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1.
SYN-AND POST-THICKENING EXTENSIONS IN THE YULONG—HABA MOUNTAIN RANGE IN SOUTHWEST CHINA 相似文献
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AbstractThe Roc de Frausa Massif, located at the Eastern Pyrenees, is formed by a stratoid Pre-Hercynian deformed granite (orthogneiss) interbedded with metasedimentary series. Hercynian granitoids (St. Llorenç — La Jonquera pluton) surround the southern and eastern part of the massif and Hercynian basic igneous rocks (Ceret stock) occupy the central part of it. The Pre-Hercynian granite and the sedimentary series were involved, during the Hercynian orogeny, in complex polyphasic tectonics and metamorphism. As a result, an ubiquitous penetrative foliation was developed during the earlier stages. This foliation was subsequently folded into a complex antiformal structural formed by a double dome : Roc de Frausa dome and Mas Blanc dome. Main lithological boundaries (gneiss — metasediments and metasediments — granitoids) are broadly parallel to the regional foliation, and they all display the dome geometry. Interference fold pattern between two late phases, an ealier one with NE-SW trending folds and a younger one with NW-SE trending folds is responsible for the dome geometry. Mylonitic deformation, with W-E to NW-SE orientations has been attributed to the last folding phase. Regional metamorphic climax and contact metamorphism, the last one resulting from Hercynian granitoid emplacement, preceeded the above mentioned late folding event, which developed under retrograde metamorphic conditions. Regional peak metamorphism is recognized by the static crystallization of cordierite + potassium feldspar. This paragenesis indicates pressure — temperature conditions of about 3.1 Kbar and 660 °C maximum. Contact metamorphism overprints the earlier regional metamorphism. Parageneses and thermal gradient of contact metamorphism around La Jonquera pluton are very similar to those related to regional metamorphism, whereas parageneses produced around Ceret stock present garnet + potassium feldspar. Geothermometry indicates metamorphic conditions locally higher for this paragenesis (around 700 °C). 相似文献
3.
Kyle P.Larson Asghar Ali Sudip Shrestha Mathieu Soret John M.Cottle Rafique Ahmad 《地学前缘(英文版)》2019,10(3):849-861
New metamorphic petrology and geochronology from the Loe Sar dome in the Swat region of northern Pakistan place refined constraints on the pressure, temperature and timing of metamorphism and deformation in that part of the Himalayan orogen. Thermodynamic modelling and monazite petrochronology indicate that metamorphism in the area followed a prograde evolution from ～525 ± 25 ℃and 6 士 0.5 kbar to ～610 ± 25 ℃ and 9 士 0.5 kbar, between ca. 39 Ma and 28 Ma. Partitioning of heavy rare earth elements between garnet rims and 30-28 Ma monazite are interpreted to indicate coeval crystallization at peak conditions. Microtextural relationships indicate that garnet rim growth post-dated the development of the main foliation in the area. The regional foliation is folded about large-scale N-S trending fold axes and overprinting E-W trending folds to form km-scale domal culminations. The textural relationships observed indicate that final dome development must be younger than the 30-28 Ma monazite that grew with garnet rims post-regional foliation development, but pre-doming-related deformation. This new timing constraint helps resolve discrepancy between previous interpretations,which have alternately suggested that N-S trending regional folds must be either pre-or post-early Oligocene. Finally, when combined with existing hornblende and white mica cooling ages, these new data indicate that the study area was exhumed rapidly following peak metamorphism. 相似文献
4.
Himalayan structure and metamorphism south of the Main Mantle Thrust, Lower Swat, Pakistan 总被引：2，自引：0，他引：2
Abstract During the Eocene-Oligocene, the Indian plate collided with the Kohistan arc along the Main Mantle Thrust (MMT) zone. The structure of the Lower Swat rock sequence, on the Indian plate directly south of the MMT, is a dome with a basement of granitic gneiss and quartz-rich schist unconformably overlain by amphibolitic and calcareous schist. The earliest superposed small-scale folds (F1 & F2) represent a progressive F1/F2 deformation that is associated with a single set of WSW-vergent large-scale folds (termed F2). These folds are inferred to have developed during oblique, WSW-directed overthrusting of the MMT suture complex onto the Lower Swat rock sequence. Metamorphism began during F1/F2 as indicated by an S1 foliation that developed during biotite-grade metamorphism. S1 is preserved as a relict texture in porphyroblasts that grew during a subsequent interkinematic phase during garnet- and higher grade metamorphism. The dominant, regional foliation (S2) developed following the interkinematic phase. S2 is associated with transposition of S1 and rotation or dismemberment of porphyroblasts. Annealing recrystallization followed S2 and continued during F3 thereby destroying or masking possible pre-existing stretching fabrics. Superposed F3 folds are upright and open with N-S axial trends. They may correlate with early doming of the Lower Swat rock sequence and with strike-slip displacement in the northern part of the MMT zone, north of the Lower Swat area. F3 was followed by retrograde metamorphism and development of E-W-trending, S-vergent F4 folds. F4 may be associated with a final phase of southward directed thrusting and inactivity in the MMT zone. Correlation of published 40 Ar/39 Ar ages with the metamorphic fabrics suggests that F1/F2 and F3 occurred in the Eocene, and that F4 developed in the Oligocene. F4 is the earliest indication of southward verging structures on this part of the Indian plate. 相似文献
5.
Chandra Shekhar Dubey 《地学前缘》2000,(Z1)
GEOLOGICAL STUDIES OF METAMORPHIC ROCKS IN THE VICINITY OF M.C.T./LESSER HIMALAYAN SHEAR ZONE, PARTS OF SIKKIM HIMALAYAS 相似文献
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Joaquín García-Sansegundo P. Farias G. Gallastegui R. E. Giacosa N. Heredia 《International Journal of Earth Sciences》2009,98(7):1599-1608
In the Bariloche region, the Gondwanan basement consists of metamorphic and deformed igneous rocks intruded by Mesozoic and
Tertiary granitoids. Metasediments and amphibolites have been affected by three main deformation events (D1, D2 and D3). D1
(S1 foliation) is well shown preserved in the microlithons of the S2 regional foliation and in albite and garnet porphyroblasts.
Both foliations have been folded by upright open folds with associated crenulation (S3) locally developed in the D3 folds
hinge zones. An early-stage (syn-D1) subduction episode can be invoked based on evidence of high pressure (HP) metamorphism
in schists and amphibolites as well as on the presence of pre-collisional I-type granitoids. D2–D3 developed under regional
intermediate pressure–low pressure (IP–LP) metamorphic conditions. High temperature (HT) conditions were reached, as deduced
from regional migmatization and the intrusion of syn- to late-orogenic S-type granitoids. The transition from HP to IP metamorphic
conditions could be associated with the emplacement of NE directed crustal-scale thrusts during D2. 相似文献
8.
STRUCTURAL AND THERMAL EVOLUTION OF THE SOUTH ASIAN CONTINENTAL MARGIN ALONG THE KARAKORAM AND HINDU KUSH RANGES,NORTH PAKISTAN 相似文献
9.
该区的构造格局主要由早期近东西向紧闭的褶皱带和晚期北北东向构造组成。早期的南北向缩短构造以龙王庙平卧褶皱和大小长山岛的直立紧闭褶皱为代表,分别具有扇状间隔性压溶劈理和透入性轴面片理,褶面倒向以北为主。北北东向构造切割近东西向构造,表层表现为北西西向薄皮逆冲推覆构造,浅层构造具有扇状压溶劈理的紧闭褶皱,深层表现为基底与盖层间的拆离断层及其下的韧性剪切带。早期的研究者将该断层作为辽南推覆构造底部的滑脱面,现今则压倒性地采用变质核杂岩的构造理念。根据相关剪切带早期面内褶皱发育,晚期伸展褶劈理发育,通过运动学涡度和应力状态分析,论证早期滑脱-推覆到晚期伸展拆离的演化过程。野外观测证明,辽南基底变质岩西侧的金州断层为一伸展拆离断层,它切割东侧的董家沟断层,前者平行于下伏糜棱岩中的同向伸展褶劈理,后者平行下伏糜棱岩的糜棱面理。金州拆离断层的形成及其东侧的隆起标志着辽南构造体制从缩短到伸展的转折。根据相关的年代学研究,这一构造体制转化发生在早白垩世(约120～107 Ma)。该区最新的构造事件是北东-南西向的缩短,相关的北北东向的右行走滑断层与晚白垩世以来的郯庐断层活动方式一致。 相似文献
10.
Frank Wickert 《International Journal of Earth Sciences》1988,77(2):467-482
In the Beaujolais-Lyonnais area of the northeastern Massif Central accretion of continental and possibly oceanic crustal fragments occurred between Cambrian (?) and early Carboniferous time. Three distinct lithotectonic units (terranes?) have been recognized. The southern (Lyonnais-) Unit consists of medium- to high-grade metamorphics and includes eclogites; it formed in the early Paleozoic. The Brévenne-Unit to the north contains low- to medium-grade metamorphic mafic and felsic volcanics and subordinate sedimentary rocks which possibly originated during the early Paleozoic until Devonian time, in a sialic back-arc environment or along an active continental margin. The Beaujolais-Unit is represented by volcanics on the south and predominantly shallow marine clastics and carbonates on the north. It developed in a late Devonian or early Carboniferous ensialic marginal basin. The peak of metamorphism in the Lyonnais-unit (HP/HT) was reached in Silurian time. Subsequent NW-SE to E-W oriented convergence produced mylonitic foliation, structural imbrication of the Lyonnais basement rocks with the Brévenne-Unit and SE-vergent folds accompanied by low- to medium-grade metamorphism. Late Visean to Namurian N-S to NW-SE directed N-vergent thrusting produced tectonic imbrication of the metamorphic northern Brévenne-Unit with the nonmetamorphic Beaujolais-Unit. In the southern Brévenne-Unit and in the Lyonnais-Unit updoming along right-lateral high-angle normal faults was followed by emplacement of voluminous granitic plutons of crustal origin. Late Carboniferous to early Permian crustal thinning in the Beaujolais-Lyonnais area was associated with N-S trending left-lateral strike-slip faults and E-W to NE-SW trending right-lateral strike-slip faults. Basins that developed along these faults contain continental red beds. 相似文献
11.
STUDY ON THE ISOTOPIC CHRONOLOGY AND THE TECTONIC SIGNIFICANCE OF DUGUER GRANITIC GNEISS IN CENTRAL QIANGTANG, TIBET 相似文献
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The Gaoligong metamorphic zone is located southeast of the Eastern Himalayan Syntaxis in western Yunnan, China. The zone is characterized by four stages of deformation (D1–D4). D1 structures record early compressive deformation during the Indosinian orogeny, which formed tight to isoclinal F1 folds of bedding with a penetrative S1 foliation developed parallel to fold axial planes. Mid-crustal horizontal shearing during D2 resulted in overprinting of D1 structures. D1 and D2 structures are associated with granulite facies metamorphism. D3 doming resulted in late crustal thickening and the development of a regional NW–SE trending F3 antiform. Synchronous with or slightly subsequent to D3 deformation, the zone experienced D4 ductile strike-slip shearing, resulting in its exhumation to shallow crustal levels and retrograde metamorphism. Granitic D4 mylonites predominantly yield 40Ar/39Ar mica ages of 15–16 Ma, indicating that D4 dextral strike-slip shearing occurred in the Miocene. Weakly deformed leucogranite and protomylonite yield 40Ar/39Ar ages of 10–11 Ma, suggesting that ductile strike-slip shearing continued to the Late Miocene. The new 40Ar/39Ar data indicate that escape-related deformation along the Gaoligong strike-slip shear zone occurred in the Miocene. In association with recent geophysical studies, and on the basis of the structural, crystal preferred orientation (CPO), and geochronological data presented in this paper, we suggest that the Gaoligong metamorphic zone formed in response to intracontinental transpression in the southeast of Tibet, characterized as intense deformation and metamorphism at middle–upper crustal levels. 相似文献
14.
TWO EPISODES OF MONAZITE CRYSTALLIZATION DURING METAMORPHISM AND CRUSTAL MELTING IN THE EVEREST REGION OF THE NEPALESE HIMALAYA 总被引：4，自引：2，他引：2
TWO EPISODES OF MONAZITE CRYSTALLIZATION DURING METAMORPHISM AND CRUSTAL MELTING IN THE EVEREST REGION OF THE NEPALESE HIMALAYA 相似文献
15.
大别-苏鲁超高压和高压变质带构造演化 总被引：12，自引：0，他引：12
大别—苏鲁是世界上超高压 (UHP) ( >2 .7GPa)和高压 (HP)变质岩石出露最为广泛的地区。通过区域研究 ,尤其是在选择的 30多个关键位置上不同尺度构造记录的深入观察 ,结合已有的可利用的变质、热事件及同位素年代学资料分析 ,揭示出它们曾遭受过一个复杂的从深俯冲到折返构造演化历程 ,识别出 5个主要的构造变质事件 :( 1)由块状榴辉岩中发育的微弱面理和线理所代表的第 1期变形变质事件 (D1) ;( 2 )面状榴辉岩中发育的含拉伸线理的透入性主面理、中小型鞘状褶皱及网络状韧性剪切带 ,代表第 2期构造变质事件 (D2 ) ;( 3)第 3期变形事件主体发生于麻粒岩 /角闪岩相后成合晶形成之后 ,主要构造记录是区域性陡倾斜面理及不均一置换的成分层、榴辉岩透镜体及布丁群、面理内褶皱、网状韧性剪切带系统以及减压部分熔融作用形成的混合岩和含榴花岗质岩石组构 ;( 4)区域性的碰撞期后地壳韧性薄化及剪张作用 (D4)形成缓倾斜角闪岩相主面理及线理、穹状及弧形构造和多层韧性拆离带 ,它们主导了现今观察到的大别—苏鲁超高压和高压变质带的区域构造几何图像 ;( 5 )第 5期构造热事件 (D5)表现为不均一断块抬升、红色沉积盆地发育及大规模的岩体和岩脉就位 ,代表造山晚期的构造揭顶及坍陷作用 ,该期构造控制着造山带 相似文献
16.
THE BALANCED CROSS-SECTION AND SHORTENING IN QIANGTANG TERRAIN QINGHAI—TIBET PLATEAU 总被引：1，自引：0，他引：1
THE BALANCED CROSS-SECTION AND SHORTENING IN QIANGTANG TERRAIN QINGHAI—TIBET PLATEAU 相似文献
17.
In the high‐grade (granulite facies) metamorphic rocks at Broken Hill the foliation is deformed by two groups of folds. Group 1 folds have an axial‐plane schistosity and a sillimanite lineation parallel to their fold axes; the foliation has been transposed into the plane of the schistosity by these folds. Group 2 folds deform the schistosity and distort the sillimanite lineation so that it now lies in a plane. Both groups of folds are developed as large folds. The retrograde schist zones are zones in which new fold structures have formed. These structures deform Group 1 and Group 2 folds and are associated with the formation of a new schistosity and strain‐slip cleavage. The interface between ore and gneiss is folded about Group 1 axial planes but about axes different from those in the foliation in the gneiss. On the basis of this, the orebody could not have been parallel to the foliation prior to the first recognizable structural and metamorphic events at Broken Hill. The orebody has been deformed by Group 2 and later structures. 相似文献
18.
The Wadi Fatira area occurs at the southern margin of the Northern Eastern Desert (NED) of Egypt and is occupied by highly sheared metavolcanics tectonically alternated with banded iron formations and intruded by Barud tonalite–granodiorite, post-tectonic gabbroic and granitic intrusions. Detailed structural investigation showed that the schists and migmatitic amphibolites are formed by shearing in metavolcanics and syntectonic Barud tonalite–granodiorite due to movement along the Wadi Fatira shear zone (WFSZ). This shear zone starts as a NW–SE striking fault along Wadi Barud Al Azraq and the Eastern part of Wadi Fatira and turns to a E–W trending fault to the north of Wadi Fatira. Microstructural shear sense indicators such as asymmetric geometry of porphyroclasts such as σ-type and asymmetric folds deforming fine-grained bands which are frequently found around porphyroclasts indicate sinistral sense of shearing along the WFSZ. This shear zone is characterized by transitions from local convergence to local extension along their E–W and NW–SE trending parts, respectively. The NW–SE part of the WFSZ is of about 200 m in width and characterized by synmagmatic extensional features such as intrusion of synkinematic tonalite, creation of NE–SE trending normal faults, and formation of migmatitic amphibolites and schlieric tonalites. This part of the shear zone is metamorphosed under synthermal peak metamorphic conditions (725°C at 2–4 kbar). The E–W compressional part of the WFSZ is up to 3 km in width and composed of hornblende, chlorite, actinolite, and biotite schists together with sheared intermediate and acidic metatuffs. Contractional and transpressional structures in this part of the WFSZ include E–W trending major asymmetrical anticline and syncline, nearly vertical foliation and steeply pitching stretching lineations, NNE dipping minor thrusts, and minor intrafolial folds with their hinges parallel to the stretching lineation. P–T estimates using mineral analyses of plagioclase and hornblende from schists and foliated metavolcanics indicate prograde metamorphism under medium-grade amphibolite facies (500–600°C at 3–7 kbar) retrogressed to low-grade greenschist facies (227–317°C). The foliation in Barud tonalite–granodiorite close to the E–W part of the WFSZ runs parallel to the plane of shearing and the tonalite show numerous magmatic flow structures overprinted by folding and ductile shearing. The WFSZ is similar to structures resulted from combined simple shear and orthogonal shortening of oblique transpressive shear zones and their sense of movement is comparable with the characteristics of the Najd Fault System. 相似文献
19.
大别山南部的超高压变质岩在其形成及折返过程中经过5期变形。D1变形为榴辉岩相前变形,形成于扬子板块北缘陆壳基底的俯冲过程中;D2变形形成于折返初期(220-210Ma)即超高压变质岩在浮力驱动下折返至下地壳底部的过程中,变形以块状榴辉岩的糜棱岩化及层状榴辉岩和基质的紧密-同斜褶皱为特征;D3变形发生在折返中期(200-180Ma)即超高压变质岩在南北陆块持续碰撞作用下被挤出并向北逆冲折返至中地壳的过程中,变形以榴辉岩的布丁化和基质的强烈韧性剪切变形为特征;D4变形是折返晚期(130-110Ma)超高压变质岩在地壳浅部伸展体制下向南滑脱所致;在折返至近地表时,超高压变质岩受到NE向断层(D5)的切割。 相似文献
20.
Three fold generations have been recognized in Svecofennian rocks (±1,800 Ma) from West Uusimaa, SW Finland. The first one (F1) might be related to thrusting and imbrication tectonics at plate collision contacts. The main generation (F2) is due to a N-S horizontal crustal shortening, which created at first E-W trending upright folds in the whole region and later tightened these F2 folds in the western part of the belt, whereas conjugate shear zones and tectonic lenses of competent rock bodies developed in the eastern part. Simultaneously the metamorphic conditions rose from amphibolite- to granulite-facies in this eastern part, which is known as the West Uusimaa Complex. The amphibolite- to granulite-facies transition zone along the western boundary of the granulite-facies complex is studied in detail. A number of prograde mineral reactions are telescoped in this transition zone: the breakdown of biotite and amphibole to ortho- ±clino-pyroxene in metaigneous rocks, the appearance of garnet in cordierite-bearing metapelites and the appearance of scapolite in calcareous rocks. Distinct mineralogical changes also occur in this zone which cross cuts all major structures and rock units and are only affected by late-F3 folding (open, disharmonic folds with approximately N-S trending axial planes) and young shear zones, associated with pseudotachylite generation. The absence of any evidence of block faulting and tilting of the crust that could be associated with the granulite complex suggests that the whole region represents one crustal level. A fluid-inclusion study indicates similar pressures for the amphibolite facies and the granulite facies domains. Application of various independent geothermobarometric methods suggest a low pressure (3–5 K bar) and a temperature increase from 550–650° C to 700–825° C, associated with a decreasing water activity (0.12O<0.4) and a general increasing CO2 activity. Fluid inclusions strongly suggest an isobaric amphibolite/granulite transition. There-fore the granulite-facies complex is designated a thermal dome. Whole rock chemical data show that granulite-facies metamorphism is isochemical. Constraints for the Svecokarelian crustal evolution are discussed. 相似文献