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1.
A spore-pollen assemblage was established for the first time in the sediments of the Malokuril??skaya Formation (Khromova Bay, Shikotan Island, Lesser Kuril Range, Kuril island arc system). This find enabled dating of the sediments of the uppermost part of the Malokuril??skaya Formation, which, based on this data, are referred to the Maastrichtian-Danian boundary. The assemblage of radiolarian species was identified for the entire section of the Malokuril??skaya Formation. In sediments of the lower part of the section, members of the Inoceramus group were described. These findings add new information to the paleontological characteristics of the Malokuril??skaya Formation. Moreover, our work allowed detailed correlation of the palynological assemblage studied with coeval palynological assemblages of adjacent areas. The similarity of Cretaceous-Paleogene sections of the Ust-Palanskaya (West Kamchatka), Uchir (Sakhalin Island) and Malokuril??skaya Formations, the Upper Cretaceous basement and the Cenozoic cover of the underwater Vityaz Ridge support the shared history of the development of the entire transition zone from the marginal Sea of Okhotsk to the Pacific at the Maastrichtian-Danian boundary.  相似文献   

2.
This paper reports the characteristics of granitoids from the Pacific slope of the Kuril island arc system, which were discovered by the authors during geological and geophysical operations in three cruises of the R/V Akademik M. Lavrent’ev. The major and trace element compositions of these rocks were determined, their role in the formation of the submarine Vityaz Ridge was evaluated, and they were compared with granitoids from the Brouton group of submarine volcanoes and xenoliths from Simushir Island and the Sea of Okhotsk. Granitoids from various structures of the basement of the Kuril island arc system are hypabyssal rocks derived from andesite magmas. Their common features are related to the formation on the continental crust under convergent geodynamic conditions involving compression due to the movement and subduction of the Pacific plate beneath the Asian continent. The problem of the basement of the Kuril island arc system was discussed, the composition and age of its rocks were determined, and the history of the geologic development of the Pacific slope of the arc starting from the Late Mesozoic was briefly described.  相似文献   

3.
Tsunamis are reconstructed on the basis of distribution of tsunamigenic sediments in coastal lowland sections. Reflections of anomalous tsunamis are recorded in detail in the lacustrine–boggy sections of the Lesser Kuril Ridge, while only fragments of these sediments have been found on the islands of the Greater Kuril Ridge. The distribution and composition of the sediments left by recent large-scale tsunamis (locally documented 1994 and 1894 Shikotan tsunamis and transoceanic 2011 Tohoku tsunami) are analyzed for the purpose of understanding deposition features during large and megatsunamis. Interregional correlation of the events during the last ~2.5 kyr is carried out with estimation of their scales. It is established that large events took place in the 17th and 18th centuries and approximately at 1.0, 1.4–1.6, 1.7–1.8, and 2.0–2.1 ka ago. New data on large tsunami chronology since the Middle Holocene are presented. A unique natural peatland section with abundant tsunamigenic sand layers is studied on the Pacific side of Zelenyi Island (Rudnya Bay), where deposition continued through the entire Holocene. The largest tsunamis which happened on the South Kuril Islands during the last ~7.5 kyr and can be classed as megatsunamis are revealed.  相似文献   

4.
The stratigraphic subdivision of peat in the Gorobets River valley, the largest river on Shikotan Island, is conducted based on the study of palynological and diatom assemblages, tephrostratigraphy, and radiocarbon dating. The study object is one of the oldest peats in the South Kurile region and reflects the development of natural environments beginning from the early Holocene. Nine phases are distinguished in the development of vegetation on Shikotan Island. The changes in vegetable communities were determined by climatic fluctuations during the Holocene. Their ages, the factors responsible for the appearance and extinction of particular coniferous, small-, and broad-leaved taxa, and changes in their landscape-forming role during different periods of the Holocene, as well as specific features in the formation of the present-day vegetation on the Lesser Kurile Ridge representing a separate floral area, are established. In addition to the climatic and sea-level fluctuations, the development of the island landscapes was determined to a significant extent by its topography, size, and isolation.  相似文献   

5.
In 2003–2004, long-term seismic noise observations were launched on Shikotan Island (Lesser Kuril Range) based on the “Shikotan” dormant regional seismic station. The geological and geophysical data on the registration area are reported. Information about the equipment and its technical specifications is given. The precursors to the strongest local earthquakesthat occurred in the Shikotan Island region in January 2005–March 2007 are identified.  相似文献   

6.
The distribution and stratigraphic potential of the family Prunobrachidae Pessagno are studied. The recent discovery of new locations of the Prunobrachidae representatives in the Northeast of Russia increases the correlation potential of this family. In the Pacific Province in the Northern Hemisphere, the northernmost location of the prunoid radiolarians, is in the Chaun Bay region at 69° N (in modern coordinates) and the southernmost location is the Shikotan Island (Lesser Kuril Ridge) at 43° N. The biostratigraphic subdivision as the layer with Prunobrachium articulatum was first traced in the sections of the Koryak Highlands, Kamchatka Peninsula, and Shikotan Island. The level with Prunobrachium articulatum can be traced from the Russian Platform through the Urals and Western Siberia to the Pacific Margin.  相似文献   

7.
This paper describes the volcanosedimentary complexes of different ages (Late Cretaceous-Early Paleocene, Paleocene-Eocene (?), Oligocene-Early Miocene, and Pliocene-Pleistocene) that compose the basement and sedimentary cover of the submarine Vityaz Ridge. It was found that the Upper Cretaceous sedimentary rocks from the basement of the Vityaz Ridge (felsic) and the Lesser Kuril Ridge (mafic) have different compositions. Matrix mineral assemblages corresponding to the smectite and corrensite stages of epigenesis of Cenozoic rocks were distinguished, and a scheme of the Late Cretaceous-Pleistocene geological evolution of the region was proposed.  相似文献   

8.
Newly obtained precise analytical data on trace elements and radiogenic Sr, Nd, and Pb isotopes testify to anomalous geochemical characteristics of mafic and intermediate Quaternary lavas in Paramushir (in the north of the Kuril arc), Kunashir and Iturup (in the south) islands, which are the largest three islands of the Kuril island arc. The high K and LREE concentrations in the volcanic products in Paramushir Island resulted from the southward expansion of the mantle thermal anomaly of the Kamchatka Peninsula and the involvement of melts related to the melting of oceanic sediments in magma generation. The depleted characteristics of the mafic volcanics are explained by the relatively young tectono-magmatic events during the opening of the Kuril backarc basin. The Kuril island-arc system developed on a heterogeneous basement. The northern islands are a continuation of the volcanic structures of southern Kamchatka, which were formed above an isotopically depleted and hot lithospheric mantle domain of composition close to that of the Pacific MORB type. The southern islands were produced above an isotopically enriched and cold lithospheric domain of the Indian-Ocean MORB type, which was modified in relation to relatively young backarc tectono-magmatic processes. Although issues related to the genesis of the transverse geochemical zoning were beyond the originally formulated scope of our research, the homogeneous enough isotopic composition of the rear-arc lavas in the absence of any mineralogical and geochemical lines of evidence of crustal contamination suggests an independent magmatic source.  相似文献   

9.
The results of reinterpretation of the geophysical data obtained during the study of the central sector of the Kuril Island Arc (2005–2010) are reported. The new boundaries of the shallow bedding of the basement and its block uplifts of varied composition are defined within the previously discovered zone of tectonic stretching and destruction of the Vityaz submarine ridge and interarc trough. Interblock depressions filled with sedimentary and volcanogenic-sedimentary rocks are distinguished. Areas represented by volcanoplutonic complexes including basic and sialic series (up to granite) are distinguished within the unbroken basement of the Vityaz Ridge. Intrusions and volcanic edifices composed of basic rocks are registered on the whole area studied. The relationship between the formation of the destruction zone and the geodynamic processes in the mantle is illustrated by the map of the Moho relief and structural-density model of the Earth’s crust.  相似文献   

10.
The variations of petrogenic oxides and trace elements have been studied in the Cretaceous volcanic rocks recovered by a deep borehole from the depth interval of 1253–4011 m on Moneron Island. The volcanic section is subdivided into two complexes: the Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous Complex occur below 1500 m. Chemically, they belong to low-potassium island arc tholeiites, and their trace element distribution suggests their formation in a suprasubduction mantle wedge under the influence of water fluids that were subsequently released from subducted sediments and oceanic plate during the dehydration of subducted sedimentary rocks and oceanic basalts and, finally, mainly from basalts. The Early Cretaceous basalts from the borehole are interpreted as ascribing to the frontal part of the Moneron-Samarga island arc system. The volcanic rocks of the Late Cretaceous Complex are situated at depths above 1500 m. They also were formed in a suprasubduction setting, but already within the East Sikhote-Alin continental-margin volcanic belt that was initiated after the accretion of the Moneron-Samarga island arc system to the Asian continent. The island-arc section of the Moneron borehole contains basaltic andesite dikes, which are geochemically comparable with the Early-Middle Miocene volcanic rocks of Southwestern Sakhalin.  相似文献   

11.
This paper reports the results of geological studies at the submarine Vityaz Ridge carried out during cruises 37 and 41 on the R/V “Akademik Lavrent’ev” in 2005 and 2006. The studied area is located at the near-island trench of the slope in the central part of the Kurile island arc. Morphologically, it consists of two parts: inner volcanic arc represented by the Great Kurile Range and outer arc corresponding to the submarine Vityaz Ridge. Diverse rocks that compose the basement and sedimentary cover of the ridge were recovered by dredging. Based on K-Ar dating and geochemistry, the volcanics were divided into Paleocene, Eocene, late Oligocene, and Pliocene-Pleistocene complexes. Each of the distinguished complexes reflects the tectonomagmatic stage in the ridge evolution. The geochemical and isotope data on the volcanics indicate the contribution of ancient crustal material in magma source and, correspondingly, the formation of this structure on the continental basement. Two-stage model ages, TDM2, vary in a wide range from zero values in the mafic rocks to 0.77 Ga in felsic varieties, pointing to the presence of Precambrian protolith in the source of the felsic rocks of the Vityaz Ridge. The Pliocene-Pleistocene volcanics are classed with the tholeiitic, calc-alkaline, and subalkaline series, which differ in alkali contents and REE fractionation. The values of (La/Sm)N and (La/Yb)N ratios vary from 0.74 and 0,84 in the tholeiitic varieties to 1.19 and 1.44 in the calcalkaline and 2.32 and 3.73 in the subalkaline rocks. All three varieties occur within the same volcanic edifices and were formed during differentiation of magmatic melt that were channeled along fault zones from the mantle source slightly enriched in crustal component  相似文献   

12.
The Kuril islands constitute a volcanic island arc-trench system,stretching from eastern Hokkaido(Japan)to Kamchatka(Russia) along the northwestern Pacific subduction system.The current arc consists of several volcanic islands mainly with Neogene basement and capped by several,predominantly andesitic,active subduction stratovolcanoes.Kunashir Island is the southwestern-most island of the arc,just off the Hokkaido coast and represents the study area in this paper.The island is composed of a Lower Complex of mainly late Miocene to Pliocene volcanic rocks,covered by an Upper Complex of younger(basaltic)andesitic lava flows and tuffs on which currently four active volcanic edifices are built.In the Lower Complex sub-volcanic and deeper-seated intrusives of the so-called Prasolov and Dokuchaev magmatic complexes are found.More differentiated,tonalitic-granodioritic rocks were collected from these small intrusive bodies.An early Oligocene zircon LA-ICP-MS U/Pb age of 31 Ma for the Prasolov Complex was obtained,showing that the basement of Kunashir Island is older than previously thought.Thermochronometry(apatite fission-track and U-Th-Sm/He and zircon U-Th/He analyses) further shows that the magmatic basement of the island was rapidly exhumed in the Pleistocene to present levels in a differential pattern,with He-ages ranging from 1.9 to 0.8 Ma.It is shown that the northern section of the island was hereby exhumed more intensely.  相似文献   

13.
Graywackes and shales of the Bols’shoi Lyakhov Island originally attributed to the Mesozoic were subsequently considered based on microfossils as the Late Proterozoic in age. At present, these sediments in the greater part of the island are dated back to the Permian based on palynological assemblages. In the examined area of the island, this siliciclastic complex is intensely deformed and tectonically juxtaposed with blocks of oceanic and island-arc rocks exhumed along the South Anyui suture. The complex is largely composed of turbidites with members displaying hummocky cross-stratification. The studied mineral and geochemical characteristics of the rocks defined three provenances of clastic material: volcanic island arc, sedimentary cover and/or basement of the ancient platform, and exotic blocks of oceanic and island-arc rocks such as serpentinites and amphibolites. All the rock associations represent elements of an orogenic structure that originated by collision of the New Siberian continental block with the Anyui-Svyatoi Nos island arc. Flyschoid sediments accumulated in a foredeep in front of the latter structure in the course of collision. The Late Jurassic volcanics belonging to the Anyui-Svyatoi Nos island arc determine the lower age limit of syncollision siliciclastic rocks. Presence of Late Jurassic zircons in sandstones of the flyschoid sequence in Bols’shoi Lyakhov Island is confirmed by the fission-track dating. The upper age limit is determined by the Aptian-Albian postcollision granites and diorites intruding the siliciclastic complex. Consequently, the flyschoid sequence is within stratigraphic range from the terminal Late Jurassic to Neocomian. It appears that Permian age of sediments suggested earlier is based on redeposited organic remains. The same Late Jurassic-Neocomian age and lithology are characteristic of fossiliferous siliciclastic sequences of the Stolbovoi and Malyi Lyakhov islands, the New Siberian Archipelago, and of graywackes in the South Anyui area in Chukchi Peninsula. All these sediments accumulated in a spacious foredeep that formed in the course the late Cimmerian orogeny along the southern margin of the Arctic continental block.  相似文献   

14.
A theory of two-dimensional geothermic problems is elaborated by the active temperature function at the vertical contact of two horizontally layered media. The approach offered before for oceanic ridges is extended to the case of continental margins and the upper part of a descending slab, i.e. “sink”, in island-arc areas. It is assumed that the plate motion in the oceanic area exists; in a descending area it is directed downward but remains zero on a continental side. Mathematically it symbolizes a “source—span—sink” thermal model. Numerical parameters are given for a theoretical thermal model of the heat-flow profile across the Kuril island arc, from the trench through Iturup Island, Sakhalin Island and the Tatarian Trough.  相似文献   

15.
La Désirade, a small island east of Guadeloupe, is underlain by the only exposed pre-Tertiary basement rocks in the Lesser Antilles. The basement complex comprises spilitic and keratophyric flows and pillow lavas (with interbedded and overlying radiolarian cherts), swarms of mafic to silicic dikes, and subjacent plagiogranite. These features, and the absence of carbonates, terrigenous clastic sediments, or tuffaceous sediments from the complex indicate that it developed in a deep marine environment beyond the reach of terrigenous sedimentation or emergent island arc pyroclastic deposition. Previous workers have suggested that the Désirade basement complex originated either as oceanic crust or during an early (tholeiitic) stage of island arc growth. The isotopic compositions of Sr and Pb from the complex, and previously reported rare earth data (Johnston and Schilling, 1974) do not provide a clear distinction between these two possibilities. Nor does the presence of siliceous keratophyre in the complex rule out an oceanic crustal origin-such rocks are common in well studied ophiolites that originated as oceanic crust. Hence we turn to the age relationships of the complex, the surrounding ocean floor, and adjacent island arcs in an attempt to resolve this problem. The age of the complex strongly supports an oceanic crustal (ophiolitic) origin. The ages of zircons and a previously reported K-Ar age indicate that the complex is 145±5 m.y. old. The complex predates the next oldest volcanic rocks of the Lesser Antilles arc by ca. 110 m.y., and the oldest known rocks of the Aves Ridge, a possible Mesozoic precursor of the Lesser Antilles arc, by 50–60 m.y. This makes it unlikely that the Désirade complex is related to an early phase of either of these arcs. Instead, the age of the complex falls in the range of ages expected for oceanic crust in the vicinity of the Lesser Antilles prior to the development of any subduction zone and resulting arc. Thus we interpret the Désirade complex to be an uplifted segment of oceanic crust that represents the basement on which the later island arcs grew: first the Aves Ridge, an arc that was active in middle to late Cretaceous time (but whose exact mode of origin is enigmatic, and is considered in four alternate tectonic models), then the Eocene to Recent Lesser Antilles arc.  相似文献   

16.
We propose a model of the geodynamic evolution of the Dzhida island-arc system of the Paleoasian Ocean margin which records transformation of an oceanic basin into an accretion-collision orogenic belt. The system includes several Vendian-Paleozoic complexes that represent a mature oceanic island arc with an accretionary prism, oceanic islands, marginal and remnant seas, and Early Ordovician collisional granitoids. We have revealed a number of subunits (sedimentary sequences and igneous complexes) in the complexes and reconstructed their geodynamic settings. The tectonic evolution of the Dzhida island-arc system comprises five stages: (1) ocean opening (Late Riphean); (2) subduction and initiation of an island arc (Vendian-Early Cambrian); (3) subduction and development of a mature island arc (Middle-Late Cambrian); (4) accretion and formation of local collision zones and remnant basins (Early Ordovician-Devonian); and (5) postcollisional strike-slip faulting (Carboniferous-Permian).  相似文献   

17.
The data on the paleotsunami manifestations on some islands of the Lesser Kuril Ridge are presented. The sedimentation features during the different-intensity tsunamis are analyzed and the timing of the most significant events and their recurrence in the middle-late Holocene were determined.  相似文献   

18.
New mineralogical, geochemical, and isotope data in combination with numerical modeling were used to reconstruct the physicochemical and geodynamic conditions of the formation of Pleistocene basalts of Kunashir Island. Although they are petrologically close to the Holocene basalts of Tyatya Volcano, their eruption occurred during a brief period of island arc extension, which was accompanied by the high degree melting of mantle wedge asthenosphere. Numerous geological, petrological, and paleogeographical data testify that Pleistocene is an important stage in the geodynamic reorganization of the Kuril island arc. This stage was responsible for uplifting of the southern islands above sea level accompanied by catastrophic endogenous events, deformation, topographic reorganization of the large area of the Sea of Japan and adjacent land, and final folding stage in the West Sakhalin Mountains.  相似文献   

19.
东特提斯板块会聚边缘与岛弧造山作用   总被引：4，自引：2，他引：4       下载免费PDF全文
本文重点简述了特提斯构造域内古，中，新三个演化阶段的蛇绿混杂岩与岛弧带的时空展布及其沟－弧－盆体系，所识别出的蛇绿混杂岩，洋中脊拉斑玄武岩，大洋沉积物的岛弧带等地质记录，提供了东特提斯早期大洋岩石圈板块运动的有力证据。同时，与岛弧有关的不同时期不同阶段的各种弧前盆地，弧间盆地和弧后贫地成为造山带板块会聚边缘特征的标志。  相似文献   

20.
The results of the geochemical studies of the Late Oligocene-Pleistocene volcanic rocks that accompanied the formation of the deep-water basins of the Seas of Japan and Okhotsk are presented. These rocks have an initially mantle origin that is a derivative of a single source—spinel perodotites. They formed as a result of the partial melting of secondary plumes located in the head part of the major mantle plume. This plume rose very closely to the surface in the area of the Japanese (Central) basin, where the marginal-sea basaltoids with chemical properties of HIMU (OIB) sources were established. The continental lithosphere (the upper mantle and the crust) was involved in the magma formation in the area of the Kuril basin and the Vityaz Ridge at the earliest rifting stage in the Late Oligocene-Early Miocene and at the final stage in the Pliocene-Pleistocene.  相似文献   

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