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1.
Analysis of aeromagnetic data in the Grenville Province reveals the presence of two regional‐scale unmapped structural domes (the Morin and Mékinac‐Taureau domes) with an oval‐shaped magnetic pattern bounded by regional‐scale shear zones and a geometry that is similar to that produced in crustal flow models under extension, which predict two upright domes of foliation (double dome) separated by a steep shear zone. The Mékinac‐Taureau dome, a metamorphic core complex, and the Morin dome may have been exhumed by channel flow. Exhumation occurred by a combination of thrust, normal‐sense and wrench shear zones. The preservation of paragneisses in the Morin dome suggests that it underwent a lesser degree of exhumation than did the Mékinac‐Taureau dome. This study shows how the integration of local field information with magnetic data in a regional tectonic setting can reveal and delineate concealed gneiss domes and highlights a role for strike‐slip tectonics in the creation of regional structures involving the exhumation of deep crust.  相似文献   

2.
Field-based structural analysis of an exhumed, 10-km-long strike-slip fault zone elucidates processes of growth, linkage, and termination along moderately sized strike-slip fault zones in granitic rocks. The Gemini fault zone is a 9.3-km-long, left-lateral fault system that was active at depths of 8–11 km within the transpressive Late-Cretaceous Sierran magmatic arc. The fault zone cuts four granitic plutons and is composed of three steeply dipping northeast- and southwest-striking noncoplanar segments that nucleated and grew along preexisting cooling joints. The fault core is bounded by subparallel fault planes that separate highly fractured epidote-, chlorite-, and quartz-breccias from undeformed protolith. The slip profile along the Gemini fault zone shows that the fault zone consists of three 2–3-km-long segments separated by two ‘zones’ of local slip minima. Slip is highest (131 m) on the western third of the fault zone and tapers to zero at the eastern termination. Slip vectors plunge shallowly west-southwest and show significant variability along strike and across segment boundaries. Four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at, or below, greenschist facies conditions. Taken together, we interpret the fault zone to be a segmented, linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations, complex fault-segment interactions, and asymmetric slip-distance profiles.  相似文献   

3.
The Aegean Sea area is thought to be an actively extending back-arc region, north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean. The area shows extensive normal faulting, ductile ‘extensional’ shear zones and extensional S-C fabrics throughout the islands that have previously been related to regional Aegean extension associated with slab rollback on the Hellenic Subduction Zone. In this paper, we question this interpretation, and suggest the Cenozoic geodynamic evolution of the Aegean region is associated with a Late Cretaceous–Eocene NE-dipping subduction zone that was responsible for continent-continent collision between Eurasia and Adria-Apulia/Cyclades. Exhumation of eclogite and blueschist facies rocks in the Cyclades and kyanite-sillimanite grade gneisses in the Naxos core complex have pressures that are far greater than could be accounted for purely by lithospheric extension and isostatic uplift. We identify four stages of crustal shortening that affected the region prior to regional lithospheric extension, herein called the Aegean Orogeny. This orogeny followed a classic Wilson cycle from early ophiolite obduction (ca. 74 Ma) onto a previously passive continental margin, to attempted crustal subduction with HP eclogite and blueschist facies metamorphism (ca. 54–45 ?Ma), through crustal thickening and regional kyanite – sillimanite grade Barrovian-type metamorphism (ca. 22–14 ?Ma), to orogenic collapse (<14 ?Ma). At least three periods of ‘extensional’ fabrics relate to: (1) Exhumation of blueschists and eclogite facies rocks showing tight-isoclinal folds and top-NE, base-SW fabrics, recording return flow along a subduction channel in a compressional tectonic setting (ca. 50–35 ?Ma). (2) Extensional fabrics within the core complexes formed by exhumation of kyanite- and sillimanite gneisses showing thrust-related fabrics at the base and ‘extensional’ fabrics along the top (ca. 18.5–14 ?Ma). (3) Regional ductile-brittle ‘extensional’ fabrics and low-angle normal faulting related to the North Cycladic Detachment (NCD) and the South(West) Cycladic Detachment (WCD) during regional extension along the flanks of a major NW–SE anticlinal fold along the middle of the Cyclades. Major low-angle normal faults and ductile shear zones show symmetry about the area, with the NE chain of islands (Andros, Tinos, Mykonos, Ikaria) exposing the NE-dipping NCD with consistent top-NE ductile fabrics along 200 ?km of strike. In contrast, from the Greek mainland (Attica) along the SE chain of islands (Kea, Kythnos, Serifos) a SW-dipping low-angle normal fault and ductile shear zone, the WCD is inferred for at least 100 ?km along strike. Islands in the middle of the Cyclades show deeper structural levels including kyanite- and sillimanite-grade metamorphic core complexes (Naxos, Paros) as well as Variscan basement rocks (Naxos, Ios). The overall structure is an ~100 ?km wavelength NW–SE trending dome with low-angle extensional faults along each flank, dipping away from the anticline axis to the NE and SW. Many individual islands show post-extensional large-scale folding of the low-angle normal faults around the domes (Naxos, Paros, Ios, Sifnos) indicating a post-Miocene late phase of E–W shortening.  相似文献   

4.
Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike–slip faults (Mae Ping, Three Pagodas and Aliao Shan–Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike–slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene–Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene–Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene–Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene–Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike–slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.  相似文献   

5.
张八岭隆起广泛分布的平缓韧性剪切带与郯庐断裂带平移作用形成的陡立韧性剪切带明显不同。通过对平缓韧性剪切带的几何学、运动学分析,结合早白垩世盆地特征、中国东部变质核杂岩伸展拆离断层和同构造岩浆岩同位素定年结果,厘定出张八岭隆起早白垩世变质核杂岩。该变质核杂岩上盘由南华纪-奥陶纪沉积地层和早白垩世盆地组成,下盘为新元古代浅变质碎屑沉积岩、变海相火山岩（基底）以及早白垩世侵入岩,上下盘之间被一条主伸展拆离断层所分隔。变质核杂岩长轴为NE-SW向,指示构造反映上盘向SE剪切滑动,与中国东部变质核杂岩的伸展方向完全一致。通过本次变质核杂岩的厘定,结合野外地质事实,笔者认为管店-马厂断裂是郯庐断裂带的次级断裂,是对郯庐断裂带早白垩世末第三次左行平移的响应。在综合研究的基础上,建立了区域构造-岩浆-成矿关系模型,揭示了张八岭隆起早白垩世经历了早期伸展（变质核杂岩阶段）-挤压走滑（管店-马厂断裂形成阶段）-晚期伸展（闪长质脉岩侵位阶段）3个构造阶段,多期构造、岩浆的叠加作用下,形成了本区的金多金属矿产。  相似文献   

6.
The lithospheric strike‐slip Altyn Tagh Fault has accommodated hundreds of kilometres of displacement between the Qaidam and Tarim blocks since its Eocene reactivation. However, the way the deformation is accommodated in the Qilian Shan and further east remains uncertain. Based on 360 km of north‐eastward migration of the relatively rigid Qaidam block along the Altyn Tagh Fault and 3D isovolumetric balancing of the crustal deformation within the Altyn Tagh Fault–Qilian Shan system, we demonstrate that 250 ± 28 km (43.8–49.4%) of N20E directed crustal shortening and an additional ~250–370 km of eastward motion of the Qilian Shan crust must be accounted for by strike‐slip faulting in the Qilian Shan and crustal thickening in the Qinling area, as well as by extension in the adjoining North China block graben systems.  相似文献   

7.
THREE-DIMENSIONAL DEFORMATION ALONG THE ALTYN TAGH FAULT ZONE AND UPLIFT OF THE ALTYN MOUNTAIN, NORTHERN TIBET  相似文献   

8.
A special metamorphic core complex underlain by a low-angle strike-slip ductile shear zone is present near Chifeng in eastern Inner Mongolia, northern China. The geology of the study area is similar to that of several Cordilleran metamorphic core complexes, but contrasts in significant ways as well. A major ESE-dipping normal fault, the Louzidian Range frontal fault, formed during Late Cretaceous extension. This fault separates a crystalline footwall locally containing mylonitic basement gneisses and granitic rocks (0 to >3 km thick) from a non-metamorphic hanging wall that is distended by normal faults. However, the shear sense of the underlying mylonitic shear zone, a low-angle strike-slip zone, is not compatible with the Louzidian fault. It may be related to a pre-Cretaceous regional sinistral strike-slip event rather than the Late Cretaceous regional crustal extension common throughout eastern China. Pre-existing mylonitic fabric anisotropy appears to have controlled the development of the Louzidian normal fault. Chloritic breccias locally developed along the fault indicate that it cut deeply into the crust of northern China.  相似文献   

9.
In metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down-dip continuation of a detachment fault, or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault. Detailed microstructural, fabric, and strain data from mylonites in the Buckskin-Rawhide metamorphic core complex, west-central Arizona, constrain the structural development of the lower plate shear zone. Widespread exposures of ∼22–21 Ma granitoids of the Swansea Plutonic Suite enable us to separate Miocene strain coeval with core complex extension from older deformation. Mylonites across the lower plate consistently record top-to-the-NE-directed shear. Miocene quartz and feldspar deformation/recrystallization mechanisms indicate ∼450–500 °C mylonitization temperatures that were relatively uniform across a distance of ∼35 km in the extension direction. Quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction. Strain recorded in the Swansea Plutonic Suite is also relatively uniform in the extension direction, which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault. Altogether these data suggest the mylonitic shear zone initiated with a ≤4° dip and was unroofed by a more steeply dipping detachment fault system. Lower plate mylonites in the Buckskin-Rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down-dip continuation of a detachment fault.  相似文献   

10.
Mapping combined with structural analyses in the foreland edge of the metamorphic core of the Himalayas in SW Nepal highlights the existence of two north‐dipping shear zones with opposite sense of shear. Here, the metamorphic core is mainly affected by non‐coaxial top‐to‐the‐south sense of shear at temperatures between 450 °C and 550 °C that switch to a top‐to‐the‐north sense of shear at the top of the metamorphic core. We regionally correlate this upper shear zone with the South Tibetan detachment system. Ar‐dating on white mica indicates that both shear zones operated between 23 Ma and 17 Ma. Restoration of the folded South Tibetan detachment in far western Nepal yields a minimum dip‐slip distance of 190 km, compatible with predictions made by models of extrusion of a weak mid‐crustal channel. Our results support an orogenic model in which channel flow in the hinterland coexisted with thrust wedge mechanics in the foreland.  相似文献   

11.
The Castellas fault in SE France affects carbonate rocks with a plurimeter scale offset along 1.5 km of outcrop. In order to decipher the structural control on fault petrophysical and hydraulic character, we performed high resolution field structural mapping, laboratory porosity-Vp measurements, and thin sections analysis of deformations and diagenesis. Field mapping shows that the fault zone architecture displays strong lateral variations at the hectometer scale characterized by core thicknesses of 0–5 m, one or several slip planes, and varying fracture patterns within the damage zone. The fault zone heterogeneity may be related to the magnitude of the throw, the position along the fault and the affected rock facies. Laboratory measurements revealed a strong porosity reduction correlated to a Vp increase, related to the cementation of pore volumes within a decameter area around the fault plane. This fault-sealing occurred mainly through a chemical diagenesis related to fluid circulation within fault-zone heterogeneities. A 3D conceptual model of a mixed conduit/seal fault zone is proposed, characterized by sealed impermeable fault tips and more or less permeable units within which flow can occur either perpendicular or parallel to the fault strike.  相似文献   

12.
A new 140‐km‐long seismic reflection profile provides a high‐resolution crustal‐scale image of the southern Dabieshan high‐pressure (HP) metamorphic belt and the Yangtze foreland fold‐and‐thrust belt. The seismic image of the stacked section shows that the southern Dabieshan metamorphic terrane and Yangtze foreland belt are separated by a large north‐dipping fault. In the foreland the upper crust is dominated by a series of folds and thrusts formed during the collisional stage in the mid‐Triassic; it was reworked by crustal extension resulting in the formation of a late Jurassic and Cretaceous red‐bed basin. The southern Dabieshan profile shows stacked crustal slabs developed along the margin of the collisional orogenic belt. The Moho reflectors at 10–11 s (～30–33 km) are seismically prominent and segmented by a number of south‐verging thrusts that were probably developed by foreland‐directed thrusting of the deeply subducted continental crust during exhumation. The seismic reflection profile suggests that structures related to the Triassic–Jurassic subduction and exhumation of the Yangtze plate are preserved despite the severe crustal extension superimposed during the late Mesozoic and Cenozoic.  相似文献   

13.
E. Carminati  G.B. Siletto   《Tectonophysics》2005,401(3-4):179-197
The internal sectors of the Orobic Alps (Northern Italy) are characterised by Alpine age regional shortening showing a transition, through time, from plastic to brittle deformation. Thrust faults cut Alpine ductile folds and are marked by cataclasites and, locally, by pseudotachylytes, suggesting that motion was accommodated by seismic frictional slip. In the Eastern Orobic Alps the thrusting initiated at depths deeper than 10 km (the emplacement depth of the Adamello pluton) and possibly continued at shallower depths. This demonstrates that thrust motion occurred between 10 km depth and the brittle-ductile transition, i.e., at mid-crustal depths. The Orobic Alps exhumed paleoseismic zone shows different geometries along strike. In the central sectors of the Orobic Alps, thrust faults, associated with pseudotachylytes, have average dips around 40° and show no pervasive veining. Much steeper thrusts (dips up to about 85°) occur in the eastern Orobic Alps. In this area, faults are not associated with pervasive veining, i.e., fluid circulation was relatively scarce. This suggests that faulting did not occur with supralithostatic fluid pressure conditions. These reverse faults are severely misoriented (far too steep) for fault reactivation in a sublithostatic fluid pressure regime. We suggest that thrust motion likely started when the faults were less steep and that the faults were progressively rotated up to the present day dips. Domino tilting is probably responsible for this subsequent fault steepening, as suggested by a decrease of the steepness of thrust faults from north to south and by systematic rotations of previous structures consistently with tilting of thrust blocks. When the faults became inclined beyond the fault lock-up angle, no further thrusting was accommodated along them. At later stages regional shortening was accommodated by newly formed lower angle shear planes (dipping around 30–40°), consistently with predictions from fault mechanics.  相似文献   

14.
Low‐angle detachment faults are common features in areas of large‐scale continental extension and are typically associated with metamorphic core complexes, where they separate upper plate brittle extension from lower plate ductile stretching and metamorphism. In many core complexes, the footwall rocks have been exhumed from middle to lower crustal depths, leading to considerable debate about the relationship between hangingwall and footwall rocks, and the role that detachment faults play in footwall exhumation. Here, garnet–biotite thermometry and garnet–muscovite–biotite–plagioclase barometry results are presented, together with garnet and zircon geochronology data, from seven locations within metapelitic rocks in the footwall of the northern Snake Range décollement (NSRD). These locations lie both parallel and normal to the direction of footwall transport to constrain the pre‐exhumation geometry of the footwall. To determine P–T gradients precisely within the footwall, the ΔPT method of Worley & Powell (2000) has been employed, which minimizes the contribution of systematic uncertainties to thermobarometric calculations. The results show that footwall rocks reached pressures of 6–8 kbar and temperatures of 500–650 °C, equivalent to burial depths of 23–30 km. Burial depth remains constant in the WNW–ESE direction of footwall transport, but increases from south to north. The lack of a burial gradient in the direction of footwall transport implies that the footwall rocks, which today define a sub‐horizontal datum in the direction of fault transport, also defined a sub‐horizontal datum at depth in Late Cretaceous time. This suggests that the footwall was not tilted about the normal to the fault transport direction during exhumation, and hence that the NSRD did not form as a low‐angle normal fault cutting down through the lower crust. Instead, the following evolution for the northern Snake Range footwall is proposed. (i) Mesozoic contraction caused substantial crustal thickening by duplication and folding of the miogeoclinal sequence, accompanied by upper greenschist to amphibolite facies metamorphism. (ii) About half of the total exhumation was accomplished by roughly coaxial stretching and thinning in Late Cretaceous to Early Tertiary time, accompanied by retrogression and mylonitic deformation. (iii) The footwall rocks were then ‘captured’ from the middle crust along a moderately dipping NSRD that soled into the middle crust with a rolling‐hinge geometry at both upper and lower terminations.  相似文献   

15.
The Bitterroot metamorphic core complex is an exhumed, mid-crustal, plutonic–metamorphic complex that formed during crustal thickening and subsequent extension in the hinterland of the North American Cordilleran Orogen, in the northern Idaho batholith region. Extension was accommodated mainly on the Bitterroot mylonite zone, a 500–1500-m-thick shear zone that deforms granitic intrusive rocks as young as 53–52 Ma, as well as older high-grade metamorphic rocks and plutons. Exhumation of the core complex, in Eocene time, is marked in the shear zone by the transition from amphibolite-facies mylonitization, to greenschist-facies mylonitization, chloritic brecciation, to brittle faulting that progressed from shallower crustal levels in the west to deeper crustal levels in the east from ca. 53 –30 Ma based on U–Pb, Ar–Ar, and fission-track data. Apatite and zircon fission-track data record the lower-temperature part of the exhumation history and help define when the shear zone became inactive, as well as the transition from rapid, core complex-style extension to slower basin-and-range-style extension. They indicate that the western part of the complex was exhumed to within 1–2 km of the surface by 48–45 Ma, while the eastern part of the complex was still at amphibolite-facies conditions and that the eastern part of the complex was not exhumed below 60 °C until after 30 Ma. Younger apatite fission-track ages (≤26 Ma) on the eastern range front of the Bitterroot Mountains suggest that the present topographic expression of the mylonite front was due to Miocene high-angle faulting and widening of the Bitterroot Valley.  相似文献   

16.
本文系统论述了西南三江地区那邦、高黎贡山、崇山-澜沧江、点苍山-哀牢山-红河剪切走滑带、区域性伸展与变质核杂岩、新生代盆地及走滑过程中的碱性岩浆活动等特征,认为西南三江地区经历了挤压收缩变形(60～40Ma)、走滑伸展热隆(40～38Ma)、走滑剪切深熔(38～23Ma)、走滑剪切伸展(23～11Ma)、走滑剥蚀隆升(...  相似文献   

17.
THE LATE QUATERNARY RIGHT LATERAL STRIKE-SLIPPING OF ZHONGDIAN—DAJU FAULT IN NORTHWEST YUNNAN, CHINAthesubject“TherecentdisplacementandDynamicsoflithosphereintheQinghai XizangPlateau”ofnation alclimbingproject“Therecentdisp  相似文献   

18.
The Red River shear zone (RRSZ) is a major left‐lateral strike‐slip shear zone, containing a ductilely deformed metamorphic core bounded by brittle strike‐slip and normal faults, which stretches for >1000 km from Tibet through Yunnan and North Vietnam to the South China Sea. The RRSZ exposes four high‐grade metamorphic core complexes along its length. Various lithologies from the southernmost core complex, the Day Nui Con Voi (DNCV), North Vietnam, provide new constraints on the tectonic and metamorphic evolution of this region prior to and following the initial India–Asia collision. Analysis of a weakly deformed anatectic paragneiss using P–T pseudosections constructed in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (MnNCKFMASHTO) system provides prograde, peak and retrograde metamorphic conditions, and in situ U–Th–Pb geochronology of metamorphic monazite yields texturally controlled age constraints. Tertiary metamorphism and deformation, overprinting earlier Triassic metamorphism associated with the Indosinian orogeny and possible Cretaceous metamorphism, are characterized by peak metamorphic conditions of ~805 °C and ~8.5 kbar between c. 38 and 34 Ma. Exhumation occurred along a steep retrograde P–T path with final melt crystallizing at the solidus at ≥~5.5 kbar at ~790 °C. Further exhumation at ~640–700 °C and ~4–5 kbar at c. 31 Ma occurred at subsolidus conditions. U–Pb geochronological analysis of monazite from a strongly deformed pre‐kinematic granite dyke from the flank of the DNCV provides further evidence for exhumation at this time. Magmatic grains suggest initial emplacement at 66.0 ± 1.0 Ma prior to the India–Asia collision, whereas grains with metamorphic characteristics indicate later growth at 30.6 ± 0.4 Ma. Monazite grains from a cross‐cutting post‐kinematic dyke within the core of the DNCV antiform provide a minimum age constraint of 25.2 ± 1.4 Ma for the termination of fabric development. A separate and significant episode of monazite growth at c. 83–69 Ma is suggested to be the result of fluid‐assisted recrystallization following the emplacement of magmatic units.  相似文献   

19.
The slip rate predicted from geodetic and geomorphological measurements is quite uniform on ~800–1,000 km length of the Altyn Tagh and the Kunlun faults. GPS velocity field documents that tectonic loading on the two active faults changes greatly along their strikes. To explore the mechanical relationship between far‐field tectonic loading and fault slip‐rate accumulation, we built a 3D viscoelastic finite‐element model with fault motion governed by frictional strength of contact interfaces. Based on numerical experiments, it is found that the observed uniform slip rate could reflect lateral variation of frictional strength along fault strike. Variation of predicted frictional coefficient ranges from ~0.13 to ~0.02, verifying that the two active faults must be weak for their mechanical strength. In addition, the good fitness between the relatively weak segment of faults and the location of strong earthquakes suggests that seismic activity along the two faults could be related to their frictional strength.  相似文献   

20.
The Simav metamorphic core complex of the northern Menderes massif, western Turkey, consists of a plutonic (Tertiary) and metamorphic (Precambrian) core (footwall) separated from an allochthonous cover sequence (hanging wall) by a low-angle, ductile-to-brittle, extensional fault zone (i.e. detachment fault). The core rocks below the detachment fault are converted into mylonites with a thickness of a few hundred metres. Two main deformation events have affected the core rocks. The first deformational event (D1) was developed within the Precambrian metamorphic rocks. The second event (D2), associated with the Tertiary crustal extension, includes two distinct stages. Stage one is the formation of a variably developed ductile (mylonitic) deformation (D2d) in metamorphic and granitic core rocks under greenschist facies conditions. The majority of the mylonites in the study area have foliations that strike NNW to NNE and dip SW to SE. Stretched quartz and feldspar grains define the mineral lineation trending SW-NE direction and plunging gently to SW. The kinematic indicators indicate a top-to-NE sense of shear. Stage two formation of brittle deformation (D2b) that affected all core and cover rocks. D2b involves the development of cataclasites and high-angle normal faults. An overall top towards the north sense of shear for the ductile (mylonitic) fabrics in the core rocks is consistent with the N-S regional extension in western Turkey.  相似文献   

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