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1.
Prof. Dr. Ernst Cloos 《International Journal of Earth Sciences》1965,54(2):812-834
Our knowledge of the Appalachians has grown very satisfoctorily during the last ten years. Folding took place at least twice: 1. In the Ordovician the basement including the crystalline axis as far as the Blue Ridge became consolidated. This region became highland and furnished the material for upper Ordovician to Carboniferous sediments. This has been established by three methods: first, facies examinations; second,Pettijohn and his students found that sediments were transported from East to West during the upper Ordovician, Silurian, Devonian, and Carboniferous periods; and finallyHopson has summarized absolute age determinations which show that the basement, (Cambrian, and lower Ordovician rocks included) were consolidated and uplifted about 440 million years ago. Thus, in the first period of folding the Blue Ridge Zone, which is the western margin of the basement complex, was uplifted and crowded westward. Cambrian and Ordovician sediments which cover the basement as a thin layer were folded simultaneously. Folding intensity decreases from East to West and regional cleavage and lineation disappear at the “tectonite Front”. 2. The upper part of the Paleozoic column was folded during Appalachian orogeny presumably near the surface and with little or no influence by the basement. Maybe both the Foreland and the folded Appalachians “crept” over the basement forming sharply marked anticlinal axes and broad synclinal troughs. However,Cooper supposes that the basement took part through vertical movements and in this way was partly responsible for sedimentation and possibly also for structures. In the Maryland profile lateral reduction is less than further south where folds grade into nappe-like overthrusts and the foothill folds disappear below great horizontal thrusts. 相似文献
2.
根据天然气热发光、微量元素、微体古生物等资料的对比,二连盆地可划分为南北两个拗陷体系。二连-贺根山岩石圈断裂和西拉木伦岩石圈断裂对拗陷体系的形成起着重要作用,拗陷的形态、延伸均依附于此两断裂。南北带的油源同属下白垩统,但成熟度不同,南带有上二叠统油混入的可能。上二叠统或古生界地层的油源是不容忽视的。因为历史事件(岩浆活动和变质作用等)的不平衡发展是地槽褶皱带的普遍规律。在古生界找油有其重要的现实意义。 相似文献
3.
本文通过对中国东部海域地质地球物理资料进行综合分析,特别是近十年来海洋区域地质调查最新采集的地球物理资料,梳理了研究区基础地质特征,探讨了陆区大地构造单元在海区的延伸。研究表明:渤海和北黄海为典型的华北型基底并发育华北型沉积盖层;南黄海为典型的扬子型基底并发育扬子型沉积盖层;东海陆架为华夏型基底,东部很可能发育晚古生代沉积盖层,其上叠置了晚三叠世以来沉积盖层。下扬子地块西侧通过左旋走滑的郯庐断裂带,东侧通过右旋走滑的朝鲜西缘断裂带揳入华北地块中,朝鲜西缘断裂带兼具走滑和俯冲带性质。整个朝鲜半岛无论从变质基底和沉积盖层来看都类似于华北地块。扬子地块在北侧和东侧都发育“鳄鱼嘴”式构造,扬子地块的下地壳向北、向东俯冲于华北地块之下,而上地壳则仰冲于华北地块之上。江绍结合带表现为宽50~70 km的NE向高磁异常条带,进入杭州湾后走向转为近EW向,经舟山群岛、大衢山岛及附近岛屿,过东海陆架虎皮礁凸起向东进入日本九州岛。虎皮礁凸起的岩石很可能类似于大衢山岛,为一套俯冲增生杂岩。 相似文献
4.
位于华北克拉通中部的吕梁山的形成代表了华北克拉通在晚侏罗世-早白垩世的挤压变形事件,为了更好地理解该期变形的样式、时代、机制和背景,对吕梁山地区开展了详细的野外调查,同时搜集了前人的低温热年代学工作.结果表明,吕梁山是一个中生代期间形成的发育有典型单褶（monocline）构造的陆内基底卷入型大型褶皱系统.早前寒武纪造山作用在基底中形成早期面理（片麻理、片理、劈理以及节理）,这些面理在后期近东西向挤压作用下再次活动形成了基底断裂,并导致了上覆沉积地层褶皱变形,吕梁山不同地区褶皱的古应力场方向总体为SE（122°）~NW（302°）.吕梁山单褶构造的构造样式、形成机制以及分布,与北美西部的Laramide造山带中的厚皮构造相似,形成的构造环境也类似.吕梁山褶皱及其单褶构造总体形成于晚侏罗世期间古太平洋板块向西低角度俯冲的环境中,该期俯冲也导致了华北克拉通同期陆内挤压变形. 相似文献
5.
Mohammed Warrak 《Arabian Journal of Geosciences》2010,3(4):369-393
At the western end of the Hatta Zone (the Jebel Rawdha area), Northern Oman Mountains, the neoautochthonous Late Cretaceous–Early Tertiary sequence (“cover”) lies with an angular unconformity on the obducted Semail ophiolite, Haybi Complex and Sumeini Group (“basement”). Structural analysis of the faults in both the basement and cover sequences has shown that they are similar in type and configuration to those that develop in a transpressional left-lateral strike-slip deformational regime (a restraining bend) that is characterised by the dominance of the dip-slip component over the strike-slip component. The WNW–ESE (Po) faults together with the linking NW–SE (P) faults have divided the basement into elongated blocks. These blocks, in turn, are subdivided by transverse normal faults into horst and graben sub-blocks. The cover sequence is gently folded into a generally WNW–ESE-trending ‘Main’ folds and NE–SW-trending ‘Cross’ folds superimposed on them. These folds appear to be dominantly forced folds that developed as a result of repeated uplift and depression of basement blocks. Their trends correspond to the trends of the subjacent basement blocks. Hence, the Jebel Rawdha folds trend differently from other post-obduction major folds in the foreland region of the Northern Oman Mountains, such as the Hafit and Jebel Faiyah folds. Differences in stratigraphic thicknesses and lateral facies changes of the cover sequence within the blocks and sub-blocks indicate that the earliest differential movement of the blocks must have occurred during the early Maastrichtian, and the latest movement in post-mid-Eocene. Thus, pushing back the initiation of the post-obduction deformation in the Northern Oman Mountains to the early Maastrichtian. 相似文献
6.
D. Bannert J. Brinckmann K. -Ch. Käding G. Knetsch M. KÜrsten H. Mayrhofer 《International Journal of Earth Sciences》1970,59(2):409-443
Geological and geophysical investigations in the Northern part of Afar-Region were carried out by a group of scientists in 1967 and 1968. The Afar-structure is framed by the Ethiopian Highland in the West, the Somali Plateau in the South and the Danakil horst in the E. Its northern part is occupied by the NNW trending Danakil Depression (Danakil Graben), a branch of the NW trending Red Sea-Graben. The block mosaic border land in the West as well as the Danakil Alps consist of basement overlain by unfolded Mesozoic strata. Within the Afar Depression the pre-Tertiary formations are covered by limnic-fluviatile — in upper portions marine — sediments, Miocene and Pliocene in age, thickening towards the centre of the Depression. These basin fillings indicate a major phase of rift faulting prior to and during their deposition. Marginal extensions of these “Danakil-Formation” on both flanks of the Depression accompany the structural borders of the Danakil Graben, coinciding with the “outer rift structural margin” (Mohr 1967). Evaporites occupy the deepest part of the structure, “the inner Danakil Graben”, downfaulted or opened by major rift movements during Pliocene. A NW trending fault zone cutting through the flat plain north of Dallol covered by gypsum beds, seems to form the Eastern margin of the inner Danakil Graben. In its southeastern prolongation the fault and fissure system of the Amarti Volcanic Range is situated. Still active rift faulting during Quaternary caused the present topographic form of the region. These movements were followed by a marine ingression. Its sediments (Zariga-Formation, 14 C Modell ages 25 000–34 000 y) ring the depression and pass into gypsum beds towards the centre of the basin. The deepest parts of the Depression are hidden beneath the Afrera-Formation (14 C Modell ages 5800 y) framing the Lake Assale/Bakili and the Lake Afrera (soft limestones, clay and gypsum beds). The rift-forming movements in the northern Afar were accompanied by strong volcanic activity. Besides different igneous rocks intruding the pre-Tertiary and Tertiary strata of the rift margin, extensive basaltic lava flows intercalate and locally underly the Danakil-Formation. Potassium-argon age determinations on these “Afar Basalts” yielded Miocene to Pliocene age. In the southern area of the Danakil Graben the Upper Tertiary sedimentary basin fillings are replaced by “Afar Basalts” (plateau-forming flood basalt) flows. They are succeeded by scoriaceous fissure alkali-olivine-basalts and their differentiated lavas forming huge volcanoes aligned parallel to the rift structures. The Central Volcanic Range (Erta Ale volcanic chain) marking the central part of the Danakil Graben, remains active today. Besides the basaltic activity, numerous huge volcanoes display rhyolitic rocks with strong alkaline affinity. 相似文献
7.
龙门山断裂带以东、江南雪峰隆起带以西的华南地区，在断裂、褶皱变形等构造形迹上存在非常规律的有序性。其构造形迹（断裂、褶皱等）大都沿NE－NNE排列，并且变形强度从SE向NW逐渐减弱。这种有序变形规模巨大，仅川东的隔挡式褶皱－冲断带规模就超过了著名的侏罗山式褶皱。这种变形的有序性是与基底存在多层次的倾向SE的拆离滑脱面密切相关的，它们起始于印支－早燕山期，定型于晚燕山－喜马拉雅期，其形成动力来自于华南板块向NW方向的运动。 相似文献
8.
《International Geology Review》2012,54(3):367-381
The Asturian Arc was produced in the Early Permian by a large E–W dextral strike–slip fault (North Iberian Megashear) which affected the Cantabrian and Palentian zones of the northeastern Iberian Massif. These two zones had previously been juxtaposed by an earlier Kasimovian NW–SE sinistral strike–slip fault (Covadonga Fault). The occurrence of multiple successive vertical fault sets in this area favoured its rotation around a vertical axis (mille-feuille effect). Along with other parallel faults, the Covadonga Fault became the western margin of a proto-Tethys marine basin, which was filled with turbidities and shallow coal-basin successions of Kasimovian and Gzhelian ages. The Covadonga Fault also displaced the West Asturian Leonese Zone to the northwest, dragging along part of the Cantabrian Zone (the Picos de Europa Unit) and emplacing a largely pelitic succession (Palentian Zone) in what would become the Asturian Arc core. The Picos de Europa Unit was later thrust over the Palentian Zone during clockwise rotation. In late Gzhelian time, two large E–W dextral strike–slip faults developed along the North Iberian Margin (North Iberian Megashear) and south of the Pyrenean Axial Zone (South Pyrenean Fault). The block south of the North Iberian Megashear and the South Pyrenean Fault was bent into a concave, E-facing shape prior to the Late Permian until both arms of the formerly NW–SE-trending Palaeozoic orogen became oriented E–W (in present-day coordinates). Arc rotation caused detachment in the upper crust of the Cantabrian Zone, and the basement Covadonga Fault was later resurrected along the original fault line as a clonic fault (the Ventaniella Fault) after the Arc was completed. Various oblique extensional NW–SE lineaments opened along the North Iberian Megashear due to dextral fault activity, during which numerous granitic bodies intruded and were later bent during arc formation. Palaeomagnetic data indicate that remagnetization episodes might be associated with thermal fluid circulation during faulting. Finally, it is concluded that the two types of late Palaeozoic–Early Permian orogenic evolution existed in the northeastern tip of the Iberian Massif: the first was a shear-and-thrust-dominated tectonic episode from the Late Devonian to the late Moscovian (Variscan Orogeny); it was followed by a fault-dominated, rotational tectonic episode from the early Kasimovian to the Middle Permian (Alleghenian Orogeny). The Alleghenian deformation was active throughout a broad E–W-directed shear zone between the North Iberian Megashear and the South Pyrenean Fault, which created the basement of the Pyrenean and Alpine belts. The southern European area may then be considered as having been built by dispersal of blocks previously separated by NW–SE sinistral megashears and faults of early Stephanian (Kasimovian) age, later cut by E–W Early Permian megashears, faults, and associated pull-apart basins. 相似文献
9.
Prof. Dr. M. Roubault Dr. H. de la Roche 《International Journal of Earth Sciences》1966,55(2):301-316
The granitic “Lys-Caillaouas” Massive outcrops on 50 km2 in the paleozoic series of the axial zone, situated in the North West of the Maladetta. It is known for its apparent stratified formations, emphasized by pelitic (Northern and French part of the Massive) and calcareous (Southern and Spanish part) enclaves. Its “emplacement” by syncinematic intrusion of a “granite magma” was formerly postulated with reference to the then wide-spread theory of magmas and “magmatical phases” of orogeneses. However care had not been taken to examine if this scheme would take into account the particular features of this Massive as they appear through a detailed study. Starting from entirely different points of view, the authors do not think it permissible, as a method of thinking, to consider a priori the granite as extraneous to the formations in which it crops out. For this reason, starting with the mainly structural observations of M.Clin (1959), which were completed by recent mapping done by a geological group of Nancy, they have undertaken in the “Lys-Caillaouas” massive and in its vicinity, a comparative geochemical study of the paleozoic basement of the axial zone and of the igneous formations therein enclosed. These different igneous facies, from porphyroblastic granites to quartz diorite, countain enclaves, some of them mainly pelitic and others calcareous. Besides these facies are arranged in sequences and in folded structures well related to those of the paleozoic host formation. These two facts clearly show:
- -the sedimentary origin of the most apparent differenciations of the igneous complex.
- -the “keeping in place“ of sedimentary horizons during the granitization which is an observed fact and not a hypothesis as is the case with the “emplacement” of granites.
10.
在前人研究成果和野外地质调查的基础上,系统研究了东天山南北两侧（准噶尔东缘和吐哈北缘）早二叠世沉积序列、岩相组合、古流向及盆地演化。研究表明,早二叠世准噶尔盆地东缘石人子沟组和塔什库拉组发育枕状玄武岩、流纹岩等双峰式火山岩建造和海相砂、泥质及碳酸盐岩复理石相沉积,并含有大量的海相生物化石,指示了海相裂谷盆地环境。吐哈北缘发育依尔希土组,以安山岩、流纹质火山岩及火山碎屑岩夹陆相碎屑岩为主,表现为陆相裂谷盆地环境。东天山南北两侧古流向及物源显示,东天山北侧,早二叠世古水流指向东南方向,在其南侧古水流指向西北部凹陷区,并且物源主要来自下伏前二叠纪岩石建造,表明早二叠世时期东天山博格达地区为汇水沉积区,且由东至西分别发育陆相和海相裂谷盆地,至早二叠世末期整体演化为陆相坳陷盆地。而导致东天山南北两侧早二叠世沉积环境迥异的原因是,石炭纪博格达裂谷东段祁家沟-天池地区和西段吐哈北缘地区演化的差异,造成随后的闭合阶段中东段早闭合、沉积环境“突变”,西段晚闭合和沉积环境“渐变”的不同过程。 相似文献
11.
中国北方磷矿成矿特征及找矿潜力 总被引：1，自引：0，他引：1
中国北方磷矿在华北、东北以岩浆岩型磷矿和海相沉积型磷矿为主 ,在西北则以海相沉积型磷矿为主。海相沉积型磷块岩矿床主要形成于早寒武世 ,受南面和西面海水侵入影响最大、侵入距离最近的已知含磷地区可作为磷块岩矿床重点研究靶区 ;岩浆岩型磷灰石矿床所赋存的岩体类型比较多 ,但矿床规模较大 ,品位较高 ,具有较大的找矿潜力的磷灰石矿床产于超基性碱性碳酸岩杂岩体中 ,这类杂岩体在我国北方有一定的分布 ,对其做详细工作 ,可望找到规模大、品位高的磷灰石矿床 相似文献
12.
江西赣中新余铁矿是我国重要的铁矿类型之一,产于震旦纪火山-沉积浅变质岩系硅铁建造中。铁矿体普遍呈现"红绸带"式形态,前人认为是多期次褶皱叠加的结果。本文通过野外调查,在整个铁矿区发现,区域透入性的拉伸线理、A型褶曲十分发育,局部地段甚至出现鞘褶皱;系统测量表明,区域拉伸线理、A型褶皱的脊线走向稳定在295°~320°之间,倾角一般小于25°。推测赣中铁矿经历了强烈的塑性流变,"红绸带"式铁矿体是塑性流变,而非多期褶皱叠加变形的结果;整个铁矿区的原始形态应是一个鼻端向南封闭的巨形鞘褶皱,但变形期后不均匀的构造抬升和剥蚀,导致了不同铁矿区现今地表出露了原始形态的不同部位。结合褶皱构造对铁成矿物质的控制作用和矿区的地层出露状态分析,认为大陂-陂头、寨口-太平山-良山一带皆处于鞘褶皱的前缘部位,具有寻找富大厚矿体的找矿前景,松山-杨家桥处于鞘褶皱的西翼,平剖面上都发育小型鞘褶皱和红绸带式重叠矿体,因而也具有良好的找矿前景。 相似文献
13.
This study investigates the rifting structures of Santos Basin at the Southeastern Brazilian margin, based on an integrated geophysical approach. Our aim is to constrain the crustal basement topography of central and northern Santos basin, the presence of magmatism and the role of inherited structures in space and time through the rifting processes. We present a new high resolution aeromagnetic dataset, which in correlation with gravity anomalies enables us to interpret the tectonic trends and crustal basement structures. We calculated the magnetic basement depth for the central and northern Santos Basin using power spectrum analysis. The obtained depths range between 2 and 9 kms, and are comparable with results from previous works. From our integrated study, three margin domains could be identified, which display distinct rifting structures and are characterized by important lateral variation along the margin. The proximal domain displays trends and magnetic basement blocks NE–SW oriented, i.e., parallel to inherited onshore crustal basement with an inflexion to E–W oriented trends; the necking domain is characterized by oblique magnetic basement highs and lows (E–W and NW–SE) and a structural trend change. The trends and magnetic basement highs are bounded by NW–SE negative anomalies, interpreted as transfer zones. Oceanwards at the distal domain, the lineaments and transfer zones show a progressive structural inflexion to ENE and E–W, sub-parallel to adjacent South Atlantic Fracture Zones. The observed crustal basement architecture and segmentation suggest the reactivation of pre-rift structures at the proximal margin and the obliquity of rifting relative to them. From the proximal domain oceanwards the structural pattern may reflect the passage from a “continental type” domain, where lithospheric inheritance controls the deformation, to a distal margin where this influence diminishes and “new” structural trends are formed. We propose that northern Santos Basin show evidences of an intensely deformed zone, where rift evolved under oblique extension, similar to that observed at transform margin segments. 相似文献
14.
Benjamin R. Jordan Haraldur Sigurdsson Robert Rogers 《Geochimica et cosmochimica acta》2007,71(14):3581-3591
An analysis of 70 samples, collected from Miocene-age ignimbrites in 68 locations in Nicaragua and Honduras, indicates that geochemical processes and a subduction zone geometry similar to those in the modern arc were also present in the paleoarc. Samples were plotted along two transects, parallel and perpendicular to the inferred paleoarc. Most of the oxide plots exhibit flat profiles along the arc from NW to SE, except for SiO2, which decreases. FeO, CaO, TiO2, and MgO increase from NW to SE. There are no clear trends in the oxides from SW to NE, except K2O. K2O increases to the SW. Most trace elements show little to no variation along the province from NW to SE, with the exception of La, Ce, Rb, Ba, Th, Nb, Ta, Pb, and Sr, which all appear to decrease in abundance from NW to SE. While Ba increases to the SW, toward the paleotrench, it also shows remarkable variation parallel to the arc, with highs in Nicaragua, and decreasing concentrations to the NW and SE. This trend is especially apparent in Ba/La with lows near 1 in the NW and highs approaching 80 in Nicaragua. This trend is similar to that of the modern arc, which suggests that the geometry of the arc in the Miocene was very similar to that of the modern arc. In addition, the data also becomes more scattered to the southeast as a basement boundary is crossed (determined by gravity-anomaly mapping), probably due to a higher degree of contamination by continental crust. 相似文献
15.
似新华夏式伸展盆海系的基本特征及其形成演化的力学机制 总被引：1，自引：1，他引：0
晚中生代(白垩纪)以来,中国东部及西太平洋大陆边缘发育一系列NNE、NE乃至NEE向(与纬向构造联合)的巨型右行张扭性断陷(地堑、半地堑)在平面上组成平行雁列的多字型构造,其深部发育同走向的上地幔隆起和基底拆离,地表常出现变质核杂岩和大型低缓倾角的伸展剥离断层,它主要是东亚及西太平洋大陆边缘陆缘扩张的产物,其地球动力学过程为晚燕山期以来的后造山期的大陆隆升和水平侧向伸展以及晚白垩世末一早第三纪、45Ma以来的印度板块与欧亚板块碰撞所产生的碰撞效应。 相似文献
16.
Early studies in the Rum Jungle area suggested an intrusive relationship between the Rum Jungle and Waterhouse “Granites”, and the overlying sediments. It was later shown that the granitic “intrusions” were Archaean basement complexes onto which Lower Proterozoic sediments had been deposited. Polyphase folding was postulated as being responsible for doming of the basement and cover rocks.This paper proposes to show that the domed structures in the Rum Jungle area, and the emplacement of Middle Proterozoic granites in the Pine Creek Geosyncline were related, and caused by diapiric intrusion of granites, in a solid state, into basement complexes and cover rocks.Structural and metamorphic evidence in support of diapiric intrusion in the Rum Jungle area includes: pebble deformation within steeply dipping beds of quartz conglomerate; disappearance of polyphase fold structures away from the basement complexes; bending of folded country-rock strata into concordance with the complex—sediment contact; and metamorphic and metasomatic alteration of sediments in contact with the basement complexes. Gravity data show mass deficiencies in the Archaean complexes which possibly coincide with young granite diapirs. 相似文献
17.
This work integrates stress data from Global Positioning System measurements and earthquake focal mechanism solutions, with new borehole breakout and natural fracture system data to better understand the complex interactions between the major tectonic plates in northwestern South America and to examine how the stress regime in the Eastern Cordillera and the Llanos foothills in Colombia has evolved through time. The dataset was used to generate an integrated stress map of the northern Andes and to propose a model for stress evolution in the Eastern Cordillera. In the Cordillera, the primary present-day maximum principal stress direction is WNW–ESE to NW–SE, and is in the direction of maximum shortening in the mountain range. There is also a secondary maximum principal stress direction that is E–W to ENE–WSW, which is associated with the northeastward “escape” of the North Andean block, relative to stable South America. In the Cupiagua hydrocarbon field, located in the Llanos foothills, the dominant NNE–SSW fractures are produced by the Panama arc–North Andes collision and range-normal compression. However, less well developed asymmetrical fractures oriented E–W to WSW–ENE and NNW–SSE are also present, and may be related to pre-folding stresses in the foreland basin of the Central Cordillera or to present-day shear associated with the northeastward “escape” of the north Andean block. Our study results suggest that an important driver for orogenic deformation and changes in the stress field at obliquely convergent subduction zone boundaries is the arrival of thickened crust, such as island arcs and aseismic ridges, at the trench. 相似文献
18.
Georges Busson 《International Journal of Earth Sciences》1982,71(3):857-880
- In the Earth history not a system probably comprises so many evaporites than Triassic. They are not restricted to such or such protoocean but cover huge epicontinental cratonic plateforms with very finely bedded deposits as well as they fill rifts located in very diversified geodynamic areas. The first condition in order that such deposits can exist is a severe aridity.
- Triassic corresponds to an extraordinary transgression in the sense of a new onlap of the sedimentary realm, a reconquest of ancient areas by new deposits, however their facies may be. In that general setting evaporites are themselves remarkably transgressive and from two points of view a) they sometimes onlap directly — that is to say without any basal detritic intercalation — different terms of peneplaned basement, b) these evaporites often succeed Permian emersion or continental detritic deposits of lower parts of Triassic. They extract their salts from Ocean. They often underlie pure marine Jurassic facies. For all these reasons evaporites appear as the first emissaries of oceanic realm and so as the first witnesses of a marine transgression.
- Evaporites occur in Triassic, particularly in the Middle East, North Africa, on the two present margins of North Atlantic, on Western and Northern Europe, etc. The whole constitutes a huge saline ring round the western part of Triassic Tethysian sea. In that area, on the less tectonized plateforms a grandiose facies distribution pattern appears clearly: going farther from open sea in a centrifugal way, there are salts more and more soluble, until detritic deposits from continent. The pellicular sheets of water which covered the large plateforms resulting from late permian peneplanation should be favourable to modification of chemism, very gradual and at last very total, producing a geographical distribution of salt deposits. The most probable mover of these “floods” could be a very likely multiphase rise of eustatic level, the effects of which we cannot imagine because they occured on plateforms unknown in the geography of recent world. Effects of local morphology which induced a pecular distribution of salts can modify the general plateform distribution pattern.
19.
U. Giese U. Glasmacher V. I. Kozlov I. Matenaar V. N. Puchkov L. Stroink W. Bauer S. Ladage R. Walter 《International Journal of Earth Sciences》1999,87(4):526-544
The Bashkirian anticlinorium of the southwestern Urals shows a much more complex structural architecture and tectonic evolution than previously known. Pre-Uralian Proterozoic extensional and compressional structures controlled significantly the Uralian tectonic convergence. A long-lasting Proterozoic rift process created extensional basement structures and a Riphean basin topography which influenced the formation of the western fold-and-thrust-belt with inversion structures during the Uralian deformation. A complete orogenic cycle during Cadomian times, including terrane accretion at the eastern margin of the East European platform, resulted in a high-level Cadomian basement complex, which controlled the onset of Uralian deformation, and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the Main Uralian fault. The Uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes. Tectonic convergence started in the Late Devonian with ophiolite obduction, tectonic accretion of basin and slope units and early flysch deposits (Zilair flysch). The accretionary complex prograded from the SE to the NW. Continuous NW/SE-directed convergence resulted finally in the formation of an early orogenic wedge thrusting the Cadomian basement complex onto the East European platform. The main tectonic shortening was connected with these two stages and, although not well constrained, appears to be of Late Devonian to Carboniferous age. In the Permian a final stage of E–W compression is observed throughout the SW Urals. In the west the fold-and-thrust-belt prograded to the west with reactivation of former extensional structures and minor shortening. In the east this phase was related to intense back thrusting. The East European platform was subducted beneath the Magnitogorsk magmatic arc during the Late Paleozoic collision. The thick and cold East European platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening, tectonic stacking and high strain at its eastern margin. Whereas the first orogenic wedge is of thick-skinned type with the involvement of crystalline basement, even the later west-directed wedge is not typically thin-skinned as the depth of the basal detachment appears below 15 km and the involvement of Archean basement can be assumed. 相似文献
20.
Emmanuel Ball 《Tectonophysics》1980,61(4):363-379
Brittle deformation during the latter part of the Pan-African orogeny in the Hoggar and Nigeria was characterized by a conjugate strike slip fault system, consisting of NE—SW dextral and NW—SE sinistral trending sets of faults. This system is considered to be the result of a horizontal maximum stress axis orientated E—W.In the crystalline basement, the faults have offset the N—S trending Pan-African mylonitic shear zones, and have cut the late orogenic granites (Taourirt) and ring complexes of Adrar des Iforas.In the western Hoggar, folding of the post-orogenic molassic “série pourprée” considered as Cambrian in age (Caby, 1970), is probably associated with the same stress regime. A similar fault system also affects the Phanerozoic sedimentary cover of the North-Saharian platform, the Ténéré desert, and the Djado basin. Later reactivation of this fault system by phanerozoic epeirogenic events, and recent uplift is demonstrated.The geometry of this late Pan-African brittle deformation is very consistent over a large area and may reflect the stress field operative during indentation of a “plastic” Pan-African shield, by a more rigid West-African craton. 相似文献