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1.
The 1370 km long 4-AR reference profile crosses the North Barents Basin, the northern end of the Novaya Zemlya Rise, and the North Kara Basin. Integrated geophysical studies including common deep point (CDP) survey and deep seismic sounding (DSS) were carried out along the profiles. The DSS was performed using autonomous bottom seismic stations (ABSS) spaced 10–20 km apart and a powerful air gun producing seismic signals with a step size of 250 m. As a result, detailed P- and S-wave velocity structures of the crust and upper mantle were studied. The basic method was ray-tracing modeling. The Earth’s crust along the entire profile is typically continental with compressional wave velocities of 5.8–7.2 km/s in the consolidated part. Crustal thickness increases from 30 km near the islands of Franz Josef Land to 35 km beneath the North Barents Basin, 50 km beneath the Novaya Zemlya Rise, and 40 km beneath the North Kara Basin. The North Barents Basin 15 km deep is characterized by unusually low velocities in the consolidated crust: The upper crust layer with velocities of 5.8–6.4 km/s has a thickness of about 15 km beneath the basin (usually, this layer wedges beneath deep sedimentary basins). Another special property of the crust in the North Barents Basin is the destroyed structure of the Moho.  相似文献   

2.
Since 1995 SEVMORGEO has collected wide-angle reflection/refraction profiling (WARRP), multichannel seismic data (MCS) and seismoacoustic profiling, along regional lines 1-AR, 2-AR and 3-AR. These lines cross the whole Barents–Kara Region and Novozemelskiy Fold Belt. As a result, new geological data about the deep structure of the Earth's crust have become available. Four main tectono-stratigraphic units are distinguished in the section of the Earth's crust: (1) a sedimentary cover; (2) the Upper Proterozoic (mainly Riphean for the Barents Plate) and Riphean–Paleozoic (the South-Kara Syneclise) deformed and folded complexes; (3) the upper crystalline crust (granite-gneissic metamorphic Archean–Proterozoic complex); (4) the lower crust (basalt complex). The Barents–Kara Region is characterized by moderately thinned continental and subcontinental crust with an average thickness of 37–39 km. On islands and areas of uplifts with ancient massifs, the thickness of the crust (38–42 km) approaches the typical crust for a continental platform. In the Novozemelskiy Fold Belt the thickness of the crust reaches 40–42 km. Rift-related grabens are characterized by significant crustal thinning with thicknesses of 33–36 km. Several grabens are revealed: the Riphean Graben on the Kola-Kanin Monocline, the Lower Paleozoic West-Kola Graben, the Devonian Demidovskiy Aulacogen, the Upper Paleozoic Malyginskiy Graben in the Barents Region and Upper Paleozoic–Triassic Noyabr'skiy and the Chekinskiy grabens in the Kara Region. Data concerning the deep structure lead us to conclude that mainly destructive processes contributed to the dynamics of the forming of the Barents–Kara Region.  相似文献   

3.
The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements. Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain. Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s−1 at the top to 6.6 km s−1 at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s−1. Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High.  相似文献   

4.
Processing of data from regional geophysical surveys completed in the northern Barents Sea has provided updates to gravity and magnetic databases, structural maps of seismic interfaces, and positions of anomaly sources, which made a basis for 3D density and magnetic models of the crust. The new geological and geophysical results placed constraints on the boundaries between basement blocks formed in different settings and on the contours of deposition zones of different ages in the northeastern Barents Sea. The estimated thicknesses of sedimentary sequences that formed within certain time spans record the deposition history of the region. There is a 20-50 km wide deep suture between two basins of Mesozoic and Paleozoic ages in the eastern part of the region, where pre-Late Triassic reflectors have no clear correlation. The suture slopes eastward at a low angle and corresponds to a paleothrust according to seismic and modeling data. In the basement model, the suture is approximated by a zone of low magnetization and density, which is common to active fault systems. The discovery of the suture has important geological and exploration implications.  相似文献   

5.
Seismogeologic sections for the Barents-Kara region along geotraverses 1-AR, 2-AR, and 3-AR with a total length of about 4000 km were obtained using the GODOGRAF software package developed at the Department of Seismometry and Geoacoustics of the Moscow State University. The data were travel times of refracted waves excited by approximately 100 sources along each traverse. This paper reports sections for the 3-AR traverse covering areas of the White Sea, Pechora Sea, and Kara Sea, and a geological interpretation of these. The sections cover depths down to 40–50 km and show basic crustal discontinuities, fold-thrust, rift, and paleospreading structural features, and paleosubduction zones. We characterize the possible character of the junction between the South Kara and North Kara basins. A geodynamic interpretation of the structures is provided for the Barents-Kara region.  相似文献   

6.
In 1976, the Institute of Physics of the Earth and the Institute of Oceanology, the U.S.S.R. Academy of Sciences, carried out deep seismic soundings in the Barents Sea along a profile 700 km long northeast of Murmansk. A system of reversed and overlapping traveltime curves from 200 to 400 km long has been obtained. The wave correlation was effected by several independent approaches, which identified on the records the refracted and reflected waves from boundaries in the Earth's crust and the upper mantle. Different methods were applied for the solution of the inverse problem: the isochrone method, the intercept-time method, and the iteration method.The use of these different methods gives an indication of the general applicability of the interpretation and of the most reliable elements in the seismic model.All the interpretations and representations of the section positively establish an essentially horizontal inhomogeneity of the Earth's crust in the Barents Sea. On the whole the structure is similar to that of deep sedimentary basins of the East European platform. The thickness of the sedimentary layer varies from 8 to 17 km, the average crustal thickness is about 35–40 km; the velocities in the upper part of the consolidated crust are 5.8–6.4 km/s; in the lower crust they are 6.8–7.0 km/s and higher.  相似文献   

7.
A hitherto unknown terrane and its bounding sutures have been revealed by a combined study of normal-incidence and wide-angle seismic data along the BABEL profile in the Baltic Sea. This Intermediate Terrane is situated between a Northern Terrane of Svecofennian age and a Southwestern Terrane of Gothian age. It is delimited upwards by two low-angle and oppositely dipping sutures and occupies mainly middle and lower crustal levels with a width of 300 km at Moho level. The 1.86 Ga suture against the Northern Terrane is imaged by a prominent almost continuous NE-dipping crustal reflection from 3.5 to 14 s twt over 175 km. Where it downlaps on the Moho, sub-Moho velocities change from 8.2 to 7.8 km/s (±0.2) over less than 25 km. A relatively strong, NE-dipping normal-incidence and wide-angle reflection at 19–23 s twt indicates that the suture extends into the upper mantle. The pervasive NE-dipping reflection fabric of the Intermediate Terrane is interpreted as shear zones that developed during collision and possibly were reactivated by later events. High Poisson's ratios suggest a mafic composition or high fluid content. The 1.86 Ga collision was probably succeeded by continental break-up and removal of an unknown continent, except for the Intermediate Terrane. Subsequent formation of an east-dipping subduction zone further to the west led to the emplacement of 1.81-1.77-Ga-old granitoids in the southern part of the Transscandinavian Igneous Belt. The 1.65-1.60 Ga suture against the Southwestern Terrane is defined by a semi-continuous band of strong SW-dipping reflections between 3 and 8 s twt over 65 km, which are interpreted as a low-angle thrust zone along which Gothian crust overrode the Intermediate Terrane. The identification of three individual seismic terranes in the southeastern part of the Baltic Shield provides new evidence for Palaeoproterozoic plate tectonic processes.  相似文献   

8.
The amalgamation of the southern Río de la Plata craton involves two possibly coeval Rhyacian sutures associated with the Transamazonian orogeny,rather than a single one as previously envisaged,i.e.the El Cortijo suture zone and the Salado suture.We circumscribe the Tandilia terrane to the region between these two sutures.The El Cortijo suture zone runs along a roughly WNW oriented magnetic low aligned along the southern boundary of the Tandilia terrane,i.e.boundary between the Tandilia and Balcarce terranes.This extensive magnetic low,ca.300 km long,and ca.90 km wide,would be caused by demagnetization associated with shearing.At a more local scale,the trend of the El Cortijo suture zone often turns toward the EeW.At this scale,WNW trending tholeiitic dykes of Statherian age are seen to cut the Rhyacian El Cortijo suture zone.Spatially associated with the El Cortijo suture zone,there are small magnetic highs interpreted to be related to unexposed basic bodies of ophiolitic nature related to those forming part of the El Cortijo Formation.We envisage the pre-Neoproterozoic evolution of the Tandilia belt to have been initiated by the extension of Neoarchean(w2650 Ma)crust occurred during Siderian times(2500e2300 Ma),causing the separation between the Balcarce,Tandilia and Buenos Aires terranes,and the development of narrow oceans at both north and south sides of the Tandilia terrane,accompanied by w2300e2200 Ma sedimentation over transitional econtinental to oceanice crust,and arc magmatism developed in the Tandilia terrane.The island arc represented by the El Cortijo Formation was also developed at this time.At late Rhyacian times,it occurred in both the closure of the narrow oceans developed previously,the entrapment of the El Cortijo island arc,as well as anatectic magmatism in the Balcarce terrane.  相似文献   

9.
Comparison of a new compilation of available Arctic bathymetric data north of 85° N latitude with previously published charts shows large discrepancies in the position and morphology of several major Arctic sea-floor features. Near the North Pole the Lomonosov Ridge pinches to a width of about 20 km with very steep slopes. The crest of the Ridge at this location is displaced dextrally by about 80 km. Also, the crest of this ridge curves towards Ellesmere Island and does not continue towards Greenland. The Marvin Spur is actually a series of knolls or sea mounts with relief varying from 500 to over 1300 m. The 600 km wide arch known as the Alpha Cordillera consists of closed, wide (10–40 km) elongated (180–260 km) troughs and ridges with relief of over 1000 m. Circular sea mounts and deeps are also noted along this Cordillera. The Arctic Mid-Oceanic Cordillera is a rather flat 200 km wide feature that tilts gently upward by about 500 m from the Pole Abyssal Plain to the Barents Abyssal Plain. It is characterized by a series of narrow ridges and troughs usually less than 20 km wide with a central deep trough over 5100 m deep and shallow ridges rising to heights of 2600 m. These features generally parallel the Lomonosov Ridge. This cordillera appears to be abruptly truncated along the Greenwich meridian. The Morris Jesup Plateau is a single pronged northeast trending feature with relatively shallow westward slopes and steeply dipping eastward slopes.  相似文献   

10.
The Barents Sea is located in the northwestern corner of the Eurasian continent, where the crustal terrain was assembled in the Caledonian orogeny during Late Ordovician and Silurian times. The western Barents Sea margin developed primarily as a transform margin during the early Tertiary. In the northwestern part south of Svalbard, multichannel reflection seismic lines have poor resolution below the Permian sequence, and the early post-orogenic development is not well known here. In 1998, an ocean bottom seismometer (OBS) survey was collected southwest to southeast of the Svalbard archipelago. One profile was shot across the continental transform margin south of Svalbard, which is presented here. P-wave modeling of the OBS profile indicates a Caledonian suture in the continental basement south of Svalbard, also proposed previously based on a deep seismic reflection line coincident with the OBS profile. The suture zone is associated with a small crustal root and westward dipping mantle reflectivity, and it marks a boundary between two different crystalline basement terrains. The western terrain has low (6.2–6.45 km s−1) P-wave velocities, while the eastern has higher (6.3–6.9 km s−1) velocities. Gravity modeling agrees with this, as an increased density is needed in the eastern block. The S-wave data predict a quartz-rich lithology compatible with felsic gneiss to granite within and west of the suture zone, and an intermediate lithological composition to the east. A geological model assuming westward dipping Caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust, as well as the observed structuring. Due to the transform margin setting, the tectonic thinning of the continental block during opening of the Norwegian-Greenland Sea is restricted to the outer 35 km of the continental block, and the continent–ocean boundary (COB) can be located to within 5 km in our data. Distinct from the outer high commonly observed on transform margins, the upper part of the continental crust at the margin is dominated by two large, rotated down-faulted blocks with throws of 2–3 km on each fault, apparently formed during the transform margin development. Analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile, and that the downfaulting dominates the whole margin segment from Spitsbergen to Bjørnøya. South of Bjørnøya, the faulting leaves the continental margin to terminate as a graben 75 km south of the island. Adjacent to the continental margin, there is no clear oceanic layer 2 seismic signature. However, the top basement velocity of 6.55 km s−1 is significantly lower than the high (7 km s−1) velocity reported earlier from expanding spread profiles (ESPs), and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7–8-km-thick sedimentary overburden.  相似文献   

11.
《Gondwana Research》2011,19(4):547-564
The Central India Tectonic Zone (CITZ) is a prominent divide and a major suture zone between the North Indian and South Indian crustal blocks. The resistive upper crust as modeled in the magnetotelluric data from CITZ suggests a dominant tonalite–trdondhjemite–granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components. The highly conductive bodies in this zone might represent mafic/ultramafic-layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the Cretaceous Deccan flood basalts. The uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of Archaean and Paleoproterozoic subducted slabs. We redefine the nature of deep faults traversing the CITZ, which were described as steep and penetrating the Moho by previous workers, and classify them as listric faults with gentle dips at depth.Seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the Bhandara Craton. Reflection data from the central part of the CITZ show northerly dip in the southern part suggesting northward subduction of the Dharwar Craton. However, an opposite trend is observed in the northern part of the suture with a southward dip of the Bundelkhand craton. Based on these features, and in conjunction with existing magnetotelluric models, we propose a double-sided subduction history along the CITZ. This would be similar to the ongoing subduction–accretion process in the western Pacific region, which possibly led to the development of paired collision-type and Pacific-type orogens. One important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust. The high resistivity felsic domain suggests underplated sediments/felsic crust that would have caused the doming. Our model also accounts for the extrusion of regional metamorphic belts at the orogenic core, and the occurrence of high pressure–ultrahigh-temperature paired metamorphic belts within the suture.  相似文献   

12.
The article considers problems related to the geological structure and geodynamic history of sedimentary basins of the Barents Sea. We analyze new seismic survey data obtained in 2005–2016 to refine the geological structure model for the study area and to render it in more detail. Based on the data of geological surveys in adjacent land (Novaya Zemlya, Franz Josef Land, and Kolguev Island), drilling, and seismic survey, we identified the following geodynamic stages of formation of the East Barents megabasin: Late Devonian rifting, the onset of postrift sinking and formation of the deep basin in Carboniferous–Permian, unique (in terms of extent) and very rapid sedimentation in the Early Triassic, continued thermal sinking with episodes of inversion vertical movements in the Middle Triassic–Early Cretaceous, folded pressure deformations that formed gently sloping anticlines in the Late Cretaceous–Cenozoic, and glacial erosion in the Quaternary. We performed paleoreconstructions for key episodes in evolution of the East Barents megabasin based on the 4-AR regional profile. From the geometric modeling results, we estimated the value of total crustal extension caused by Late Devonian rifting for the existing crustal model.  相似文献   

13.
The data on catastrophic earthquakes with magnitudes of 8.3 and 8.1 that occurred in the Simushir Island area on November 15, 2006, and January 13, 2007, respectively, were compared with the results of land-sea deep seismic studies by different methods (deep seismic sounding, the correlation method of refracted waves, the earthquake converted-wave method, the common mid-point) in the Central Kuril segment. The structure of the Earth’s crust and the hypocentral zones of these earthquakes were analyzed. It was established that the hypocenter of the main shock of the first earthquake was located at the bend of the seismofocal zone under the island slope of the trench on the outer side of the subsiding lithospheric plate in the rapidly rising granulite-basite (ìbasalticî) crustal layer, which, at depths of 7–15 km, replaced the granulite-gneiss layer. This was accompanied by an increase of the seismic wave velocity from 6.4 to 7.1 km/s. The focus of the second earthquake was located beneath the axis of the deep-sea trench. The aftershocks were concentrated in two bands 60–120 km wide that extend along the trench, as well as in the third zone orthogonal to the island arc. It was shown that the epicenters of the earthquakes are linked with regional faults. The main shock of the first earthquake (November 15, 2006) was interpreted as a thrust fault and the second one (January 13, 2007) was attributed to a normal fault.  相似文献   

14.
2D and 3D modeling of the geothermal field was carried out along seven extended geotraverses in the Barents Sea compiled on the basis of CMP profiling and results of deep drilling. Depths of the zone characterized by catagenetic transformation of organic matter were calculated for different areas of the sedimentary basin. The minimal depth is confined to the South Barents Basin with the highest hydrocarbon resource potential established by geological exploration. In 3D models, this area is distinguished by a thermal dome recognized for the first time.  相似文献   

15.
High-pressure conditions of 11–13 kbar/500–540 °C during maximum burial were derived for garnet amphibolite in the Tapo Ultramafic Massif in the Eastern Cordillera of Peru using a PT pseudosection approach. A Sm–Nd mineral-whole rock isochron at 465 ± 24 Ma dates fluid influx at peak temperatures of ∼600 °C and the peak of high pressure metamorphism in a rodingite of this ultramafic complex. The Tapo Ultramafic Complex is interpreted as a relic of oceanic crust which was subducted and exhumed in a collision zone along a suture. It was buried under a metamorphic geotherm of 12–13 °C/km during collision of the Paracas microcontinent with an Ordovician arc in the Peruvian Eastern Cordillera. The Ordovician arc is represented by the western Marañon Complex. Here, low PT conditions at 2.4–2.6 kbar, 300–330 °C were estimated for a phyllite–greenschist assemblage representing a contrasting metamorphic geotherm of 32–40 °C/km characteristic for a magmatic arc environment.  相似文献   

16.
The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sørkapp Basin, bordered by a 7 km deep basement high to the west, and 7–9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between 19°E and 20°E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the VP, VP/VS ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10–50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles.  相似文献   

17.
The Shyok Suture Zone (Northern Suture) of North Pakistan is an important Cretaceous-Tertiary suture separating the Asian continent (Karakoram) from the Cretaceous Kohistan–Ladakh oceanic arc to the south. In previously published interpretations, the Shyok Suture Zone marks either the site of subduction of a wide Tethyan ocean, or represents an Early Cretaceous intra-continental marginal basin along the southern margin of Asia. To shed light on alternative hypotheses, a sedimentological, structural and igneous geochemical study was made of a well-exposed traverse in North Pakistan, in the Skardu area (Baltistan). To the south of the Shyok Suture Zone in this area is the Ladakh Arc and its Late Cretaceous, mainly volcanogenic, sedimentary cover (Burje-La Formation). The Shyok Suture Zone extends northwards (ca. 30 km) to the late Tertiary Main Karakoram Thrust that transported Asian, mainly high-grade metamorphic rocks southwards over the suture zone.The Shyok Suture Zone is dominated by four contrasting units separated by thrusts, as follows: (1). The lowermost, Askore amphibolite, is mainly amphibolite facies meta-basites and turbiditic meta-sediments interpreted as early marginal basin rift products, or trapped Tethyan oceanic crust, metamorphosed during later arc rifting. (2). The overlying Pakora Formation is a very thick (ca. 7 km in outcrop) succession of greenschist facies volcaniclastic sandstones, redeposited limestones and subordinate basaltic–andesitic extrusives and flow breccias of at least partly Early Cretaceous age. The Pakora Formation lacks terrigenous continental detritus and is interpreted as a proximal base-of-slope apron related to rifting of the oceanic Ladakh Arc; (3). The Tectonic Melange (<300 m thick) includes serpentinised ultramafic rocks, near mid-ocean ridge-type volcanics and recrystallised radiolarian cherts, interpreted as accreted oceanic crust. (4). The Bauma–Harel Group (structurally highest) is a thick succession (several km) of Ordovician and Carboniferous to Permian–Triassic, low-grade, mixed carbonate/siliciclastic sedimentary rocks that accumulated on the south-Asian continental margin. A structurally associated turbiditic slope/basinal succession records rifting of the Karakoram continent (part of Mega–Lhasa) from Gondwana. Red clastics of inferred fluvial origin (‘molasse’) unconformably overlie the Late Palaeozoic–Triassic succession and are also intersliced with other units in the suture zone.Reconnaissance further east (north of the Shyok River) indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs, derived from nearby volcanic centres, presumed to lie within the Ladakh Arc. In addition, comparison with Lower Cretaceous clastic sediments (Maium Unit) within the Northern Suture Zone, west of the Nanga Parbat syntaxis (Hunza River) reveals notable differences, including the presence of terrigenous quartz-rich conglomerates, serpentinite debris-flow deposits and a contrasting structural history.The Shyok Suture Zone in the Skardu area is interpreted to preserve the remnants of a rifted oceanic back-arc basin and components of the Asian continental margin. In the west (Hunza River), a mixed volcanogenic and terrigenous succession (Maium Unit) is interpreted to record syn-deformational infilling of a remnant back-arc basin/foreland basin prior to suturing of the Kohistan Arc with Asia (75–90 Ma).  相似文献   

18.
为揭示中亚造山带浅表结构,对地壳演化与深部过程提供浅部精准约束,利用横过中亚造山带东段（奈曼旗—东乌珠穆沁旗）长达400 km的深地震反射剖面共2 186炮的初至波走时数据,运用初至波层析成像方法获得了自地表向下约3 km厚度的浅表速度结构精细模型。通过模型计算了沉积厚度变化与基岩起伏特征,并在贺根山和西拉木伦缝合带附近获得了呈低速特征的弧前沉积盆地规模与沉积厚度变化特征;在此基础上,综合速度模型与深地震反射剖面的强振幅反射信息,建立了符合剖面南北两侧的古亚洲洋双向俯冲并与中部的残存微陆块发生拼合的构造模型。结果表明：研究区的沉积厚度在0.3~3.0 km范围内变化,区内存在多期岩浆活动及活动构造,林西地区隐伏连续分布的高速结构多为造山花岗岩所导致;古亚洲洋消亡过程在经数亿年演变后仍能在大陆边缘的浅表构造中有迹可循。  相似文献   

19.
New methods are presented for processing and interpretation of shallow marine differential magnetic data,including constructing maps of offshore total magnetic anomalies with an extremely high resolution of up to 1-2 nT,mapping weak anomalies of 5-10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks,estimating depths to upper and lower boundaries of anomalous magnetic sources,and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called "seismic gap" region in the central Kuril Arc vary from 10 to 100 km,with typical dimensions of 25-30 km.The area of the "seismic gap" is a zone of intense tectonic activity and recent volcanism.Deep sources causing magnetic anomalies in the area are similar to the "magnetic belt" near Hokkaido. In the southern and central parts of Barents Sea,tectonic blocks with widths of 30-100 km,and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km are calculated.Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea-Barents Sea paleorift indicate depths to the lower boundary of the layer of 12-30 km.Weak local magnetic anomalies of 2-5 nT in the northern and central Caspian Sea were identified using the new methods,and drilling confirms that the anomalies are related to concentrations of hydrocarbon.Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra.The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30-40 m and 150-200 m.  相似文献   

20.
从尼玛地区地质新资料看中特提斯洋的构造演化   总被引：10，自引：0，他引：10       下载免费PDF全文
班公湖—怒江结合带南缘存在一套中、晚侏罗世稳定浅海碎屑岩沉积，属残余海盆地沉积，表明尼玛地区的俯冲消减机制在中侏罗世以后已结束。结合带南侧三叠系确哈拉群为一套半深水—深水沉积，是陆架边缘沉积序列，代表结合带打开之初的较早期沉积。确哈拉群之上不整合覆盖了一套中侏罗世钙碱性岛弧火山岩系，是班公湖—怒江结合带在早侏罗世向南俯冲对应的滞后弧火山岩。在结合带南侧80～100km范围内分布着一条东西长超过100km的中晚侏罗世后碰撞强过铝花岗岩带，属班公湖—怒江结合带向南俯冲碰撞作用的后碰撞阶段产物。综合认为，尼玛地区中特提斯洋是在三叠纪打开、中侏罗世以前向南俯冲闭合的。结合区域上该结合带闭合时间有早有晚、俯冲方向有南有北的事实，提出中特提斯是一个具有众多互不相通的、时代早晚各不相同的小洋盆共同组成的多岛洋，其间存在许多大小不一、运动方向和性质各不相同的地体。不同时期、不同方向的弧—弧碰撞、弧—陆碰撞造山(造陆)机制是解释中特提斯洋发展演化诸多问题的理想模式。  相似文献   

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