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1.
Analysis of the Gachsar structural sub-zone has been carried out to constrain structural evolution of the central Alborz range situated in the central Alpine Himalayan orogenic system. The sub-zone bounded by the northward-dipping Kandovan Fault to the north and the southward-dipping Taleghan Fault to the south is transversely cut by several sinistral faults. The Kandovan Fault that controls development of the Eocene rocks in its footwall from the Paleozoic–Mesozoic units in the fault hanging wall is interpreted as an inverted basin-bounding fault. Structural evidences include the presence of a thin-skinned imbricate thrust system propagated from a detachment zone that acts as a footwall shortcut thrust, development of large synclines in the fault footwall as well as back thrusts and pop-up structures on the fault hanging wall. Kinematics of the inverted Kandovan Fault and its accompanying structures constrain the N–S shortening direction proposed for the Alborz range until Late Miocene. The transverse sinistral faults that are in acute angle of 15° to a major magnetic lineament, which represents a basement fault, are interpreted to develop as synthetic Riedel shears on the cover sequences during reactivation of the basement fault. This overprinting of the transverse faults on the earlier inverted extensional fault occurs since the Late Miocene when the south Caspian basin block attained a SSW movement relative to the central Iran. Therefore, recent deformation in the range is a result of the basement transverse-fault reactivation.  相似文献   

2.
Active faults in the Zagros and central Iran   总被引：1，自引：0，他引：1  
Active tectonic movements in the northwestern Zagros include right lateral slip at the rate of about 10 mm/a along the Main Recent Fault, which inherits the position of the Main Thrust, now inactive, and active thrusting and accompanying folding distributed between several zones southwest of the Main Recent Fault. In the southeastern Zagros (the Fars Province), there are several right lateral faults that extend N–S obliquely to the overall trend of the Zagros fault-and-fold belt. These may be either branches of the Main Recent Fault, or faults accommodating relative broadening of the outer Zagros in its southeastern segment. The Main Thrust in the southeastern Zagros also remains inactive.

The Ipak, North Tehran, and Mosha fault zones and several minor structures in the eastern Alborz form the E–W-trending active fault system with combined reverse and left lateral slip. On the Ipak and Mosha zones, lateral movements with the late Quaternary mean rate exceeding 1 mm/a dominate over vertical fault movements. Together with right lateral faults stretching northeast of Zagros, the faults of the Alborz may accommodate east-directed motion of the Iranian microplate.  相似文献   


3.
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   

4.
Eurasia has largely grown to its present enormous size through episodic addition of crustal blocks by recurring birth and demise of oceans such as Paleotethys and Neotethys. Excluding the Kopet Dagh Mountains in the northeast, crystalline basement rocks of various dimensions are exposed in all continental tectonic zones of Iran. These rocks have traditionally been viewed as continental fragments with Gondwanan affinity and summarily been assigned Precambrian or younger ages, despite the fact that evidence from isotopic dating has largely been lacking. This study presents new ion microprobe and thermal-ionization zircon U-Pb geochronological data from granitoids and orthogneisses from several locations in central Iran and the Sanandaj–Sirjan structural zones to determine crystallization ages and investigate the origin and continental affinity of these various crustal fragments. The resulting U-Pb crystallization ages for the granites and orthogneisses range from late Neoproterozoic to Early Cambrian, matching the mostly juvenile Arabian–Nubian shield and Peri-Gondwanan terranes constructed after the main phase of Pan-African orogenesis. TIMS analyses of zircons with inherited cores from western Iran suggest that the Neoproterozoic crust of Iran might not be entirely juvenile, pointing to the potential presence of inherited older Proterozoic components as is common in the eastern Arabian shield. More importantly, the new zircon U-Pb crystallization ages unequivocally demonstrate that crystalline basement underlying the Sanandaj–Sirjan zone, central Iran, and the Alborz Mountains is composed of continental fragments with Gondwanan affiliation, characterized by wide spread late Neoproterozoic subduction-related magmatism. The exposure of these late Neoproterozoic–Early Cambrian basement rocks in the Iranian regions north of the Zagros is structurally controlled and linked to both large-scale crustal extension and exhumation during Mesozoic and Tertiary time as well as Tertiary collisional tectonics associated with the closure of Neotethys.  相似文献   

5.
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   

6.
The article describes the characteristics of the Yagan metamorphic core complex, especially the associated detachment fault and various extensional structures in its footwall. The age of the complex is discussed in some detail as well. The basic features of the Yagan metamorphic complex (Jurassic in age) are similar to those of the metamorphic core complex (Tertiary in age) in the Cordilleran area; they are as follows: (a) mylonitic gneisses in the footwall, (b) chloritized sheared mylonitic rocks, (c) pseudotachylites and flinty cataclasites or microbreccias, (d) unmetamorphosed or epimetamorphic rocks in the hanging wall with a layer of fault gouges or incohesive fault breccia next to the detachment fault. In contrast to its Cordilleran counterpart, however, there are many extensional faults with different styles (from dactile low-angle normal faults through brittle-ductile to brittle high-angle normal faults)in the footwall.  相似文献   

7.
On the basis of the previous regional geological survey, based on the macroscopic and microscopic structural survey, combined with the comprehensive analysis of the regional magmatic activity and dating data, the authors in this paper revealed that there is another metamorphic core complex structure in Lizifang area of Southern Liaoning, namely Lizifang metamorphic core complex. A typical three-layer structure and five parts exist in the core complex, which are the footwall composed of Neo-archean metamorphic plutonic rocks and mesozoic granite intrusive rocks, the detachment fault zone composed of different levels of tectonic rocks, and the upper plate composed of Precambrian sedimentary cap and Cretaceous extensional basin. Lizifang metamorphic core complex formed in the Early Cretaceous Epoch, and the upper plate moved from NWW to SEE relaive to the footwall, which was similar with Jinzhou metamorphic core complex and Wanfu metamorphic core complex in geometry, kinematics polarity and formation time, indicating the same dynamic background. The determination of the metamorphic core complex may provide a basis for the late Mesozoic lithospheric thinning process and the mechanical and rheological properties of the lithosphere in the east of North China Craton. At the same time, the metamorphic core complex is closely related to the mineralization of gold deposits. So the detachment fault zone of Lizifang metamorphic core complex can serve as the key work area for further gold exploration, which may possess large mineralization potential.  相似文献   

8.
在区域地质调查资料基础上,根据宏观与微观构造测量,通过分析区域岩浆活动性及其测年资料等,揭示了在辽南庄河栗子房地区存在另一个变质核杂岩构造,即栗子房变质核杂岩。该核杂岩具有3层结构和5个部分,即由新太古代变质深成岩及中生代花岗岩侵入体构成的下盘、由不同层次的构造岩组成的中部拆离断层带以及由前寒武纪沉积盖层和白垩纪伸展盆地构成的上盘。栗子房变质核杂岩形成于早白垩世,运动方向为上盘相对下盘由NWW向SEE方向运动,与辽南金州变质核杂岩和万福变质核杂岩在几何学、运动学极性和形成时间等方面具有很多相似性,形成于同一动力学背景。该变质核杂岩的厘定可为阐明华北克拉通东部晚中生代岩石圈减薄过程及岩石圈的力学和流变学属性提供依据。同时,变质核杂岩与金矿床成矿关系密切,栗子房变质核杂岩的拆离断层带附近可作为下一步金矿勘查的重点工作区,成矿潜力较大。  相似文献   

9.
Abstract The article describes the characteristics of the Yagan metamorphic core complex, especially the associated detachment fault and various extensional structures in its footwall. The age of the complex is discussed in some detail as well. The basic features of the Yagan metamorphic complex (Jurassic in age) are similar to those of the metamorphic core complex (Tertiary in age) in the Cordilleran area; they are as follows: (a) mylonitic gneisses in the footwall, (b) chloritized sheared mylonitic rocks, (c) pseudotachylites and flinty cataclasites or microbreccias, (d) unmetamorphosed or epimetamorphic rocks in the hanging wall with a layer of fault gouges or incohesive fault breccia next to the detachment fault. In contrast to its Cordilleran counterpart, however, there are many extensional faults with different styles (from dactile low-angle normal faults through brittle — ductile to brittle high — angle normal faults) in the footwall.  相似文献   

10.
A number of Variscan nappe complexes were recognized in the Late Mesozoic structure of the Front Range Zone of the Greater Caucasus in the 1970s. They consist predominantly of greenstone units and override one another in a consecutive order. The only exception is the upper, Atsgara Nappe, which is composed of crystalline schists, amphibolites, and microgneisses. Crystalline schists, gneisses, amphibolites, and other rocks of the so-called Blyb Complex occur at the base of the nappe packet. The affinity of crystalline rocks of the Blyb Complex to one of the upper Variscan nappes is substantiated in this paper. The Middle Paleozoic rocks, which originally were located below the Blyb Complex in the Front Range structure, overrode its rocks along the surface of the Blyb Thrust Fault in the Early Triassic. Since that time, the crystalline rocks of the Blyb Complex have occupied the lowermost position in the structure of the Front Range. The absence of Upper Paleozoic rocks in the footwall of the thrust fault is due to the fact that, in the Late Paleozoic, the area underlain by the Blyb Complex was an inlier and a source of clastic material. The hanging wall of the Blyb Thrust Fault may be traced farther southward into the Main Range Zone, where it most likely consists of the Laba Group and other rocks. As has been established previously, the lower portion of the Laba Group consists of analogues of the Middle Paleozoic successions of the Front Range Zone, while its upper portion consists of crystalline schists of the Lashtrak Nappe, which occupy a position similar to that of the Atsgara Nappe metamorphic rocks. These relationships suggest that the rock complexes of the Front Range Zone could have undergone repeated displacements due to post-Variscan (Indosinian) tectonic events and overrode crystalline rocks in the Main Range Zone and more easterly areas. Owing to the uplift of the Central Caucasus, they are now eroding. The difference in the metamorphic grade of the Blyb Complex and the rocks of the Atsgara and Marukha nappes is due to the fact the Blyb Complex lies close to the root zones of nappes or belongs to different nappe sheets. The Blyb Thrust Fault pertains to the Indosinian faults that played the main role in the formation of the Front Range structure.  相似文献   

11.
This study is based on measurement of hundreds of fractures (small faults, joints, cracks) in the crystalline rocks (Precambrian) and in Quaternary deposits of the investigated area east of Aqaba. Fault-slip data, joints, and any weakness zone data from the study area were collected from 20 stations. These stations represent wadi cliffs, stream channels, alluvial fans in the Pleistocene to Holocene sediments, and granitic rocks. During this study, it was assumed that any discontinuity in granitic rocks is a plane of weakness neoformed or inherited and reactivated during the successive tectonic phases. Whereas any cracks, joints, or small displacement in the Pleistocene and Holocene deposits are assumed to represent the activity or, more recently, deformation of the local area where they found. This study found the main trends of weakness zones, the kinematics, and the relation to main stress field in the region. Results show that the Late Neoproterozoic structures were reactivated during the Cenozoic and controlled the recent movement along the Dead Sea Rift. The NNE to N-S trend sets explain the reactivation of the late Neoproterozoic structures during Tertiary times. On the other hand, the formation of the Dead Sea Transform during the Miocene occurred along the N-S to NNE-SSW trending fault system, which was reactivated as sinistral fault.  相似文献   

12.
The Central Patagonian Batholith is a suite of acid and meso-silicic rocks cropping out in central Patagonia. The emplacement of these rocks has been proposed to be related to the activity of a system of dextral transcurrent faults, the NW-SE Gastre Fault System. This fault system has been ascribed a transcontinental magnitude and a ∼500 km dextral displacement during Gondwana dismembering in Jurassic times. However, the timing, kinematics and amount of displacement of the Gastre Fault System are still controversial. In this work we have visited two localities which were subject of controversial observations, in order to perform petrographical, microstructural and anisotropy of the magnetic susceptibility studies to contribute to the ongoing discussion. The results mostly agree with the findings von Gosen and Loske (2004) in that rocks spatially and temporally associated to the Gastre Fault System do not show evidence supporting the existence of a major dextral fault system active during Jurassic times.  相似文献   

13.
河南省崤山地区金银矿床控矿构造特征与成矿模式   总被引：1，自引：0，他引：1  
崤山位于华北陆块南缘,是河南省重要的有色金属成矿区。为进一步明确崤山地区控矿构造特征,分析探讨成矿就位机制,指导崤山地区中深部地质找矿工作,本文对崤山地区矿床地质特征、构造性质等要素进行了分析研究,将崤山地区控矿构造分为拆离断层控矿构造、韧性剪切带控矿构造和张扭性断裂控矿构造三类。①拆离断层沿太古界太华岩群的结晶基底与中元古界熊耳群盖层间发育,带内发育糜棱岩,崤山北部主要含矿石英脉多发育在紧靠拆离断层带下盘的太华岩群中,矿体就位于拆离剪切形成的拆离断层及其次级断裂带中;②韧性剪切带主要位于崤山中西部和北部,早期呈压扭特性,发育绿泥片岩质初糜棱岩、糜棱岩、花岗质超糜棱岩等,申家窑韧性剪切带晚期表现为张性特征,在其下盘发育有多组与其走向一致的羽列状次级断裂构造,矿体就位于韧性剪切带及其下盘羽状次级断裂带中;③张扭性断裂多发育于崤山中东部,断裂内充填有含金石英脉条带,围岩中多具绿泥石化、绿帘石化、钾化、黄铁矿化等,矿体就位于张扭性断裂带中。按照岩体、构造对成矿的作用关系,建立了崤山地区以深源岩浆为流体、以构造侵位为空间的"双控"成矿模式,指出韧性剪切带、拆离断层带中深部及其次级断裂带是寻找脉型金银矿床的有利地段,燕山期中酸性侵入岩体周缘有斑岩型铜钼矿成矿潜力。  相似文献   

14.
The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip–slip thrusting movements. The recent faulting mainly occurs on new traces trending E–W to ENE–WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike–slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike–slip motion is transferred along the ENE–WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.  相似文献   

15.
Iran has long been known as one of the most seismically active areas of the world, and it frequently suffers destructive and catastrophic earthquakes that cause heavy loss of human life and widespread damage. The Alborz region in the northern part of Iran is an active EW trending mountain belt of 100 km wide and 600 km long. The Alborz range is bounded by the Talesh Mountains to the west and the Kopet Dagh Mountains to the east and consists of several sedimentary and volcanic layers of Cambrian to Eocene ages that were deformed during the late Cenozoic collision. Several active faults affect the central Alborz. The main active faults are the North Tehran and Mosha faults. The Mosha fault is one of the major active faults in the central Alborz as shown by its strong historical seismicity and its clear morphological signature. Situated in the vicinity of Tehran city, this 150-km-long N100° E trending fault represents an important potential seismic source. For earthquake monitoring and possible future prediction/precursory purposes, a test site has been established in the Alborz mountain region. The proximity to the capital of Iran with its high population density, low frequency but high magnitude earthquake occurrence, and active faults with their historical earthquake events have been considered as the main criteria for this selection. In addition, within the test site, there are hot springs and deep water wells that can be used for physico-chemical and radon gas analysis for earthquake precursory studies. The present activities include magnetic measurements; application of methodology for identification of seismogenic nodes for earthquakes of M ≥ 6.0 in the Alborz region developed by International Institute of Earthquake Prediction Theory and Mathematical Geophysics, IIEPT RAS, Russian Academy of Science, Moscow (IIEPT&MG RAS); a feasibility study using a dense seismic network for identification of future locations of seismic monitoring stations and application of short-term prediction of medium- and large-size earthquakes is based on Markov and extended self-similarity analysis of seismic data. The establishment of the test site is ongoing, and the methodology has been selected based on the IASPEI evaluation report on the most important precursors with installation of (i) a local dense seismic network consisting of 25 short-period seismometers, (ii) a GPS network consisting of eight instruments with 70 stations, (iii) magnetic network with four instruments, and (iv) radon gas and a physico-chemical study on the springs and deep water wells.  相似文献   

16.
In the Precambrian rocks west and southwest of the Mount Isa Fault three significant fold generations are recognized. Within individual successions, units containing an early phase of deformation are juxtaposed by a late fault against a sequence that does not share these earlier events.

Many of the large‐scale structures in the Judenan Beds are first‐generation folds, whereas west of the Judenan Beds the area is dominated by second‐generation folds. These two sets of folds are tentatively correlated and are referred to as the Judenan Folds. An earlier set of pre‐Judenan folding is only found in the units west of the Judenan Beds. One phase of the Sybella Granite is also associated with the Judenan folding. Later small‐scale folds associated with a crenulation cleavage are, however, of little regional importance and are commonly found only in zones of highly deformed rocks.  相似文献   

17.
The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well–known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high–angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high–angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip–slip was 1.67–2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid–Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging–wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall.  相似文献   

18.
The Halloran Hills consist of Precambrian (?) metamorphites, Mesozoic igneous intrusive rocks, Tertiary volcanic and sedimentary breccias, and Quaternary alluvia. The Precambrian Halloran Complex has been subdivided into the following formations: (1) Silver Lake Peak Formation, mostly quartzofeldspathic gneisses; (2) Cree Camp Formation, quartzites and metarhyolites; (3) Riggs Formation, metamorphosed carbonate rocks. This complex is intruded by dioritic rocks. Regional metamorphism produced parageneses of the almandine amphibolite facies. Metablastesis was a major phenomenon, partial fusion was a local one. The rocks are, therefore, metatexites. Regional metamorphism was followed by diaphthoresis, accentuated in a zone of dislocation. A mesozonal pluton (Wander Mine Pluton) invaded the Halloran Complex during the Laramide (?) orogeny. The plutonic core consists of quartz monzonite, whereas the peripheral parts are more basic in composition. Contact relationships with the country rock are both concordant and discordant. Locally, a tectonic breccia marks marginal upthrusts. Foliation exists to various degrees in the periphery of the pluton. The sequence of the emplacement phases of the pluton is as follows: (1) metasomatism, (2) flow, and (3) movement of the dead body. All three phases overlapped each other, but at the present level of erosion the rocks in any one restricted area depict only two phases. Younger granitic rocks and various dike-swarm intrusions followed the emplacement of the pluton. During the Tertiary, autoclastic friction breccias of andesitebasalt composition intruded along faults. These intrusions were followed by the deposition of arkosic breccias (Halloran Spring Formation) and coarse sedimentary breccias (rubble). At the end of the Tertiary (Pliocene?), basalt flows buried much of the ancient land surface near Halloran Spring. The configuration of the Halloran complex indicates a domelike structure, partially bounded in the north by a fault zone (Cree Camp Fault Zone). Outlines of the Wander Mine Pluton indicate a phacolithic geometry modified by regional faults. The most important fault in the area is the Cree Camp Fault Zone, which has a general east-west trend. It was probably formed before the emplacement of the pluton, and was revived three times after its initiation. Faulting ceased after the outpouring of the basalt flows. Within the regional framework, the Halloran Hills lie east of the quartz-diorite line. There seems to be a trend for association of tonalites with sillimanite-cordierite-bearing metamorphites west of the quartz-diorite line, and of quartz monzonites with potassium-rich metamorphites east of it. If the plutonic rocks are anatexitic, or palingenetic, their compositional differences on either side of the line find a suitable explanation. Results of recent experiments agree with this assumption. “Anormal” rock suites are explained as ectectic mobilizates. The age of orogenies in California generally decreases from west to east, and the potassium-sodium ratio increases in the same direction. It is submitted that time determines the site of the orogeny and that the site determines the possible range in composition of the granitic magma. The spreading sea-floor hypothesis serves as the unifying framework for the above considerations.  相似文献   

19.
Wadi Fatima, east of jiddah on the Red Sea coast of Saudi Arabia, is a microcosm of the geology of the jiddah area. Rocks ranging in age from 800-million-year-old metamorphic rocks to Tertiary lava flows are exposed, and illustrate the geological richness of western Saudi Arabia. The valley is a major south-west-trending fault zone that has been active since Precambrian times. A major Tertiary dyke swarm in the vicinity of Wadi Fatima is related to the opening of the Red Sea as the African-Arabian landmass split apart.  相似文献   

20.
吐哈盆地中央构造带正反转演化特征   总被引：5，自引：3，他引：5  
吐哈盆地中央构造带由火焰山构造和七克台构造组成。中央构造带形成于三叠纪晚期至侏罗纪早期,表现为伸展构造特征,生长断层上盘地层厚度明显大于下盘,并于断层上盘所在的台北凹陷形成沉降中心。晚侏罗世,由于拉萨陆块与欧亚大陆的碰撞作用导致吐哈盆地由伸展盆地转变为挤压盆地,中央构造带也于此时发生构造反转,由早期的伸展正断层转变为挤压逆断层。发生于55Ma的喜山构造事件对天山地区产生了深刻的影响,但影响时间略有滞后,大致发生在晚渐新世至早中新世,中央构造带即在此次构造事件中强烈变形,逆冲出露于地表。  相似文献   

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