporal patterns were observed for p-value changes. In order to evaluate failure probabilities and simulate earthquake occurrence in the western NAFZ, we applied a modified version of the renormalization group method. Assuming an increase in small earthquakes is indicative of larger shocks, we apply the mentioned model to micro-seismic (M<= 3.0 activity, and test our results using San Andreas Fault Zone (SAFZ data. We propose that fractal dimension is a direct indicator of material heterogeneity and strength. Results from a model suggest simulated and observed earthquake occurrences are coherent, and may be used for seismic hazard estimation on creeping strike-slip fault zones.

  2. Spatial distribution correlation of soil-gas radon (222Rn) and mercury with leveling deformation in northern margin fault zone of West Qinling, China.

    Science.gov (United States)

    Li, Chenhua; Zhang, Hui; Su, Hejun; Zhou, Huiling; Wang, Yanhong

    2017-11-01

    This study concerns measurement of 222 Rn and mercury concentrations in soil-gas in the northern margin fault zone of West Qinling, Tibet (China). Based on profiles crossing perpendicularly the different segments of the fault at six different locations, the relations between the gas measurements, fault deformation, and seismic activity in each segment of the studied fault were analyzed, determining seismic risks in the fault zone. Soil-gas data are heterogeneous, but appear relatively organized along the three segments of the fault. The detailed multidisciplinary analysis reveals complex interactions between the structural setting, uprising fluids, leveling and seismic activity in different fault segments. The results for both fault soil gas and deformation indicated relatively stronger fault activity in the Wushan segment in the middle-eastern segment of the northern margin fault zone of West Qinling and lower activity in the Zhangxian segment, whereas the fault in the Tianshui segment was relatively locked. Additionally, in the Wushan strike-slip pull-apart area, the active influence of fluid activities facilitated the occurrence of small to medium-sized seismic events, which prevented the occurrence of larger events; in contrast, in the Tianshui segment, the west Zhangxian segment, the weak fluid activities and the corresponding strain rate will probably lead to strong earthquake buildup. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Oblique reactivation of lithosphere-scale lineaments controls rift physiography - the upper-crustal expression of the Sorgenfrei-Tornquist Zone, offshore southern Norway

    Science.gov (United States)

    Phillips, Thomas B.; Jackson, Christopher A.-L.; Bell, Rebecca E.; Duffy, Oliver B.

    2018-04-01

    Pre-existing structures within sub-crustal lithosphere may localise stresses during subsequent tectonic events, resulting in complex fault systems at upper-crustal levels. As these sub-crustal structures are difficult to resolve at great depths, the evolution of kinematically and perhaps geometrically linked upper-crustal fault populations can offer insights into their deformation history, including when and how they reactivate and accommodate stresses during later tectonic events. In this study, we use borehole-constrained 2-D and 3-D seismic reflection data to investigate the structural development of the Farsund Basin, offshore southern Norway. We use throw-length (T-x) analysis and fault displacement backstripping techniques to determine the geometric and kinematic evolution of N-S- and E-W-striking upper-crustal fault populations during the multiphase evolution of the Farsund Basin. N-S-striking faults were active during the Triassic, prior to a period of sinistral strike-slip activity along E-W-striking faults during the Early Jurassic, which represented a hitherto undocumented phase of activity in this area. These E-W-striking upper-crustal faults are later obliquely reactivated under a dextral stress regime during the Early Cretaceous, with new faults also propagating away from pre-existing ones, representing a switch to a predominantly dextral sense of motion. The E-W faults within the Farsund Basin are interpreted to extend through the crust to the Moho and link with the Sorgenfrei-Tornquist Zone, a lithosphere-scale lineament, identified within the sub-crustal lithosphere, that extends > 1000 km across central Europe. Based on this geometric linkage, we infer that the E-W-striking faults represent the upper-crustal component of the Sorgenfrei-Tornquist Zone and that the Sorgenfrei-Tornquist Zone represents a long-lived lithosphere-scale lineament that is periodically reactivated throughout its protracted geological history. The upper-crustal component of

  4. Examining shear processes during magma ascent

    Science.gov (United States)

    Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

    2017-12-01

    Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

  5. Shear-Rate-Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels

    Science.gov (United States)

    Scaringi, Gianvito; Hu, Wei; Xu, Qiang; Huang, Runqiu

    2018-01-01

    The behavior of reactivated and first-failure landslides after large displacements is controlled by the available shear resistance in a shear zone and/or along slip surfaces, such as a soil-bedrock interface. Among the factors influencing the resistance parameter, the dependence on the shear rate can trigger catastrophic evolution (rate-weakening) or exert a slow-down feedback (rate-strengthening) upon stress perturbation. We present ring-shear test results, performed under various normal stresses and shear rates, on clayey soils from a landslide shear zone, on its parent lithology and other lithologies, and on clay-rock interface samples. We find that depending on the materials in contact, the normal stress, and the stress history, the shear-rate-dependent behaviors differ. We discuss possible models and underlying mechanisms for the time-dependent behavior of landslides in clay soils.

  6. Influence of obliquely subducting slab on Pacific-North America shear motion inferred from seismic anisotropy along the Queen Charlotte margin

    Science.gov (United States)

    Cao, L.; Kao, H.; Wang, K.; Wang, Z.

    2016-12-01

    Haida Gwaii is located along the transpressive Queen Charlotte margin between the Pacific (PA) and North America (NA) plates. The highly oblique relative plate motion is partitioned, with the strike-slip component accommodated by the Queen Charlotte Fault (QCF) and the convergent component by a thrust fault offshore. To understand how the presence of a obliquely subducting slab influences shear deformation of the plate boundary, we investigate mantle anisotropy by analyzing shear-wave splitting of teleseismic SKS phases recorded at 17 seismic stations in and around Haida Gwaii. We used the MFAST program to determine the polarization direction of the fast wave (φ) and the delay time (δt) between the fast and slow phases. The fast directions derived from stations on Haida Gwaii and two stations to the north on the Alaska Panhandle are predominantly margin-parallel (NNW). However, away from the plate boundary, the fast direction transitions to WSW-trending, very oblique or perpendicular to the plate boundary. Because the average delay time of 0.6-2.45 s is much larger than values based on an associated local S phase splitting analysis in the same study area, it is reasonable to infer that most of the anisotropy from our SKS analysis originates from the upper mantle and is associated with lattice-preferred orientation of anisotropic minerals. The margin-parallel fast direction within about 100 km of the QCF (average φ = -40º and δt = 1.2 s) is likely induced by the PA-NA shear motion. The roughly margin-normal fast directions farther away, although more scatterd, are consistent with that previously observed in the NA continent and are attributed to the absolute motion of the NA plate. However, the transition between the two regimes based on our SKS analysis appears to be gradual, suggesting that the plate boundary shear influences a much broader region at mantle depths than would be inferred from the surface trace of the QCF. We think this is due to the presence

  7. Mechanical analysis of a shear-cracked RC beam

    Directory of Open Access Journals (Sweden)

    Shahriar Shahbazpanahi

    2017-07-01

    Full Text Available Shear crack analysis is essential for engineers to estimate repair work in concrete structures. So far, conventional theoretical and numerical analyses in fracture mechanics have been applied to study concrete flexural beams, but there is still little knowledge regarding the shear capacity for beams with a diagonal initial notch. In this study, a theoretical analysis is presented to obtain fracture resistance in a four-point RC beam with two inclined initial notch on supports. Here, a fictitious crack approach is adopted for estimating the equivalent effect of the fracture process zone of concrete in shear-cracked. Based on equilibrium equation in the beam notch cross section, shear force was expressed in terms of fracture process zone length. Then, in a double notch four-point beam, Mode II of the stress intensity factor due to the external load is determined. Finally, this process presents the relationship between the shear capacity and the fracture process zone length and expresses the fracture resistance as a function of fracture process zone length.The predicted results of loading capacities are then shown.

  8. Static stress transfer within the Cephalonia Transfer Fault Zone (CTFZ) during the 2014 seismic sequence in Cephalonia and the 2015 earthquake in Lefkada

    Science.gov (United States)

    Sboras, Sotiris; Chatzipetros, Alexandros; Pavlides, Spyros; Karastathis, Vassilis; Papadopoulos, Gerassimos

    2017-04-01

    The 2014 seismic sequence in Cephalonia and the following 2015 earthquake in Lefkada Islands, Greece, showed that the Cephalonia Transfer Fault Zone (CTFZ), which runs along the western coasts of both islands, comprises a wide fault zone of parallel to sub-parallel fault segments. The January-February 2014 sequence of Cephalonia consisted of three moderate to strong events. According to published focal mechanisms, the first strongest shock (January 26, Mw 6.1) was produced by a W-dipping, oblique (right-lateral reverse) fault, the second (January 26, Mw 5.3) by a ENE-dipping, pure reverse fault and the third by a ESE-dipping, almost pure right-lateral strike slip fault. The November 17 2015 (Mw 6.4) Lefkada earthquake was produced by a WNW-dipping, roughly vertical, almost pure right-lateral strike-slip fault. None of the shocks above produced any direct coseismic ground rupture, while published relocated hypocentral locations for the Cephalonia sequence revealed various depths indicating a complex fault pattern. Based on published seismological, geological and satellite data (i.e. InSAR), the respective seismic sources were modelled in order to calculate the static stress changes i) during the Cephalonia and Lefkada sequences, and ii) after the sequences for the surrounding faults from the Greek Database of Seismogenic Sources (GreDaSS). Results showed that the February 3 2014 Cephalonia fault was variously affected by the rupture of the two January 26 faults. Stress change distribution on the fault plane showed that both stress drop and rise occurred. The November 17 2015 Lefkada fault was slightly loaded after the rupture of the whole Cephalonia fault system due to the great distance. The post-sequence stress changes variously affect the surrounding faults: the southern segment of the CTFZ is relieved from stresses, while the central ones show a mixed situation. The large northern segment, offshore from Lefkada Island, is mainly under stress drop. Stress drop is

  9. The Kefalonia Transform Zone (offshore Western Greece) with special emphasis to its prolongation towards the Ionian Abyssal Plain

    Science.gov (United States)

    Kokinou, E.; Papadimitriou, E.; Karakostas, V.; Kamberis, E.; Vallianatos, F.

    2006-12-01

    Information concerning two seismic lines, the first located northwest of the Lefkada Island and the second from the deep Ionian basin to the gulf of Patras, is used to trace the Kefalonia Transform Zone (KTZ) and to explore its relation with the sedimentary sequences and the deeper geologic structures in the study area. In addition, sea bottom topography and fault plane solutions are combined in order to explore the prolongation of the KTZ into the Ionian Abyssal Plain (IoAP) and to describe its properties. The boundary between the subduction of the eastern Mediterranean oceanic crust under the overriding continental crust and the KTZ is well constrained by the seismic data in association with seismicity and regional stress field. The southern prolongation of the KTZ is located in the IoAP towards the direction between Kefalonia and Zakynthos Islands at depth greater than 15 km. The southern part of the KTZ exhibits a strike slip motion with a thrust component according to fault plane solutions of moderate and strong earthquakes. The seismic section mostly confirms the existence of the thrust component and gives information about the tectonic status east and west of the KTZ.

  10. Micro-seismicity and seismotectonic study in Western Himalaya-Ladakh-Karakoram using local broadband seismic data

    Science.gov (United States)

    Kanna, Nagaraju; Gupta, Sandeep; Prakasam, K. S.

    2018-02-01

    We document the seismic activity and fault plane solutions (FPSs) in the Western Himalaya, Ladakh and Karakoram using data from 16 broadband seismographs operated during June 2002 to December 2003. We locate 206 earthquakes with a local magnitude in the range of 1.5 to 4.9 and calculate FPSs of 19 selected earthquakes based on moment tensor solutions. The earthquakes are distributed throughout the study region and indicate active tectonics in this region. The observed seismicity pattern is quite different than a well-defined pattern of seismicity, along the Main Central Thrust zone, in the eastern side of the study region (i.e., Kumaon-Garhwal Himalaya). In the Himalaya region, the earthquakes are distributed in the crust and upper mantle, whereas in the Ladakh-Karakoram area the earthquakes are mostly confined up to crustal depths. The fault plane solutions show a mixture of thrust, normal and strike-slip type mechanisms, which are well corroborated with the known faults/tectonics of the region. The normal fault earthquakes are observed along the Southern Tibet Detachment, Zanskar Shear Zone, Tso-Morari dome, and Kaurik-Chango fault; and suggest E-W extension tectonics in the Higher and Tethys Himalaya. The earthquakes of thrust mechanism with the left-lateral strike-slip component are seen along the Kistwar fault. The right-lateral strike-slip faulting with thrust component along the bending of the Main Boundary Thrust and Main Central Thrust shows the transpressional tectonics in this part of the Himalaya. The observed earthquakes with right-lateral strike-slip faulting indicate seismically active nature of the Karakoram fault.

  11. Offset of latest pleistocene shoreface reveals slip rate on the Hosgri strike-slip fault, offshore central California

    Science.gov (United States)

    Johnson, Samuel Y.; Hartwell, Stephen R.; Dartnell, Peter

    2014-01-01

    The Hosgri fault is the southern part of the regional Hosgri–San Gregorio dextral strike‐slip fault system, which extends primarily in the offshore for about 400 km in central California. Between Morro Bay and San Simeon, high‐resolution multibeam bathymetry reveals that the eastern strand of the Hosgri fault is crossed by an ∼265  m wide slope interpreted as the shoreface of a latest Pleistocene sand spit. This sand spit crossed an embayment and connected a western fault‐bounded bedrock peninsula and an eastern bedrock highland, a paleogeography resembling modern coastal geomorphology along the San Andreas fault. Detailed analysis of the relict shoreface with slope profiles and slope maps indicates a lateral slip rate of 2.6±0.9  mm/yr, considered a minimum rate for the Hosgri given the presence of an active western strand. This slip rate indicates that the Hosgri system takes up the largest share of the strike‐slip fault budget and is the most active strike‐slip fault west of the San Andreas fault in central California. This result further demonstrates the value and potential of high‐resolution bathymetry in characterization of active offshore faults.

  12. Recurring extensional and strike-slip tectonics after the Neoproterozoic collisional events in the southern Mantiqueira province

    Directory of Open Access Journals (Sweden)

    Renato P. Almeida

    2012-06-01

    Full Text Available In Eastern South America, a series of fault-bounded sedimentary basins that crop out from Southern Uruguay to Southeastern Brazil were formed after the main collisional deformation of the Brasiliano Orogeny and record the tectonic events that affected the region from the Middle Ediacaran onwards. We address the problem of discerning the basin-forming tectonics from the later deformational events through paleostress analysis of more than 600 fault-slip data, mainly from the Camaquã Basin (Southern Brazil, sorted by stratigraphic level and cross-cutting relationships of superposed striations, and integrated with available stratigraphic and geochronological data. Our results show that the Camaquã Basin was formed by at least two distinct extensional events, and that rapid paleostress changes took place in the region a few tens of million years after the major collision (c.a. 630 Ma, probably due to the interplay between local active extensional tectonics and the distal effects of the continued amalgamation of plates and terranes at the margins of the still-forming Gondwana Plate. Preliminary paleostress data from the Castro Basin and published data from the Itajaí Basin suggest that these events had a regional nature.No Leste da América do Sul, um conjunto de bacias sedimentares que afloram do sul do Uruguai ao sudeste do Brasil formou-se após os eventos colisionais da Orogenia Brasiliana, registrando os eventos tectônicos que afetaram a região a partir do Mesoediacarano. O problema da distinção entre a tectônica formadora das bacias e os eventos deformacionais posteriores é aqui abordado através da análise de paleotensões de mais de 600 dados de falhas com estrias, obtidos principalmente na Bacia Camaquã (Sul do Brasil, que foram classificados por nível estratigráfico e relações de corte entre estrias sobrepostas, e intergrados a dados estratigráficos e geocronológicos disponíveis. Nossos resultados revelam que a Bacia Camaquã teve origem em ao menos dois eventos distensivos, e que modificações rápidas no campos de tensões ocorreram na região alguns poucos milhões de anos após a colisão principal (c.a. 630 Ma, provavelmente em decorrência da interação entre esforços distensivos locais e os efeitos distais da contínua amalgamação de placas e terrenos nas margens da placa Gondwana, ainda em formação. Dados preliminares de paleotensões da Bacia de Castro e dados publicados da Bacia Itajaí sugerem que esses eventos tiveram um caráter regional.

  13. A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle

    NARCIS (Netherlands)

    Caniven, Y.; Dominguez, S.; Soliva, R.; Cattin, R.; Peyret, M.; Marchandon, M.; Romano, C.; Strak, V.

    2015-01-01

    Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting

  14. Fault slip and earthquake recurrence along strike-slip faults — Contributions of high-resolution geomorphic data

    KAUST Repository

    Zielke, Olaf

    2015-01-01

    Understanding earthquake (EQ) recurrence relies on information about the timing and size of past EQ ruptures along a given fault. Knowledge of a fault\\'s rupture history provides valuable information on its potential future behavior, enabling seismic hazard estimates and loss mitigation. Stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing EQs. Analysis of the latter data sets culminated during the mid-1980s in the formulation of now classical EQ recurrence models, now routinely used to assess seismic hazard. Within the last decade, Light Detection and Ranging (lidar) surveying technology and other high-resolution data sets became increasingly available to tectono-geomorphic studies, promising to contribute to better-informed models of EQ recurrence and slip-accumulation patterns. After reviewing motivation and background, we outline requirements to successfully reconstruct a fault\\'s offset accumulation pattern from geomorphic evidence. We address sources of uncertainty affecting offset measurement and advocate approaches to minimize them. A number of recent studies focus on single-EQ slip distributions and along-fault slip accumulation patterns. We put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation CV for EQ inter-event time and slip-per-event and find that a) single-event offsets vary over a wide range of length-scales and the sources for offset variability differ with length-scale, b) at fault-segment length-scales, single-event offsets are essentially constant, c) along-fault offset accumulation as resolved in the geomorphic record is dominated by essentially same-size, large offset increments, and d) there is generally no one-to-one correlation between the offset accumulation pattern constrained in the geomorphic record and EQ occurrence as identified in the stratigraphic record, revealing the higher resolution and preservation potential of the latter. While slip accumulation along a fault segment may be dominated by repetition of large, nearly constant offset increments, timing of surface-rupture is less regular. (C) 2014 Elsevier B.V. All rights reserved.

  15. Plasticity Approach to Shear Design

    DEFF Research Database (Denmark)

    Hoang, Cao Linh; Nielsen, Mogens Peter

    1998-01-01

    The paper presents some plastic models for shear design of reinforced concrete beams. Distinction is made between two shear failure modes, namely web crushing and crack sliding. The first mentioned mode is met in beams with large shear reinforcement degrees. The mode of crack sliding is met in non......-shear reinforced beams as well as in lightly shear reinforced beams. For such beams the shear strength is determined by the recently developed crack sliding model. This model is based upon the hypothesis that cracks can be transformed into yield lines, which have lower sliding resistance than yield lines formed...

  16. Sheared Electroconvective Instability

    Science.gov (United States)

    Kwak, Rhokyun; Pham, Van Sang; Lim, Kiang Meng; Han, Jongyoon

    2012-11-01

    Recently, ion concentration polarization (ICP) and related phenomena draw attention from physicists, due to its importance in understanding electrochemical systems. Researchers have been actively studying, but the complexity of this multiscale, multiphysics phenomenon has been limitation for gaining a detailed picture. Here, we consider electroconvective(EC) instability initiated by ICP under pressure-driven flow, a scenario often found in electrochemical desalinations. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of sheared EC: unidirectional vortex structures, its size selection and vortex propagation. Selected by balancing the external pressure gradient and the electric body force, which generates Hagen-Poiseuille(HP) flow and vortical EC, the dimensionless EC thickness scales as (φ2 /UHP)1/3. The pressure-driven flow(or shear) suppresses unfavorably-directed vortices, and simultaneously pushes favorably-directed vortices with constant speed, which is linearly proportional to the total shear of HP flow. This is the first systematic characterization of sheared EC, which has significant implications on the optimization of electrodialysis and other electrochemical systems.

  17. Sheared solid materials

    Indian Academy of Sciences (India)

    cores eventually breaks the Peierls potential leading to slow relaxations in the stress and the free energy (aging). .... Figure 1 displays the stress–strain curves at constant shear rate ˙γ applied for t > 0 in units of µ0 and τ−1 ..... In particular, the slow structural relaxations evidently arise from migration of the free volume.

  18. The Okhotsk Plate and the Eurasia-North America plate boundary zone.

    Science.gov (United States)

    Hindle, David; Mackey, Kevin

    2014-05-01

    The Eurasia-North America plate boundary zone transitions from spreading at rates of ~ 25mm/yr in the North Atlantic, to compression at rates of ~ 5mm/yr in the region of the Okhotsk plate. Because the pole of rotation between Eurasia and North America lies more or less on their mutual boundary, there is a linear change in rate along the boundary, and regions near the euler pole are subject to extremely low deformation rates. The Okhotsk - Eurasia - North America triple junction lies slightly south of the rotation pole, placing the Okhotsk plate entirely in a weakly contractional setting. Regions near the triple junction absorb 1mm/yr contraction. Further south, towards the shoreline of the Okhotsk sea, up to 5 mm/yr contraction may be absorbed within the plate. How shortening is accommodated across the boundary remains an open question. One possibility is wholesale extrusion of the entire Okhotsk plate (or possibly its northwestern corner) along two plate boundary strike slip faults (Eurasia-Okhostk and North America Okhotsk). The problem with this model is that the seismic record does not presently clearly support it, with the largest events distributed both within the plate interior and on its boundaries. This may suggest that instead, the Okhotsk plate, and particularly its north-western end, consists of a series of smaller blocks which shuffle against each other, partially accommodating extrusion, but also permitting some internal deformation and change of shape of the Okhotsk plate itself. We present analyses of the very sparse seismic record from the region, as well as geometric-kinematic, tectonic models of the possible deformation of northwest Okhotsk to try to better understand the different probabilities of how this slowly deforming plate boundary zone is behaving.

  19. Bathymetry & Geomorphology - A New Seafloor Mapping of the Israeli Exclusive Economic Zone

    Science.gov (United States)

    Tibor, G.; Hall, J. K.; Kanari, M.; Sade, R. A.; Sade, H.; Amit, G.; Gur-Arie, L.; Ketter, T.

    2017-12-01

    Recent extensive activities of oil and gas exploration and production companies in the Israeli Exclusive Economic Zone (EEZ) raised the need for an up-to-date baseline mapping of the seafloor to assist policy makers. The baseline mapping focused on bathymetry, geomorphology, geology, biodiversity, infauna and habitat in order to compile a sensitivity map for the Petroleum Commissioner in the Ministry of Energy in the bid for opening the sea to new natural gas and oil explorations. The Israeli EEZ covers an area of 25,950 sq. km. and reaches a maximum water depth of 2,100 m. It is located within the Levantine Basin, a zone of compression and strike-slip tectonics as Africa pushes into Eurasia. These forces operate on a half kilometer thick of Messinian evaporates and over a dozen kilometers of Pliocene and Pleistocene sediments to produce a complex seafloor morphology. The margin is cut by numerous slumps and canyons, while the basin is traversed by deep sea channels emptying into the moat around Eratosthenes Seamount farther north. The bathymetric and geomorphological mapping was done in three phases using Kongsberg and Elac multibeam sonars installed on different research vessels. The last phase (Aug.-Sept., 2016) covering depths from 1,400 to 2,100 m used the Kongsberg EM302 sonar installed on our new governmental research vessel Bat Galim. It has "state of the art" capabilities to map, sample and analyze the water column, seafloor and sub-bottom from water depths of 10m to 7,000 m. These mapping capabilities are unique in our region, the Eastern Mediterranean and the Red Sea, so we hope to promote research collaborations with our neighbors.

  20. Experiments on sheet metal shearing

    OpenAIRE

    Gustafsson, Emil

    2013-01-01

    Within the sheet metal industry, different shear cutting technologies are commonly used in several processing steps, e.g. in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material.Numerical models to predict forces and sheared edge geometry for different sheet metal grades and different shear parameter set-ups a...

  1. Reaction enhanced channelised fluid-flux along midcrustal shear ...

    Indian Academy of Sciences (India)

    ... 6.6±0.25 kbar (corresponding to ∼20 km depth). Textural modeling integrating the textural features and balanced chemical reaction of the calc-silicate rocks of Mesoproterozoic Phulad Shear Zone thus indicate that extremely channelled fluid flow was reaction enhanced and caused major change in the rock rheology.

  2. Shear Behavior of Concrete Beams Reinforced with GFRP Shear Reinforcement

    Directory of Open Access Journals (Sweden)

    Heecheul Kim

    2015-01-01

    Full Text Available This paper presents the shear capacities of concrete beams reinforced with glass fiber reinforced polymer (GFRP plates as shear reinforcement. To examine the shear performance, we manufactured and tested a total of eight specimens. Test variables included the GFRP strip-width-to-spacing ratio and type of opening array. The specimen with a GFRP plate with a 3×2 opening array showed the highest shear strength. From the test results, the shear strength increased as the strip-width-to-strip-spacing ratio increased. Also, we used the experimental results to evaluate whether the shear strength equations of ACI 318-14 and ACI 440.1R can be applied to the design of GFRP shear reinforcement. In the results, the ACI 440 equation underestimated the experimental results more than that of ACI 318.

  3. Offshore extension of the Great Sumatra Fault revealed by seismic, bathymetric and seafloor imaging

    Science.gov (United States)

    Gaedicke, C.; Soh, W.; Djajadihardja, Y.; Saito, S.; Ikeda, Y.; Kudrass, H.; Djamaluddin, R.

    2003-12-01

    The northwestern Sunda Arc is cut by two giant dextral shear zones, which accommodate the oblique subduction of the Indo-Australian Plate against Eurasia along this portion of the Sunda Arc. These are the Sumatra Fault Zone on Sumatra Island and the Mentawai Fault Zone off west Sumatra. The strike-slip shear zones bear a high earthquake risk potential. Several Indonesian-Japanese-German marine expeditions focused on the tectonics and the evolution of the Sumatra and Java forearc region. Now a dense grid of multi- and single-channel reflection seismic profiles, high resolution bathymetry and seafloor direct observations using submersible SHINKAI 6500 allow tracing the Sumatra and Mentawai Fault Zones south off west Java. The geometry of transtensional basins, transpressional horst structures and elongated ridges and valleys clearly shows the dextral sense of motion and the splay character of the fault zones in the study area. Multi-channel reflection profiles image the deep structure of the major strike slip faults which originate from reactivated thrust planes within the Java accretionary wedge. During SHINKAI 6500 dives one master fault could be followed. Recent offset along the fault is documented on sea floor images by young unweathered fault scarps.

  4. Shear-thinning Fluid

    Science.gov (United States)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  5. Forflytning: shear og friktion

    DEFF Research Database (Denmark)

    2005-01-01

    friktion). Formålet med filmprojektet er: At give personalet i Apopleksiafsnittet viden om shear og friktion, så det motiveres til forebyggelse. Mål At udarbejde et enkelt undervisningsmateriale til bed-side-brug Projektbeskrivelse (resume) Patienter med apopleksi er særligt udsatte for tryksår, fordi de...... ofte er immobile, har svært ved at opretholde en god siddestilling eller ligger tungt i sengen som følger efter apopleksien Hvis personalet bruger forkert lejrings-og forflytningsteknik, udsættes patienterne for shear og friktion. Målgruppen i projektet er de personer, der omgås patienterne, dvs...

  6. Shear Roll Mill Reactivation

    Science.gov (United States)

    2012-09-13

    pneumatically operated paste dumper and belt conveyor system , the loss in weight feeder system , the hydraulically operated shear roll mill, the pellet...out feed belt conveyor , and the pack out system comprised of the metal detector, scale, and pack out empty and full drum roller conveyors . Page | 4...process equipment sprinkler protection systems , and the 5 psig steam supply serving the building heating and make-up air systems . It also included

  7. Direct Shear Tests of Sandstone Under Constant Normal Tensile Stress Condition Using a Simple Auxiliary Device

    Science.gov (United States)

    Cen, Duofeng; Huang, Da

    2017-06-01

    Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.

  8. Cosmic muon imaging of hidden seismic fault zones: Rainwater permeation into the mechanical fractured zones in Itoigawa-Shizuoka Tectonic Line, Japan

    Science.gov (United States)

    Tanaka, Hiroyuki K. M.; Miyajima, Hiroshi; Kusagaya, Taro; Taketa, Akimichi; Uchida, Tomohisa; Tanaka, Manobu

    2011-06-01

    We have developed a novel radiographic imaging method to survey the seismic fault hidden beneath the surface by measuring the rainfall permeation around the fault zone with cosmic-ray muon radiography. As an example, we performed measurements in Itoigawa-Shizuoka Tectonic Line (ISTL), Japan, and studied the feasibility of using this method. In this method, muons after passing through a fault zone are measured for different depths after major rain-fall events. When large amount of rain permeated gravitationally into the mechanical fractured zone around the fault gouge, the average density increases, hence, decreasing the number of muon events. The principle of the technique is that by measuring the time-dependent changes in muon absorption along different paths through the fault, one can image the permeable region in the interior of the object. A muon detector with an area of 3969 cm 2 was located 6 m from the fault outcrop in UNESCO Itoigawa Geopark. The outcrop is geologically well studied and the direction of the fault is approximately determined by linear extrapolation from the site, but is not parallel to the ISTL. An angular resolution of the muon detector of 100 milliradians (mrad) corresponds to a spatial resolution of 10 m at a distance of 100 m. The measurements would be ideal for studying the vertical or near-vertical strike-slip faults which cannot be well resolved by the conventional standard seismic reflection acquisition and processing that are designed to image reflectors that are close to horizontal. In this work, we have radiographically imaged the fault zone up to 50 m below the surface. A systematic delay in response to the rain-fall events was observed with increasing depth only along the fault zone, which corresponds to the position and direction of the seismic fault estimated from the geometry of the fault outcrop. Applying the same method to another direction, we discovered a new permeable region that is parallel to the ISTL. This permeable

  9. Late Miocene extension in coastal Sonora, México: Implications for the evolution of dextral shear in the proto-Gulf of California oblique rift

    Science.gov (United States)

    Darin, M. H.; Bennett, S. E. K.; Dorsey, R. J.; Oskin, M. E.; Iriondo, A.

    2016-12-01

    The timing, kinematics, and processes responsible for the rapid transition from subduction to oblique rifting and the localization of the Pacific-North America plate boundary in the Gulf of California are not well understood. Well exposed volcanic rocks deposited between 15 and 10 Ma in the Sierra Bacha (coastal Sonora, México) preserve a record of late Miocene deformation on the eastern rifted margin of the Gulf of California and offer new insights into the timing and kinematic evolution of oblique rifting. Detailed geologic mapping, fault kinematic analysis, U-Pb and 40Ar/39Ar geochronology, and paleomagnetic data reveal that the > 2 km-thick composite volcanic section is cut by a series of southwest-dipping, domino-style normal faults and uniformly tilted down-to-the-northeast. Palinspastic cross-section restoration suggests that the region experienced ca. 55-60% northeast-southwest-directed extension between 11.7 and 10-9 Ma. Fault kinematic data reflect relatively minor dextral transtension either following or during the later stages of extension. Paleomagnetic results indicating modest clockwise vertical-axis block rotation suggest that dextral shear was concentrated in the southwest of the study area near the modern coastline. These results support an emerging model in which dextral strain was not ubiquitous across Sonora and did not initiate immediately following the 12.5 Ma transition from subduction to oblique rifting. Instead, strain east of the Baja California microplate at this latitude evolved from extension-dominated transtension prior to 8 Ma to dextral shear-dominated transtension by 7-6 Ma. The onset of dextral shear in coastal Sonora likely resulted from an increase in rift obliquity due to a change in relative plate motion direction at 8 Ma. The increase in rift obliquity and resultant onset of significant strike-slip faulting played a crucial role in facilitating subsequent plate boundary localization and marine incursion in the northern Gulf

  10. Combined structural and magnetotelluric investigation across the West Fault Zone in northern Chile

    Science.gov (United States)

    Hoffmann-Rothe, Arne

    2002-08-01

    The characterisation of the internal architecture of large-scale fault zones is usually restricted to the outcrop-based investigation of fault-related structural damage on the Earth's surface. A method to obtain information on the downward continuation of a fault is to image the subsurface electrical conductivity structure. This work deals with such a combined investigation of a segment of the West Fault, which itself is a part of the more than 2000 km long trench-linked Precordilleran Fault System in the northern Chilean Andes. Activity on the fault system lasted from Eocene to Quaternary times. In the working area (22°04'S, 68°53'W), the West Fault exhibits a clearly defined surface trace with a constant strike over many tens of kilometers. Outcrop condition and morphology of the study area allow ideally for a combination of structural geology investigation and magnetotelluric (MT) / geomagnetic depth sounding (GDS) experiments. The aim was to achieve an understanding of the correlation of the two methods and to obtain a comprehensive view of the West Fault's internal architecture. Fault-related brittle damage elements (minor faults and slip-surfaces with or without striation) record prevalent strike-slip deformation on subvertically oriented shear planes. Dextral and sinistral slip events occurred within the fault zone and indicate reactivation of the fault system. Youngest deformation increments mapped in the working area are extensional and the findings suggest a different orientation of the extension axes on either side of the fault. Damage element density increases with approach to the fault trace and marks an approximately 1000 m wide damage