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1.
The El Sibai area of the Central Eastern Desert (CED) of Egypt consists of an ophiolitic association of arc metavolcanics, ophiolitic rocks, mélange, metasediments and minor mafic intrusions; and a gneissic association of amphibolite, gneissic diorite, tonalite, granodiorite and granite. Previous studies of the El Sibai area have identified the gneissic association as a lower crustal infrastructure in sheared contact with upper crustal ophiolitic association suprastructure, and have presented it as an example of a metamorphic or magmatic core complex. Detailed structural remapping of the El Sibai area reveals that the gneissic association rocks are not infrastructural but form a unit within the ophiolitic association nappes. Furthermore, the El Sibai structure is not domal in shape, and is not antiformal. The main gneissic association rocks are tabular intrusions roughly concordant with the shears dividing the ophiolitic association into nappes, and are syn-kinematic with the nappe stacking event (∼700–650 Ma). The gneissic granite tabular intrusions and their ophiolitic host were later folded about upright NW–SE trending mainly open folds during a NE–SW directed shortening event (∼625–590 Ma). Subsequently, NW–SE regional extension effects became evident including low angle normal ductile shear zones and mylonites. The latest gneissic red granites are syn-kinematic with respect to these shear zones. Probably continuing from the low-angle shearing event were steep normal faults, and sinistral WNW and N–S trending transcurrent faults (∼590–570 Ma). The normal faults mark the southeastern and maybe also the northwestern limits of the El Sibai gneissic association rocks. The El Sibai complex is not a core complex, but exemplifies the overlap of NW–SE folding and NW–SE extensional which is a significant theme of CED regional structure.  相似文献   

2.
The northerly dipping Sha’it–Nugrus shear zone (SNSZ) is the boundary separating the Central Eastern Desert from the South Eastern Desert of Egypt. The hangingwall of this shear zone is composed of low-grade metavolcanics and ophiolitic nappes of the Central Eastern Desert, while the footwall consists of South Eastern Desert high-grade metapsammitic gneisses (Migif-Hafafit gneissic complex). The SNSZ is about 700 m thick and represents the shear foliated lower parts of the hangingwall and upper parts of the footwall. A significant part of the SNSZ has been truncated by a later normal fault along Wadi Sha’it, however the SNSZ is well-preserved along Wadi Nugrus. Features of the SNSZ include shear-related schistosity (termed Ss), mylonite zones, sheared syn-kinematic granitoid intrusions, diverse metasomatism and metamorphic effects (higher T overprinting of hangingwall lithologies and retrogression of footwall lithologies). Shear-sense indicators clearly show top-to-N or NW displacement sense. SNSZ structures overprint arc collision related nappe structures (～680 Ma) and are therefore post-arc collision. SNSZ syn-kinematic intrusives have been dated at ～600 Ma. The SNSZ is deformed (regionally and locally folded and thrust dissected) during later NE–SW compressive tectonism. The SNSZ had an originally approximately E–W strike, low-angle N-dip and a normal shear sense, making this an example of a low-angle normal ductile shear (LANF) or detachment fault. The steep NE dip of Ss foliations and low-pitching slip lineations along Wadi Nugrus are due to NW–SE folding of the SNSZ, and do not indicate a sinistral strike-slip shear zone. The normal shear sense activity is responsible for juxtaposing the low-grade Central Eastern Desert lithologies against South Eastern Desert gneisses. A displacement of 15–30 km is estimated on the SNSZ, which is comparable to LANF displacements in the Basin and Range province of the western USA. Frictional resistance along this shear was probably reduced by high magmatic fluid pressure and hydrothermal fluid pressure. The vastness and diversity of the hydrothermal activity along this shear zone is a characteristic of other LANFs in the Eastern Desert, e.g. at Gabal El-Sibai, and may be Gabal Meatiq. The SNSZ formed during the Neoproterozoic extensional tectonic phase of Eastern Desert that began ～600 Ma, and followed arc collision and NW-ward ejection of nappes.  相似文献   

3.
The Bundelkhand massif, located in the northern part of the Indian shield, is a poly-deformed and poly-metamorphic terrain. This paper reports a new shear system developed throughout the massif in the form of N–S trending quartz veins that are sometimes quartzo-feldspathic and rarely granitic in composition. The veins are vertical and commonly occur in conjugate sets. This tectono-magmatic event appears to represent the youngest shear system of the massif as it cross-cuts all the earlier shear systems (E–W, NE–SE and NW–SE). Emplacement of this N–S vein system may have taken place due to extensional processes that developed some cracks along which siliceous magma was vertically emplaced. The complete absence of signature of the N–S event from the surrounding sedimentary cover of Vindhyan Supergroup, Bijawar and Gwalior Groups suggests that this shear system is pre-tectonic to the nearly E–W trending passive basins developed at the margins of the Bundelkhand craton. Further, several workers have considered the Bundelkhand massif as a part of the Aravalli craton. However, due to the absence of N–S, as well as the other (i.e., E–W, NW–SE and NW–SE), tectonic fabrics of the Bundelkhand massif in other cratons of the Peninsular India, and vice versa, makes the Bundelkhand block a separate and unique craton of its own and is not part of the Aravalli craton.  相似文献   

4.
The Wadi El-Shush area in the Central Eastern Desert (CED) of Egypt is occupied by the Sibai core complex and its surrounding Pan-African nappe complex. The sequence of metamorphic and structural events in the Sibai core complex and the enveloping Pan-African nappe can be summarized as follows: (1) high temperature metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks, (2) between 740 and 660 Ma, oblique island arc accretion resulted in Pan-African nappe emplacement and the intrusion of syn-tectonic gneissic tonalite at about 680 ± 10 Ma. The NNW–SSE shortening associated with oblique island arc accretion produced low angle NNW-directed thrusts and open folds in volcaniclastic metasediments, schists and isolated serpentinite masses (Pan-African nappe) and created NNE-trending recumbent folds in syn-tectonic granites. The NNW–SSE shortening has produced imbricate structures and thrust duplexes in the Pan-African nappe, (3) NE-ward thrusting which deformed the Pan-African nappe into SW-dipping imbricate slices. The ENE–WSW compression event has created NE-directed thrusts, folded the NNW-directed thrusts and produced NW-trending major and minor folds in the Pan-African nappe. Prograde metamorphism (480–525 °C at 2–4.5 kbar) was synchronous with thrusting events, (4) retrograde metamorphism during sinistral shearing along NNW- to NW-striking strike-slip shear zones (660–580 Ma), marking the external boundaries of the Sibai core complex and related to the Najd Fault System. Sinistral shearing has produced steeply dipping mylonitic foliation and open plunging folds in the NNW- and NE-ward thrust planes. Presence of retrograde metamorphism supports the slow exhumation of Sibai core complex under brittle–ductile low temperature conditions. Arc-accretion caused thrusting, imbrication and crustal thickening, whereas gravitational collapse of a compressed and thickened lithosphere initiated the sinistral movement along transcurrent shear zones and low angle normal ductile shear zones and consequently, development and exhumation of Sibai core complex.  相似文献   

5.
In the Oman ophiolite, the large scale Makhibiyah shear zone, in Wadi Tayin massif was generated with no or little relative motion between the two adjacent blocks, in contrast with what is reported from otherwise similar shear zones in deep crust and upper mantle. This shear zone is asymmetrical with, along one margin an asthenospheric mantle (～1200 °C) and along the adjacent margin, a lithospheric mantle (～1000 °C). Within the hotter side and with increasing shear strain, horizontal flow lines smoothly swing towards the shear zone direction before abutting against the wall of the lithosphere side. Profuse mafic melts issued from the hotter mantle are frozen in the shear zone by cooling along this lithospheric wall. Tectonic and magmatic activities are entirely localized within the asthenospheric compartment. Mantle flow lines were rotated, during their channelling along this NW‐SE shear zone, in the NW and SE opposite directions. Depending on whether the flow lines are deviated NW or SE, dextral or sinistral shear sense is recorded in the shear band mylonitic peridotites. This demonstrates that the shear zone was not generated by strike‐slip motion, a conclusion supported by regional observations.  相似文献   

6.
First results of the analysis of GPS measurement data obtained from 18 sites of two local networks in the vicinity of Ulaanbaatar (Mongolia) for the period 2010–2015 have been presented. Horizontal velocity vectors are consistent with each other in the ITRF2014 system and with the velocities of the IGS permanent station ULAB. The sites move in the E–SE direction at a rate of 25–30 mm/yr, with the displacement azimuth averaging 105°. With respect to Eurasia, the vectors for most of the sites are slighly turned to the south, but they are still of SE orientation with the azimuth range of 130°–150° and magnitude values of 2–4 mm/yr. Relative horizontal velocities tend to decrease towards southeast that determines a zonal distribution of different type of relative strain patterns. The western part of the Ulaanbaatar network is characterized by the W–E oriented extension with the elongation rate ε1 = 12–16 × 10–8 yr–1. The shortening NW–SE trending strain with calculated value ε2 = 22.4 × 10–8 yr–1 characterizes the network’s eastern part. The highest values of the maximum shear strains (εmax = 10–14 × 10–8 yr–1) form an extended area in the center of the testing ground, which is elongated in the northeastern direction, conformably with the strike of the major geologic structures. The strain distribution pattern of the Emeelt network located within the eponymous seismogenic structures is characterized by the crustal elongation (5 × 10–6 yr–1) trending SE–NW and less pronounced shortening in the SW–SE directions.The axial part of the fault crossing the network in the NW direction exhibits maximum deformations.  相似文献   

7.
In the eastern part of southern Peninsular India, the charnockitic hills of the Madras block are cut across by the E-W trending Attur shear zone (ASZ) which is characterised by a thick (1 to 1.5 km) phyllonite zone, showing intense mylonitisation due to ductile shearing. Steeply plunging (70°–80°) stretching lineation on steeply dipping mylonitic foliation within this zone indicates a relative vertical upliftment of the adjacent blocks. A dextral shearing event from west to east is envisaged from the kinematic analysis of shear sense indicators such as S-C fabric, asymmetric folds, asymmetric augens and asymmetric porphyroclasts. Simultaneous development of these features, related to vertical and horizontal movements may be explained by the mechanism of transpressional deformation. The Attur shear zone may be correlated with the Moyar shear zone based on distinct lithological and structural similarities.  相似文献   

8.
Amphibolites from the crystalline basement of the Western Tatra Mountains, which are found as small lenses within migmatitic gneisses and mica schists, were formed during pre‐ or early Variscan amphibolite‐facies metamorphic events, and subsequently intruded by the post‐metamorphic Variscan Tatra Granite. The amphibolites occur in both the upper and lower metamorphic complexes, which are separated by a major subhorizontal shear zone in the Western Tatra Mountains. The amphibolites can be divided into three types: massive, striped and garnetiferous. The striped and massive amphibolites, concordant with a dominant S1 foliation, and the garnet amphibolites, which cross‐cut the S1 banding in the gneisses, were all originally intrusive dolerites. The striped amphibolites (consisting primarily of hornblende, andesine and quartz), and later, cross‐cutting garnet‐hornblende‐andesine‐quartz‐bearing amphibolites, predominate in the lower part of the dominantly migmatitic upper complex, and are exposed mainly on the ridges. The massive amphibolites, which contain a similar mineral assemblage, mainly occur in the usual unmigmatized lower structural unit. Chemical studies indicate that three amphibolite suites are present, which probably originated as a series of enriched tholeiites, similar to more recent plume‐influenced magmas, which were derived by partial melting of a spinel lherzolite with primitive mantle composition and compositionally slightly modified by crustal contamination. The amphibolites were intruded as dolerites into clastic sediments which had accumulated in an extensional basin floored by attenuated continental crust, a situation similar to that of amphibolites found in metamorphic complexes within the Variscan belt, e.g. in the Orlica–Snieznik area of the Sudetes, where amphibolites chemically similar to those in the Western Tatra also occur. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

9.
New data suggest syn-convergent extrusion and polyphase tectonics followed by late Variscan extension in the Strudengau area of the southern Moldanubian zone in Austria. The tectonic history can be summarized as follows: (1) The oldest ductile event is observed in HT/LP metamorphic pelitic gneisses, which preserve E-dipping foliation planes (D1-fabric) with NW–SE-trending lineations. (2) The overlying gneisses record HT/HP conditions with decompression-induced anatexis in the central part of the domain. These gneisses exhibit N–S trending, horizontal lineations along steep-dipping foliation planes (D2-fabric) crosscutting the D1-fabric of the pelitic gneisses. Along the margin, these rocks have been strongly mylonitized under amphibolite facies conditions (D2). D2 is interpreted as a significant vertical shear zone, which juxtaposes the HT/LP rocks against the orogenic lower crust. (3) Lastly, the whole area is overprinted by localized shear zones (D3-fabric) with top-to-the-NW kinematics. This newly discovered Strudengau shearing event is associated with isoclinal folding that possesses axial planes parallel to the mylonitic foliation and fold axes parallel to the stretching lineations. Initial mylonitization occurred under greenschist facies, representing the latest ductile event of the Strudengau area. The new geochronological data presented here indicate a narrow time frame (c. 323–318 Ma) for the D3 deformation. Therefore, this event is contemporaneous with the intrusion of the granites of the South Bohemian Batholith (330–310 Ma). The nearby South Bohemian Batholith and generally steep dyke swarms in the Strudengau area and to the north trend in a NE–SW preferred orientation, interpreted to be D3-synkinematic magmatism. In a regional context, the NW–SE stretching during D3 together with the synkinematic intrusion of dykes is associated with late orogenic extension in the Austrian Moldanubian Zone. Kinematic data of brittle normal faults and tension gashes are consistent with NW–SE-oriented extension under cooler conditions.  相似文献   

10.
This paper examines the morphotectonic and structural–geological characteristics of the Quaternary Martana Fault in the Umbria–Marche Apennines fold‐and‐thrust belt. This structure is more than 30 km long and comprises two segments: a N–NNW‐trending longer segment and a 100°N‐trending segment. After developing as a normal fault in Early Pleistocene times, the N–NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE–ENE‐trending σ3 axis and NW–NNW σ1 axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N–NNW‐trending fault segments and almost pure normal faulting on newly formed NW–SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left‐lateral kinematic along N–NNW‐trending fault segments is also revealed by the 1.8 m horizontal offset of the E–W‐trending Decumanus road, at the Roman town of Carsulae. We interpret the present‐day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred north‐northwest trending lithospheric shear zone marking the western boundary of the Adria Plate. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

11.
丁宝林 《矿产与地质》2006,20(2):138-141,159
双旗山金矿床的矿体主要受断裂构造控制,按控矿断裂构造的形态、产状及其力学性质,将控矿断裂分为四类,即NW向压扭性断裂、NE向扭性断裂、近SN向或NNE向剪切带和NWW向张性或张扭性断裂.受NW向断裂控制的金矿化属片岩＋石英脉型金矿化;受近SN向或NNE向剪切带控制的金矿化属蚀变岩型金矿化.  相似文献   

12.
The Rhodope Metamorphic Province represents the core of an Alpine orogen affected by strong syn- and postorogenic extension. We report evidence for multiple phases of extensional unroofing from the western border of the Rila Mountains in the lower Rila valley, SW Bulgaria. The most prominent structure is the Rila-Pastra Normal Fault (RPNF), a major extensional fault and shear zone of Eocene to Early Oligocene age. The fault zone includes, from base to top, mylonites, ultramylonites and cataclasites, indicating deformation under progressively decreasing temperature, from amphibolite-facies to low-temperature brittle deformation. It strikes E–W with a top-to-the-N-to NW-directed sense of shear. Basement rocks in the hanging wall and footwall both display amphibolite-facies conditions. The foliation of the hanging-wall gneisses, however, is discordantly cut by the fault, while the foliation of the footwall gneisses is seen to curve into parallelism with the fault when approaching it. Two ductile splays of the RPNF occur in the footwall, which are subparallel to the foliation of the surrounding gneisses and merge laterally into the mylonites of the main fault zone. The concordance between the foliation in the footwall and the RPNF suggests that deformation and cooling in the footwall occurred simultaneously with extensional shearing, while the hanging-wall gneisses had already been exhumed previously. The RPNF is associated with thick deposits of an Early Oligocene, syntectonic breccia on top of its hanging wall. Integrating our results with previous studies, we distinguish the following stages of extensional faulting: (1) Late Cretaceous NW–SE extension (Gabrov Dol Detachment), exhumation of the present day hanging wall of the RPNF; (2) Eocene to Early Oligocene NW–SE to N–S extension (RPNF); (3) Miocene to Pliocene E–W extension (Western Border Fault), formation of the Djerman Graben; (4) Holocene to recent N–S to NW–SE extension (Stob Fault), reactivating the SW part of the Western Border Fault.  相似文献   

13.
This study assesses the significance, geometry, and kinematics of greenschist-facies deformation along the Dent Blanche Basal Thrust (DBBT), a major tectonic contact in the Internal Western Alps of Switzerland and Italy. The DBBT separates continental units of the Dent Blanche nappe, the structurally highest unit in the Western Alps, from underlying Piemont-Ligurian ophiolites. Mylonites and deformation structures along the contact provide a record of its retrograde greenschist-facies evolution after earlier high-pressure metamorphism. A first phase of foreland-directed, reverse-sense, top-(N)W shearing (D1) occurred between ca. 43 and 39 Ma, related to exhumation of the Dent Blanche nappe from high-pressure conditions. It led to the formation of mylonitic fabrics under high- to medium-grade greenschist-facies conditions along the entire DBBT. A phase of ductile normal-sense top-SE shearing (D2) at ca. 38–37 Ma was mainly localized within underlying ophiolitic units and only partly affected the DBBT. Another phase of ductile deformation (D3) under medium- to low-grade greenschist-facies conditions at ca. 36–35 Ma occurred in response to underthrusting of European continental margin units and resulted in the updoming of the nappe stack. Especially the southeastern DBBT was characterized by bulk top-NW shearing, partly conjugate top-NW/top-SE shearing, and resulting orogen-perpendicular crustal extension. Subsequently, the DBBT was affected by a phase of orogen-perpendicular shortening (D4) and formation of folds and crenulations at ca. 34–33 Ma due to increasing compressional tectonics. Finally, a phase of semi-ductile to brittle normal-sense top-NW and conjugate shearing (D5) from ca. 32 Ma onwards particularly affected the southeastern segment and indicates exhumation of the DBBT through the ductile–brittle transition. This was followed by brittle NW–SE extensional deformation. This study suggests that the DBBT experienced a polyphase deformation and reactivation history under decreasing greenschist-facies metamorphic conditions during which different segments of this major shear zone were variably affected.  相似文献   

14.
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15.
Amphibolite-grade quartzofeldspathic gneiss domes surrounded by greenschist-grade island arc and ophiolitic assemblages is a characteristic feature of the Arabian–Nubian Shield in the Eastern Desert of Egypt. The mode of formation of these domes, including the Meatiq Gneiss Dome, is controversial, as is the protolith age of these gneisses. Reinvestigation of selected segments of the Eastern Desert Shear Zone (EDSZ), a high-strain zone separating the eugeoclinal units from the underlying quartzofeldspathic gneisses show it to be a top-to-the NW shear zone which was later folded about a NW–SE trending fold axis (long axis of the gneiss dome). Kinematic indicators (shear bands, duplex structures, etc.) along the north-eastern and south-western flanks of the dome therefore show apparent left-lateral and right-lateral strike-slip displacement across the EDSZ. These observations are in conflict with most previous tectonic models which link formation of the dome to extension in a NW–SE oriented corridor bordered by two sub-parallel left-lateral NW–SE oriented strike-slip faults. Emplacement of upper crustal, low-grade, eugeoclinal rocks tectonically on top of middle crustal amphibolite-grade quartzofeldspathic gneisses indicates that the EDSZ may represents an extensional fault with a possible break-away zone in the southern part of the Eastern Desert. Alternatively it can be explained as the result of two (or more) tectonometamorphic events with an intervening episode of erosion and exhumation of high grade rocks prior to emplacement of the eugeoclinal thrust complex. Recent U–Pb TIMS ages on syntectonic orthogneisses and post-tectonic granites in the area show that shearing and subsequent doming must be younger than 630 Ma, possibly as young as 600 Ma.  相似文献   

16.
There is a cross-cutting relationship between the E-W trending structures and the NE-trending structures in the northern Longmen-Micang Mountains region,which reflects possible regional tectonic transi...  相似文献   

17.
Age calibrated deformation histories established by detailed mapping and dating of key magmatic time markers are correlated across all tectono-metamorphic provinces in the Damara Orogenic System.Correlations across structural belts result in an internally consistent deformation framework with evidence of stress field rotations with similar timing,and switches between different deformation events.Horizontal principle compressive stress rotated clockwise ~180°in total during Kaoko Belt evolution,and~135° during Damara Belt evolution.At most stages,stress field variation is progressive and can be attributed to events within the Damara Orogenic System,caused by changes in relative trajectories of the interacting Rio De La Plata,Congo,and Kalahari Cratons.Kaokoan orogenesis occurred earliest and evolved from collision and obduction at ~590 Ma,involving E-W directed shortening,progressing through different transpressional states with ~45° rotation of the stress field to strike-slip shear under NW-SE shortening at ~550-530 Ma.Damaran orogenesis evolved from collision at ~555-550 Ma with NW-SE directed shortening in common with the Kaoko Belt,and subsequently evolved through ~90°rotation of the stress field to NE-SW shortening at ~512-508 Ma.Both Kaoko and Damara orogenic fronts were operating at the same time,with all three cratons being coaxially convergent during the 550-530 Ma period;Rio De La Plata directed SE against the Congo Craton margin,and both together over-riding the Kalahari Craton margin also towards the SE.Progressive stress field rotation was punctuated by rapid and significant switches at ~530-525 Ma,~508 Ma and ~505 Ma.These three events included:(1)Culmination of main phase orogenesis in the Damara Belt,coinciding with maximum burial and peak metamorphism at 530-525 Ma.This occurred at the same time as termination of transpression and initiation of transtensional reactivation of shear zones in the Kaoko Belt.Principle compressive stress switched from NW-SE to NNW-SSE shortening in both Kaoko and Damara Belts at this time.This marks the start of Congo-Kalahari stress field overwhelming the waning Rio De La Plata-Congo stress field,and from this time forward contraction across the Damara Belt generated the stress field governing subsequent low-strain events in the Kaoko Belt.(2)A sudden switch to E-W directed shortening at ~508 Ma is interpreted as a far-field effect imposed on the Damara Orogenic System,most plausibly from arc obduction along the orogenic margin of Gondwana(Ross-Delamerian Orogen).(3)This imposed stress field established a N-S extension direction exploited by decompression melts,switch to vertical shortening,and triggered gravitational collapse and extension of the thermally weakened hot orogen core at ~505 Ma,producing an extensional metamorphic core complex across the Central Zone.  相似文献   

18.
A similar succession of Foliation Inflection/Intersection Axis (FIAs) trends preserved within porphyroblasts is present in two areas separated by 200 km along the Rocky Mountains. The Precambrian rocks in Central Colorado and Northern New Mexico were affected by deformation and metamorphism from ～1506 to 1366 Ma. A succession of five FIAs trending W–E, SSW–NNE, NNW–SSE, NW–SE and WSW–ENE is distinguished in Central Colorado and dated at 1506 ± 15 Ma, 1467 ± 23 Ma, 1425 ± 18 Ma, not dated and 1366 ± 20 Ma respectively. To the south in Northern New Mexico, a succession of five FIAs trending SSW–NNE, WNW–ESE, NNW–SSE, NW–SE and WSW–ENE is distinguished and dated at 1482 ± 48 Ma, 1448 ± 12 Ma, 1422 ± 35 Ma, not dated and 1394 ± 22 Ma. The excellent correlation of the sequence of FIA trends and their ages between regions reveals a sixfold‐FIA succession across the region with the first developed FIA set in Central Colorado not present in Northern New Mexico and the third FIA set in the region not present in Central Colorado. Preferential partitioning of W–E trending deformation into the Central Colorado region ～1506 ± 15 Ma was followed by SSW–NNE trending deformation that affected both regions at 1470 ± 20 Ma. However, preferential partitioning of WNW–ESE trending deformation into Northern New Mexico at 1448 ± 12 Ma left Central Colorado unaffected. Both regions were then affected by the three remaining periods of orogenesis, the first trending NNW–SSE at 1424 ± 15 Ma followed by one trending NW–SE that has not yet been dated, and then one trending WSW–ENE at 1390 ± 19 Ma. This suggests that the Yavapai terrane was tectonized at ～1506 Ma, prior to amalgamation with the Mazatzal terrane ～1470 Ma. Subsequent orogenesis was initially partitioned preferentially into the Mazatzal terrane, but the following three periods of tectonism affected both terranes in a similar manner.  相似文献   

19.
The Hamisana shear zone (HSZ), is an excellent example of high strain shear belt of the Neoproterozoic Arabian–Nubian Shield (ANS), situated in a position between three major Pan-African terranes (SE Desert, Gabgaba, and Gebeit terranes). The north Hamisana shear zone area (NHSZ), cuts across sequences of island arc-related metasediment-metavolcanic, which are structurally overlain by ophiolitic nappes and intruded by a number of granitoids and gabbroic rocks. Although it is interesting geological-tectonic setting for base metal sulfide and gold ores, there is a lack of detailed studies on structure, geology and mineralization in this area, which considered as poorly mapped remote region not only in Egypt but also in Sudan.For these reasons, we integrated image transformation methods include; Principal Components Analysis (PCA), Band Ratios (BR), False-Color Composite (FCC) and filtering on the spectral bands of two distinct datasets ETM + and ASTER for detailed mapping of the NHSZ area. Spectral data fusion with structural data analysis and field observations provide a better understand of the temporal and spatial relationships between the litho-tectonic units and regional tectonic setting in the course of controls on base-metal sulfide and associated gold mineralization. Merging these different data sources in the study area suggests that, the base-metal sulfide and associated gold mineralization are restricted to quartzites, (member of island arc-related metasediments), and mostly controlled by D3 deformational event (main HSZ deformational event). This event characterized by transpressional stress regime, with σ1 trending E–W and σ3 trending N–S, activated conjugate NNW sinistral and NNE–SSW dextral strike-slip faulting, likely during syn-tectonic granodiorite emplacement.  相似文献   

20.
《Geodinamica Acta》2003,16(2-6):131-147
Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE–SW, E–W and NW–SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N–S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE–SW in the graben. After a transitional minor E–W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE–SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE–SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.  相似文献   

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