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1.
Lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation. We propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation. Five styles are recognised: pure shear (P), simple shear (S), compressional (C), vertical (V) and undeformed (U). These dictate the first letter of the codes; the remaining letters conveying the evidence. This information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed. Individual structures are not diagnostic of particular environments but the suite of structures, their relative scale, stratigraphical relationships, and orientation relative to palaeoslopes and to palaeoice‐flow directions can be used to infer the environment in which they formed. This scheme is applied at five sites in west Wales. The typical succession is interpreted as subglacial sediments overlain by meltout tills, flow tills and sediment flows. Paraglacial redistribution of glacial sediments is widespread. Large‐scale compressional deformation is restricted to sites where glaciers readvanced. Large‐scale vertical deformation occurs where water was locally ponded near the ice margin. There is no evidence for glaciomarine conditions. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
Estimates of large magnitude Late Cambrian earthquakes from seismogenic soft‐sediment deformation structures: Central Rocky Mountains 
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下载免费PDF全文 A variety of unusual early post‐depositional deformation structures exist in grainstone and flat‐pebble conglomerate beds of Upper Cambrian strata, western Colorado, including slide scarps, thrusted beds, irregular blocks and internally deformed beds. Thrusted beds up to tens of centimetres thick record thrust movement of a part of a bed onto itself along a moderate to steeply inclined (15° to 40°) ramp, locally producing hanging wall lenses with fault‐bend geometries. Thrust plane orientations are widely distributed, and in some cases nearly oppositely oriented in close proximity, indicating that they did not form as failures acted upon by gravity forces. Irregular bedded to internally deformed blocks are isolated on generally flat upper bedding surfaces. These features represent parts of beds that detached, moved up onto and some distances across, the laterally adjacent undisturbed bed surfaces. Deformation of thin intervals of mud on the ocean floor by moving blocks rules out the possibility of storm‐induced deformation, because the mud was not eroded by high shear stresses that would accompany the extremely large forces required to produce and move the blocks. Finally, internally deformed beds are characterized by large blocks, fitted fabrics of highly irregular fragments and contorted lamination, which represent heterogeneous deformation, such as brecciation and liquefaction. The deformation structures were produced by earthquakes linked to the reactivation of Mesoproterozoic, crustal‐scale shear zones in the central Rockies during the Late Cambrian. Analysis of the deformation structures indicates very large body forces and calculated earthquake‐generated ground motion velocities of ca 1·6 m sec?1. These correspond to moment magnitudes of ca 7·0 or more and a Mercalli Intensity of X+. These are the only known magnitude estimates of Phanerozoic (other than Quaternary) large‐intensity earthquakes for the Rocky Mountain region, and they are as large as, or larger than, previous estimates of Proterozoic earthquakes along these major shear zones of the central Rockies. 相似文献
3.
A common facies observed in deep‐water slope and especially basin‐floor rocks of the Neoproterozoic Windermere Supergroup (British Columbia, Canada) is structureless, coarse‐tail graded, medium‐grained to coarse‐grained sandstone with from 30% to >50% mud matrix content (i.e. matrix‐rich). Bed contacts are commonly sharp, flat and loaded. Matrix‐rich sandstone beds typically form laterally continuous units that are up to several metres thick and several tens to hundreds of metres wide, and commonly adjacent to units of comparatively matrix‐poor, scour‐based sandstone beds with large tabular mudstone and sandstone clasts. Matrix‐rich units are common in proximal basin‐floor (Upper Kaza Group) deposits, but occur also in more distal basin‐floor (Middle Kaza Group) and slope (Isaac Formation) deposits. Regardless of stratigraphic setting, matrix‐rich units typically are directly and abruptly overlain by architectural elements comprising matrix‐poor coarse sandstone (i.e. channels and splays). Despite a number of similarities with previously described matrix‐rich beds in the literature, for example slurry beds, linked debrites and co‐genetic turbidites, a number of important differences exist, including the stratal make‐up of individual beds (for example, the lack of a clean sandstone turbidite base) and their stratigraphic occurrence (present throughout base of slope and basin‐floor strata, but most common in proximal lobe deposits) and accordingly suggest a different mode of emplacement. The matrix‐rich, poorly sorted nature of the beds and the abundance and size of tabular clasts in laterally equivalent sandstones imply intense upstream scouring, most probably related to significant erosion by an energetic plane‐wall jet or within a submerged hydraulic jump. Rapid energy loss coupled with rapid charging of the flow with fine‐grained sediment probably changed the rheology of the flow and promoted deposition along the margins of the jet. Moreover, these distinctive matrix‐rich strata are interpreted to represent the energetic initiation of the local sedimentary system, most probably caused by a local upflow avulsion. 相似文献
4.
Coarse‐grained deep‐water strata of the Cerro Toro Formation in the Cordillera Manuel Señoret, southern Chile, represent the deposits of a major channel belt (4 to 8 km wide by >100 km long) that occupied the foredeep of the Magallanes basin during the Late Cretaceous. Channel belt deposits comprise a ca 400 m thick conglomeratic interval (informally named the ‘Lago Sofia Member’) encased in bathyal fine‐grained units. Facies of the Lago Sofia Member include sandy matrix conglomerate (that show evidence of traction‐dominated deposition and sedimentation from turbulent gravity flows), muddy matrix conglomerate (graded units interpreted as coarse‐grained slurry‐flow deposits) and massive sandstone beds (high‐density turbidity current deposits). Interbedded sandstone and mudstone intervals are present locally, interpreted as inner levée deposits. The channel belt was characterized by a low sinuousity planform architecture, as inferred from outcrop mapping and extensive palaeocurrent measurements. Laterally adjacent to the Lago Sofia Member are interbedded mudstone and sandstone facies derived from gravity flows that spilled over the channel belt margin. A levée interpretation for these fine‐grained units is based on several observations, which include: (i) palaeocurrent measurements that indicate flows diverged (50° to 100°) once they spilled over the confining channel margin; (ii) sandstone beds progressively thin, away from the channel belt margin; (iii) evidence that the eroded channel base was not very well indurated, including a stepped margin and injection of coarse‐grained channel material into surrounding fine‐grained units; and (iv) the presence of sedimentary features common to levées, including slumped units inferring depositional slopes dipping away from the channel margin, lenticular sandstone beds thinning distally from the channel margin, soft sediment deformation and climbing ripples. The tectonic setting and foredeep architecture influenced deposition in the axial channel belt. A significant downstream constriction of the channel belt is reflected by a transition from more tabular units to an internal architecture dominated by lenticular beds associated with a substantially increased degree of scour. Differential propagation of the fold‐thrust belt from the west is speculated to have had a major control on basin, and subsequently channel, width. The confining influence of the basin slopes that paralleled the channel belt, as well as the likelihood that numerous conduits fed into the basin along the length of the active fold‐thrust belt to the west, suggest that proximal–distal relationships observed from large channels in passive margin settings are not necessarily applicable to axial channels in elongate basins. 相似文献
5.
Benjamin Ntieche M. Ram Mohan Moundi Amidou 《Journal of the Geological Society of India》2017,89(1):33-46
The Magba Shear Zone is made up of granites, migmatites, orthogneiss, metagabbro, mafic dyke and mylonites with coarse grained texture, porphyroblastic, granoblastic, cataclastic and mylonitic texture respectively. Structural features and kinematic indicators testify the syntectonic emplacement of Magba granitoids and also provide detailed information on the relative timing of deformation as follows: (1) D1 of tangential movement immediately followed by (2) the D2 phase which is heterogeneous simple shear in dextral transpressive context with a NW-SE direction (3) D3 tectonic phase is marked by sinistral transpressive tectonic and superposed folding with a NE-SW kinematic direction. Combined ductile NE-SW shear movements and NWSE compressional movements defined a transpressional tectonic regime during the D3 deformation (4) A brittle stage D4 is controlled by transcurrent tectonics and responsible for the emplacement of faults, and joints. The Magba granites would have intruded along sub-vertical mid-crustal feeder channels and were emplaced as a sheet or sheets along the shear zone during the early stage of the C3 shearing, followed by gabbro and mafic dyke at the late stage. Strike-slip dilatancy pumping under transpressive tectonic is suggested as a possible mechanism for the emplacement of the Magba granites. 相似文献
6.
M. G. Kale Ashwin S. Pundalik R. A. Duraiswami N. R. Karmalkar 《Journal of the Geological Society of India》2016,87(2):194-204
Soft sediment deformation structures such as slump folds, clastic dyke, syn-sedimentary faults and convolute bedding are present in the coarse–fine grained yellowish buff coloured sandstone, and interbedded reddish brown fine grained sandstone and yellowish–white siltstone at the Khari River section belonging to Rudramata member of Jhuran Formation (Upper Jurassic), Kutch. These soft sediment deformation structures are confined to lower and middle parts of the section and are invariably underlain as well as overlain by undeformed beds that have restricted lateral and vertical extent and occur in close proximity of Kutch Mainland Fault, thereby suggesting that these structures were formed by seismic activity and therefore represents seismites. 相似文献
7.
Five main deformation units, discrete sheets of deformed sediments that lie between a significant thickness of undeformed sediment, were selected for study within Late Pleistocene lacustrine sands and clays in the Onikobe and Nakayamadaira Basins, northeastern Japan. The deformed units show evidence of deformation by a variety of mechanisms including fluidization, liquefaction, brittle failure and cohesive flow. Driving forces are thought to be primarily reverse density gradient systems, but also include gravitational body force, shear stress and unequal loading. The main trigger mechanisms are firstly earthquakes, secondly overloading from volcanic sands and thirdly, to a lesser extent, subaqueous currents. Consideration is given to criteria that allow the trigger mechanism to be identified. This study shows that the following criteria can be used to identify a seismic triggering agent: (i) setting; (ii) the extent of the deformation units; (iii) absence of evidence relating to other potential trigger mechanisms; and (iv) evidence relating to other potential trigger mechanisms is present but can be seen elsewhere in the stratigraphic section associated with undeformed sediment. Conversely, the following criteria, while they are important in interpreting the driving force and deformation mechanism, have no relevance to the trigger mechanism: (i) sediment composition; (ii) deformation structures being restricted to a single stratigraphic interval (<1 m thick) (not necessarily correlatable over large areas); and (iii) similarity to structures in the literature. 相似文献
8.
David P. Vaughan‐Hirsch Emrys Phillips Jonathan R. Lee Jane K. Hart 《Boreas: An International Journal of Quaternary Research》2013,42(2):376-394
The ability of glaciers to detach and transport bedrock as glaciotectonic rafts is widely observed throughout Quaternary sections. However, the glaciological, hydrological and geological parameters controlling rafting are currently poorly constrained. There is a lack of structural and sedimentary evidence concerning rafting, and therefore the processes driving raft detachment, transport and emplacement are poorly understood. This paper contributes to our understanding by presenting a macro‐ and microstructural study of deformation associated with a chalk raft at West Runton, north Norfolk. Detailed thin‐section analysis reveals several discrete micro‐fabric orientations, representing poly‐phase deformation occurring during raft transport and emplacement. A four‐stage conceptual model for raft transport and emplacement is proposed, with deformation being partitioned into the relatively weaker Happisburgh Till member, the latter forming the host to the raft. Stage 1 is the main transport phase of the chalk raft, and was dominated by easterly (down‐ice) directed ductile shearing. During Stage 2 a narrow ductile shear zone within the Happisburgh Till member propagated upwards through the base of the raft, leading to the detachment of an elongate block of chalk. Attenuated lenses of diamicton in this shear zone possess kinematics recording an easterly directed sense of shear. As deformation progressed, during Stage 3, the detached block impinged on the ‘high‐strain’ zone wrapping the base of the raft, influencing the style of deformation partitioning and leading to localized, up‐ice‐directed kinematics. Stage 4 represents the final stages of raft emplacement, when the detachment zone at the base of the raft began to ‘lock‐up’. These results demonstrate the relative importance of the hydrological controls associated with raft transport and emplacement underneath an actively advancing glacier. Furthermore, the model represents an example of how micromorphological analysis can reveal detailed poly‐phase deformation histories in deformed glacial sediments. 相似文献
9.
《Geodinamica Acta》2013,26(5):363-374
Granitoid rocks of the southern Menderes Massif, SW Turkey include widespread possibly Ediacaran high-grade granitic orthogneisses and younger (Tertiary) sheets, sills and/or dikes of variably deformed tourmaline-bearing leucogranites. The latter are confined to the immediate footwall of the regional-scale ductile southern Menderes shear zone. Although both sets of granitoid rocks are essentially calc-alkaline and peraluminous, the syn- to post-collisional tourmaline-bearing leucogranites are chemically distinguishable from both the granitoid orthogneisses and from two sets of mostly sodic siliceous dyke rocks. The leucogranites were generated by partial melting induced by shear heating during the waning stages of the Eocene main Menderes metamorphism and associated top-to-the-NNE thrusting along the southern Menderes ductile shear zone, which transported schists northwards over the granitoid orthogneisses of the core Menderes complex. Upward migration and emplacement of leucogranitic melt weakened formerly sheared rocks, so that when thrust-related deformation ceased it facilitated rapid crustal extension along the shear zone. The emplacement of leucogranites, in turn, promoted the reactivation of the southern Menderes shear zone as a top-to-the-SSW extensional feature. Continued extensional deformation affected the leucogranites which became parallel to the shear-zone foliation; local S-C fabrics were also generated. The additional occurrence of less or almost undeformed leucogranites suggests that the latest stages of extension might have induced adiabatic decompressional melting. Hence the leucogranite melt generation and emplacement in the southern Menderes Massif occurred in pulses. Both compressional and extensional processes played key roles in melt generation, emplacement, deformation and exhumation of the massif. A clear distinction may also be made between the composition of granite-hosted tourmalines and those from metasedimentary schists. Tourmalines from a pebble of uncertain provenance in the Gökçay metaconglomerate plotted with schist-hosted tourmalines, suggesting that it was unlikely to be derived from granitoid gneiss. This crucial piece of evidence suggests that the presence of a major (Pan-African) unconformity at the so-called “core (orthogneiss)-cover (schist)” boundary in the southern Menderes Massif is unnecessary. 相似文献
10.
顺斜向坡变形破坏特征研究 总被引：5，自引：0，他引：5
本文通过对黄河上游某水电站坝前坝后顺斜向坡变形破坏特征的分析,提出了顺斜向坡的变形破坏类型分类,并对边坡产生旋转滑移破坏的临界条件作了分析。 相似文献
11.
西藏阿里札达韧性剪切带特征及其X光岩组分析 总被引：1，自引：0，他引：1
文中简述了西藏阿里札达盆地的地质背景、区域地层和札达韧性剪切带的基本特征。采用X射线衍射法对札达韧性剪切带中的石英、方解石和白云母等三种矿物,进行了X光岩组分析,确定了韧性变形岩石的组构特征、韧性剪切带的属性和变形岩石的应变类型,以及韧性剪切带形成时的温压条件。研究表明,韧性变形岩石均具不对称组构,反映韧性带属于南盘(下盘)俯冲型韧性剪切带,韧性变形是在高温、高压、低应变速率条件下发生的,处于>10km的地壳深度,岩石应变类型以压扁应变为主。 相似文献
12.
淮北夹沟—桃山集地区推覆构造研究 总被引：1，自引：0，他引：1
本区存在大型中生代推覆构造,所有震旦纪—古生代的沉积岩层都卷入了褶皱和断裂,构造推覆发生在较高构造部位,属脆性变形域,以台阶状逆断层和断层相关褶皱为特征。区内存在若干推覆构造,每个岩片均可分为上盘、下盘和滑动层系三部分,共查明8个滑动岩系。是一种发生在早中生代的盖层推覆,无根褶皱,也是徐宿地区最重要的控煤构造。最后对推覆构造的地球动力学机制进行了讨论。 相似文献
13.
Much of our understanding of submarine sediment‐laden density flows that transport very large volumes (ca 1 to 100 km3) of sediment into the deep ocean comes from careful analysis of their deposits. Direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic. In order to understand how submarine sediment‐laden density flows evolve in space and time, lateral changes within individual flow deposits need to be documented. The geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events. This study of the Miocene Marnoso Arenacea Formation (Italy) provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence. One hundred and nine sections were logged through a ca 30 m thick interval of time‐equivalent strata, between the Contessa Mega Bed and an overlying ‘columbine’ marker bed. Correlations extend for 120 km along the axis of the foreland basin, in a direction parallel to flow, and for 30 km across the foredeep outcrop. As a result of post‐depositional thrust faulting and shortening, this represents an across‐flow distance of over 60 km at the time of deposition. The correlation of beds containing thick (> 40 cm) sandstone intervals are documented. Almost all thick beds extend across the entire outcrop area, most becoming thinly bedded (< 40 cm) in distal sections. Palaeocurrent directions for flow deposits are sub‐parallel and indicate confinement by the lateral margins of the elongate foredeep. Flows were able to traverse the basin in opposing directions, suggesting a basin plain with a very low gradient. Small fractional changes in stratal thickness define several depocentres on either side of the Verghereto (high) area. The extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle, substantially less than the thickness of flows. Thick beds contain two distinct types of sandstone. Ungraded mud‐rich sandstone intervals record evidence of en masse (debrite) deposition. Graded mud‐poor sandstone intervals are inferred to result from progressive grain‐by‐grain (turbidite) deposition. Clast‐rich muddy sandstone intervals pinch‐out abruptly in downflow and crossflow directions, in a fashion consistent with en masse (debrite) deposition. The tapered shape of mud‐poor sandstone intervals is consistent with an origin through progressive grain‐by‐grain (turbidite) deposition. Most correlated beds comprise both turbidite and debrite sandstone intervals. Intrabed transitions from exclusive turbidite sandstone, to turbidite sandstone overlain by debrite sandstone, are common in the downflow and crossflow directions. This spatial arrangement suggests either: (i) bypass of an initial debris flow past proximal sections, (ii) localized input of debris flows away from available sections, or (iii) generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and/or abrupt flow deceleration. A single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud‐rich and mud‐poor sandstone. 相似文献
14.
The Maastrichtian Kathikas mélange is shown to be of sedimentary origin, being a succession of undeformed, submarine, matrix-supported debris-flow deposits up to 270 m thick. Internal sedimentological features include beds emphasized by colour or clast size variation, pelagic chalk interbeds, planar clast fabrics and channels. A trend of upwards-thinning beds in the mélange is interpreted as due to debris-flow initiation on gradually increasing slopes. Debris was shed locally from the deformed and fragmented Mamonia Complex, a series of disrupted gravity-slide sheets of Mesozoic sedimentary rocks and deformed igneous rocks. All Mamonia lithologies are represented in the mélange, and local facies variations permit identification of individual sources. The mélange probably pre-dates emplacement of serpentinite into the Mamonia Complex. There was also local inter-mixing of material from the adjacent and underlying Troodos sequences. The mélange rests unconformably on both Mamonia and Troodos sequences, and formed after the main deformation episode of the Mamonia Complex. The degree of resedimentation increases gradually away from the disrupted Mamonia source rocks. The thickness and volume of the Kathikas mélange are comparable with those of recent submarine debris flow deposits on unstable or seismically active continental margins. 相似文献
15.
《Sedimentology》2018,65(3):952-992
Hybrid event beds comprising both clean and mud‐rich sandstone are important components of many deep‐water systems and reflect the passage of turbulent sediment gravity flows with zones of clay‐damped or suppressed turbulence. ‘Behind‐outcrop’ cores from the Pennsylvanian deep‐water Ross Sandstone Formation reveal hybrid event beds with a wide range of expression in terms of relative abundance, character and inferred origin. Muddy hybrid event beds first appear in the underlying Clare Shale Formation where they are interpreted as the distal run‐out of the wakes to flows which deposited most of their sand up‐dip before transforming to fluid mud. These are overlain by unusually thick (up to 4·4 m), coarse sandy hybrid event beds (89% of the lowermost Ross Formation by thickness) that record deposition from outsized flows in which transformations were driven by both substrate entrainment in the body of the flow and clay fractionation in the wake. A switch to dominantly fine‐grained sand was accompanied initially by the arrest of turbulence‐damped, mud‐rich flows with evidence for transitional flow conditions and thick fluid mud caps. The mid and upper Ross Formation contain metre‐scale bed sets of hybrid event beds (21 to 14%, respectively) in (i) upward‐sandying bed set associations immediately beneath amalgamated sheet or channel elements; (ii) stacked thick‐bedded and thin‐bedded hybrid event bed‐dominated bed sets; (iii) associations of hybrid event bed‐dominated bed sets alternating with conventional turbidites; and (iv) rare outsized hybrid event beds. Hybrid event bed dominance in the lower Ross Formation may reflect significant initial disequilibrium, a bias towards large‐volume flows in distal sectors of the basin, extensive mud‐draped slopes and greater drop heights promoting erosion. Higher in the formation, hybrid event beds record local perturbations related to channel switching, lobe relocations and extension of channels across the fan surface. The Ross Sandstone Formation confirms that hybrid event beds can form in a variety of ways, even in the same system, and that different flow transformation mechanisms may operate even during the passage of a single flow. 相似文献
16.
Sa’ad Zeki Abdul-Kader Al-Mashaikie Suhad Kalaf Abdul-Razzak Madhat Eliwie Naser 《Arabian Journal of Geosciences》2016,9(19):723
The Baluti Formation is exposed succession of the Rhaetian age (Upper Triassic). These strata are interpreted herein for the first time to redeposit in a deep marine setting (distally steepened carbonate ramp/medial to distal slope) on the northwestern margin of the Neo-Tethys. The Galley Derash section is apparently continuous with no evidence for either subaerial exposure or submarine erosion. The absence of erosional scours in the study area confirms emplacement of these strata below both fair-weather and storm wave base. Event beds, particularly those resulting from sediment gravity flows, dominate the Rhaetian interval. The Upper Rhaetian strata are primarily assigned to the Galley Derash Valley. It records an upward transition from moderate-scale, olistolith-bearing debris flow deposits (debrite) to medium-/thin-bedded turbidites remobilized as sediment slumps/slides. The succession is dominated by medium- to thin-bedded calcareous turbidites and hemipelagic suspension deposits. Very low fossil assemblages, particularly stromatolite fragments, and planktonic bivalves occur within some intervals in the section. Rapid and relatively continuous sedimentation is attested to by the thickness of the section, the abundance of calcareous turbidites, and the thin nature of the intercalated hemipelagic beds. Low content of badly preserved fossils and evidence of continuous and rapid sedimentation refer to alteration by tectonic disturbances or diagenesis. This makes the Baluti Beds as a supplementary section for the Rhaetian successions in Iraq. 相似文献
17.
18.
Dilce De Fátima Rossetti 《Sedimentology》1999,46(6):1065-1081
Soft-sediment deformation structures from the Alcântara Formation (late Albian to Cenomanian), São Luís Basin, northern Brazil, consist of (1) contorted structures, which include convolute folds, ball-and-pillow structures, concave-up paths with consolidation lamination, recumbently folded cross-stratification and irregular convolute stratification that grades into massive beds; (2) intruded structures, which include pillars, dykes, cusps and subsidence lobes; and (3) brittle structures, represented by fractures and faults displaying planes with a delicate, ragged morphology and sharp peaks. These structures result from a complex combination of processes, mostly including reverse density gradients, fluidization and liquefaction. Reverse density gradients, promoted by differential liquefaction associated with different degrees of sediment compaction, led to the genesis of convolute folds. More intense deformation promoted the development of ball-and-pillow structures, subsidence lobes and sand rolls, which are attributed to denser, and thus more compacted (less liquefied), portions that sank down into less dense, more liquefied sediments. Irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation. The subsidence of beds was accompanied by lateral current drag and fluid escape from water-saturated sands. In addition, the fractures and faults record brittle deformation penecontemporaneous with sediment deposition. All these mechanisms were triggered by a seismic agent, as suggested by a combination of criteria, including (1) the position of the study area at the edge of a major strike-slip fault zone that was reactivated several times from the Albian to the Holocene; (2) a relative increase in the degree of deformation in sites located closer to the fault zone; (3) continuity of the deformed beds over large distances (several kilometres); (4) restriction of soft-sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata; (5) recurrence through time; and (6) similarities to many other earthquake-induced deformational structures. 相似文献
19.
《Journal of Structural Geology》2001,23(2-3):379-392
Fault-slip data are used to reconstruct varying tectonic regimes associated with transverse fold development along the eastern and southern margins of the Jaca basin, southern Pyrenees, Spain. The Spanish Pyrenean foreland consists of thrust sheets and leading-edge décollement folds which developed within piggyback basins. Guara Formation limestones on the margins of the Jaca basin were deposited synchronously with deformation and are exposed in the External Sierra. Within the transverse folds, principal shortening axes determined from P and T dihedra plots of fault-slip data show a shift from steep shortening in stratigraphically older beds to NNE–SSW horizontal shortening in younger beds. Older strata are characterized by extensional faults interpreted to result from halotectonic (salt tectonics) deformation, whereas younger strata are characterized by contraction and strike-slip faults interpreted to result from thrust sheet emplacement. The interpretation of the timing for the shortening axes in the younger strata is supported by the observation that these axes are parallel to shortening axes determined from finite strain analysis, calcite twins, and regional thrusting directions determined from fault-related folds and slickenlines. This study shows that fault population analysis in syntectonic strata provides an opportunity to constrain kinematic evolution during orogeny. 相似文献
20.
E. J. M. Bloem N. J. McNaughton D. I. Groves J. R. Ridley 《Australian Journal of Earth Sciences》2013,60(5):447-451
The Corinthia lode‐gold deposit in amphibolite‐facies greenstone belt rocks in the Southern Cross Province of the Archaean Yilgarn Block contains a largely undeformed pegmatite dyke emplaced during the last phases of movement along the Fraser's‐Corinthia shear zone. Gold mineralization and shear zone development were synchronous, and a Pb‐Pb isochron age of 2620 ±6 Ma for pegmatite emplacement either indirectly dates mineralization, or places a minimum age constraint on the timing of mineralization. This age is in accord with a broadly synchronous dominant episode of Archaean lode‐gold mineralization throughout the Yilgarn Block. 相似文献