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1.
A 2000 km long dextral Talas-Fergana strike–slip fault separates eastern terranes in the Kyrgyz Tien Shan from western terranes. The aim of this study was to constrain an age of dextral shearing in the central part of the fault utilizing Ar–Ar dating of micas. We also carried out a U–Pb–Hf zircon study of two different deformed granitoid complexes in the fault zone from which the micas for Ar dating were separated. Two samples of the oldest deformed Neoproterozoic granitoids in the area of study yielded U–Pb zircon SHRIMP ages 728 ± 11 Ma and 778 ± 11 Ma, characteristic for the Cryogenian Bolshoi Naryn Formation, and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and their calculated tHfc ages varied from 2.42 to 2.71 Ga. Thus varying Cryogenian ages and noticeable heterogeneity of Meso- to Paleoproterozoic crustal sources was established for mylonitic granites of the Bolshoi Naryn Formation. Two samples of mylonitized pegmatoidal granites of the Kyrgysh Complex yielded identical 206Pb/238U ages of 279 ± 5 Ma corresponding to the main peak of Late-Paleozoic post-collisional magmatism in the Tien Shan (Seltmann et al., 2011), and zircon grains analyzed for their Lu–Hf isotopic compositions yielded εHf(t) values from −11.43 to −16.73, and calculated tHfc ages from 2.42 to 2.71 Ga indicating derivation from a Paleoproterozoic crustal source. Microstructural studies showed that ductile/brittle deformation of pegmatoidal granites of the Kyrgysh Complex occurred at temperatures of 300–400 °C and caused resetting of the K–Ar isotope system of primary muscovite. Deformation of mylonitized granites of the Bolshoi Naryn Formation occurred under high temperature conditions and resulted in protracted growth and recrystallization of micas. The oldest Ar–Ar muscovite age of 241 Ma with a well defined plateau from a pegmatoidal granite of the Kyrgysh Complex is considered as a “minimum” age of dextral motions along this section of the fault in the Triassic while younger ages varying from 227 Ma to 199 Ma with typical staircase patterns indicate protracted growth and recrystallization of micas during ductile deformations which continued until the end of the Triassic. 相似文献
2.
《Journal of Structural Geology》1999,21(8-9):1199-1207
This paper presents a new model of fault development in carbonate rocks involving a crack–seal–slip sequence. The structures of sheared calcite veins from the Les Matelles outcrop, Languedoc (S. France), and the observations used to construct this new model which integrates aspects of `crack–seal' evolution of calcite-filled veins with concepts of fault valve behaviour are described. In our model, hydraulic mode I reopening of an oblique pre-existing vein in an overall strike-slip stress regime is accompanied by precipitation of calcite, but significant fault slip cannot occur initially despite this obliquity because the ends of the pre-existing structure limit further reopening propagation beyond the tips. The rate of aligned calcite precipitation keeps pace with the rate of dilation of the structure, so that calcite cement essentially seals the system. Stress concentrations at the tips are allowed to rise with reopening until failure of the tip zone results in branch crack formation, triggering both slip along the vein and hydraulic pressure drop. This is followed by sealing within the branch cracks. Such a crack–seal–slip cycle may be repeated several times, as evidenced by fault-perpendicular calcite vein growth interlayered with calc-mylonite lamellae within these structures. Later cycles will become less pronounced because strength recovery of the sealed branch cracks does not regain the initial strength of the intact rock. This model could apply at various scales, and could be a mechanism for triggering earthquakes. 相似文献
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The Longmu–Gozha Co left-lateral strike-slip fault system (LGCF) is located in remote western Tibet, forming a triple junction with both the Altyn Tagh fault (ATF) and the Karakorum fault (KF), the two major strike-slip faults in the region. The Ashikule, Gozha Co and Longmu Co faults are clear and distinct left-stepping en-echelon faults, together forming the LGCF system. Although poorly documented, quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost Tibetan Plateau. Indeed, the Karakax fault (NW segment of the ATF), LGCF and KF together control the tectonics of western Tibet which itself controls the extrusion of Tibet towards the east, with the LGCF acting as a natural boundary for eastward motion of the Tibetan Plateau due to India's northward impingement. The LGCF system shows clear and impressive morphological indications of left-lateral active shear, that we quantify using field measurements (terrestrial LIDAR) along with 10Be surface-exposure dating. Our data suggest a slip-rate < 3 mm/yr, consistent with geodetic and block model studies. While it is on the order of the Karakax fault slip-rate (~ 2 mm/yr), it is smaller than those along the ATF and KF (> 9 and > 8 mm/yr, respectively), yielding a few mm/yr of extension accommodated most likely in the Ashikule graben and surroundings, located between the ATF and Karakax faults. Numerous evidences of recent tectonic-related events are present in the vicinity, such as the 1951 volcanic eruption as well as the 2008 and 2014 Ms 7.3 Yutian earthquakes, attesting of its high activity. In addition, the LGCF's en-echelon geometry and identical direction with the ATF, as well as smaller geological offsets and lower slip-rate compared to those on the surrounding faults, suggest that this segment of the ATF may be the most recent. 相似文献
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The chemical and isotopic compositions of clay minerals such as illite and chlorite are commonly used to quantify diagenetic and low-grade metamorphic conditions, an approach that is also used in the present study of the Monte Perdido thrust fault from the South Pyrenean fold-and-thrust belt. The Monte Perdido thrust fault is a shallow thrust juxtaposing upper Cretaceous–Paleocene platform carbonates and Lower Eocene marls and turbidites from the Jaca basin. The core zone of the fault, about 6 m thick, consists of intensely deformed clay-bearing rocks bounded by major shear surfaces. Illite and chlorite are the main hydrous minerals in the fault zone. Illite is oriented along cleavage planes while chlorite formed along shear veins (<50 μm in thickness). Authigenic chlorite provides essential information about the origin of fluids and their temperature. δ18O and δD values of newly formed chlorite support equilibration with sedimentary interstitial water, directly derived from the local hanging wall and footwall during deformation. Given the absence of large-scale fluid flow, the mineralization observed in the thrust faults records the P–T conditions of thrust activity. Temperatures of chlorite formation of about 240°C are obtained via two independent methods: chlorite compositional thermometers and oxygen isotope fractionation between cogenetic chlorite and quartz. Burial depth conditions of 7 km are determined for the Monte Perdido thrust reactivation, coupling calculated temperature and fluid inclusion isochores. The present study demonstrates that both isotopic and thermodynamic methods applied to clay minerals formed in thrust fault are useful to help constrain diagenetic and low-grade metamorphic conditions. 相似文献
6.
《International Geology Review》2012,54(13):1562-1578
The Tan–Lu fault is a well-known active fault belt in eastern China that has been the focus of geologic studies over the past 40 years. Since the late 1990s, numerous geophysical and geological investigations of this dislocation zone have been carried out by Chinese oil companies, as well as by universities. However, its deep structure, active periods of slip, and fault mechanism remain obscure. This study focuses on the deep structures within the Jiashan–Lujiang segment of the Tan–Lu fault belt, using high-precision geophysical tools, including magnetotelluric and magnetic sounding, and artificial seismic exploration using active source methods. Our results suggest that this segment is composed of several sub-faults. The southern part of the Tan–Lu fault belt, along the Jiashan–Lujiang sub-fault, can be divided into two parts on the basis of contrasting geological features. The Chihe–Taihu sub-fault is taken as the boundary between the two. The region east of the Chihe–Taihu sub-fault is dominated by strike–slip activity along several sub-faults. Only the Jiashan–Lujiang sub-fault is exposed at the surface, forming a large, positive flower structure, the result of late Middle Jurassic to early Late Jurassic strike–slip movement along the dislocation zone. Three sub-faults are present in Dingyuan County, two of which disappear in the southern Hefei Basin. Only the Chihe–Taihu sub-fault extends to the eastern edge of this basin, creating a half-graben depression that formed during the Early Cretaceous. Our results indicate that the present-day deep structure of the southern portion of the Tan–Lu fault zone is the result of a combination of strike–slip and extensional tectonics. 相似文献
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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. 相似文献
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A common problem encountered in studies of gouge-bearing natural faults is the difficulty of ascertaining whether the observed gouge was sheared seismically or aseismically; this problem arises because of the scarcity of indicators of fault slip rates for gouge. Recently, clay–clast aggregates (CCAs; a CCA comprises a clastic core mantled by a rim of ultrafine particles) were proposed as a possible indicator of seismic slip in gouge, on the basis of shear experiments on gouge at seismic slip rates. To examine the processes and conditions of CCA formation, we conducted rotary shear experiments on quartz and quartz–bentonite gouges under normal stresses (0.3–3.0 MPa) and slip rates (0.0005–1.3 m s−1), and in both room-humidity (room-dry) and water-saturated (wet) conditions. We found that CCAs could be produced in room-dry gouges even at the lowest slip rates, which are considerably slower than actual seismic slip rates. This finding demonstrates that thermal pressurization and fluidization at elevated temperature during seismic slip are not necessarily needed for the formation of CCAs, contrary to previous views. Given the occurrence of CCAs over a wide range of slip rates, we suggest that the presence of CCAs is not an unequivocal indicator of fault slip at seismic slip rates. 相似文献
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Determining fault activity through time has typically utilised high-resolution seismic data to identify stratigraphic thickness changes or displacement vs distance plots; however, this approach is not possible in regions with low-resolution seismic data. We present a new approach for determining fault reactivation (tensile and shear) through time by integrating three-dimensional seismic data, geomechanical modelling and complete paleostress tensors from calcite twin stress inversion. The Cooper–Eromanga Basin is used as a case study to model the stress conditions present during six tectonic events that have affected the basin and, in doing so, constrain the effective paleostress magnitudes through time. Results show that the likelihood of dilation and shear reactivation of individual fault sets varies through time, with N–S- and E–W-striking faults likely to have been open to fluid flow after the critical moment in the hydrocarbon system. These results have substantial implications for hydrocarbon migration pathway models and structural and stratigraphic models for the Cooper–Eromanga Basin. This approach would benefit other provinces with low-resolution seismic data preventing fault growth analysis, or in regions where hydrocarbon migration pathways are poorly defined. 相似文献
11.
Vivek Walia Shih Jung Lin Ching Chou Fu Tsanyao Frank Yang Wei-Li Hong Kuo-Liang Wen Cheng-Hong Chen 《Applied Geochemistry》2010
Many studies have shown the soil gas method to be one of the most reliable investigation tools in the research of earthquake precursory signals and fault delineation. The present research is aimed finding the relationship between soil gas distribution and tectonic systems in the vicinity of the Hsinhua Fault zone in the Tainan area of Southern Taiwan. More than 110 samples were collected along 13 traverses to find the spatial distribution of Rn, He, CO2 and N2. The spatial congruence of all the gases shows that N2 is the most probable carrier gas of He, whereas CO2 seems to be a good carrier gas of Rn in this area. From the spatial distribution of Rn, He, CO2 and N2 the trace of Hsinhua Fault and neotectonic features can be identified. The spatial distribution of studied gases shows a clear anomalous trend ENE–SWS along the Hsinhua Fault. 相似文献
12.
犁式正断层也有称剥离断层(Denudational fault),它是一种倾角随深度变缓的低角度正断层,形态似犁状,故名为犁式正断层。其特点,上盘地层沿倾向下滑,较浅层位的年青岩层直接盖于较深层位的岩层之上,断层上陡,向下变平而联合成一个基底滑脱面,断层面 相似文献
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A new approach for paleostress analysis using the multiple inverse method with calcite twin data including untwinned e-plane was performed in the East Walanae fault (EWF) zone in South Sulawesi, Indonesia. Application of untwinned e-plane data of calcite grain to constrain paleostress determination is the first attempt for this method. Stress states caused by the collision of the south-east margin of Sundaland with the Australian microcontinents during the Pliocene were successfully detected from a combination of calcite-twin data and fault–slip data. This Pliocene NE–SW-to-E–W-directed maximum compression activated the EWF as a reverse fault with a dextral component of slip with pervasive development of secondary structures in the narrow zone between Bone Mountain and Walanae Depression. 相似文献
14.
The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip–slip thrusting movements. The recent faulting mainly occurs on new traces trending E–W to ENE–WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike–slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike–slip motion is transferred along the ENE–WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics. 相似文献
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The paper considers the morphology, deep structure, and geodynamic features of the Ural–Herirud postorogenic strike-slip fault (UH fault), along which the Moho (the “M”) shifts along the entire axial zone of the Ural Orogen, then further to the south across the Scythian–Turan Plate to the Herirud sublatitudinal fault in Afghanistan. The postcollisional character of dextral displacements along the Ural–Herirud fault and its Triassic–Jurassic age are proven. We have estimated the scale of displacements and made an attempt to make a paleoreconstruction, illustrating the relationship between the Variscides of the Urals and the Tien Shan before tectonic displacements. The analysis of new data includes the latest generation of 1: 200000 geological maps and the regional seismic profiling data obtained in the most elevated part of the Urals (from the seismic profile of the Middle Urals in the north to the Uralseis seismic profile in the south), as well as within the sedimentary cover of the Turan Plate, from Mugodzhary to the southern boundaries of the former water area of the Aral Sea. General typomorphic signs of transcontinental strike-slip fault systems are considered and the structural model of the Ural–Herirud postcollisional strike-slip fault is presented. 相似文献
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Andrea Zanchi Paolo D’Adda Stefano Zanchetta Fabrizio Berra 《Swiss Journal of Geoscience》2012,105(1):19-38
The lateral continuity of the E?CW trending thrust sheets developed within the Lower to Middle Triassic cover of the central Southern Alps (Orobic belt) is disturbed by the occurrence of several N?CS trending transverse zones, such as the poorly known Grem?CVedra Transverse Zone (GVTZ). The GVTZ developed during the emplacement of the up to six S-verging thrust sheets consisting of Lower to Middle Triassic units, occurring immediately south of the Orobic Anticlines. The transverse zone, active during thrust emplacement related to the early Alpine compressions which pre-date the Adamello intrusion, includes three major vertical shear zones, the Grem, Pezzel and Zuccone faults. The major structure of the transverse zone is the dextral Grem fault, forming a deep lateral ramp between thrust sheets 3 and 5. A similar evolution also occurred along the Zuccone and Pezzel faults, which show a left-lateral displacement of syn-thrust folds. The Grem fault was later reactivated as an oblique tear fault during the emplacement of the Orobic Anticlines, due to back-thrusting along out-of-sequence thrust surfaces (Clusone fault). Transpressional deformations along the fault zone are recorded by the rotation of major syn-thrust folds, which also suggest a horizontal offset close to 0.5?km. Records of the first stage of evolution of the Grem fault are better preserved along its northern segment, and structural relationships suggest that it propagated southward and downward in the growing thrust stack. The study of the meso and megascopic structures developed along the GVTZ constrains the evolution of the transverse zone, illustrating the complex deformational phenomena occurring in a transpressional regime. The GVTZ probably reflects the existence of pre-existing tectonic lineaments with a similar orientation. Evidence of pre-existing structures are not preserved in the exposed units, nevertheless the N?CS extensional fault systems that characterize the Norian to Jurassic rifting history of the Lombardian basin are valid candidates. 相似文献
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《Journal of Structural Geology》2001,23(6-7):1167-1178
S–C fabrics similar to those found in mylonites are observed in foliated cataclastic granitic rocks from the Nojima fault zone, southwest Japan. The foliated cataclastic rocks comprise cataclasite, fault breccia, gouge, and crushing-originated pseudotachylyte. The S–C fabrics observed in these cataclastic rocks involve S-surfaces defined by shape preferred orientation of biotite fragments or aggregates of quartz and feldspar fragments, and C-and C′-surfaces defined by microshears and shear bands, respectively, where fine-grained material is concentrated. Striations on the main fault plane are oriented parallel to the cataclasite lineations. A significant microstructural difference between the foliated cataclastic rocks and S–C mylonites is the absence of dynamically recrystallized grains in the foliated cataclasites. The striations, cataclastic lineations, and the S–C fabrics in the cataclastic rocks formed from the late Tertiary to the late Holocene indicate that the Nojima fault zone has moved as a dextral strike-slip fault, with a minor reverse component since it formed. S–C fabrics in cataclastic rocks provide important information on the tectonic history and are reliable kinematic indicators of the shear sense in brittle shear zones or faults. 相似文献
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Oligocene–Miocene strata in the Subei and Xiaobiegai basins of the Subei area, located in the eastern Altyn Tagh fault (ATF), northern Tibetan Plateau, record important characteristics of the ATF evolution. Detrital zircons laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb ages from two samples, together with paleocurrent directions and clastic composition in the Xishuigou section demonstrate that sediments in the Subei basin originated from the Danghenanshan range along its southern margin. Detrital zircons U–Pb ages from three samples in the Xiaobiegai basin, together with paleocurrent directions and clastic composition, indicate that sediments in the Xiaobiegai basin may partly originate from terranes along the northeastern margin of the basin in addition to the Danghenanshan range. Our results, combined with regional evolution, suggest that the Xiaobiegai and the Subei basins was a combined basin in Oligocene–early Miocene. This basin was folded, tilted, and dislocated at ca. 8 Ma by rapid uplift of the northern Tibetan plateau and rapid strike-slip of the ATF. As a result, the Subei basin became a thrust–fold belt of the Danghenanshan range front, and the Xiaobiegai basin grew into an intermontane basin in the northeastern part of the Danghenanshan range. Thus, the Subei area gradually acquired its present morphotectonic patterns. 相似文献
20.
This generic 2D elastic-plastic modelling investigated the reactivation of a small isolated and critically-stressed fault in carbonate rocks at a reservoir depth level for fluid depletion and normal-faulting stress conditions. The model properties and boundary conditions are based on field and laboratory experimental data from a carbonate reservoir. The results show that a pore pressure perturbation of −25 MPa by depletion can lead to the reactivation of the fault and parts of the surrounding damage zones, producing normal-faulting downthrows and strain localization. The mechanism triggering fault reactivation in a carbonate field is the increase of shear stresses with pore-pressure reduction, due to the decrease of the absolute horizontal stress, which leads to an expanded Mohr's circle and mechanical failure, consistent with the predictions of previous poroelastic models. Two scenarios for fault and damage-zone permeability development are explored: (1) large permeability enhancement of a sealing fault upon reactivation, and (2) fault and damage zone permeability development governed by effective mean stress. In the first scenario, the fault becomes highly permeable to across- and along-fault fluid transport, removing local pore pressure highs/lows arising from the presence of the initially sealing fault. In the second scenario, reactivation induces small permeability enhancement in the fault and parts of damage zones, followed by small post-reactivation permeability reduction. Such permeability changes do not appear to change the original flow capacity of the fault or modify the fluid flow velocity fields dramatically. 相似文献