首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 35 毫秒
1.
The results of ICP-MS trace-element (LILE, HFSE, REE) study of the Late Mesozoic–Early Cenozoic volcanic rocks of the Okhotsk and Japan seas and geochronological K-Ar dating of the Eocene volcanic rocks are presented. Specifics of volcanism developed on submarine rises of these seas was characterized for the first time, and magma sources and geodynamic settings of the volcanic complexes predating the formation of the deep-water basins were determined. It is established that the Late Mesozoic magmas were formed in a subduction setting from spinel peridotites of suprasubduction mantle wedge, which was metasomatically reworked by aqueous fluids that were released by dehydration of sedimentary layer of subducting oceanic plate. This follows from the elevated concentrations of H2O, alkalis, potassium, LILE and LREE, and lowered HFSE (including Ta-Nb minimum) and HREE contents, at lowered Sm/Yb, Nb/Ta, Nb/Y and elevated La/Nb, Ba/La, and Zr/Y ratios. Eocene adakite-like volcanic rocks were identified for the first time in the Sea of Okhotsk. They vary from andesitic to more felsic compositions with elevated MgO (>4%) and elevated La/Yb (>14) and Sr/Y (50–60) ratios. Identification of adakite-like volcanic rocks serves as evidence in support of the transform continental-margin (or plate sliding) setting, which is characterized by breaking apart of subduction slab and formation of slab “windows” acting as pathways for the transfer of asthenospheric mantle into continental lithosphere. New geochemical data on the Late Mesozoic–Early Cenozoic volcanic rocks of the Okhotsk and Japan seas and analysis of literature data were used to distinguish two geodynamic settings within these seas: subduction and transform margin. Similar settings operated at that time in the adjacent continental- margin volcanic belts (Akinin and Miller, 2011; Martynov and Khanchuk, 2013; et al.).  相似文献   

2.
Geochronological studies of rocks from a bimodal high-alkali volcanic–plutonic complex collected in the area of Kharkhorin zone of the Early Mesozoic Mongolian–Transbaikalian igneous province (MTIP) are made. The age of alkali granites from Olziit sum is 211 ± 1 Ma (U–Pb ID-TIMS on zircon) to 209 ± 2 and 217 ± 4 Ma (40Ar/39Ar on alkali amphibole); the age of alkali granite-porphyries from the area of Sant sum is 206 ± 1 Ma (U–Pb ID-TIMS on zircon). These rock series formed syncronously to the analogous magmatism episode in the Northern Gobi and Western Transbaikalian rift zones of the MTIP. The similarity of the age and composition of igneous associations of the MTIP suggests a common mechanism of its formation related to the effect of a mantle plume on the continental lithosphere at the base of the entire igneous zone having a zonal structure.  相似文献   

3.
In Central Iran, the mixed siliciclastic?carbonate Nakhlak Group of Triassic age is commonly seen to have a Cimmerian affinity, although it shows considerable resemblances with the Triassic Aghdarband Group in far northeastern Iran, east of Kopeh-Dagh area, with Eurasian affinity. The Nakhlak Group is composed of the Alam (Late Olenekian?Anisian), Baqoroq (Late Anisian??Early Ladinian), and Ashin (Ladinian??Early Carnian) formations consisting mainly of volcanoclastic sandstone and shale and fossiliferous limestone. The Baqoroq Formation contains also metamorphic detritus. Sandstone petrofacies reflect the detrital evolution from active volcanism to growing orogen and again active volcanism. Textural and modal analyses of volcanic lithic fragments from the Alam Formation reflect the eruption style and magma composition of a felsic to intermediate syn-sedimentary arc activity. The detrital modes of the Baqoroq Formation sediments suggest a recycled orogenic source followed by arc activity in a remnant fore-arc basin. The sandstone samples from the Ashin Formation demonstrate a continuity of felsic to intermediate arc activity. Major and trace element concentrations of the Nakhlak Group clastic samples support sediment supply from first-cycle material and felsic magmatic arc input. The enrichment in LREE, the negative Eu anomalies, and the flat HREE patterns indicate origination from the old upper continental crust and young arc material. The chemical index of alteration (CIA ～51–70 for sandstone and 64–76 for shale samples) indicates medium degrees of chemical weathering at the source. Petrographical and geochemical evidence together with facies analysis constructed the following depositional conditions for the Nakhlak Group sediments: In the Olenekian, a fore-arc shallow to deep marine depositional basin developed that later was filled by recycled and arc-related detritus and changed into a continental basin in the Anisian. Ladinian extension let to a deepening of the basin. With respect to the similarities between the Nakhlak and Aghdarband (NE Iran) groups and unusual present-day position of the Nakhlak Group with no stratigraphic connection to the surrounding area, the development of first a fore-arc basin and later change into a back-arc depositional basin in close relation with the Aghdarband basin at the southern Eurasian active margin in the Triassic are here proposed. Understanding the basin development recorded in the Nakhlak Group provides constraints on the closure history of Palaeotethys and of the tectonic evolution of early Mesozoic basins at the southern Eurasian margin before the Cimmerian Orogeny.  相似文献   

4.
ＥａｒｌｙＭｅｓｏｚｏｉｃＢａｓｉｎ┐ＭｏｕｎｔａｉｎＣｏｕｐｌｉｎｇＭｅｃｈａｎｉｓｍａｎｄＢａｓｉｎＧｅｏｄｙｎａｍｉｃｓｏｆＥａｓｔＣｈｉｎａ＊ＬｉｕＳｈａｏｆｅｎｇＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｌｏｇｙ，ＮｏｒｔｈｗｅｓｔＵｎｉｖｅｒｓｉｔｙ...  相似文献   

5.
Yarmolyuk  V. V.  Kozlovsky  A. M.  Salnikova  E. B.  Eenjin  G. 《Doklady Earth Sciences》2019,488(1):1022-1026
Doklady Earth Sciences - A zonal igneous areal appeared at the western end of the Mongol–Okhotsk Belt in the Early Mesozoic. Its central part is comprised of the Khentei–Daurian giant...  相似文献   

6.
The Tangquan granodioritic pluton in Dalian County, southwestern Fujian, China, which extends in a NE direction with an exposed area of about 130 km2, used to be considered a product of Early Cretaceous magmatism. The present study suggests for the first time that the pluton was formed in the Early Jurassic by using multiple methods for isotopic dating, which give zircon U-Pb ages of 186.8 Ma and 179.0 Ma, Rb-Sr isochron age of 162.02±4.5 Ma, and biotite 40Ar/39Ar plateau age of 158.1±0.7 Ma. The cooling rate for the pluton was relatively low (4.76℃/Ma) during the early stage (183-162 Ma) because of the compressional environment. It was emplaced in a higher cooling rate (50℃/Ma) in an extensional environment during the later stage (162-158 Ma). The granodiorites are metaluminous-peraluminous, relatively enriched in Na2O and depleted in K2O, and characteristic of I-type granites of crust-mantle mixed sources. They are moderately enriched in Rb, Th, Hf and LREE, and depleted in Ti, Nb, Ta and Sr, and  相似文献   

7.
International Journal of Earth Sciences - The Tisza Megaunit in the Southern Pannonian Basin formed part of the southern margin of the European Plate in the Early Mesozoic era. Its exact...  相似文献   

8.
New data on the structure, age, and composition of the tectonostratigraphic complexes of the western part of the Koryak Highland are presented. The conclusions on the sedimentation conditions are drawn and primary relations are interpreted for most complexes. New Kimmeridgian–Tithonian and Berriasian assemblages of radiolarians are established. Campanian radiolarians are found for the first time in the region.  相似文献   

9.
《Comptes Rendus Geoscience》2008,340(2-3):151-165
This paper provides some new evidences on stratigraphic sequence, zircon SHRIMP dating from ophiolite, granitoids, and fold-and-thrust tectonic styles in the South China Block (SCB). Stratigraphic studies suggest that the eastern and central parts of the SCB show a SW-dipping palaeoslope framework during the Late Palaeozoic–Early Mesozoic. These areas were not in a deep-sea environment, but in a shallow-sea or littoral one. Coeval volcanic rocks are missing. Deep-water deposits and submarine volcanism only took place in the western part of the SCB. The three ophiolitic mélanges of the eastern SCB formed in the Neoproterozoic, but not in the Permian or the Triassic. The sedimentary rocks associated with the Neoproterozoic oceanic relics contain abundant Proterozoic acritarchs, but no radiolarians. The Early Mesozoic granitoids (235–205 Ma) belong to the post-collision peraluminous S-type granites; they are widely exposed in the central-western SCB, and rare in the eastern SCB. The fold-and-thrust belt developed in the eastern SCB shows a top-to-the-south displacement, whereas the Xuefengshan Belt of central SCB indicates a north- or northwest-directed shearing. The geodynamic settings of the different parts of the SCB during the Triassic are discussed.  相似文献   

10.
The authors have proposed a dynamic model in this paper based on the ages,rock series and associations,Sr-Nd isotopic signatures of the Mesozoic intracontinental magmatism overlying the Cathaysian and Yangtze blocks.The model describes the relation of intracontinental collision and subduction in the Tethyan tectonic regie with Paleo-Pacific oceanic plate sudbuction-strike slip-extension in the Pacific tectonic regime.During 220-150Ma,the horizontal collision between the North China block and the Yangtze block,as well as the intracontinental subduction of some divergent microcontinental terranes in the southwestern part of South China are ascribed to the influence of the Tethyan tectonic regime,giving rise to a volume of high-Isr and low-εNd(t) S-type granites only in the Cathaysian Block.During 145-90Ma,under the geodynamic backgound of subduction-strike slip-extension of the Paleo-Pacific oceanic plate on the basis of the deep tectonic process in the Tethyan tectonic regime,high-K,alkalirich calc-alkaline and shoshonitic volcano-plutonic complexes were generated in the Yangtze block,and high-K calc-alkalic and bimodal volcano-plutonic complexes were generated in the Cathaysian block.The occurrence of A-type peralkaline granites in the coastal areas of South east China indicates the end of Mesozoic intracontinental magmatism.  相似文献   

11.
R.L.M. Vissers  P.Th. Meijer 《Earth》2012,110(1-4):93-110
Following on paleomagnetic studies in the sixties showing ~ 35° counterclockwise rotation of Iberia during the Mesozoic, two classes of scenarios have been proposed for the motion history of Iberia which are currently competing. One class infers convergence in the Pyrenees in response to a scissor-type opening of the Bay of Biscay, described by a pole of rotation for Iberia with respect to Europe located within the Bay. The other class of scenarios assumes extensional or transtensional motions in the Pyrenees, compatible with opening of the Bay of Biscay described by a pole of rotation located in northern France. Although plate-kinematic studies over the last decade increasingly support the scissor-type model, geological studies in the Pyrenees have accumulated arguments in favour of an extensional or transtensional regime in the Pyrenean realm.We perform a detailed plate-kinematic analysis of the Late Jurassic and Cretaceous motion history of Iberia and surrounding plates with respect to Europe. A total of six sea-floor reconstructions in combination with paleomagnetic studies onland allow to recognize four distinct stages. (1) Early rifting and ultraslow spreading since the Kimmeridgean led to the development of an oceanic Neotethys domain north of Iberia. (2) This was followed by ~ 35° CCW rotation of Iberia during the Aptian, kinematically linked to progressive opening of the Bay of Biscay. (3) Motions in the Bay became stagnant during the Albian till Santonian, followed by the latest stages of spreading in the Bay, and (4) onset of largely Tertiary continental collision between Iberia and Europe eventually leading to the present day structure of the belt.Our analysis confirms the results of previous studies indicating that extensional or transtensional motions in the Pyrenean realm during opening of the Bay of Biscay and concurrent rotation of Iberia are incompatible with plate-kinematic reconstructions based on sea-floor anomalies. This invites a reappraisal of the geological data. Convergence in the Pyrenean realm during opening of the Bay and rotation of Iberia was accommodated by up to 300 km of subduction of mantle-dominated ocean floor exhumed during the late Jurassic and early Cretaceous. The stagnant stage in the progressive opening of the Bay indicates that convergence in the Pyrenean realm virtually came to a halt during the Albian. We hypothesize that the lithosphere previously subducted during Aptian convergence became gravitationally unstable, leading to asthenospheric upwelling and consequent magmatism and high temperature metamorphism in the overlying European margin now exposed in the North Pyrenean Zone. Aside from these magmatic and thermal effects, an enhanced gravitational potential energy of the remaining lithosphere column underlain by shallow asthenosphere may have led to a stress state allowing belt-parallel extensional deformation. Such a detachment scenario, inspired by plate-kinematic results, may provide an alternative to explain many of the geological data commonly quoted to infer a transtensional or extensional tectonic regime in the Pyrenees during the rotation of Iberia.  相似文献   

12.
Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.  相似文献   

13.
The coastal Changle-Nan’ao tectonic zone of SE China contains important geological records of the Late Mesozoic orogeny and post-orogenic extension in this part of the Asian continent. The folded and metamorphosed T3–J1 sedimentary rocks are unconformably overlain by Early Cretaceous volcanic rocks or occur as amphibolite facies enclaves in late Jurassic to early Cretaceous gneissic granites. Moreover, all the metamorphic and/or deformed rocks are intruded by Cretaceous fine-grained granitic plutons or dykes. In order to understand the orogenic development, we undertook a comprehensive zircon U–Pb geochronology on a variety of rock types, including paragneiss, migmatitic gneiss, gneissic granite, leucogranite, and fine-grained granitoids. Zircon U–Pb dating on gneissic granites, migmatitic gneisses, and leucogranite dyke yielded a similar age range of 147–135 Ma. Meanwhile, protoliths of some gneissic granites and migmatitic gneisses are found to be late Jurassic magmatic rocks (ca. 165–150 Ma). The little deformed and unmetamorphosed Cretaceous plutons or dykes were dated at 132–117 Ma. These new age data indicate that the orogeny lasted from late Jurassic (ca. 165 Ma) to early Cretaceous (ca. 135 Ma). The tectonic transition from the syn-kinematic magmatism and migmatization (147–136 Ma) to the post-kinematic plutonism (132–117 Ma) occurred at 136–132 Ma.  相似文献   

14.
Plate subduction leads to complex exhumation processes on continents. The Huangling Massif lies at the northern margin of the South China Block. Whether the Huangling Massif was exhumed as a watershed of the middle reaches of the Paleo-Yangtze River during the Mesozoic remains under debate. We examined the exhumation history of the Huangling Massif based on six granite bedrock samples, using apatite fission track (AFT) and apatite and zircon (U-Th)/He (AHe and ZHe) thermochronology. These samples yielded ages of 157–132 Ma (ZHe), 119–106 Ma (AFT), and 114–72 Ma (AHe), respectively. Thermal modeling revealed that three phases of rapid cooling occurred during the Late Jurassic–Early Cretaceous, late Early Cretaceous, and Late Cretaceous. These exhumation processes led to the high topographic relief responsible for the emergence of the Huangling Massif. The integrated of our new data with published sedimentological records suggests that the Huangling Massif might have been the watershed of the middle reaches of the Paleo-Yangtze River since the Cretaceous. At that time, the rivers flowed westward into the Sichuan Basin and eastward into the Jianghan Basin. The subduction of the Pacific Plate beneath the Asian continent in the Mesozoic deeply influenced the geomorphic evolution of the South China Block.  相似文献   

15.
Three melting events of the earth's crust occurred during the period of 220-120 Ma in the Shandong Pe-ninsula. Three subcycles of granitoid magma including six rock series were generated in the faulted granitoidmagma belt. The parent magma of several rock series formed earliest originated from the lower crust ofgranulite facies; following the increase of geothermal temperature the source magma would migrate into themiddle crust of amphibolite facies. In the diapiric granitoid magma belt, the granitoid magma was formed firstin granitic layer of the upper crust, and then in the middle crust. In each subcycle the generation of magmastarted with the generation of more mafic one and finished with low eutectic one; they were formed in the formof layered melting in a particular position of the crust.  相似文献   

16.
The eastern pari of the Xing-Meng Orogenic Belt( XMOB )consists of the Lesser Xing'an-Zhangguangcai Range Orogenic belt, the Bureya-Jiamusi-khanka Block and the Sikhote-Alin accretionary belt. This area is located between the Paleo-Asian oceanic and Paleo-Pacific tectonic regimes. Recent researches imply that the Paleo-Pacific subduction might have begun since early Permian and influenced the both sides of the Mudanjiang Fault during Triassic, which generated a N-S trending magmatic belt and accretionary complexes, such as the Heilongjiang Complex. In Late Jurassic to Early Cretaceous, some tectono st rati graph ic terranes were produced in Sikhote-Alin, which were then dismembered and migrated northwards in late Early Cretaceous by sinistral strike-slip faults. The continental margin parallel transportion weakened subduction-related magmatism in NE China which was under an extensional setting. However, in Lite Cretaceous, the Paleo-Pacific subduction was re-Activated in the eastern XMOB, which contributed to the magmatism in Sikhote-Alin.  相似文献   

17.
LA-ICP-MS U-Pb dating, whole -rock geochemistry and Hf isotopic analyses for the Jianshanzi volcanic rocks in the Kaiyuan area are presented to explore the Late Paleozoic -Early Mesozoic tectonic evolution history of the eastern segment of the northern margin of the North China block. The detailed research indicates that the protolith of Jianshanzi metamorphic volcanic rocks includes rhyolite, dacite and andesite, they are calc-alkaline series and metaluminous-weak peraluminous rocks. According to the zircon U-Pb dating, the metamorphic rhyolite and metamorphic andesite formed in the Late Permian (256. 1 +/- 1. 5Ma, 252.4 +/- 1. 7Ma) and the Late Triassic (222. 4 +/- 1. 8Ma, 227. 9 +/- 1. 2Ma), respectively. They are characteristized by enrichment in light rare earth elements and large ion lithophile elements, and depletion of heavy rare earth elements and high field strength elements. Metamorphic rhyolite has an obvious negative Eu anomaly with epsilon(Hf) ( t) values of 10. 83 + 8. 10 and the second -stage model are 698 similar to 1967Ma. They are mainly due to the partial melting of the juvenile basaltic lower crust and the contamination of a small amount of ancient crustal materials. Metamorphic andesite has no obvious Eu anomaly, and the epsilon(Hf)( t) value and the second -stage model are +4.54 similar to + 6. 79 and 825 similar to 968 Ma, which may be the product of partial melting of basic lower crust. There are two periods of magmatism in Jianshanzi volcanic rocks: Late Permian -Early Triassic (247 similar to 256Ma) and Late Triassic (similar to 225Ma). The material composition of the Jianshanzi volcanic rocks is characterized by different times and different tectonic backgrounds. It is comprehensively believed that the eastern segment of the northern margin of the North China block was in an active continental margin tectonic environment during the Permian, and the Palaeo-Asian Ocean subducted in both directions; Mantle -derived magma ascends and emplaces, forming a nascent crust and causing crustal thickening. The Paleo-Asian Ocean finally closed in the early Middle Triassic, and the impact of collisional orogeny may have continued until the early Late Triassic.  相似文献   

18.
Numerous traces of paleoseismic events (seismites) were established in Mesozoic–Cenozoic marine sedimentary sequences of the northern Caucasus. These traces are most prominent in the terrigenous Middle Miocene sandy–clayey sediments. Impact of seismic shocks upon the relatively weakly lithified sediments provoked distortion of the primary sedimentary structure, liquefaction of the sandy material, and injections of different morphologies (neptunic dikes and sills). The formation of jointing in sediments fostered their vertical permeability and promoted the migration of diagenetic solutions into the adjacent horizons, which stimulated the formation of subvertical carbonate bodies. The amount and intensity of seismic events varied at different stages of the accumulation of sequences and in different areas of the paleobasin. In the eastern sector of the northern Caucasus, seismic activity similar to the present-day general pattern was likely developed as early as the Middle Miocene: maximum activity in the Dagestan and its westward attenuation. Traces of seismic activity are also recorded in the Maikopian (Oligocene–Lower Miocene) and Lower–Middle Jurassic rocks.  相似文献   

19.
This report presents the results of U–Pb geochronological LA–ICP–MS studies of detrital zircons from metasedimentary rocks of the western part of the Tukuringra terrane. The obtained data show that the Algainskaya, Garmakanskaya, and Teploklyuchevskaya series in the western part of the Tukuringra terrane are not of Middle Paleozoic but of Early Mesozoic age. It is shown that the main sources of clastic matter for these formations were Late Precambrian, Paleozoic, and Late Triassic–Early Jurassic complexes of continental massifs of the Amur superterrane.  相似文献   

20.
The spatial and temporal characteristics of magmatism caused by the Barents–Amerasian Jurassic–Cretaceous plume in conjunction with the geodynamics of destructive transformations of the lithosphere are presented here. The localities of manifestation of magmatism were concentrated mainly out of general contour of the areal occupied by the Siberian superplume, and they demonstrated certain gravitation to the Caledonide–Ellesmeride belts. This suggests an inherited position of both the J–K plume and the initial detachment zone produced by it: this led to formation of the Canadian Basin. The stages in the evolution and character of polycyclic multiphase plume magmatism are substantiated by the geochronology of magmatic provinces in the Arctic region during formation of the Amerasian Basin.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号