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1.
The lateral variability of structural elements in the collision zone of the Cretaceous-Paleocene Achaivayam-Valagin island arc with the northeastern Asian margin is considered. The similarity and difference of Eocene collision structural elements in the north and the south of Kamchatka are shown. In northern Kamchatka, the continent-arc boundary is traced along the Lesnaya-Vatyn Thrust Fault, which completed its evolution about 45 Ma ago. The thin, near-horizontal allochthon of this thrust, composed of island-arc rocks, overlies the deformed but unmetamorphosed terrigeneous sequences of the Asian margin. The general structure of this suture in the Kamchatka Isthmus and southern Koryakia is comparable with the uppermost subduction zone, where a thin lithospheric wedge overlaps intensely deformed sediments detached from the plunging plate. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago with thrusting of island-arc complexes over terrigenous rocks of continental margin. However, the thickness of the allochthon was much greater than in the north. Immediately after this event, both the autochthon and lower part of allochthon were deformed and subsided to a significant depth. This subsidence gave rise to metamorphism of both the autochthon (Kolpakov and Kamchatka groups, Kheivan Formation) and lower allochthon (Andrianovka and Khimka formations). The anomalously fast heating of the crust was most likely related to the ascent of asthenospheric masses due to slab breakoff, when the Eurasian Plate was plunging beneath the Achaivayam-Valagin arc.  相似文献   

2.
This article gives an account of the results of the U-Pb-SHRIMP study of zircons derived from gneissoid and equigranular granitoids of the Malka Uplift of the Sredynnyi Range in Kamchatka. It was established that intrusion and crystallization of granitoids occurred in the time interval from 76.2 ± 1.5 to 83.1 ± 2.0 Ma. The texture of zircon crystals suggests their magmatic origin. The obtained data reliably confirm that granite formation and emplacement of the recently formed continental crust in Kamchatka took place in the Late Cretaceous (Campanian).  相似文献   

3.
Migmatization and granite-forming processes were widespread in the southern Sredinnyi Range of the Kamchatka Peninsula in the Early Eocene (at approximately 52 ± 2 Ma). The paper presents data on the composition and genesis of the Early Eocene granitoids. The Malka Rise contains both equigranular peraluminous garnet-bearing granites, on the one hand, and migmatites and tonalites and trondhjemites (TTG), on the other. The petrography and petrochemistry of most granites in the Malka Rise in the Sredinnyi Range (high SiO2 concentrations, the presence of muscovite and garnet, the proportions of their Al saturation index ASI and SiO2, FeOt + MgO + TiO2, and SiO2, Al2O3/TiO2, and CaO/Na2O), and the composition of biotite in these rocks highlight their similarities with S-granites. The character of the REE patterns and the Sr and Y concentrations suggest that the granites and TTG were formed via the melting of sources of two types: metasediments and metabasites. The metasedimentary nature of the protolith of most of the granitoids also follows from similarities between the REE patterns of the granitoids and host metaterrigenous rocks of the Kolpakova and Kamchatka groups. The variations in the Rb/Ba and Rb/Sr ratios of the granites imply that their protoliths could be sedimentary rocks both depleted and enriched in pelite components. The facts that, along with S-granites, some of the granites are TTG, which likely had mafic protoliths, make the Early Eocene granites generally similar to S-granites of the Cordilleran type. The collision of the Achaivayam-Valaginskii ensimatic island arc with the Kamchatka margin of Eurasia started at 55–53 Ma and predated Early Eocene magmatism. In the course of this collision, arc complexes were obducted over continental marginal rocks, and this resulted in their rapid subsidence, crustal heating, magma generation, and the derivation of the granites, tonalites, and trondhjemites at 52 ± 2 Ma at temperatures of 645–815°C. This rapid heating (duirng no more than 3–5 Ma) required an additional heat source, which was likely the mantle. The latter heated the bottom of the crust at the detachment of the slab. The influx of mantle material resulted in intrusions of the norite-cortlandite association, which was coeval with the granites and was accompanied by Cu-Ni sulfide mineralization. The composition of the granitoids and data on the intrusions of the norite-cortlandite association suggest that mantle material was involved in Early Eocene syncollisional magma generation in Kamchatka. Newly obtained U-Pb zircon SHRIMP dates of the granitoids and recently published data on the age of the norite-cortlandite intrusions indicate that they are coeval and make it possible to recognize an Early Eocene phase of magmatic activity in Kamchatka.  相似文献   

4.
For the first time, the age of the beginning of the volcanic activity within Sredinny metamorphic Massif is determined (7–6 Ma). We suppose that this event was caused by the collision of Kamchatka with the Kronotsk arc that started about 7 Ma from accretion of Shipunsky peninsula. We demonstrate that at least two types of rocks were erupted within Sredinny Range of Kamchatka in late Miocene times: typical islandarc rocks were produced in the central and northern parts of the Range, and hybrid type rocks—in its southernmost part.  相似文献   

5.
In the Late Cretaceous starting from the early Coniacian, three parallel suprasubduction structural units have developed contemporaneously in the northwestern Paleopacific framework: (1) the Okhotsk-Chukchi arc at the Asian continental margin, (2) the West Kamchatka and Essoveem ensialic arcs at the northwestern margins of the Kamchatka and Central Koryak continental blocks, and (3) the Achaivayam-Valagin ensimatic arc that extended to the southwest as the Lesser Kuril ensialic arc at the southern margin of the Sea of Okhotsk continental block. In this setting, the geodynamics of the Paleopacific plates exerted an effect only on the evolution of the outer (relative to the continent) ensimatic island arc, whereas the vast inner region between this arc and the continent evolved independently. As is seen from the character of the gravity field and seismic refractor velocity, the Kamchatka and Sea of Okhotsk continental blocks differ in the structure of the consolidated crust. These blocks collided with each other and the Asian continent in the middle Campanian (77 Ma ago). The extensive pre-Paleogene land that existed on the place of the present-day Sea of Okhotsk probably supplied the terrigenous material deposited since the late Campanian on the oceanic crust of the backarc basin to the south of the rise of inner continental blocks as the Khozgon, Lesnaya, and Ukelayat flysch complexes. The accretion of the Olyutor (Achaivayam) and Valagin segments of the ensimatic arc had different consequences due to the difference in thickness of the Earth’s crust. The Valagin segment was formed on an older basement and had a much greater thickness of the crust than the Olyutor segment. As follows from computations and the results of physical modeling, the island arcs having crust more than 25 km in thickness collide with the continental margin and are thrust over the latter. In the case under consideration, the thrusting of the Valagin segment led to metamorphism of the underlying rocks. The crust of the Olyutor segment was much thinner. The contact of this segment with the continental margin resulted only in surficial accretion, which did not bring about metamorphism, and the underlying lithospheric plate continued to plunge into the subduction zone.  相似文献   

6.
台湾造山带是中新世晚期以来相邻菲律宾海板块往北西方向移动,导致北吕宋岛弧系统及弧前增生楔与欧亚大陆边缘斜碰撞形成的。目前该造山带仍在活动,虽然规模很小,但形成了多数大型碰撞造山带中的所有构造单元,是研究年轻造山系统的理想野外实验室,为理解西太平洋弧-陆碰撞过程和边缘海演化提供了一个独特的窗口。本文总结了二十一世纪以来对台湾造山带的诸多研究进展,讨论了其构造单元划分及演化过程。我们将台湾造山带重新划分为6个构造单元,由西至东分依次为:(1)西部前陆盆地;(2)中央山脉褶皱逆冲带;(3)太鲁阁带;(4)玉里-利吉蛇绿混杂岩带;(5)纵谷磨拉石盆地;(6)海岸山脉岛弧系统。其中,西部前陆盆地为6.5Ma以来伴随台湾造山带的隆升剥蚀形成沉积盆地。中央山脉褶皱逆冲带为新生代(57~5.3Ma)欧亚大陆东缘伸展盆地沉积物由于弧-陆碰撞受褶皱、逆冲及变质作用改造形成的。太鲁阁带是造山带中的古老陆块,主要记录中生代古太平洋俯冲在欧亚大陆活动边缘形成的岩浆、沉积和变质岩作用。玉里-利吉蛇绿混杂岩带和海岸山脉岛弧系统分别为中新世中期(~18Ma)以来南中国海板块向菲律宾海板块之下俯冲形成的岛弧和弧前增生楔,其中玉里混杂岩中有典型低温高压变质作用记录,变质年龄为11~9Ma;岛弧火山作用的主要时限为9.2~4.2Ma。纵谷磨拉石盆地记录1.1Ma以来的山间盆地沉积。台湾造山带的构造演化可划分为4个阶段:(a)古太平洋板块俯冲与欧亚大陆边缘增生阶段(200~60Ma);(b)欧亚大陆东缘伸展和南中国海扩张阶段(60~18Ma);(c)南中国海俯冲阶段(18~4Ma);(d)弧-陆碰撞阶段(<6Ma)。台湾弧-陆碰撞造山带是一个特殊案例,其弧-陆碰撞并不伴随着弧-陆之间的洋盆消亡,而是由于北吕宋岛弧及弧前增生楔伴随菲律宾海板块运动向西北方走滑,仰冲到欧亚大陆边缘,形成现今的台湾造山带。  相似文献   

7.
杨帆  姜艳艳  陈井胜  韩兴 《岩石学报》2022,(8):2467-2488
本文对华北克拉通北缘中段赤峰撰山子矿区二长闪长岩、花岗(斑)岩等进行了岩相学、地球化学、锆石U-Pb定年以及Hf同位素研究,以期对古亚洲洋演化形成制约。锆石U-Pb定年显示,二长闪长岩和花岗岩形成于早石炭世(341.0±2.2Ma、324.1±4.3Ma),花岗斑岩形成于晚二叠世(252.8±3.2Ma、252.0±1.5Ma)。岩石地球化学及Hf同位素表明,二长闪长岩为高钾钙碱性I型花岗岩,形成于火山弧环境,其源区可能是俯冲板片脱水交代的地幔楔部分熔融产生玄武质岩浆上涌,导致新生地壳物质的部分熔融,并有部分玄武质岩浆加入形成的产物;花岗岩及花岗斑岩均为高钾钙碱性A型花岗岩,花岗岩形成于火山弧环境,花岗斑岩形成于造山后伸展环境,二者皆为新生地壳部分熔融的产物。综合前人研究认为,早石炭世-晚二叠世,研究区经历了古亚洲洋俯冲、弧-陆碰撞以及造山后伸展等阶段。  相似文献   

8.
Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.  相似文献   

9.
Two belts of subaerial volcanic rocks—the Eocene Kinkil belt and the Neogene belt of the Sredinny Range—extend along the Kamchatka Isthmus. It is suggested that their formation is related to subduction of the oceanic lithosphere beneath the continental margin of North Kamchatka. The oceanic lithosphere consumed in the subduction zones could have been formed as a result of active spreading in the Komandorsky Basin. In the simplest case, both spreading and subduction reflect the northwestward motion of the lithosphere of the Komandorsky Plate relative to Kamchatka, the Shirshov Ridge, and the Aleutian Basin combined into one relatively immobile plate conventionally called the North American Plate. The authors perform a simulation of conjugate spreading and subduction. The most important parameter determining the regional geodynamics—the velocity of the Komandorsky Plate moving relative to the North American Plate—is taken as 2.5, 5.0, and 7.5 cm/yr. The calculated ages of the onset and end of volcanic activity in the aforementioned belts are compared with the dates obtained with the isotopic and paleontological methods. For the Eocene Kinkil belt, where volcanism started 44 Ma ago, the model age of the onset of subduction depends on the accepted velocity of the motion of the Komandorsky Plate and varies from 54 Ma at the velocity of 2.5 cm/yr to 47.5 Ma at the velocity of 7.5 cm/yr. It can be assumed that the model of fast subduction in this age interval is most consistent with the geological data. For the Miocene-Pliocene belt of the Sredinny Range, assuming the velocity of the motion of the Komandorsky Plate at 5.0 and 7.5 cm/yr, multiple rifting at the boundary with the Shirshov Ridge should be assumed. Therefore, for the end of the Neogene, a model with low velocity (2.5–5.0 cm/yr, i.e., about 4.0 cm/yr) is preferable.  相似文献   

10.
Structural evolution of the Kamchatka–Aleutian junction area in late Mesozoic and Tertiary was generally controlled by (1) the processes of subduction in Kronotskiy and Proto-Kamchatka subduction zones and (2) collision of the Kronotskiy arc against NE Eurasia margin. Two structural zones of the pre-Pliocene age and six structural assemblages are recognized in studied region. 1: Eastern ranges zone comprises SE-vergent thrust folded belt, which evolved in accretionary and collisional setting. Two structural assemblages (ER1 and ER2), developed there, document shortening in the NW–SE direction and in the N–S direction, respectively. 2: Eastern Peninsulas zone generally corresponds to Kronotskiy arc terrane. Four structural assemblages are recognized in this zone. They characterize (1) precollisional deformations in the accretionary wedge (EP1) and in the fore-arc basin and volcanic belt (EP2), and (2) syn-collisional deformation of the entire Kronotskiy terrane in plunging folds (EP3) and deformations in the foreland basin (EP4). Analysis of paleomagnetic declinations versus present day structural strike in the Kronotskiy arc terrane shows that originally the arc was trending from west to east. Relative position of the accretionary wedge, fore-arc basin and volcanic belt, as well as northward dipping thrusts in accretionary wedge indicate, that a northward dipping subduction zone was located south of the arc. The accretionary wedge developed from the Late Cretaceous through the Eocene, and it implies that the subduction zone maintained its direction and position during this time. It implies that Kronotskiy arc was neither a part of the Pacific nor Kula plates and was located on an individual smaller plate, which included the arc and Vetlovka back-arc basin. Motion of the Kronotskiy arc towards Eurasia was connected only with NW-directed subduction at Kamchatka margin since Middle Eocene (42–44 Ma). Emplacement of the Kronotskiy arc at the Kamchatka margin occurred between Late Eocene and Early Miocene. This is based on the age of syn-collisional plunging folds in Kronotskiy terrane, and provenance data for the Upper Eocene to Middle Miocene Tyushevka basin, which indicate in situ evolution of the basin with respect to Kamchatka. Collision was controlled by the common motion of the Kronotskiy arc with Pacific plate towards the northwest, and by the motion of the Eurasian margin towards the south. The latter motion was responsible for the southward deflection of the western part of the Kronotskiy arc (EP3 structures), and for oblique transpressional structures in the collisional belt (ER2 structures).  相似文献   

11.
A comparative analysis of the geological setting and composition was carried out for the Cretaceous, Eocene, and Miocene-Pliocene granitoids of Kamchatka. New petrochemical, geochemical, and isotope data are reported. The alkaline granitoids and granites of the Sredinny Range in Kamchatka have an enriched isotope composition and elevated contents of Rb, Th, U, and LREE as compared to their analogs in the eastern part of the region. The largest scale Cretaceous crustal magmatism was formed in a setting of intense tectonic motions and metamorphism. The smaller scale Eocene magmatism produced crustal granitoid melts in the Sredinny Range of Kamchatka and mantle initially basaltic melts that evolved to granites in the southeastern Kamchatka and Ganalsky Range. These processes were accompanied by the rejuvenated of the older crust and the local formation of a new crust. The low-volume crustal-mantle Miocene-Pliocene magmatism of variable composition was developed in volcanic belts, forming the upper crustal horizons on the existing crystalline basement.  相似文献   

12.
The problem of the geochemical classification of granitoid magmatism in the zone of interaction of oceanic and continental plates is considered in this paper by the example of Mesozoic granitoids of the Krutogorova and Kol’ intrusive complexes of the Sredinny Range, Kamchatka. Based on new geological, petrological, and geochemical data (including the Sr, Nd, and Pb isotope systematics of rocks), it was shown that the protoliths of the granitoids were volcanic-terrigenous sequences accumulated within a Cretaceous marginal basin in the eastern Asian continent. The granitoids crystallized at ～80 Ma (SHRIMP U-Pb age) under the conditions of the andalusite-sillimanite depth facies corresponding to a pressure of approximately 2 kbar and induced contact metamorphism in the host sequences, which are made up of sediments with sheetlike bodies of mafic and ultramafic volcanics (Kikhchik Group and its metamorphic analogues of the Kolpakova, Kamchatka, and Malki groups). The lower age boundary of sedimentation of the host sequences and the time of basic volcanism coincide with the beginning of the formation of the Okhotsk-Chukotka volcanic belt. Such a correlation is not accidental and reflects a genetic connection between the processes of magmatic activation in the continental-margin sedimentary basin and the formation of the continental margin volcanic belt in eastern Asia. The development of basic volcanism in the sedimentary basin accompanied by the ascent of deep fluids resulted in the entrainment of crustal materials into magmatic processes and the formation of crustal magma chambers, the activity of which was manifested by the eruption of intermediate and silicic lavas and emplacement of shallow granitoid intrusions of considerable areal extent. These intrusions induced contact metamorphism in the enclosing volcanosedimentary complexes. The subsequent Eocene (60-50 Ma) collision processes related to the obduction of the oceanic segment of the crust of the transitional zone onto the Asian continental margin resulted in the tectonic piling of the rocks of Central Kamchatka and strong crustal thickening, which was favorable for its metamorphic alteration reaching the kyanite-sillimanite depth level of the amphibolite facies under the influence of a thermal front and deep fluids affecting lower crustal zones. The Eocene regional metamorphism caused not only metamorphic transformations, migmatization, and granitization in the sequences of the Sredinny Range, which underwent only contact hornfels formation during the first stage, but also metamorphism, migmatization, and extensive foliation in the igneous rocks of the Kol’ and Krutogorova complexes, which were transformed into gneissic metagranites.  相似文献   

13.
俯冲陆壳部分熔融形成埃达克质岩浆   总被引：4，自引：0，他引：4  
在岛弧背景,埃达克质岩浆形成于俯冲洋壳板片的部分熔融已得到共识,但在大陆碰撞背景,埃达克质岩浆是否形成于俯冲陆壳的部分熔融尚未有研究报导。对祁连山东南部关山花岗岩（229 Ma）的地球化学和岩石成因研究提供了俯冲陆壳部分熔融形成埃达克质岩浆的一个实例。关山花岗岩以高K（K2O=4.12%~5.16%,K2O/Na2O=0.97~1.64）、高Sr/Y比值（13.6~84.1）、低Y （6.8×10-6 ~15.7×10-6 ）和低HREE（eg. Yb=0.62×10-6~1.31×10-6）为特征,并具有强分异的稀土元素组成模式[（La/Yb）N=17.5~41.6]和演化的Sr-Nd同位素组成[初始87Sr/86Sr=0.70587~0.70714, εNd（t）=-10.9~-5.16, tDM=1.10~1.49 Ga]。这些地球化学特征表明关山花岗岩属于大陆型（C型）埃达克质岩石,而明显不同于俯冲洋壳板片或底侵玄武质下地壳部分熔融形成的埃达克岩。关山花岗岩Pb-Sr-Nd同位素组成与商丹断裂北侧的祁连山前寒武纪基底岩石、早古生代火山岩和花岗岩类存在显著差异,但类似于商丹断裂南侧秦岭早中生代花岗岩类的Pb-Sr-Nd同位素组成,由此认为具有埃达克质的关山花岗岩的岩浆来自于南部俯冲陆壳物质的部分熔融,并提出了大陆碰撞背景中埃达克质岩浆产生的一个新的地质模型。  相似文献   

14.
The active Taiwan orogen is the product of a two stage collision, that included first the collision of the Hengchun ridge, an accretionary wedge, with the Chinese continental margin, and second the collision of the Luzon trough and volcanic arc, from the Philippine Sea plate, with the Central Range of Taiwan. During the first stage, the strength of the continental margin induced a decrease of the convergence rate that controlled the final Central Range orientation and induced the second stage of the collision. Taking into account the kinematics of the plate interaction, a reconstruction of the Taiwan collision during the last 4 Ma is proposed.  相似文献   

15.
《Gondwana Research》2013,24(4):1402-1428
The formation of collisional orogens is a prominent feature in convergent plate margins. It is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision. The Paleozoic convergence between the South China Block (SCB) and the North China Block (NCB) is associated with a series of tectonic processes such as oceanic subduction, terrane accretion and continental collision, resulting in the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt. While the arc–continent collision orogeny is significant during the Paleozoic in the Qinling–Tongbai–Hong'an orogens of central China, the continent–continent collision orogeny is prominent during the early Mesozoic in the Dabie–Sulu orogens of east-central China. This article presents an overview of regional geology, geochronology and geochemistry for the composite orogenic belt. The Qinling–Tongbai–Hong'an orogens exhibit the early Paleozoic HP–UHP metamorphism, the Carboniferous HP metamorphism and the Paleozoic arc-type magmatism, but the three tectonothermal events are absent in the Dabie–Sulu orogens. The Triassic UHP metamorphism is prominent in the Dabie–Sulu orogens, but it is absent in the Qinling–Tongbai orogens. The Hong'an orogen records both the HP and UHP metamorphism of Triassic age, and collided continental margins contain both the juvenile and ancient crustal rocks. So do in the Qinling and Tongbai orogens. In contrast, only ancient crustal rocks were involved in the UHP metamorphism in the Dabie–Sulu orogenic belt, without involvement of the juvenile arc crust. On the other hand, the deformed and low-grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late Permian to early Triassic along the northern margin of the Dabie–Sulu orogenic belt, and it was developed on the passive oceanic margin during subduction in the early Paleozoic along the northern margin of the Qinling orogen.Three episodes of arc–continent collision are suggested to occur during the Paleozoic continental convergence between the SCB and NCB. The first episode of arc–continent collision is caused by northward subduction of the North Qinling unit beneath the Erlangping unit, resulting in UHP metamorphism at ca. 480–490 Ma and the accretion of the North Qinling unit to the NCB. The second episode of arc–continent collision is caused by northward subduction of the Prototethyan oceanic crust beneath an Andes-type continental arc, leading to granulite-facies metamorphism at ca. 420–430 Ma and the accretion of the Shangdan arc terrane to the NCB and reworking of the North Qinling, Erlangping and Kuanping units. The third episode of arc–continent collision is caused by northward subduction of the Paleotethyan oceanic crust, resulting in the HP eclogite-facies metamorphism at ca. 310 Ma in the Hong'an orogen and low-P metamorphism in the Qinling–Tongbai orogens as well as crustal accretion to the NCB. The closure of backarc basins is also associated with the arc–continent collision processes, with the possible cause for granulite-facies metamorphism. The massive continental subduction of the SCB beneath the NCB took place in the Triassic with the final continent–continent collision and UHP metamorphism at ca. 225–240 Ma. Therefore, the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc-type magmatism to arc–continent and continent–continent collision.  相似文献   

16.
New data on the chemical and rare-element composition and age of the rocks referred earlier to the Iruney suite of the Kamchatka Isthmus are received. In the recent structure these rocks compose the structural–strata complexes of the nappe-folded Lesnovsky Rise. Radiolarian analysis data substantiate that the deposits belonging to the Ening series and the middle and upper parts of the Iruney suite were formed in a single sedimentation basin in the Campanian time. The discovery of a new occurrence of Prunobrachidae representatives on the Kamchatka Peninsula allows us to draw wide interregional correlations and reconstruct the sedimentation conditions. The studied volcanites relate to different igneous series and were formed in geodynamic conditions of the marginal sea and the volcanic arc. The igneous rocks of the Ening stratum are similar to the N-MOR and OI basalts that were formed within the marginal sea (Iruney Marginal Sea) basin. The Upper Cretaceous formations of the eastern slope of the Sredinny Range were formed within the volcanic rise with the island-arc type of volcanism. The younger Eocene igneous rocks of the neo-autochthon (granites and granodiorites) and the volcanic rocks of the Kinkil suite mark a new orogenic stage of development of the Kamchatka margin.  相似文献   

17.
青藏高原拉萨地块发育着中新世斑岩,该后碰撞时期的斑岩因与斑岩型Cu-Mo矿床有着密切关系已被前人做过大量研究。然而对于拉萨地块西部未成矿斑岩岩体的年代学、地球化学报道研究较少。本文对拉萨地块西部亚热南复式岩体识别出的两类侵入岩进行了锆石LA-ICP-MS U-Pb定年和岩石地球化学研究表明,亚热南复式岩体主要由始新世黑云母二长花岗岩(年龄49.4±0.9Ma)和中新世花岗斑岩(年龄16.3~16.5Ma)组成。始新世黑云母二长花岗岩属钾玄岩系列准铝质-弱过铝质,具有低的Sr/Y、(La/Yb)N值高Y、YbN值具有典型的岛弧岩浆岩性质;中新世花岗斑岩为钾玄岩系列、准铝质,具有类埃达克质特征。这两种岩性所反映的源区亦存在差别,始新世黑云母二长花岗岩源区为地幔楔混染过的中下地壳;而具有埃达克性质的花岗斑岩则可能是源于古老地壳部分熔融。结合年代学及构造背景,推论出始新世黑云母二长花岗岩的岩石成因为新特提斯洋板片断离引发混染过的中下地壳发生熔融并结晶分异形成;而中新世花岗斑岩则形成于某种动力学机制引发的古老下地壳熔融后侵位于上地壳。  相似文献   

18.
Jean-Luc Epard  Albrecht Steck   《Tectonophysics》2008,451(1-4):242-264
A continental subduction-related and multistage exhumation process for the Tso Morari ultra-high pressure nappe is proposed. The model is constrained by published thermo-barometry and age data, combined with new geological and tectonic maps. Additionally, observations on the structural and metamorphic evolution of the Tso Morari area and the North Himalayan nappes are presented. The northern margin of the Indian continental crust was subducted to a depth of > 90 km below Asia after continental collision some 55 Ma ago. The underthrusting was accompanied by the detachment and accretion of Late Proterozoic to Early Eocene sediments, creating the North Himalayan accretionary wedge, in front of the active Asian margin and the 103–50 Ma Ladakh arc batholith. The basic dikes in the Ordovician Tso Morari granite were transformed to eclogites with crystallization of coesite, some 53 Ma ago at a depth of > 90 km (> 27 kbar) and temperatures of 500 to 600 °C. The detachment and extrusion of the low density Tso Morari nappe, composed of 70% of the Tso Morari granite and 30% of graywackes with some eclogitic dikes, occurred by ductile pure and simple shear deformation. It was pushed by buoyancy forces and by squeezing between the underthrusted Indian lithosphere and the Asian mantle wedge. The extruding Tso Morari nappe reached a depth of 35 km at the base of the North Himalayan accretionary wedge some 48 Ma ago. There the whole nappe stack recrystallized under amphibolite facies conditions of a Barrovian regional metamorphism with a metamorphic field gradient of 20 °C/km. An intense schistosity with a W–E oriented stretching lineation L1 and top-to-the E shear criteria and crystallization of oriented sillimanite needles after kyanite, testify to the Tso Morari nappe extrusion and pressure drop. The whole nappe stack, comprising from the base to top the Tso Morari, Tetraogal, Karzok and Mata–Nyimaling-Tsarap nappes, was overprinted by new schistosities with a first N-directed and a second NE-directed stretching lineation L2 and L3 reaching the base of the North Himalayan accretionary wedge. They are characterized by top-to-the S and SW shear criteria. This structural overprint was related to an early N- and a younger NE-directed underthrusting of the Indian plate below Asia that was accompanied by anticlockwise rotation of India. The warping of the Tso Morari dome started already some 48 Ma ago with the formation of an extruding nappe at depth. The Tso Morari dome reached a depth of 15 km about 40 Ma ago in the eastern Kiagar La region and 30 Ma ago in the western Nuruchan region. The extrusion rate was of about 3 cm/yr between 53 and 48 Ma, followed by an uplift rate of 1.2 mm/yr between 48 and 30 Ma and of only 0.5 mm/yr after 30 Ma. Geomorphology observations show that the Tso Morari dome is still affected by faults, open regional dome, and basin and pull-apart structures, in a zone of active dextral transpression parallel to the Indus Suture zone.  相似文献   

19.
The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision–related intrusive rock series, i.e., a gabbro–quartz diorite–granodiorite series that formed at 224±2.0 Ma and a monzonitic granite–syenogranite series that formed at 222±2.0 Ma. The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin(material source and thermal source), tectonic setting, genesis and geotectonic implications of these rocks. The results of this analysis indicate that the parent magma of the first series, representing a transition from I-type to S-type granites, formed from thermally triggered partial melting of deep crustal components in an early island–arc–type igneous complex, similar to an I-type granite, during the continental collision orogenic stage. The parent magma of the second series, corresponding to an S-type granite, formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic–Triassic. During continued collision, the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region, forming an immiscible puncture-type complex. The deep tectonothermal events associated with the continent–continent collision during the orogenic cycle are constrained by the compositions and origins of the two series. The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.  相似文献   

20.
The geology of Cretaceous accretionary–collision complexes in central Indonesia is reviewed in this paper. The author and his colleagues have investigated the Cretaceous accretionary–collision complexes by means of radiolarian biostratigraphy and metamorphic petrology, as well as by geological mapping. The results of their work has revealed aspects of the tectonic development of the Sundaland margin in Cretaceous time. The Cretaceous accretionary–collision complexes are composed of various tectonic units formed by accretionary or collision processes, forearc sedimentation, arc volcanism and back arc spreading. The tectonic units consist of chert, limestone, basalt, siliceous shale, sandstone, shale, volcanic breccia, conglomerate, high P/T and ultra high P metamorphic rocks and ultramafic rocks (dismembered ophiolite). All these components were accreted along the Cretaceous convergent margin of the Sundaland Craton. In the Cretaceous, the southeastern margin of Sundaland was surrounded by a marginal sea. An immature volcanic arc was developed peripherally to this marginal sea. An oceanic plate was being subducted beneath the volcanic arc from the south. The oceanic plate carried microcontinents which were detached fragments of Gondwanaland. Oceanic plate subduction caused arc volcanism and formed an accretionary wedge. The accretionary wedge included fragments of oceanic crust such as chert, siliceous shale, limestone and pillow basalt. A Jurassic shallow marine allochthonous formation was emplaced by the collision of continental blocks. This collision also exhumed very high and ultra-high pressure metamorphic rocks from the deeper part of the pre-existing accretionary wedge. Cretaceous tectonic units were rearranged by thrusting and lateral faulting in the Cenozoic era when successive collision of continental blocks and rotation of continental blocks occurred in the Indonesian region.  相似文献   

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