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1.
The Pan-African basement exposed in the Meatiq area west of Quseir, Egypt, consists of an infracrustal basement overthrusted by a supracrustal cover. The infracrustal rocks were developed as a result of an old orogeny referred to as the Meatiqian orogeny where granite—gneiss, migmatitic gneisses and migmatized amphibolites were formed. The granite—gneiss represents a deformed granite pluton emplaced at 626±2 Ma, whereas the migmatitic gneisses and amphibolites are of mixed igneous and sedimentary parentage. In view of the data so far available, the nature of the Meatiqian orogeny could not be deciphered. In spite of the young isotopic ages, it is suggested that at least the metasedimentary gneisses represent older rocks in the stratigraphic sequence of the infracrustal basement.The supracrustal cover represents a part of an extensive ophiolitic mélange obducted onto the infracrustal basement during the next orogeny (Abu Ziran orogeny) which culminated at 613±2 Ma. An active continental margin-type regime can adequately explain the evolution of such a supracrustal cover. During obduction, the ophiolitic mélange and the upper 2 km thick part of the infracrustal basement were intensely deformed and metamorphosed under PT conditions of the greenschist—epidote amphibolite facies. The deformed infracrustal basement was converted into mylonitic—blastomylonitic rocks and schists composing five thrust sheets, and subsequently intruded by synkinematic granitoid sheets. Later, both the infracrustal basement and the overlying supracrustal cover were isostatically uplifted, subjected to complex shallow folding giving rise to the major Meatiq domal structure, and were intruded by a postkinematic adamellite pluton at 579±6 Ma.  相似文献   

2.
The Serbo-Macedonian Massif (SMM) represents a composite crystalline belt within the Eastern European Alpine orogen, outcropping from the Pannonian basin in the north, to the Aegean Sea in the south. The central parts of the massif (i.e. southeastern Serbia, southwestern Bulgaria, eastern Macedonia) consist of the medium- to high-grade Lower Complex, and the low-grade Vlasina Unit. New results of U–Pb LA-ICP-MS analyses, coupled with geochemical analyses of Hf isotopes on magmatic and detrital zircons, and main and trace element concentrations in whole-rock samples suggest that the central SMM and the basement of the adjacent units (i.e. Eastern Veles series and Struma Unit) originated in the central parts of the northern margin of Gondwana. These data provided a basis for a revised tectonic model of the evolution of the SMM from the late Ediacaran to the Early Triassic.The earliest magmatism in the Lower Complex, Vlasina Unit and the basement of Struma Unit is related to the activity along the late Cadomian magmatic arc (562–522 Ma). Subsequent stage of early Palaeozoic igneous activity is associated with the reactivation of subduction below the Lower Complex and the Eastern Veles series during the Early Ordovician (490–478 Ma), emplacement of mafic dykes in the Lower Complex due to aborted rifting in the Middle Ordovician (472–456 Ma), and felsic within-plate magmatism in the early Silurian (439 ± 2 Ma). The third magmatic stage is represented by Carboniferous late to post-collisional granites (328–304 Ma). These granites intrude the gneisses of the Lower Complex, in which the youngest deformed igneous rocks are of early Silurian age, thus constraining the high-strain deformation and peak metamorphism to the Variscan orogeny. The Permian–Triassic (255–253 Ma) stage of late- to post-collisional and within-plate felsic magmatism is related to the opening of the Mesozoic Tethys.  相似文献   

3.
Some granites, granitoid dykes and volcanic rocks of the Southern Black Forest were dated by U–Pb techniques using zircon and monazite. An effusive rhyolite, which is interbedded in upper Visean sedimentary sequences of the Badenweiler-Lenzkirch zone, was dated at 340 ±2?Ma. This weakly metamorphic zone of supracrustal rocks borders high-grade gneiss terrains in the north and the south, which are intruded by a series of granitoid intrusions: the strongly sheared Schlächtenhaus granite is dated by monazite at 334±2?Ma and the hypothesis of a Devonian emplacement is therefore discarded. The emplacement of all other granites, crosscutting dykes and of an ignimbrite were all within analytical uncertainty: St. Blasien granite 333±2?Ma; Bärhalde granite 332±3?Ma; Albtal granite 334±3?Ma; and a porphyry dyke at Präg 332+2/-4?Ma. Deformation and thrusting of the basement units near the Badenweiler-Lenzkirch zone occurred after the emplacement of the Schlächtenhaus granite, but before the intrusion of the other granitoids, and may therefore be constrained to the time period unresolved between 334±2 and 333±2?Ma. The ignimbritic rhyolite of Scharfenstein was deposited in a caldera 333±3?Ma ago. This age coincides within error limits with published U–Pb monazite and Rb–Sr small slab ages of mimatitic gneisses, Ar–Ar hornblende ages of metabasites and Sm–Nd mineral isochron ages of eclogitic rocks in the underlying basement. This suggests that exhumation and cooling of this basement unit must have been active at rates of approximately 20?km and a few 100°C per million years. The silicic melts are interpreted to be of hybrid crust/mantle origin and their formation was most likely linked to these exhumation tectonics. A phase of mantle upwelling and heat advection into the crust is proposed to be the reason for this short-episodic magmatic pulse.  相似文献   

4.
The Cycladic blueschist belt in the central Aegean Sea has experienced high‐pressure (HP) metamorphism during collisional processes between the Apulian microplate and Eurasia. The general geological and tectonometamorphic framework is well documented, but one aspect which is yet not sufficiently explored is the importance of HP mélanges which occur within volcano‐sedimentary successions. Unresolved issues concern the range in magmatic and metamorphic ages recorded by mélange blocks and the significance of eventual pre‐Eocene HP metamorphism. These aspects are here addressed in a U‐Pb zircon study focusing on the block–matrix association exposed on the island of Syros. Two gneisses from a tectonic slab of this mélange, consisting of an interlayered felsic gneiss‐glaucophanite sequence, yielded zircon 206Pb/238U ages of 240.1 ± 4.1 and 245.3 ± 4.9 Ma, respectively, similar to Triassic ages determined on zircon in meta‐volcanic rocks from structurally coherent sequences elsewhere in the Cyclades. This strongly suggests that parts of these successions have been incorporated in the mélanges and provides the first geochronological evidence that the provenance of mélange blocks/slabs is neither restricted to a single source nor confined to fragments of oceanic lithosphere. Zircon from a jadeitite and associated alteration zones (omphacitite, glaucophanite and chlorite‐actinolite rock) all yielded identical 206Pb/238U ages of c. 80 Ma. Similar Cretaceous U‐Pb zircon ages previously reported for mélange blocks have been interpreted by different authors to reflect magmatic or metamorphic ages. The present study adds a further argument in favour of the view that zircon formed newly in some rock types at c. 80 Ma, due to hydrothermal or metasomatic processes in a subduction zone environment, and supports the interpretation that the Cycladic blueschist belt records both Cretaceous and Eocene HP episodes and not only a single Tertiary HP event.  相似文献   

5.
The Rhodope Domain in NE Greece consists of different tectonometamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates. In the Kechros Complex, which is the lowermost tectonic unit in the East Rhodope, a lense of kyanite eclogite occurs within orthogneiss and common eclogites are found between serpentinized peridotite and underlying pelitic gneisses. In kyanite eclogite, the high-pressure (HP) mineral assemblage is Grt?+?Omp (Jd35–55)?+?Ky?+?Ph?+?Qz?+?Rt?+?(indirectly inferred Tlc?+?Law); a Na-rich tremolite and zoisite formed at or near peak metamorphic conditions. In common eclogites, the HP mineral assemblage is Grt?+?Omp (Jd29–41)?+?Rt and, with less certainty, Amp (Gln-rich?+?Brs?+?Wnc?+?Hbl)?±?Czo. The inclusions in garnet are glaucophane, actinolite, barroisite, hornblende, omphacite, clinozoisite, titanite, rutile and rarely paragonite and albite. In kyanite eclogite, peak P–T conditions are constrained at 2.2?GPa and 615°C using garnet–omphacite–phengite geothermobarometry and very similar values of 585?±?32°C and 2.17?±?0.11?GPa with the average P–T method, by which conditions of formation could also be narrowed down for the common eclogite (619?±?53°C and 1.69?±?0.17?GPa) and for a retrogressed eclogite (534?±?36°C and 0.77?±?0.11?GPa). Ages for the HP metamorphism in the Kechros Complex are not yet available. A Rb–Sr white mica age of 37?Ma from orthogneiss records a stage of the exhumation. The HP event may be coeval with the Eocene HP metamorphism (49–55?Ma) recorded in the Nestos Shear Zone in Central Rhodope and in the Attic-Cycladic crystalline belt, where it is interpreted as the result of subduction and final closure of the Axios/Vardar ocean and subsequent subduction of the Apulian continental crust (a promontory of the Africa continent) under the southern margin of the European continent in the late Cretaceous and early Tertiary.  相似文献   

6.
The Adula nappe belongs to the Lower Penninic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U–Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Garenstock Augengneiss); Ordovician metamorphic volcanic–sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Variscan + Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre-Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, mélange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity.  相似文献   

7.
Abstract

The transition from the Alpine tectonic assembly to the exhumation of the units in the Rhodope metamorphic province in northernmost Greece has been refined by 40Ar/39Ar laserprobe mica analyses. Preservation of pre-Alpine (~ 280 Ma and 145 Ma) muscovite cooling ages at the western margin of the Rhodope indicate that subsequent events failed to reset the argon system thermally in white mica in the outcropping basement of this region. The central and eastern Rhodope are characterized by white mica cooling ages of 40–35 Ma with ages gradually decreasing to ca. 15 Ma near the eastern margin of the Strymon Valley. The Eo-Oligocene ages reflect the regional exhumation of the metamorphosed units to shallow crustal levels, with corresponding temperatures below ca. 350 °C, by 40–35 Ma. The younger cooling ages are attributed to the initiation and subsequent operation of the Strymon-Thasos detachment system since ca. 30 Ma. This study provides a crucial contribution to future regional tectonic models for the Rhodope region as it recognizes an early stage of development of the Strymon-Thasos detachment system, and has constrained the regional exhumation of the Rhodope metamorphic province since 40 Ma indicating that the regionally observed amphibolite facies metamorphism had terminated by this time. © 2000 Editions scientifiques et médicales Elsevier SAS  相似文献   

8.
阿拉善地区新元古代岩浆事件及其地质意义   总被引：17，自引：0，他引：17  
在阿拉善西部地区分布有一些眼球状片麻岩和条带状片麻岩,以往将它们作为阿拉善群的地层对待。本文研究表明它们是受到变形改造的正片麻岩。通过锆石LA-ICPMSU-Pb分析,4个样品分别获得了913±7Ma、921±7Ma、926±15Ma和904±7Ma的年龄结果。新元古代早期变形花岗岩的发现表明,阿拉善地区经历了新元古代早期(格林威尔期)造山作用的强烈改造,它们可能与祁连地块等相似,应属于不同于华北克拉通的独立的变质地块。  相似文献   

9.
岩湾-鹦鸽咀蛇绿混杂岩是秦岭商丹蛇绿混杂岩带的重要组成部分,由变质基性火山岩(玄武岩)、蛇纹岩、变辉长岩、硅质岩、变复理石(云母石英片岩)等构造岩块组成.其中变基性火山岩具有N-MORB的地球化学特征,安山岩具有与俯冲作用密切相关的岛弧火山岩的性质.玄武岩的锆石SHRIMP U-Pb年龄为483 Ma±13Ma,与天水关子镇和丹风蛇绿混杂岩的时代相一致.对岩湾-鹦鸽咀蛇绿混杂岩的岩石组成和形成时代进行研究,可为进一步探讨商丹蛇绿混杂岩带和秦岭造山带的增生造山作用提供重要证据.  相似文献   

10.
Pan-African basement rocks and a Paleozoic cover series, which were intruded by the protoliths of leucocratic orthogneisses, have been recognized in the Menderes Massif, located in the western part of the Alpine orogenic belt of Turkey. This geochemical and geochronological study focuses on the evolution of the Menderes Massif at the end of Paleozoic time. Geochemical data suggest that the crustally derived leucocratic orthogneisses have chemical composition typical of calc-alkaline and S-type granite. Zircon grains which are euhedral with typical igneous morphologies were dated by the 207Pb/206Pb evaporation method. Single-zircon dating of three samples yielded mean 207Pb/206Pb ages of 246LJ, 241LJ and 235Lj Ma. These ages are interpreted as the time of protolith emplacement in Triassic. Geological and geochronological data suggest that leucocratic granites were emplaced in a period following a metamorphic event related to the closure of the Paleo-Tethys. The leucocratic granites were metamorphosed during the Alpine orogenesis and transformed into orthogneisses. The similar Triassic magmatic event at 233DŽ Ma was also occurred, using single-zircon evaporation method, from granitic gneisses which rest upon the migmatites with tectonic contacts in Naxos, Cycladic complex. This indicates that the Menderes Massif and Cycladic complex had a common pre-Early Triassic magmatic evolution.  相似文献   

11.
Eclogite and blueschist facies rocks occurring as a tectonic unit between the underlying Menderes Massif (MM) and the overlying Afyon Zone/Lycian Nappes and the Bornova Flysch Zone in western Anatolia represent the eastward continuation of the Cycladic Blueschist Unit (CBU) in Turkey. This high-P unit is attributed to the closure of the Pindos Ocean and consists of (a) a Triassic to Upper Cretaceous coherent series derived from passive continental margin sediments and (b) the tectonically overlying Upper Cretaceous Selçuk mélange with eclogite blocks embedded in a pelitic epidote-blueschist matrix. The coherent series has experienced epidote-blueschist facies metamorphism (490 ± 25°C/11.5 ± 1.5 kbar; 38 km depth). 40Ar/39Ar white mica and 206Pb/238U monazite dating of quartz metaconglomerate from coherent series yielded middle Eocene ages of 44 ± 0.3 and 40.1 ± 3.1 Ma for epidote-blueschist facies metamorphism, respectively. The epidote-blueschist facies metamorphism of the matrix of the Selçuk mélange culminates at 520 ± 15°C/13 ± 1.5 kbar, 43 km depth, and is dated at 57.5 ± 0.3–54.5 ± 0.1 Ma (40Ar/39Ar phengite). Eclogite facies metamorphism of the blocks (570 ± 30°C/18 ± 2 kbar, 60 km depth) is early Eocene and dated at 56.2 ± 1.5 Ma by 206Pb/238U zircon. Eclogites experienced a nearly isothermal retrogression (490 ± 40°C/~6 to 7 kbar) during their incorporation into the Selçuk mélange. The retrograde overprints of the coherent series (410 ± 15°C/7 ± 1.5 kbar from Dilek Peninsula and 485 ± 33°C/~6 to 7 kbar from Selçuk–Tire area) and the Selçuk mélange (510 ± 15°C/6 ± 1 kbar) are dated at 35.8 ± 0.5–34.3 ± 0.1 Ma by 40Ar/39Ar white mica and 31.6 ± 6.6 Ma by 206Pb/238U allanite dating methods, respectively. Regional geological constrains reveal that the contact between the MM and the CBU originally formed a lithosphere-scale transform fault zone. 40Ar/39Ar white mica age from the contact indicates that the CBU and the MM were tectonically juxtaposed under greenschist facies conditions during late Eocene, 35.1 ± 0.3 Ma.  相似文献   

12.
Field, geochemical, and geochronologic data of high-grade basement metamafic and evolved rocks are used to identify the nature and timing of pre-Alpine crustal growth of the Rhodope Massif. These rocks occur intrusive into clastic-carbonate metasedimentary succession. Petrography and mineral chemistry show compositions consistent with Alpine amphibolite-facies metamorphism that obliterated the original igneous textures of the protoliths. Bulk-rock geochemistry identifies low-Ti tholeiitic to calc-alkaline gabbroic-basaltic and plagiogranite precursors, with MORB-IAT supra-subduction zone signature and trace elements comparable to modern back-arc basalts. The U-Pb zircon dating revealed a mean age of 455 Ma for the magmatic crystallization of the protoliths that contain inherited Cambrian (528–534 Ma) zircons. Carboniferous, Jurassic, and Eocene metamorphic events overprinted the Ordovician protoliths. The radiometric results of the metamorphic rocks demonstrate that Ordovician oceanic crust was involved in the build-up of the Rhodope high-grade basement. Dating of Eocene-Oligocene volcanic rocks overlying or cross-cutting the metamorphic rocks supplied Neoproterozoic, Ordovician and Permo-Carboniferous xenocrystic zircons that were sampled en route to the surface from the basement. The volcanic rocks thus confirm sub-regionally present Neoproterozoic and Paleozoic igneous and metamorphic basement. We interpret the origin of the Middle-Late Ordovician oceanic magmatism in a back-arc rift-spreading center propagating along peri-Gondwanan Cadomian basement terrane related to the Rheic Ocean widening. The results highlight the presence of elements of Cadomian northern Gondwana margin in the high-grade basement and record of Rheic Ocean evolution. The eastern Rhodope Massif high-grade basement compared to adjacent terranes with Neoproterozoic and Cambro-Ordovician evolution shares analogous tectono-magmatic record providing a linkage among basement terranes incorporated in the Alpine belt of the north Aegean region.  相似文献   

13.
The granitic magmatism occurred at the precollisional stage of the continentalization of the mafic basement of the Shchuch’ya island arc system. The first U–Pb (SIMS, SHRIMP II) data on zircons indicate three pulses of transformation of the oceanic crust into a continental crust: in the Silurian and Middle and Late Devonian. The age of the Yanganape granite is 429 ± 4 Ma, which corresponds to the Late Wenlockian; that of the Yurmeneku massif is 385 ± 2 Ma (Givetian); and that of the Canyon Massif is 368 ± 3 Ma (Famennian). The zircons from the Yanganape granite yielded an age of 335 ± 4 Ma, which corresponds to the Early Carboniferous (Visean). Similar ages were noted in uranium-rich zircons from the Canyon Massif granite. They correlate with the collision time of the island arc with the eastern edge of the Eastern European paleocontinent, and it is possible that this event caused disturbance of the U–Pb system of zircons in the islandarc granites of the Shchuch’ya zone.  相似文献   

14.
东昆仑祁漫塔格花岗片麻岩记录的岩浆和变质事件   总被引：14，自引：6，他引：8  
东昆仑青海祁漫塔格尕林格一带原定为金水口群的眼球状花岗片麻岩,实际为新元古代早期形成的花岗岩.采用SHRIMP和LA-MC-ICP-MS两种方法对其中的锆石进行了测试,获得的年龄分别为938±5Ma和938±2Ma,代表了花岗岩的形成时代.花岗岩地球化学特征显示为S-型,属于钙碱性系列的弱过铝-过铝质花岗岩,εNd(0)为-9.4～-11.7,εNd(t=938Ma)为-0.6～-3.2,显示低的负值,tDM为1.6 ～2.1Ga,推测其源岩与白沙河岩组类似.东昆仑东段、柴北缘以及阿尔金均有1000～900Ma的花岗岩形成,表明这次岩浆活动比较广泛,可能与我国西部不同陆块间的汇聚有关,是我国西部新元古代克拉通基底形成的反映,同时也响应于全球Rodinia超大陆的形成.花岗片麻岩中1粒锆石边部获得了416±11Ma的年龄,与区域上志留-泥盆纪花岗岩形成时代一致,代表了新元古代花岗岩发生变质作用的时代,其中白云母40Ar/39Ar的坪年龄和等时线年龄为406±2Ma,代表了变质花岗岩的冷却年龄,这些年龄表明新元古代花岗岩卷入了古生代中期与祁漫塔格洋/海盆关闭有关的造山事件.  相似文献   

15.
《Gondwana Research》2013,24(4):1342-1364
Based mainly on field geological observation and geochronologic data, six tectonic units have been recognized in western Inner Mongolia (China), including, from south to north: North China Craton (NCC), Southern Orogenic Belt (SOB), Hunshandake Block (HB), Northern Orogenic Belt (NOB), South Mongolia microcontinent (SMM), and Southern margin of Ergun Block (SME), suggesting that the tectonic framework of the CAOB in western Inner Mongolia is characterized by an accretion of different blocks and orogenic belts. The SOB includes, from north to south, fold belt, mélange, arc-pluton belt, and retroarc foreland basin, representing a southern subduction–collision system between the NCC and HB blocks during 500–440 Ma. The NOB consists also of four units: arc-pluton belt, mélange, foreland molasse basin, and fold belt, from north to south, representing a northern subduction–collision system between the HB and SMM blocks during 500–380 Ma. From the early Paleozoic, the Paleo-Asian oceanic domains subducted to the north and the south, resulting in the forming of the SOB and the NOB in 410 Ma and 380 Ma, respectively. This convergent orogenic system, therefore, constrained the consumption process of the Paleo-Asian Ocean in western Inner Mongolia. A double subduction–collision accretionary process is the dominant geodynamic feature for the eastern part of the CAOB during the early to middle Paleozoic.  相似文献   

16.
Rb-Sr whole rock data for gneisses and granites from the oriental Pyrénées yield cadomian ages for the basement gneisses and hercynian ages for the granites. Granites occur in two generations. An alkaline granite dated at 335±15 m.y. is syn.—or slightly post-tectonic, and a later calcalkaline granite dated at 275±12 m.y, is clearly intrusive and marks the end of hercynian tectono-metamorphism. Initial 87Sr/86Sr ratios of the granites put limits on the proportion of juvenile contribution from the mantle to their formation. Petrogenetic models are tested using Rb and Sr as tracers.  相似文献   

17.
In north-eastern Greece the mid-greenschist facies Makri Unit and the anchizonal Melia Formation belong to the eastern Circum-Rhodope Belt that forms the uppermost tectonostratigraphic unit of the Rhodope metamorphic nappe pile. The two metasedimentary successions had different source areas, although they now lie in close proximity in the Rhodope Massif. The U-Pb isotopic ages of detrital zircons from a metasandstone of the Makri Unit analysed using LA-SF-ICP-MS and SHRIMP-II gave age clusters at ca. 310-290 Ma and at ca. 240 Ma for magmatic zircons, which may have been derived from Carboniferous-Permian basement rocks of the Thracia Terrane (Lower Tectonic Unit of the Rhodope Massif) that subsequently underwent Triassic rifting. The youngest detrital zircon grains found so far indicate that the metasedimentary succession of the Makri Unit, or at least parts of it, cannot be older than Late Triassic. By contrast, clastic sedimentary rocks of the Melia Formation contain the primary detrital mineral assemblage of epidote, zoisite, garnet, and phengitic mica, which is absent in the Makri Unit, and clearly points to metamorphic rocks being the major source for these sediments. U-Pb analyses of detrital zircons gave a prominent age cluster at ca. 315-285 Ma for magmatic zircons. Inherited cores indicate the involvement of Pan-African and Late Ordovician-Early Silurian crustal sources during Late Carboniferous-Early Permian igneous event(s). Moreover, U-Pb detrital zircon geochronology indicates that the Melia Formation cannot be older than latest Middle Jurassic. We suggest that the Melia Formation was deposited in front of a metamorphic nappe pile with Rhodopean affinities in Tithonian or Cretaceous times. Both the Makri Unit and the Melia Formation have been tectonically juxtaposed from different sources to their present location during Balkan and Alpine orogenic processes.  相似文献   

18.
U-Pb geochronological and Sm-Nd isotopic-geochemical studies of granitoids of different structural-age position established that the collision between the Daldyn and Khapchan terranes of the Anabar shield and formation of the Billyakh tectonic mélange zone occurred between 1971 ± 4-1983 ± 3 Ma, while structural-metamorphic transformations corresponding to this collisional event lasted for 5?C19 Ma. It was shown that the granitoids of different structural-age position of the Billyakh zone were mainly derived from the Early Proterozoic crustal rocks with insignificant input of the Archean continental crust.  相似文献   

19.
阿拉善地块北缘恩格尔乌苏地区发现志留纪侵入体   总被引：8，自引：0，他引：8  
阿拉善地块北缘地区位于中亚造山带的南缘中段,连接了兴蒙造山带和北山造山带等构造单元,其古生代的构造演化对于中亚造山带南缘构造单元的对比连接具有重要的意义,是研究中亚造山带古生代构造演化的关键位置。统计归纳近年来阿拉善地块北缘地区的年代学数据发现,该地区的岩浆活动主要集中在晚古生代期间,特别是二叠期间,尚没有早古生代侵入岩的报道。恩格尔乌苏蛇绿混杂岩是阿拉善地块北缘地区出露的一条重要蛇绿岩带,本次研究在该混杂岩带中发现了早古生代的黑云母花岗岩。通过锆石LA-ICP-MS U-Pb年代学测试发现其时代为423±4.5 Ma和434±1Ma,代表了其岩浆结晶年龄,表明该侵入岩形成于志留纪期间,是阿拉善地块北缘地区最早发现的早古生代侵入体之一。该志留纪岩体的发现,表明恩格尔乌苏混杂岩在带志留纪期间已经出现岩浆活动,具有多期活动的特征。该志留纪岩体的发现,是研究、认识阿拉善地块北缘地区早古生代构造环境的重要对象,对于连接对比东、西相邻构造单元具有重要的意义。结合相邻白山组地层的碎屑锆石时代及晚泥盆世侵入岩的发现等研究成果推断,阿拉善地块北缘地区在早古生代开始就存在岩浆活动,该地区可能并非是早古生代的稳定被动大陆边缘。  相似文献   

20.
张能  李剑波  杨云松  那福超 《岩石学报》2012,28(4):1291-1304
弯岛湖蛇绿混杂岩带是金沙江缝合带西段的重要组成部分。蛇绿岩混杂于上三叠统变质碎屑岩夹变质火山岩中,成份主要为镁铁质-超镁铁质杂岩,岩石类型有变质橄榄岩、变质堆晶质辉长岩及其伴生的岛弧型花岗岩系。岩石化学及地球化学特征表明:蛇绿岩主要为低Ti(岛弧-弧后)型、富集型洋中脊(E-MORB)拉斑玄武岩;与之共(伴)生的基性喷出岩、辉绿岩脉属板内洋岛型裂谷型碱性玄武岩及其过渡类型系列。在变质辉长岩获得全岩Sm-Nd等时线年龄值为232±11Ma,代表了镁铁质-超镁铁质杂岩的形成年龄,可能为洋壳初始俯冲变质的时间。在蛇绿岩上覆的硅质岩中发现有中三叠世拉丁晚期至晚三叠世卡宁早期的放射虫化石,表明弯岛湖镁铁质-超镁铁质杂岩可能形成于中三叠世多岛洋盆或弧后盆地构造环境。  相似文献   

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