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Fault System (fault + system)
Selected AbstractsBasement controls on Acadian thrusting and fault reactivation along the southern margin of the Welsh BasinGEOLOGICAL JOURNAL, Issue 5 2009D. I. Schofield Abstract Inversion of the Lower Palaeozoic Welsh Basin during the Early to Mid-Devonian is generally thought to have been achieved by a combination of approximately co-axial shortening and transcurrent movement along major faults to produce a strongly partitioned transpressional strain. However, new field observations from Rhydwilym in southwest Wales reveal superimposed deformations which indicate that thrust tectonics operated within the Welsh Borderland Fault System (WBFS) along this segment of the basin margin. An increasing regional magnetic response towards the south suggests that contrasting depth to magnetic basement across the WBFS may have buttressed basin shortening and provided the focus for thrusting and late-Caledonian or proto-Variscan reactivation. British Geological Survey © Nerc 2009. All rights reserved. [source] Stress behavior from fault data sets within a transtensional zone, South Central Cordillera, Luzon, Philippines: Implications for mineral occurrencesISLAND ARC, Issue 1 2009Mario A. Aurelio Abstract The structural signature in the area between the Baguio mineral district and Ansagan, Tuba, Benguet in the South Central Cordillera, northern Luzon, Philippines, is dominated by northeast- to ENE-trending faults, contained within a NNW,SSE-trending transtensional strip. This 50-km-long, 25-km-wide elongated tectonic zone is bounded to the west by the Pugo Fault and to the east by the Tebbo Fault, both being branches of the Philippine Fault System. Detailed structural geological (particularly microtectonic) analysis of fracture and mineral vein systems indicates strong conformity with the regional structural direction. Computed extensional stress axis ,3 directions are oriented N150° on average, sub-parallel to the strike of the bounding faults. The existence of known mineral deposits and prospects within the tectonic strip implies an intimate relationship between transtension and mineral occurrence. [source] Hydraulic observations from a 1 year fluid production test in the 4000 m deep KTB pilot boreholeGEOFLUIDS (ELECTRONIC), Issue 1 2006W. GRÄSLE Abstract A long-term pump test was conducted in the KTB pilot borehole (KTB-VB), located in the Oberpfalz area, Germany. It produced 22 300 m3 of formation fluid. Initially, fluid production rate was 29 l min,1 for 4 months, but was then raised to an average of 57 l min,1 for eight more months. The aim of this study was to examine the fluid parameters and hydraulic properties of fractured, crystalline crusts as part of the new KTB programme ,Energy and Fluid Transport in Continental Fault Systems'. KTB-VB has an open-hole section from 3850 to 4000 m depth that is in hydraulic contact with a prominent continental fault system in the area, called SE2. Salinity and temperature of the fluid inside the borehole, and consequently hydrostatic pressure, changed significantly throughout the test. Influence of these quantities on variations in fluid density had to be taken into account for interpretation of the pump test. Modelling of the pressure response related to the pumping was achieved assuming the validity of linear Darcy flow and permeability to be independent of the flow rate. Following the principle ,minimum in model dimension', we first examined whether the pressure response can be explained by an equivalent model where rock properties around the borehole are axially symmetric. Calculations show that the observed pressure data in KTB-VB can in fact be reproduced through such a configuration. For the period of high pumping rate (57 l min,1) and the following recovery phase, the resulting parameters are 2.4 × 10,13 m3 in hydraulic transmissivity and 3.7 × 10,9 m Pa,1 in storativity for radial distances up to 187 m, and 4.7 × 10,14 m3 and 6.0 × 10,9 m Pa,1, respectively, for radial distances between 187 and 1200 m. The former pair of values mainly reflect the hydraulic properties of the fault zone SE2. For a more realistic hydraulic study on a greater scale, program FEFLOW was used. Parameter values were obtained by matching the calculated induced pressure signal to fluid-level variations observed in the KTB main hole (KTB-HB) located at 200 m radial distance from KTB-VB. KTB-HB is uncased from 9031 to 9100 m and shows indications of leakage in the casing at depths 5200,5600 m. Analysis of the pressure record and hydraulic modelling suggest the existence of a weak hydraulic communication between the two boreholes, probably at depths around the leakage. Hydraulic modelling of a major slug-test in KTB-HB that was run during the pumping in KTB-VB reveals the effective transmissivity of the connected formation to be 1 to 2 orders of magnitude lower than the one determined for the SE2 fault zone. [source] Extensional development of the Fundy rift basin, southeastern CanadaGEOLOGICAL JOURNAL, Issue 6 2009Martha O. Withjack Abstract The Fundy rift basin of Nova Scotia and New Brunswick, Canada, is part of the Eastern North American rift system that formed during the breakup of Pangaea. Integrated seismic-reflection, field, digital-elevation and aeromagnetic data indicate that the Fundy rift basin underwent two phases of deformation: syn-rift extension followed by post-rift basin inversion. Inversion significantly modified the geometries of the basin and its rift-related structures. In this paper, we remove the effects of inversion to examine the basin's extensional development. The basin consists of three structural subbasins: the Fundy and Chignecto subbasins are bounded by low-angle, NE-striking faults; the Minas subbasin is bounded by E- to ENE-striking faults that are steeply dipping at the surface and gently dipping at depth. Together, these linked faults form the border,fault system of the Fundy rift basin. Most major faults within the border,fault system originated as Palaeozoic contractional structures. All syn-rift units imaged on seismic profiles thicken towards the border,fault system, reflecting extensional movement from Middle Triassic (and possibly Permian) through Early Jurassic time. Intra-rift unconformities, observed on seismic profiles and in the field, indicate that uplift and erosion occurred, at least locally, during rifting. Based on seismic data alone, the displacement direction of the hanging wall of the border,fault system of the Fundy rift basin ranged from SW to SE during rifting. Field data (i.e. NE-striking igneous dykes, sediment-filled fissures and normal faults) indicate NW,SE extension during Early Jurassic time, supporting a SE-displacement direction. With a SE-displacement direction, the NE-striking border,fault zones of the Fundy and Chignecto subbasins had predominantly normal dip slip during rifting, whereas the E-striking border,fault zone of the Minas subbasin had oblique slip with left-lateral and normal components. Sequential restorations of seismic-reflection profiles (coupled with projections from onshore geology) show that the Fundy rift basin underwent 10,20,km of extension, most of which was accommodated by the border,fault system, and was considerably wider and deeper prior to basin inversion. Post-rift deformation tilted the eastern side of the basin to the northwest/north, producing significant uplift and erosion. Copyright © 2009 John Wiley & Sons, Ltd. [source] Three-dimensional elastic earthquake modelling based on integrated seismological and InSAR data: the Mw= 7.2 Nuweiba earthquake, gulf of Elat/Aqaba 1995 NovemberGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2003G. Shamir SUMMARY The Nuweiba earthquake (1995 November 22; Mw= 7.2), the largest seismic event along the Dead Sea Transform (DST) in at least 160 yr, ruptured 45,50 km along the Aragonese segment of the left-stepping strike-slip fault system occupying the gulf of Elat/Aqaba (southern segment of the DST). The rupture initiated in a partly normal, low-slip first subevent near the southern end of the fault and propagated unilaterally north-northeastward as a high-slip, nearly pure sinistral second subevent, which was responsible for over 90 per cent of the total seismic moment. The source mechanism and slip distribution, derived from inversion of teleseismic broad-band waveforms, are used to construct a 3-D elastic model of the earthquake based on the boundary elements method, resulting in the full 3-D displacement and stress fields induced by the earthquake. In the absence of sufficient Global Positioning System data, the only other constraints on the geometry and slip distribution of the rupture are provided by interferometric synthetic aperture radar (InSAR) measurements spanning the coseismic and early post-seismic period. We calculate simulated interferograms by transforming the calculated surface displacement field into the satellite coordinate system and comparing them with the observed interferograms. The model parameters are then iteratively modified until a best-fitting model is obtained, providing a refined set of static source parameters for the mainshock. This model is then used to calculate the static Coulomb stress changes induced by the mainshock on the step-over faults, suggesting that the major (Mw, 5) aftershocks in the first eight post-seismic months were triggered by small changes (<1 bar) in the left-lateral Coulomb stress, with effective friction coefficient not higher than 0.2. Aftershock distribution and mechanisms indicate that the available Coulomb stress dropped below the frictional strength of the fault but was not complete. [source] Seismicity of the Sea of Marmara (Turkey) since 1500GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000N. N. Ambraseys Summary We use the earthquake history of the last 500 years to help evaluate the tectonic and hazard contexts of the 1999 earthquakes at Izmit and Düzce in western Turkey. The 20th century has been unusually active, but over the 500 year period the seismic moment release can account for the known right-lateral shear velocity across the Marmara region observed by GPS. Two areas of known late Quaternary faulting stand out as unusually quiet over this period: the northwest shore of the Sea of Marmara and the southern branch of the North Anatolian fault system between Bursa and Mudurnu. [source] Thrust geometries in unconsolidated Quaternary sediments and evolution of the Eupchon Fault, southeast KoreaISLAND ARC, Issue 3 2004Young-Seog Kim Abstract The Korean peninsula is widely regarded as being located at the relatively stable eastern margin of the Asian continent. However, more than 10 Quaternary faults have recently been discovered in and reported from the southeastern part of the Korean Peninsula. One of these, the Eupchon Fault, was discovered during the construction of a primary school, and it is located close to a nuclear power plant. To understand the nature and characteristics of the Quaternary Eupchon Fault, we carried out two trench surveys near the discovery site. The fault system includes one main reverse fault (N20°E/40°SE) with approximately 4 m displacement, and a series of branch faults, cutting unconsolidated Quaternary sediments. Structures in the fault system include synthetic and antithetic faults, hanging-wall anticlines, drag folds, back thrusts, pop-up structures, flat-ramp geometries and duplexes, which are very similar to those seen in thrust systems in consolidated rocks. In the upper part of the fault system, several tip damage zones are observed, indicating that the fault system propagates upward and terminates in the upper part of the section. Pebbles along the main fault plane show a preferred orientation of long axes, indicating the fault trace. The unconformity surface between the Quaternary deposits and the underlying Tertiary andesites or Cretaceous sedimentary rocks is displaced by this fault with a reverse movement sense. The stratigraphic relationship shows normal slip sense at the lower part of the section, indicating that the fault had a normal slip movement and was reversely reactivated during the Quaternary. The inferred length of the Quaternary thrust fault, based on the relationship between fault length and displacement, is 200,2000 m. The current maximum horizontal compressive stress direction in this area is generally east-northeast,west-southwest, which would be expected to produce oblique slip on the Eupchon Fault, with reverse and right-lateral strike-slip components. [source] Exhumation during oblique transpression: The Feiran,Solaf region, EgyptJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2009T. S. ABU-ALAM Abstract The Feiran,Solaf metamorphic complex of Sinai, Egypt, is one of the highest grade metamorphic complexes of a series of basement domes that crop out throughout the Arabian-Nubian Shield. In the Eastern Desert of Egypt these basement domes have been interpreted as metamorphic core complexes exhumed in extensional settings. For the Feiran,Solaf complex an interpretation of the exhumation mechanism is difficult to obtain with structural arguments as all of its margins are obliterated by post-tectonic granites. Here, metamorphic methods are used to investigate its tectonic history and show that the complex was characterized by a single metamorphic cycle experiencing peak metamorphism at ,700,750 °C and 7,8 kbar and subsequent isothermal decompression to ,4,5 kbar, followed by near isobaric cooling to 450 °C. Correlation of this metamorphic evolution with the deformation history shows that peak metamorphism occurred prior to the compressive deformation phase D2, while the compressive D2 and D3 deformation occurred during the near isothermal decompression phase of the P,T loop. We interpret the concurrence of decompression of the P,T path and compression by structural shortening as evidence for the Najd fault system exhuming the complex in an oblique transpressive regime. However, final exhumation from ,15 km depth must have occurred due to an unrelated mechanism. [source] Late Miocene,Pliocene eclogite facies metamorphism, D'Entrecasteaux Islands, SE Papua New GuineaJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2007B. D. MONTELEONE Abstract The D'Entrecasteaux Islands of south-eastern Papua New Guinea are active metamorphic core complexes that formed within a region where the plate tectonic regime has transitioned from subduction to rifting. While rapid, post 4 Myr exhumation and cooling of amphibolite and greenschist facies rocks that constitute the footwall of the crustal scale detachment fault system have been previously documented on Fergusson and Goodenough Islands of the D'Entrecasteaux chain, the timing of eclogite facies metamorphism in rocks of the footwall was unknown. Recent work revealed that at least one of the eclogite bodies formed during the Pliocene. We present combined in situ ion microprobe U,Pb age analyses of zircon from five variably retrogressed eclogite samples from Fergusson and Goodenough Islands that document Late Miocene,Pliocene (8,2 Ma) eclogite formation on these islands. Textural relationships and zircon,garnet rare earth element partition coefficients indicate that U,Pb ages constrain zircon crystallization under eclogite facies conditions in all samples. Results suggest westward younging of eclogite facies metamorphism from Fergusson to Goodenough Island. Present-day exposure of Late Miocene,Pliocene eclogites requires exhumation rates > 2.5 cm yr,1. [source] Dating metamorphic reactions and fluid flow: application to exhumation of high- P granulites in a crustal-scale shear zone, western Canadian ShieldJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2006K. H. MAHAN Abstract The Legs Lake shear zone is a crustal-scale thrust fault system in the western Canadian Shield that juxtaposes high-pressure (1.0+ GPa) granulite facies rocks against shallow crustal (< 0.5 GPa) amphibolite facies rocks. Hangingwall decompression is characterized by breakdown of the peak assemblage Grt + Sil + Kfs + Pl + Qtz into the assemblage Grt + Crd + Bt ± Sil + Pl + Qtz. Similar felsic granulite occurs throughout the region, but retrograde cordierite is restricted to the immediate hangingwall of the shear zone. Textural observations, petrological analysis using P,T/P,MH2O phase diagram sections, and in situ electron microprobe monazite geochronology suggest that decompression from peak conditions of 1.1 GPa, c. 800 °C involved several distinct stages under first dry and then hydrated conditions. Retrograde re-equilibration occurred at 0.5,0.4 GPa, 550,650 °C. Morphology, X-ray maps, and microprobe dates indicate several distinct monazite generations. Populations 1 and 2 are relatively high yttrium (Y) monazite that grew at 2.55,2.50 Ga and correspond to an early granulite facies event. Population 3 represents episodic growth of low Y monazite between 2.50 and 2.15 Ga whose general significance is still unclear. Population 4 reflects low Y monazite growth at 1.9 Ga, which corresponds to the youngest period of high-pressure metamorphism. Finally, population 5 is restricted to the hydrous retrograded granulite and represents high Y monazite growth at 1.85 Ga that is linked directly to the synkinematic garnet-consuming hydration reaction (KFMASH): Grt + Kfs + H2O = Bt + Sil + Qtz. Two samples yield weighted mean microprobe dates for this population of 1853 ± 15 and 1851 ± 9 Ma, respectively. Subsequent xenotime growth correlates with the reaction: Grt + Sil + Qtz + H2O = Crd. We suggest that the shear zone acted as a channel for fluid produced by dehydration of metasediments in the underthrust domain. [source] Pressure,temperature,time evolution of the Central East Greenland Caledonides: quantitative constraints on crustal thickening and synorogenic extensionJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2003A. P. White Abstract Whereas geologists have known for three-quarters of a century that there was significant crustal thickening in the central East Greenland Caledonides, the crucial role of extensional faulting during Caledonian orogenesis has only been recognized during the past decade. In this paper, new petrographic and thermobarometric observations are presented from migmatitic metasedimentary gneisses of the Forsblad Fjord region (c. 72.5°N). Samples of the Krummedal Sequence, collected from the footwall of the upper of two significant splays of the main extensional fault system in the region,the Fjord Region Detachment (FRD),enable us to establish a relative sequence of metamorphism. Our pressure (P),temperature (T) results imply a clockwise loop in P,T space. As recorded by mineral assemblages in the Krummedal gneisses, prograde metamorphism involved a net increase of c. 4 kbar and 250 °C, with peak conditions of c. 10.5 kbar at 785 °C. Early burial and heating was followed by near-isothermal decompression of 4.5 kbar, a process which is attributed to roughly 18 km of tectonostratigraphic throw on the upper splay of the FRD. Combining data reported here with the published data, it is estimated that the approximate tectonostratigraphic throw along the lower splay of the FRD was c. 16 km. In situ U,Th,Pb-monazite electron microprobe dating suggests that the earliest phase of metamorphism recorded in the Krummedal Sequence gneisses of Forsblad Fjord occurred during the Caledonian orogeny. Furthermore, the combination of our new data with existing conventional TIMS U-Pb and 40Ar/39Ar data imply that: (1) movement along the uppermost splay of the FRD (c. 425,423 Ma) occurred at maximum time-averaged slip-rates equivalent to c. 9 mm of vertical displacement per year; and (2) that the final stages of metamorphism occurred prior to c. 411 Ma, although part of this denudation was likely accommodated on overlying extensional structures that may have been active more recently. There is close agreement between our data and results from the Krummedal Sequence north of the field area (72.5°,74°N), and rocks of the Smallefjord Sequence (75°,76°N) that are suggested to correlate with the Krummedal Sequence. This leads us to infer that the events recorded in the Forsblad Fjord region are of orogen-scale significance. [source] Tectonic Controls on the Formation of the Liwu Cu-rich Sulfide Deposit in the Jianglang Dome, S W ChinaRESOURCE GEOLOGY, Issue 2 2003Dan-Ping Yan Abstract. The Liwu Cu-rich sulfide deposit occurs within the Jianglang dome in the eastern margin of the Tibetan plateau. The dome consists of a core, a middle slab and a cover sequence. The main deposit is hosted in the core with minor ore bodies in the middle slab. The protolith of the core consists of clastic sedimentary rocks with inter-layered volcanic rocks. All of the ore bodies are substantially controlled by an extensional detachment fault system. The ore bodies within the core are distributed along the S2 foliation in the hinge of recumbent fold (D2), whereas ore bodies with en echelon arrangement are controlled by the mylonitic foliation of the lower detachment fault. Ore bodies within the middle slab are oriented with their axes parallel to the mylonitic foliation. Pyrite and pyrrhotite from the ores contain Co ranging from 37 to 1985 ppm, Ni from 2.5 to 28.1 ppm, and Co/Ni ratios from 5 to 71. These sulfides have ,34S values ranging from 1.5 to 7.5 % whereas quartz separates have ,18O values of 11.9 and 14.3 % and inclusion fluid in quartz has ,D value of-88.1 %. These features suggest that the deposit was of hydrothermal origin. Two ore-forming stages are recognized in the evolution of the Jianglang dome. (1) A low-temperature ore-forming process, during the tectonic transport of the upper plate above the lower detachment, and the initial phase of the footwall updom-ing at 192,177 Ma. (2) A medium-temperature ore-forming stage, related to the final structural development of the initial detachment at 131,81Ma. Within the core, the ore bodies of the first stage were uplifted to, or near, the brittle/ductile horizon where the ore-forming metals were re-concentrated and enriched. A denudation stage in which a compressional tectonic event produced eastward thrusting overprinted the previous structures, and finally denuded the deposit. The Liwu Cu-rich sulfide deposit was formed during a regional extensional tectonic event and is defined as a tectono-strata-bound hydrothermal ore deposit. [source] Dashuigou Tellurium Deposit in Sichuan Province, China: S, C, O, and H Isotope Data and Their Implications on Hydrothermal MineralizationRESOURCE GEOLOGY, Issue 1 2002Jingwen MAO Abstract: Dashuigou, a unique tellurium-dominated deposit over the world, is located in the western margin of the Yangtze cra-ton in southwestern China. It is characterized by high-grade tellurium accompanied by bismuth, gold, silver, and sulfur, and occurs in the area of less than one km2. The mineralization is divided into three stages, i.e. (1) tellurium-bearing pyrrhotite,pyrite stage, (2) tetradymite stage, and (3) auriferous quartz veins stage. Tellurium mineralization coexisting with bismuth, silver, selenium, and gold predominantly develops in the stage 2, while the stage 1 is enriched only in sulfur and iron, and the stage 3 is very weakly mineralized with gold. The ,34S values of sulfides in the ore of the deposit vary in a narrow range of ,3.1 - +2.8 per mil with ,3.1 - +2.8 per mil for the stage 1 and ,0.5 - +2.1 for the stage 2, showing the isotopic characteristics of mantle derived sulfur. The ,13C values of vein dolomites vary from ,5.3 to ,7.2 per mil, with ,5.3 - ,6.6 per mil for the stage 1 and ,5.3 - ,7.2 per mil for the stage 2, which are significantly different from those of surrounding Triassic marble with ,13C values of ,0.3 - +2.8 per mil, and show characteristics of mantle derived carbon. The ,18O values of vein dolomites range from +10.2 to +13.1 per mil, which are higher than those of carbonatite, but lower than those of the marble. Their corresponding ,18Owater values are +0.6 - +3.9 per mil, with +2.7 - +3.8 per mil for the stage 1 and +0.6 - +3.9 per mil for the stage 2. The data implies that these vein carbonates were formed by the mixing fluids of magmatic or mantle source with meteoric or formation water. The ,18O values of ore-forming fluids responsible for the formation of vein quartz are estimated to be +3.2 to +6.8, the ,D values of inclusion fluids of the quartz are measured to be ,54 to ,82 per mil. All those stable isotopic data suggest the involvement of the fluids from mantle and/or mantle-derived magmas through fault system in the forming process of the Dashuigou tellurium deposit. [source] Evolution of basin architecture in an incipient continental rift: the Cenozoic Most Basin, Eger Graben (Central Europe)BASIN RESEARCH, Issue 3 2009Michal Rajchl ABSTRACT The Oligo-Miocene Most Basin is the largest preserved sedimentary basin within the Eger Graben, the easternmost part of the European Cenozoic Rift System (ECRIS). The basin is interpreted as a part of an incipient rift system that underwent two distinct phases of extension. The first phase, characterised by NNE,SSW- to N,S-oriented horizontal extension between the end of Eocene and early Miocene, was oblique to the rift axis and caused evolution of a fault system characterised by en-échelon-arranged E,W (ENE,WSW) faults. These faults defined a number of small, shallow initial depocentres of very small subsidence rates that gradually merged during the growth and linkage of the normal fault segments. The youngest part of the basin fill indicates accelerated subsidence caused probably by the concentration of displacement at several major bounding faults. Major post-depositional faulting and forced folding were related to a change in the extension vector to an orthogonal position with respect to the rift axis and overprinting of the E,W faults by an NE,SW normal fault system. The origin of the palaeostress field of the earlier, oblique, extensional phase remains controversial and can be attributed either to the effects of the Alpine lithospheric root or (perhaps more likely because of the dominant volcanism at the onset of Eger Graben formation) to doming due to thermal perturbation of the lithosphere. The later, orthogonal, extensional phase is explained by stretching along the crest of a growing regional-scale anticlinal feature, which supports the recent hypothesis of lithospheric folding in the Alpine,Carpathian foreland. [source] Seismic reflection imaging of active offshore faults in the Gulf of Corinth: their seismotectonic significanceBASIN RESEARCH, Issue 4 2002A. Stefatos ABSTRACT High resolution seismic reflection surveys over one of the most active and rapidly extending regions in the world, the Gulf of Corinth, have revealed that the gulf is a complex asymmetric graben whose geometry varies significantly along its length. A detailed map of the offshore faults in the gulf shows that a major fault system of nine distinct faults limits the basin to the south. The northern Gulf appears to be undergoing regional subsidence and is affected by an antithetic major fault system consisting of eight faults. All these major faults have been active during the Quaternary. Uplifted coastlines along their footwalls, growth fault patterns and thickening of sediment strata toward the fault planes indicate that some of these offshore faults on both sides of the graben are active up to present. Our data ground-truth recent models and provides actual observations of the distribution of variable deformation rates in the Gulf of Corinth. Furthermore they suggest that the offshore faults should be taken into consideration in explaining the high extension rates and the uplift scenarios of the northern Peloponnesos coast. The observed coastal uplift appears to be the result of the cumulative effect of deformation accommodated by more than one fault and therefore, average uplift rates deduced from raised fossil shorelines, should be treated with caution when used to infer individual fault slip rates. Seismic reflection profiling is a vital tool in assessing seismic hazard and basin-formation in areas of active extension. [source] Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat SeaBOREAS, Issue 2 2002JØRN BO JENSEN Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region. [source] Large-scale Migration of Fluids toward Foreland Basins during Collisional Orogeny: Evidence from Triassic Anhydrock Sequences and Regional Alteration in the Middle-Lower Yangtze AreaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2004HOU Zengqian Abstract The middle-lower Yangtze area underwent a series of complex tectonic evolution, such as Hercynian extensional rifting, Indosinian foreland basining, and Yanshanian transpression-transtension, resulting in a large distinctive Cu-Fe-Au metallogenic belt. In the tectonic evolution, large-scale migration and convergence of fluids toward foreland basins induced during the collisional orogeny of the Yangtze and North China continental blocks were of vital importance for the formation of the metallogenic belt. Through geological surveys of the middle-lower Yangtze area, three lines of evidence of large-scale fluid migration are proposed: (1) The extensive dolomitic and silicic alteration penetrating Cambrian-Triassic strata generally occurs in a region sandwiched between the metallogenic belt along the Yangtze River and the Dabie orogenic belt, and in the alteration domain alternately strong and weak alteration zones extend in a NW direction and are controlled by the fault system of the Dabie orogenic belt; it might record the locus of the activities of long-distance migrating fluids. (2) The textures and structures of very thick Middle-Lower Triassic anhydrock sequences in restricted basins along the river reveal the important contribution of the convergence of regional hot brine in restricted basins and the chemical deposition or their formation. (3) Early-Middle Triassic syndepositional iron carbonate sequences and Fe-Cu-Pb-Zn massive sulfide deposits alternate with anhydrock sequences or are separated from the latter, but all of them occur in the same stratigraphic horizon and are intimately associated with each other, being the product of syndeposition of high-salinity hot brine. According to the geological surveys, combined with previous data, the authors propose a conceptual model of fluid migration-convergence and mineralization during the Dabie collisional orogeny. [source] The Altun Fault: Its Geometry, Nature and Mode of GrowthACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2001CUI Junwen Abstract The Altun (or Altyn Tagh) fault displays a geometry of overlapping of linear and arcuate segments and shows strong inhomogeneity in time and space. It is a gigantic fault system with complex mechanical behaviours including thrusting, sinistral strike slip and normal slip. The strike slip and normal slip mainly occurred in the Cretaceous,Cenozoic and Plio-Quaternary respectively, whereas the thrusting was a deformation event that has played a dominant role since the late Palaeozoic (for a duration of about 305 Ma). The formation of the Altun fault was related to strong inhomogeneous deformation of the massifs on its two sides (in the hinterland of the Altun Mountains contractional deformation predominated and in the Qilian massif thrust propagation was dominant). The fault experienced a dynamic process of successive break-up and connection of its segments and gradual propagation, which was synchronous with the development of an overstep thrust sequence in the Qilian massif and the uplift of the Qinghai-Tibet plateau. With southward propagation of the thrust sequence and continued uplift of the plateau, the NE tip of the Altun fault moved in a NE direction, while the SW tip grew in a SW direction. [source] Factors affecting fluid flow in strike,slip fault systems: coupled deformation and fluid flow modelling with application to the western Mount Isa Inlier, AustraliaGEOFLUIDS (ELECTRONIC), Issue 1 2009A. FORD Abstract Deformation and focused fluid flow within a mineralized system are critical in the genesis of hydrothermal ore deposits. Dilation and integrated fluid flux due to coupled deformation and fluid flow in simple strike,slip fault geometries were examined using finite difference analysis in three dimensions. A series of generic fault bend and fault jog geometries consistent with those seen in the western Mount Isa Inlier were modelled in order to understand how fault geometry parameters influence the dilation and integrated fluid flux. Fault dip, fault width, bend/jog angle, and length were varied, and a cross-cutting fault and contrasting rock types were included. The results demonstrate that low fault dips, the presence of contrasts in rock type, and wide faults produce highest dilation and integrated fluid flux values. Increasing fault bend lengths and angles increases dilation and integrated fluid flux, but increasing fault jog length or angle has the opposite effect. There is minimal difference between the outputs from the releasing and restraining fault bend and jog geometries. Model characteristics producing greater fluid flows and/or gradients can be used in a predictive capacity in order to focus exploration on regions with more favorable fault geometries, provided that the mineralized rocks had Mohr,Coulomb rheologies similar to the ones used in the models. [source] Duplex architecture and late-orogenic backthrusting in Foredeep Units of the Northern Apennines (Italy)GEOLOGICAL JOURNAL, Issue 4 2008Andrea Cerrina Feroni Abstract The Northern Apennines of Italy is a fold and thrust belt that resulted from the NE-ward progressive overthrusting of a Mesoalpine stacking (the ocean-derived Ligurian Units) onto the detached sedimentary cover of the Adria plate continental margin (Foredeep Units). The Futa Pass area represents a key sector for the reconstruction of the deformation history of two Foredeep Units (Acquerino and Carigiola Units). The tectonic evolution of this sector is characterized by the superposition of three main deformation stages, with a constant NNE,SSW compression direction. The oldest structure is represented by the NNE-verging Acquerino Unit duplex structure, the roof thrust of which is represented by the Ligurian stacking basal thrust. The interpretation of this structure as a large-scale duplex is supported by the presence in the outer sectors of the Northern Apennines belt of Ligurian Units directly overthrust on younger Foredeep Units. In the second deformation stage the NNE-verging Tavaiano Thrust developed. This regionally significant tectonic surface juxtaposes the Acquerino Unit (already developed as a duplex) and the overlying Ligurian Units, onto the Carigiola Unit. During this stage the fault pattern of the Carigiola Unit was also developed, characterized by two conjugate fault systems, coherent with a NNE,SSW maximum compression direction. During the last deformation stage, a backthrusting with a top-to-the SSW sense of movement (the Marcoiano Backthrust) brings the Carigiola Unit and its tectonic cover over the Acquerino and Ligurian Units, with the development of a large footwall syncline. The deformation history presented here differs from previous studies, and so provides a contribution to the debate on Northern Apennines tectonic evolution. Copyright © 2008 John Wiley & Sons, Ltd. [source] Differential compaction due to the irregular topology of a diagenetic reaction boundary: a new mechanism for the formation of polygonal faultsBASIN RESEARCH, Issue 3 2009R. J. Davies ABSTRACT We propose a new mechanism for the formation of some polygonal fault arrays. Seismically imaged opal-A (biogenic silica) to opal-CT (cristobalite and tridymite) diagenetic boundaries from two regions offshore of Norway have developed regular wavelength patterns. The pattern consists of cell-shaped elevations that are 200,2600 m wide and up to 200 m high, separated by troughs. The cells represent regions that undergo diagenesis at shallower burial depths, earlier than adjacent areas. The chemical change leads to mechanical compaction and porosity reduction; therefore subsidence occurs above the cells in the overburden. Roughly circular depressions form above the cells, and a network of folds form above inter-cell areas. Networks of normal faults form on the crests and margins of the folds as a result of flexure during the folding. The progressive lateral growth of the cells causes the depressions to widen and intervening folds to narrow resulting in new differential compaction-induced faults to form with variable strike orientations. Lateral and vertical growth of cells leads to cells conjoining and the re-establishment of a uniform planar reaction boundary. This novel but simple mechanism can explain some polygonal fault arrays that form above opal-A to opal-CT reaction boundaries and in these settings the mechanism should be considered in addition to syneresis, density inversion or low coefficients of residual friction which are the most commonly cited drivers for polygonal fault systems. [source] Giant submarine collapse of a carbonate platform at the Turonian,Coniacian transition: The Ayabacas Formation, southern PeruBASIN RESEARCH, Issue 3 2008Pierre Callot ABSTRACT The Ayabacas Formation of southern Peru is an impressive unit formed by the giant submarine collapse of the mid-Cretaceous carbonate platform of the western Peru back-arc basin (WPBAB), near the Turonian,Coniacian transition (,90,89 Ma). It extends along the southwestern edge of the Cordillera Oriental and throughout the Altiplano and Cordillera Occidental over >80 000 km2 in map view, and represents a volume of displaced sediments of >10 000 km3. The collapse occurred down the basin slope, i.e. toward the SW. Six zones are characterised on the basis of deformational facies, and a seventh corresponds to the northeastern ,stable' area (Zone 0). Zones 1,3 display increasing fragmentation from NE to SW, and are composed of limestone rafts and sheets embedded in a matrix of mainly red, partly calcareous and locally sandy, mudstones to siltstones. In contrast, in Zones 4 and 5 the unit consists only of displaced and stacked limestone masses forming a ,sedimentary thrust and fold system', with sizes increasing to the southwest. In Zone 6, the upper part of the limestone succession consists of rafts and sheets stacked over the regularly bedded lower part. The triggering of this extremely large mass wasting clearly ensued from slope creation, oversteepening and seismicity produced by extensional tectonic activity, as demonstrated by the observation of synsedimentary normal faults and related thickness variations. Other factors, such as pore pressure increases or lithification contrasts probably facilitated sliding. The key role of tectonics is strengthened by the specific relationships between the basin and collapse histories and two major fault systems that cross the study area. The Ayabacas collapse occurred at a turning point in the Central Andean evolution. Before the event, the back-arc basin had been essentially marine and deepened to the west, with little volcanic activity taking place at the arc. After the event, the back-arc was occupied by continental to near-continental environments, and was bounded to the southwest by a massive volcanic arc shedding debris and tuffs into the basin. [source] The stratigraphic and structural evolution of the Dzereg Basin, western Mongolia: clastic sedimentation, transpressional faulting and basin destruction in an intraplate, intracontinental settingBASIN RESEARCH, Issue 1 2003J. P. Howard ABSTRACT The Dzereg Basin is an actively evolving intracontinental basin in the Altai region of western Mongolia. The basin is sandwiched between two transpressional ranges, which occur at the termination zones of two regional-scale dextral strike-slip fault systems. The basin contains distinct Upper Mesozoic and Cenozoic stratigraphic sequences that are separated by an angular unconformity, which represents a regionally correlative peneplanation surface. Mesozoic strata are characterized by northwest and south,southeast-derived thick clast-supported conglomerates (Jurassic) overlain by fine-grained lacustrine and alluvial deposits containing few fluvial channels (Cretaceous). Cenozoic deposits consist of dominantly alluvial fan and fluvial sediments shed from adjacent mountain ranges during the Oligocene,Holocene. The basin is still receiving sediment today, but is actively deforming and closing. Outwardly propagating thrust faults bound the ranges, whereas within the basin, active folding and thrusting occurs within two marginal deforming belts. Consequently, active fan deposition has shifted towards the basin centre with time, and previously deposited sediment has been uplifted, eroded and redeposited, leading to complex facies architecture. The geometry of folds and faults within the basin and the distribution of Mesozoic sediments suggest that the basin formed as a series of extensional half-grabens in the Jurassic,Cretaceous which have been transpressionally reactivated by normal fault inversion in the Tertiary. Other clastic basins in the region may therefore also be inherited Mesozoic depocentres. The Dzereg Basin is a world class laboratory for studying competing processes of uplift, deformation, erosion, sedimentation and depocentre migration in an actively forming intracontinental transpressional basin. [source] Geochemistry of Heavy Oil in the T Block, Oriente Basin and its Origin MechanismACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2010Ying HU Abstract: Exploration and development experience show that there is obvious oil gravity difference between the southern part and northern part of the "M1" reservoir in the Fanny oil field in the slope of the Oriente Basin, Ecuador. The American Petroleum Institute Gravity (API) values of oils in the northern part are higher than the one in the southern part of the Fanny oil field, with the values of 20° and 10.0°,13.0°, respectively. So the primary purpose of this study was to analyze the heavy oil characteristics of biodegradation and the oil,oil correlation according to the biomarker data and the ,13C signature of oil samples from T block. The results of the hydrocarbon gas chromatography fingermark and the inversion attribute characteristics indicated that there are fluid compartments between the "M1" reservoir of Fanny south. Finally, the models of oil,gas accumulation under the control of multiple-activities of complicated fault systems, as well as the origin of heavy oil, are contended. The early stage oils from the western part of the basin were biodegraded heavily in varying degrees in the whole basin, and the later stage oils were derived from the southern part in a large scale and were mature and lighter. Generally, oil mixing is the primary control of net oil properties, such as API gravity in Oriente Basin. We therefore predicted that the API gravity variation of oil pools radically depends on the injection amount of the later stage oil. Because of the shale barrier in the "M1" reservoir of Fanny south, the later stage hydrocarbon could not pass through and contribute to increase the oil API value. [source] | ||||||||||