Sinistral Strike-slip Faults Research Articles

Contemporary crustal movement of southeastern Tibet: Constraints from dense GPS measurements

The ongoing collision between the Indian plate and the Eurasian plate brings up N-S crustal shortening and thickening of the Tibet Plateau, but its dynamic mechanisms remain controversial yet. As one of the most tectonically active regions of the world, South-Eastern Tibet (SET) has been greatly paid attention to by many geoscientists. Here we present the latest three-dimensional GPS velocity field to constrain the present-day tectonic process of SET, which may highlight the complex vertical crustal deformation. Improved data processing strategies are adopted to enhance the strain patterns throughout SET. The crustal uplifting and subsidence are dominated by regional deep tectonic dynamic processes. Results show that the Gongga Shan is uplifting with 1–1.5 mm/yr. Nevertheless, an anomalous crustal uplifting of ~8.7 mm/yr and negative horizontal dilation rates of 40–50 nstrain/yr throughout the Longmenshan structure reveal that this structure is caused by the intracontinental subduction of the Yangtze Craton. The Xianshuihe-Xiaojiang fault is a major active sinistral strike-slip fault which strikes essentially and consistently with the maximum shear strain rates. These observations suggest that the upper crustal deformation is closely related with the regulation and coupling of deep material.

Late Cretaceous volcanic arc system in southwest Korea: Distribution, lithology, age, and tectonic implications

In the southwestern part of the Korean Peninsula, Cretaceous volcanic rocks occur along a NE–SW-trending, sinistral strike-slip fault (Hamyeol Fault). Based on their spatial distribution, the volcanic rocks are classified into three lithostratigraphic units: the Buan, the Seonunsan, and the Beopseongpo Volcanics. These volcanics are composed of various types of pyroclastic, sedimentary, and lavas/intrusive rocks. SHRIMP UPb ages of zircon crystals were isolated from each unit. For the Buan Volcanics, Cheonmasan Tuff = 87.23 ± 0.92 Ma; Udongje Tuff = 86.79 ± 0.71 Ma; Seokpo Tuff = 87.30 ± 0.99 Ma; and Yujeongje Tuff = 86.66 ± 0.93 Ma. For the Seonunsan Volcanics, Gyeongsusan Tuff = 84.9 ± 1.1 Ma and Yeongije Tuff = 86.61 ± 0.67 Ma. For the Beopseongpo Volcanics, Seongsan Tuff = 87.73 ± 0.89 Ma and Gyema Rhyolite = 86.2 ± 1.7 Ma. The ages correspond well to recent mapping results of volcanic rocks in the southwest and south parts of the Korean Peninsula. In addition, the age data are comparable to those of the Aioi and Arima volcanic rock groups in southwestern Japan. This suggests that regional volcanic activity in the Japanese Islands and the southwestern part of the Korean Peninsula is related, and results from magmatism together with crustal deformation due to slab rollback of the Izanagi Oceanic Plate underneath the Eurasian Plate.

Three-dimensional modelling of folds, thrusts, and strike-slip faults in the area of Val de Ruz (Jura Mountains, Switzerland)

The Val-de-Ruz syncline is a northeast-southwest trending, rhomb-shaped synclinal basin in the internal part of the central Jura Mountains. The Mesozoic sediment succession is decoupled from the basement by a decollement horizon in Middle Triassic evaporite-bearing layers at depth and folding is associated with southeast-dipping thrust splays rooting into this decollement. The folds and thrusts also interfere with a system of N-S striking, sinistral strike-slip faults. A 3D model was constructed from the following input data: A digital elevation model, the 1:25,000 geological map of Switzerland, published contours of the top of basement based on drilling and seismics, and nine newly constructed cross-sections. The latter are based on surface geology and published seismic data. Cross-sections parallel to the northwestward transport direction, i.e. perpendicular to the overall strike, are line balanced. Anticlines are interpreted as faulted detachment folds, which initiated by buckling and associated flow of evaporites from synclinal to anticlinal areas. Anticlines were later broken by northwest-vergent thrusts and subsequently developed into fault-propagation folds during decollement from the basement and northwestward translation. The model assumes no faulting in the pre-Mesozoic basement and no hidden flat-ramp tectonics in the subsurface in order to account for structurally high positions. As a consequence, the modelled cumulative, post-deformation thickness of Triassic strata locally exceeds 1500 m, which we find in accordance with regional observations. From the geological 3D model, new cross-sections in any desired orientation and tectonic thickness variations of the layers can be extracted. The three output cross-sections presented are in excellent agreement with published reflection seismic data. The most important features of our model are (1) large thickness variations due to lateral flow of evaporites, and (2) new and plausible explanation of structural highs in terms of accumulation of Triassic strata by lateral flow.

Geology, Geochemistry and Hydrothermal Fluid Characteristics of Low Sulfidation Epithermal Deposit in the Sangon Area, Kokap, Special Region of Yogyakarta

On the basis of the previous studies and reconnaissance survey in the studyarea covering Sangon, Kalirejo, Kokap Sub-district, Kulon Progo Regency, Special Region of Yogyakarta, it reveals some facts of the occurrence of quartz veins with massive, crustiform, comb, drusy cavity, saccharoidal, granular, and reniform/mammillated textures, the appearance of lattice bladed barite and hydrothermal breccia veins. Referring to those characteristics, the deposit type in the study area is interpreted to be low sulfidation epithermal type. This study is aimed to understand and characterize the geological condition, rock and ore geochemistry and the mineralizing fluids. The alteration and ore mineralization are almost observed in entire rock units particularly the intrusive andesite 1. Their formation is controlled by the tension fractures (NW–SE and NE–SW) which associate with sinistral strike slip faults (NE–SW), dilational jog (NNW–SSE), oblique normal fault (WNW–ESE), and predictable normal fault at the NE of study area (NW–SE). The alteration zones are developed to be silica-clay (quartz-illite-kaolinite-kaolinite/smectite), argillic (smectite-illite/smectite), and propylitic (chlorite-calcite±epidote). The precipitationof ore minerals is controlled by boiling, mixing, and wall-rock alteration, and canbe found in the quartz veins (quartz-adularia-sericite) and disseminated in the alteration zones, which their high variability is only can be found in the quartz veins, including pyrite, sphalerite, chalcopyrite, galena, marcasite, and arsenopyrite. Based on the ICPAES measurement of 5 quartz vein samples, the Cu, Zn, Pb, and As grade reach about 5,171 ppm, 8,995 ppm, 6,398 ppm, 34.1 ppm, and 1,010.5 ppm, respectively. Gold is not detected. Fluid inclusion microthermometric analysis shows Th of 242.1–257.6 °C and salinity of 1.57–3.87 wt.% NaCl equiv., which indicate a depth below the paleosurface of 384–516 m, and pressure of 101.7–136.6 bar. The ore deposit in the study area is interpreted to be a deep basemetal low sulfidation epithermal type. Gold might be depleted in this epithermal type.

Neotectonics and seismicity of Erzurum pull-apart basin, East Turkey

The study area is the Erzurum pull-apart basin located in the East Anatolian Tectonic Block (EATB), which is under the control of a strike-slip neotectonic regime since the beginning of Quaternary. The Quaternary Erzurum pull-apart basin is an about 1-30 km wide, 90 km long and actively growing strike-slip depression. It is bounded by the Erzurum-Dumlu sinistral strike-slip fault zone to the east-southeast, by the Askale sinistral strike-slip fault zone to the north-northwest, and by the Baskoy-Kandilli reverse fault zone and the N-S-trending Ilica oblique-slip normal fault set to the west. The Erzurum pull-apart basin was evolved by the deformation and subdivision of an E-W-trending older intermontane basin. The new basin has a 0.5 km thick, flat-lying (undeformed) and uconsolidated fill, which overlies, with an angular unconformitry, the deformed (folded and faulted) basement rocks of pre-Quaternary age. Basin fill consists of coarser-grained marginal facies (fault terrace, fan, fan-apron and superimposed fan deposits) and finer-grained depocentral facies represented by flood plain to organic material-rich marsh deposits. All gradations are seen among these lithofacies.The seismicity of the Erzurum pull-apart basin is quite high. The magnitude of the peak earthquake to be sourced from the active faults (e.g., the Erzurum fault) is about Mw = 7.0. This was proved by both the historical and recent earthquakes. Numerous settlements in the size of a large city (e.g., Erzurum), county, town and small villages with a total population of over 766,000 are located in and along the active fault-bounded margins of the Erzurum pull-apart basin. They are under the threat of destructive earthquakes to be sourced from the margin-boundary faults. Therefore, based on both the active fault parameters and the water-saturated basin fill, a large-scale earthquake hazard map has to be prepared. This map has to be used in both the earthquake hazard to risk analyses and the redesign of city planning and all type of constructions in Erzurum and other settlements in this region.

Late Variscan deformation in the Iberian Peninsula; a late feature in the Laurentia–Gondwana dextral collision

The Late Variscan deformation event in Iberia is characterized by an intraplate deformation regime induced by the dextral oblique collision between Laurentia and Gondwana. This episode in Iberia is characterized by NNE–SSW brittle to brittle–ductile strike-slip faults, which are considered by the classic works as sinistral strike-slip faults. However, the absence of Mesozoic formations constraining the age of this sinistral kinematics led some authors to consider it as the result of Alpine reworking. Structural studies in Almograve and Ponta Ruiva sectors (SW Portugal) show that NNE–SSW faults have a sinistral kinematics and are occasionally associated with E–W dextral shears. Moreover, this kinematics is related to the late deformation episodes of Variscan orogeny. In Almograve sector, the Late Variscan structures are characterized by NNE–SSW sinistral kink bands, spatially associated with E–W dextral faults. These structures are contemporaneous and affect the previously deformed Carboniferous units. The Ponta Ruiva Sector constrains the age of deformation because the E–W dextral shears affect the Late Carboniferous (late Moscovian) units, but not the overlying Triassic series. The new data show that the NNE–SSW and the E–W faults are dynamically associated and result from the Late Variscan deformation episode. The NNE–SSW sinistral faults could be considered as second-order domino structures related to first-order E–W dextral shears, linked to Laurentia–Gondwana collision during Late Carboniferous–Permian times.

Recent mantle degassing recorded by carbonic spring deposits along sinistral strike-slip faults, south-central Australia

The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle 3He and CO2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50–70 km. U-series ages on 26 samples range from 354±7 to 1.19±0.02ka (2σ errors) and suggest a clustering every ∼3–4 ka since ∼26 ka. Geochemical data demonstrate a remarkable mantle-to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths >3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. 3He/4He isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60–70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure.

Paleogene and Neogene kinematics of the Alpine-Carpathian fold-thrust belt at the Alpine-Carpathian transition

In this study we analyze a ~300km long segment of the Alpine-Carpathian orogen using novel outcrop data and regional seismic profiles from the West Carpathians to unravel the kinematics and timing of Eocene to Late Miocene deformation of the fold-thrust belt. Comparison with data from the Eastern Alps and the Vienna Basin leads to an updated tectonic model for the Paleogene and Neogene of the Alpine-Carpathian transition, which includes three stages:(1) Eocene to Early Oligocene NNW-directed foreland-propagating thrusting. Thrusts are directed perpendicular to the strike of the European foreland in the Outer West Carpathians (OWC) and sub-parallel to thrusts observed in the Eastern Alps west of the Vienna Basin.(2) Continued Late Oligocene to Early Miocene NNW-directed foreland-propagating thrusting simultaneous with sinistral strike-slip reactivation of former nappe boundaries in the hinterland of the active thrusts. This deformation corresponds to the early stage of eastward lateral extrusion of the Eastern Alps. The ENE-striking sinistral faults in the OWC are kinematic equivalents of the SEMP fault system in the Eastern Alps, which was active at the same time. The latest stage of thrusting is characterized by SSE-directed out-of-sequence thrusts in the hinterland of the OWC and the reactivation of Variscan basement thrusts in the European foreland as SSE-directed backthrusts.(3) Formation of (N)NE-striking sinistral strike-slip faults which are kinematically linked to (N)NE-directed out-of-sequence thrusts post-dating NNW-directed thrusting. The sinistral faults formed coeval with the opening of the Vienna pull-apart basin during the Middle to Late Miocene stage of lateral extrusion.Unlike proposed in previous studies the West Carpathians do not appear to be affected by Oligocene to Early Miocene crustal-scale wrenching of the Pieniny Klippen Belt. Our data show that the deformation of the PKB is in line with the Eocene to Late Miocene tectonic evolution reconstructed for the OWC.

Relationship between geo-structural evolution and development of karstic systems in the culminating area of Ouarsenis (West Algeria)

The Ouarsenis area is one of the most developed karstic systems of Algeria. It is a karst reservoir drinking water with a population of more than 50,000 people taking fully benefit from it. To understand the development of this karstic system, the local tectonic history of the four main mountain ranges of this culminating area (Ouarsenis) has been analyzed. Although previously identified primarily Cenozoic tectonic activities have been observed, a set of NW-SE joints intersecting the Jurassic limestone has been associated to a post-nappes tectonic events. Moreover, numerous joint sets oriented NNE/SSW have been identified almost over the entire culminating area. These joints are the direct consequence of the following stress history: (i) a NW/SE shortening responsible for a major overlap and the first fold (P1) phase, (ii) a second NNE/SSW shortening stage responsible for the second folding (P2) phase associated with 70° N sinistral strike-slip trend, (iii) a WNW/ESE extension phase resulting from the change of σ 3 stress vertical axis, and (iv) a shearing stress creating a 120° N sinistral strike-slip fault. Only the late phases are responsible of the development of joints, which have been karstified later on. Indeed, significant families of karstified joints, i.e., 20° and 70° N have been found. These joints are related to the extensional and shearing modes, respectively, and linked to a particular in situ karstogenesis. Moreover, this study suggests an ancient establishment of the karstic systems in the Ouarsenis region in at least two stages: pre-figured and activated behaviors during the Cenozoic.

Evolution of the Late Cretaceous Dadaepo Basin, SE Korea, in response to oblique subduction of the proto-Pacific (Izanagi/Kula) or Pacific plate

The Dadaepo Basin is a small Late Cretaceous sedimentary basin in SE Korea, located on the eastern margin of Asia. The basin is an isolated extensional basin situated between the NNE-striking Yangsan and Dongnae faults. The basin-fill sediments, named the Dadaepo Formation, consist of channelized conglomerates and sandstones intercalated with dominantly purple mudstones in the lower part. The upper part is dominated by fine- to coarse-grained tuffaceous sandstones and olive to dark gray mudstones with abundant volcanic interbeds. The formation unconformably overlies dacitic rocks dated at ca. 94Ma and is overlain by basaltic andesite dated at ca. 69Ma (Ar–Ar ages). The overall configuration of the strata of the Dadaepo Formation indicates syndepositional tilting of the basin floor to the north-northeast. A number of outcrop-scale faults are observed in the basin-fill sediments, of which the majority are NW-striking normal faults, including syndepositional growth faults. The orientations of mafic (magmatic) and clastic dikes, interpreted as being approximately contemporaneous with the deposition of the Dadaepo Formation, are also nearly parallel to the strikes of outcrop-scale normal faults. All these extensional structures consistently indicate NE–SW extension of the basin and obliquely intersect the basin-bounding Yangsan and Dongnae faults at angles of 40°–60°. It is thus concluded that the Dadaepo Formation was deposited in a pull-apart basin that subsided as a result of NNE-striking sinistral strike–slip faulting in the southeastern part of the Korean Peninsula during the Campanian (Late Cretaceous). This strike–slip faulting was related to north-northwestward oblique subduction of the proto-Pacific (Izanagi/Kula) or Pacific plate under the eastern margin of the Eurasian plate.

Late Palaeozoic mineralization and tectonic evolution of the West Junggar metallogenic belt, Central Asia: constraints from Re–Os and 40Ar/39Ar geochronology

ABSTRACTThe West Junggar Metallogenic Belt (WJMB) is located between the Tianshan fault system and the Ertix fault system in the western part of the Central Asian Metallogenic Domain (CAMD). The belt features widespread late Palaeozoic granitic plutons, strike-slip faults, and porphyry copper and orogenic gold deposits. We collected nine molybdenite samples from the Baogutu III–IV Cu–Mo deposit and the Suyunhe Mo–W deposit, and 12 granitoid samples from the Jiaman, Kangde, Kulumusu, Bieluagaxi, Hatu, Akbastau, Miaoergou, Baogutu, Karamay, and Hongshan plutons in the WJMB. Molybdenite Re–Os dating gives metallogenesis ages of 312.7 and 299.7 Ma for the Baogutu III–IV and Suyunhe deposits, respectively. 40Ar/39Ar thermochronology yields biotite ages ranging from 326 to 302 Ma and K-feldspar ages from 297 to 264 Ma, indicating a regional medium-temperature cooling history in the WJMB during the late Carboniferous to middle Permian. By integrating these data with previous zircon U–Pb, amphibole 40Ar/39Ar, and zircon and apatite fission-track ages, we reconstruct the whole thermal history of the WJMB, which includes late Palaeozoic intrusive magmatism, porphyry Cu and W–Mo mineralization, and late Mesozoic tectonic uplift and exhumation of the WJMB. The regional 40Ar/39Ar cooling ages are consistent with the timing of regional sinistral strike-slip faulting, thereby indicating the tectonic significance of the cooling ages. We suggest that the biotite 40Ar/39Ar ages represent the static cooling of the granitic plutons after emplacement, since the ages are consistent with the U–Pb ages of the plutons. Thereafter, the oldest K-feldspar 40Ar/39Ar age may record the initiation of sinistral strike-slip movement on the Darabut, Mayile, and Baerluke faults. The regional faulting resulted in significant uplift of the WJMB during the early and middle Permian.

Structural inversion of the Tamworth Belt: Insights into the development of orogenic curvature in the southern New England Orogen, Australia

The middle to late Permian Hunter Bowen Event is credited with the development of orogenic curvature in the southern New England Orogen, yet contention surrounds the structural dynamics responsible for the development of this curvature. Debate is largely centred on the roles of orogen parallel strike-slip and orogen normal extension and contraction to explain the development of curvature. To evaluate the dynamic history of the Hunter Bowen Event, we present new kinematic reconstructions of the Tamworth Belt. The Tamworth Belt formed as a Carboniferous forearc basin and was subsequently inverted during the Hunter Bowen Event. Kinematic reconstructions of the Tamworth Belt are based on new maps and cross-sections built from a synthesis of best-available mapping, chronostratigraphic data and new interpretations of depth-converted seismic data. The following conclusions are made from our study: (i) the Hunter Bowen Event was dominantly driven by margin normal contraction (east–west shortening; present-day coordinates), and; (ii) variations in structural style along the strike of the Tamworth Belt can be explained by orthogonal vs. oblique inversion, which reflects the angular relationship between the principal shortening vector and continental-arc margin. Given these conclusions, we suggest that curvature around the controversial Manning Bend was influenced by the presence of primary curvature in the continental margin, and that the Hastings Block was translated along a sinistral strike-slip fault system that formed along this oblique (with respect to the regional east–west extension and convergence direction) part of the margin. Given the available temporal data, the translation of the Hastings Block took place in the Early Permian (Asselian) and therefore preceded the Hunter Bowen Event. Accordingly, we suggest that the Hunter Bowen Event was dominantly associated with enhancing curvature that was either primary in origin, or associated with fault block translation during the Early Permian. This model differs to previously proposed reconstructions where curvature largely formed by orogen parallel strike-slip transportation during the Hunter Bowen Event.

Dextral strike-slip of Sanguankou-Niushoushan fault zone and extension of arc tectonic belt in the northeastern margin of the Tibet Plateau

The kinematic characteristics of the Sanguankou-Niushoushan fault (SGK-NSSF) are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. Using field surveys and various data collection methods, including large-scale geological mapping, measurement of typical topographies, and dating of sedimentary strata, it was determined that the SGK-NSSF exhibits obvious dextral strike-slip characteristics and thus is not a sinistral strike-slip fault, as believed by previous researchers. The results of this study show that the geological boundaries for the Paleozoic, Mesozoic, and Cenozoic eras were all dextrally dislocated by the fault, with the faulted displacements being similar. The maximum strike-slip displacement of the fault, after elimination of topographic effects, was found to be 961±6 m. The Sanguankou fault at the northern section exhibits obvious characteristics of more recent activities, with a series of small gullies having undergone synchronized dextral writhing after traversing the fault. The average horizontal slip rate of the fault since the late Quaternary was determined to be approximately 0.35 mm/a. The pre-existing fold structures formed during the late Pliocene were dislocated by the fault and became ex situ, indicating that dextral strike-slip of the fault could not have occurred prior to the late Pliocene. The maximum displacements and average slip rates were used to estimate the onset time of the dextral strike-slip activities of the fault as being after 2.7 Ma. In this study, the understanding of previous researchers concerning the extension in the northeastern margin of the Tibet Plateau was combined with analyses of the successive relationships between fold deformations and fault activities. This led to the finding that the extension in the northeastern margin of the Tibet Plateau reached the vicinity of the SGK-NSSF during the late Pliocene (∼2.7 Ma), causing regional uplift and fold deformations of the strata there. During the early Quaternary, the northeastern compression of the Tibet Plateau and the counterclockwise rotation of the Ordos block collectively resulted in the dextral strike-slip activities of the SGK-NSSF. This then formed the foremost margin of the arc tectonic belt extension in the northeastern margin of the Tibet Plateau.

Compressional tectonic inversion of the Algero-Balearic basin: Latemost Miocene to present oblique convergence at the Palomares margin (Western Mediterranean)

Interpretation of new multichannel seismic reflection profiles indicates that the Palomares margin was formed by crustal-scale extension and coeval magmatic accretion during middle to late Miocene opening of the Algero-Balearic basin. The margin formed at the transition between thinned continental crust intruded by arc volcanism and back-arc oceanic crust. Deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between ~N50°E striking reverse faults and associated folds like the Sierra Cabrera and Abubacer anticlines and N10–20°E sinistral strike-slip faults like Palomares and Terreros faults. Parametric subbottom profiles and multibeam bathymetry offshore, structural analysis, available GPS geodetic displacement data, and earthquake focal mechanisms jointly indicate that tectonic inversion of the Palomares margin is currently active. The Palomares margin shows a structural pattern comparable to the north Maghrebian margins where Africa-Eurasia plate convergence is accommodated by NE-SW reverse faults, NNW-SSE sinistral faults, and WNW-ESE dextral ones. Contractive structures at this margin contribute to the general inversion of the Western Mediterranean since ~7 Ma, coeval to inversion at the Algerian margin. Shortening at the Alboran ridge and Al-Idrisi faults occurred later, since 5 Ma, indicating a westward propagation of the compressional inversion of the Western Mediterranean.

Rock pulverization and localization of a strike-slip fault zone in dolomite rocks (Salzach–Ennstal–Mariazell–Puchberg fault, Austria)

Detailed investigations of dolomite fault rocks, formed at shallow crustal depths along the Salzach–Ennstal–Mariazell–Puchberg (SEMP) fault system in the Northern Calcareous Alps, revealed new insights into cataclasite formation. The examined Miocene, sinistral strike-slip faults reveal grain size reduction of dolomite host rocks by tensile microfracturing at a large range of scales, producing rock fragments of centimetre to micrometre sizes. In situ fracturing leads to grain size reduction down to grain sizes <25 μm, producing mosaic breccias and fault rocks which have previously been described as “initial/embryonic” and “intermediate” cataclasites. At all scales, grain fragments display little to no rotation and no or minor evidence of shear deformation. The observed microstructures are similar to those previously described in studies on pulverized rocks. Microstructural investigations of cataclasites and mosaic breccias revealed aggregations of small dolomite grains (<50 μm) that accumulated on top of large fragments or as infillings of V-shaped voids between larger grains and show constant polarity throughout the investigated samples. Fabrics indicate deposition in formerly open pore space and subsequent polyphase cementation. The newly described tectonic geopetal fabrics (geopetal-particle-aggregates, GPA) prove that these faults temporarily passed through a stage of extremely high porosity/permeability prior to partial cementation.

Application of U-Th-Pb Phosphate Geochronology to Young Orogenic Gold Deposits: New Age Constraints on the Formation of the Grass Valley Gold District, Sierra Nevada Foothills Province, California

The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping E-W veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping N-S veins hosted by the Grass Valley granodiorite; the latter have yielded about 70% of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170 to 140 Ma and 120 to 80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. Uranium-lead isotope dating of hydrothermal xenotime yielded the first absolute age of 162 ± 5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of an Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wall-rock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153 to 151 Ma gold event that was previously reported for the E-W veins. Overlapping U-Pb zircon (159.9 ± 2.2 Ma) and 40Ar/39Ar biotite and hornblende (159.7 ± 0.6–161.9 ± 1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient temperature of the surrounding country rocks (<300°C). The age of the granodiorite is indistinguishable from that of the N-S veins, as recorded by the U-Pb age of xenotime in those veins. Consequently, the N-S veins must have formed between 162 and 157 Ma, the maximum permissive age of magma emplacement and the youngest permissive xenotime U-Pb age, respectively, during an E- to ENE-directed compressional regime. The geochemistry of the Grass Valley granodiorite is consistent with it being the product of arc magmatism. It served as a receptive host for mineralization, but it is has no direct genetic relationship to gold mineralization. Initial uplift of the intrusive mass correlates with the initial voluminous fluid flow event and vein formation at depths of no greater than 3 km. The E-W gold-bearing veins hosted within greenschist-facies country rocks adjacent to the intrusion formed during a second hydrothermal event 5 to 10 million years later than the magmatism and were contemporaneous with a shift to transtensional deformation denoted by sinistral strike-slip faulting.

The relative and absolute chronology of strato-tectonic events in the Gorom-Gorom granitoid terrane and Oudalan-Gorouol belt, northeast Burkina Faso

The integration of field mapping and analytical studies of magmatic units of the northeast of Burkina Faso has provided new information on the tectonic and magmatic evolution of the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane. Structural, geochemical and geochronological analyses have helped to clarify the geological evolution of the region during the Tangaean Event (D1) and Eburnean Orogeny (D2) through to the Wabo Tampelse Event (D3). Further to this, zircon U–Pb geochronology data have demonstrated that the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane represents some of the oldest outcropping geology in the Palaeoproterozoic Baoulé-Mossi domain recognised to date, with the oldest age at 2253±9Ma. The geochronology and geology suggests that the basement or a pre-Birimian crust to the Birimian Supergroup may be found in the northeast of Burkina Faso.The Eburnean Orogeny in the northeastern Burkina is preceded by the two phases of deformation (D1−x and D1), and two phases of magmatism. D1−x is associated with the emplacement of the Dori Batholith at the onset of D1 (2164–2141Ma). D1 ductile–brittle deformation formed F1 folds and discrete high-strained mylonite zones that deformed the Oudalan-Gorouol belt and the Gorom-Gorom granitoid terrane during a southwest-directed palaeo-principal transport direction. The pre-Birimian to Birimian supracrustal rocks and intrusions were regionally metamorphosed during D1 to greenschist to amphibolite facies.The Eburnean Orogeny (2130–1980Ma) is characterised by northwest–southeast shortening; it was followed by north–northwest to south–southeast shortening with development of sinistral strike-slip faults and shears. D2 brittle-(ductile) deformation is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C foliation. Metamorphic grade attained greenschist facies during D2 with development of the mineral assemblage of quartz-chlorite–muscovite±actinolite.The Wabo Tampelse (D3) deformation event is brittle in character and does not significantly affect regional geological architecture in the study area.

Cretaceous–Cenozoic tectonic history of the Jiaojia Fault and gold mineralization in the Jiaodong Peninsula, China: constraints from zircon U–Pb, illite K–Ar, and apatite fission track thermochronometry

The Jiaojia Fault (JJF) in the Jiaodong area of eastern China is an important NNE-trending structure that is subsidiary to the regional Tancheng–Lujiang (Tan-Lu) Fault Zone, and hosts >1200 t of gold reserves contained in disseminated and stockwork ore, dominantly in the footwall of the fault. We present new zircon U–Pb, apatite fission track, and illite K–Ar data along the JJF and have delineated its tectonic history focusing on its formation and reactivation. Zircon U–Pb dating shows that the Shangzhuang granite is a composite body with ages between 132 ± 1 and 127 ± 1 Ma. Illite K–Ar ages for the fault’s gouge range from 83 ± 2 to 68 ± 2 Ma, and the measured apatite fission track ages for ores are between 55 and 21 Ma. Previous zircon U–Pb geochronology and structural studies suggest that the JJF was originally activated in the Jurassic during 160–150 Ma as a sinistral fault. The JJF was a normal fault in the Early Cretaceous due to NW–SE orientated tension and NE–SW compression, which lasted from 135 to 120 Ma. This was followed by sinistral strike–slip faulting due to NW–SE compression and NE–SW tension during 120–110 Ma, and it changed to normal displacement at ca. 110 Ma. Our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca. 55 Ma. Previous age data of ca. 130–110 Ma for gold mineralization along the JJF coincides with the Early Cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike–slip faulting of the JJF in Early Cretaceous, which is interpreted to be due to changing direction of the subducting Pacific Plate.

Field Study of the Positive Flower Structures of the Gombe Inlier, Upper Benue Trough, Northeastern Nigeria

Abstract The Gombe inlier can be considered as a geological microcosm of the Gongola basin as it vividly displays general stratigraphic and structural styles within a relatively small, easily accessible area. The Cretaceous lithostratigraphic sequence of the Gombe inlier has been affected by sinistral strike-slip faults; the Gombe and Wuro Ladde-Wurin Dole faults with a Benue and Gongola trend respectively. Detailed study of these two faults shows that the Gombe fault is older and synsedimentary fault movement started in at least the mid-Santonian. Precambrian basement upthrust along the Gombe Fault is likely to have initiated during the first of the two compressive events that affected the upper Benue trough; the mid-Santonian N - S to N 174° E compression. The Wuro Ladde - Wurin Dole fault is relatively younger because (1) it sinistrally truncates the Liji hill anticlines that occur at the northern end of Gombe hill, resulting in a NEE - SWW trend, and (2) the orientation of transpressional structures along this fault suggest they developed during the end-Cretaceous N 140° E to N 150° E compression. Well-preserved transpressional structures along these faults provide the structural geologist a rare field examples to study their 3-dimensional (3D) geometry and kinematic evolution; and also as an analog for interpreting seismic reflection data that images complex strike-slip structures in the sub-surface.

Structural Style in the Khalfani Anticline, Coastal Fars, Zagros Fold-Thrust Belt

The Khalfani anticline is located in the Coastal Fars (Zagros, adjacent Persian Gulf). This anticline with Northwest-Southeast trend is a fault bend fold. In the study area, the Khalfani anticline has increased elevation from West to East with three distinct humps. The major faults in the study area are the Hendurabi and the Razak sinistral strike slip faults. Because analysis of fold and their folding styles in different parts system is important, the analysis of folding style elements is necessary for structural studies. The main aim of this research is structural style analysis based on fold style elements in the Khalfani anticline. This analysis is important for progress in hydrocarbons exploration in the Coastal Fars area. In this research, we used Tectonics FP and Global Mapper Software for preparing some data in our study. In addition, we used the common classification of folds for our research. Based on given results, the folding pattern of this anticline has indicated that the fold style is same in different parts of the Khalfani anticline. In the study area, based on classifications of fold in different methods, fold style is same together. Fold, with close sideways requires special attention as structural view; then the Khalfani Anticline with close style in all parts has special deformation and folding style. It seems that in the study area, folding style and variation of structural style have been created by effect of the Razak and the Hendurabi sinistral strike slip fault. Because these faults are basement or deep-seated faults, special folding style and special deformation can be formed in the study area. In addition, the Khalfani anticline in the study area has restricted within the Razak and the Hendurabi sinistral strike slip faults.