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1.
Seismic refraction surveys conducted in 1976 and 1979 over the broken ice surface of the Arctic Ocean, reveal distinctly different crustal structures for the Fram, Makarov and Canada basins. The Canada Basin, characterized by a 2–4 km thick sedimentary layer and a distinct oceanic layer 3B of 7.5 km/s velocity has the thickest crust and is undoubtedly the oldest of the three. The crust of the Makarov Basin has a thin sedimentary layer of less than 1 km and is about 9 km in total thickness. The Fram Basin has a similarly thin sedimentary layer but is 3–4 km thicker than the Makarov as it approaches the Lomonosov Ridge near the North Pole. The ridge itself is cored by material with a velocity of 6.6 km/s and may be a metagabbro similar to oceanic layer 3A. This ridge root material extends to a depth of about 27 km, where a change occurs to upper-mantle material with a velocity of 8.3 km/s. The core is overlain by up to 6 km of material with a velocity of about 4.7 km/s which could be oceanic layer 2A basalts or continental crystalline rocks with some sedimentary material.The Fram Basin probably began to open contemporaneously with the North Atlantic about 70 m.y. ago, by spreading along the Nansen-Gakkel Ridge. Although not yet dated, the Makarov Basin is probably no older than the initiation of the Fram Basin and may be much younger. The Alpha Ridge may once have been part of the Lomonosov Ridge, splitting off to form the Makarov Basin between 70 and 25 m.y. ago and possibly contributing to the Eurekan Orogeny of 25 m.y. ago, evident on Ellesmere Island. In contrast, the likely age of the Canada Basin lies in the 125–190 m.y. range and may have been formed by the counter-clockwise rotation of Alaska and the Northwind Ridge away from the Canadian Arctic Islands. The Lomonosov Ridge emerges from this scenario as a block resulting from a strike-slip shear zone on the European continental shelf, related to the opening of the Canada basin (180-120 my) and then becomes an entity broken from this shelf by the opening of the Eurasia Basin (70-0 m.y.).  相似文献   

2.
The structure of the sedimentary cover and acoustic basement in the northeastern Russian Arctic region is analyzed. Beneath the western continuation of the North Chukchi trough and Vil’kitskii trough, a Late Caledonian (Ellesmere) folded and metamorphozed basement is discovered. It is supposed that Caledonides continue further into the Podvodnikov Basin until the Geofizikov branch. A large magnetic anomaly in the Central Arctic zone has been verified by seismostratigraphic data: the acoustic basement beneath the Mendeleev (and partially Alpha) Ridge is overlain by trapps. Wave field analysis showed that the acoustic basement of the Lomonosov Ridge has folded structure, whereas beneath the Mendeleev Ridge, the sporadic presence of a weakly folded stratum of Paleozoic platform deposits is interpreted. It is supposed that the Caledonian and Late Cimmerian fold belts in the periphery of the Arctida paleocontinent appeared as a result of collision between arctic continental masses and southern ones. After Miocene extension and block displacements identified from appearance of horsts, grabens, and transverse rises both on the shelf and in the ocean, a general subsidence took place and the present-day shelf, slope, and the deepwater part of the Arctic Ocean formed.  相似文献   

3.
3D models of apparent magnetization and density of rocks allow us to provide insights into the deep structure of the Volga-Ural, Pericaspian, and Fore-Caucasus petroliferous basins. In the Volga-Ural Basin, some Riphean rifts reveal close spatial relations to Paleoproterozoic linear zones, presumably of the rift nature as well. The structure of the Paleoproterozoic Toropets-Serdobsk Belt is interpreted in detail. Rocks with petrophysical properties inherent to basic volcanics are established in the pre-Paleozoic basement of the marginal zone of the Pericaspian Basin. These rocks locally spread beyond the boundary escarpment and may be regarded as a part of the Riphean plume-related basaltic province. It is shown that the Pericaspian Basin was formed on the place of a triple junction of Riphean rifts: the Sarpa and Central Pericaspian oceanic branches and the continental branch of the Pachelma Aulacogen. The drastically different petrophysical properties of the basement beneath Baltica and the Astrakhan Arch indicate that this arch is an element of the large terrane that was attached to Baltica in the Vendian. The suture along which the Astrachan Terrane is conjugated with the basement of the central and southern segments of the Karpinsky Ridge is traced beneath the Paleozoic complex. A system of northwest-verging thrust faults formed during the collision between Scythia and Eurasia is mapped in the basement of the junction zone between the Karpinsky Ridge and Scythian Platform (Terrane). According to geological data, this event took place in the Early Paleozoic.  相似文献   

4.
The nature and origin of the subsurface 85°E Ridge in the Bay of Bengal has remained enigmatic till date despite several theories proposed by earlier researchers. We reinterpreted the recently acquired high quality multichannel seismic reflection data over the northern segment of the ridge that traverses through the Mahanadi offshore, Eastern Continental Margin of India and mapped the ridge boundary and its northward continuity. The ridge is characterized by complex topography, multilayer composition, intrusive bodies and discrete nature of underlying crust. The ridge is associated with large amplitude negative magnetic and gravity anomalies. The negative gravity response across the ridge is probably due to emplacement of relatively low density material as well as ∼2–3 km flexure of the Moho. The observed broad shelf margin basin gravity anomaly in the northern Mahanadi offshore is due to the amalgamation of the 85°E Ridge material with that of continental and oceanic crust. The negative magnetic anomaly signature over the ridge indicates its evolution in the southern hemisphere when the Earth’s magnetic field was normally polarized. The presence of ∼5 s TWT thick sediments over the acoustic basement west of the ridge indicates that the underlying crust is relatively old, Early Cretaceous age.The present study indicates that the probable palaeo-location of Elan Bank is not between the Krishna–Godavari and Mahanadi offshores, but north of Mahanadi. Further, the study suggests that the northern segment of the 85°E Ridge may have emplaced along a pseudo fault during the Mid Cretaceous due to Kerguelen mantle plume activity. The shallow basement east of the ridge may have formed due to the later movement of the microcontinents Elan Bank and Southern Kerguelen Plateau along with the Antarctica plate.  相似文献   

5.
The inregrated geological and geophysical studies carried out in recent years in the Lomonosov Ridge and at its junction with the Eurasian shelf revealed evidence for thinned (reduced) crust in the ridge (20–25 km) and its relationship with shelf structures. We compared the parameters of deep seismic cross-sections of the shelf and Lomonosov Ridge, thus proving the existence of continental crust in the latter. Also, we analyzed the deep structure of the junction between the Lomonosov Ridge and the shelf and established a genetic geologic relationship, with no evidence that the Lomonosov Ridge moved as a terrane with respect to the shelf. In addition, seismological studies independently confirm the relationship between the Lomonosov Ridge and the adjacent shelf.The Lomonosov Ridge is a continental-crust block of a craton. The craton was reworked during the Caledonian tectonomagmatic activity with the formation of a Precambrian–Caledonian seismically unsegmented basement (upper crust) and an epi-Caledonian platform cover. Afterward, the block subsided to bathyal depths in the Late Alpine. This block and the adjacent areas of the Eastern Arctic shelf developed in the platform regime till the Late Mesozoic.  相似文献   

6.
Approximately 400,000 line kilometers of high quality, low level Arctic aeromagnetic data collected by the Naval Research Laboratory, the Naval Oceanographic Office and the Naval Ocean Reseach and Development Activity from 1972 through 1978 have been analyzed for depth to magnetic source. This data set covers much of the Canada Basin, the Alpha Ridge, the central part of the Makarov Basin, the Lincoln Sea, the Eurasia Basin west and south of the 55°E meridian and the Norwegian-Greenland Sea north of the Jan Mayen Fracture Zone. The analysis uses the autocorrelation algorithm developed by Phillips (1975, 1978) and based on the maximum entropy method of Burg (1967, 1968, 1975). The method is outlined, examples of various error analysis techniques shown and final results presented. Where possible, magnetic source depth estimates are compared with basement depths derived from seismic and bathymetric data.All major known bathymetric features, including Vesteris Bank and the Greenland, Molloy and Spitsbergen fracture zones, as well as the Mohns, Knipovich and Nansen spreading ridges and the Alpha Cordillera appear as regional highs in the calculated magnetic basement topography. Shallow basement was also found under the northeastern Yermak Plateau, the Morris Jesup Rise and under the southern (Greenland-Ellesmere Island) end of the Lomonsosov Ridge. Regional magnetic source deeps are associated with such bathymetric depressions as the Canada, Makarov, Amundsen, Nansen, Greenland and Lofoten basins; more localized magnetic basement deeps are found over the Molloy F.Z. deep and over the Mohns, Knipovich and Nansen rift valleys. A linear magnetic basement deep follows the extension of Nares Strait through the Lincoln Sea toward the Morris Jesup Rise, suggesting the continuation of the Nares Strait or Wegener F.Z. into the Lincoln Sea. A sharp drop in the regional magnetic source depths to the southeast of the Alpha Ridge suggests the Alpha Ridge is not connected to structures in northwest Ellesmere Island as previously postulated from high altitude aeromagnetic collected by Canadian workers. A regional deep under the east Greenland shelf west of the Greenland Escarpment suggests the presence of 5–10 km of post-Paleozoic sediments.  相似文献   

7.
A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes several steps: identification of linear magnetic anomalies along each trackline, calculation of the Euler rotation pole positions for the relative motion of the North American and Eurasian plates, analysis of temporal and spatial variations in the spreading rate, and plate reconstructions. The pattern of key Cenozoic magnetic isochrons (24, 20, 18, 13, 6, 5, 2a) is constructed for the entire Eurasia Basin. In the western half of the basin, this pattern is consistent with a recently published scheme [16]. In its eastern half, magnetic isochrons are determined in detail for the first time and traced up to the Laptev Sea shelf. The main stages in the seafloor spreading are established for the Eurasia Basin. Each stage is characterized by a specific spreading rate and the degree of asymmetry of the basin opening. The revealed differences are traced along the Gakkel Ridge. Systematic patterns in wandering of the Eurasia Basin opening pole are established for particular stages. The continent-ocean transition zone corresponding to the primary rupture between plates is outlined in the region under consideration on the basis of gravimetric data. The nature of different potential fields and bottom topography on opposite sides of the Gakkel Ridge is discussed. The characteristic features of the basin-bottom formation at main stages of its evolution are specified on the basis of new and recently published data. The results obtained are in good agreement with plate geodynamics of the North Atlantic and the adjacent Arctic basins.  相似文献   

8.
Chronological succession in the formation of spreading basins is considered in the context of reconstruction of breakdown of Wegener’s Pangea and the development of the geodynamic system of the Arctic Ocean. This study made it possible to indentify three temporally and spatially isolated generations of spreading basins: Late Jurassic-Early Cretaceous, Late Cretaceous-Early Cenozoic, and Cenozoic. The first generation is determined by the formation, evolution, and extinction of the spreading center in the Canada Basin as a tectonic element of the Amerasia Basin. The second generation is connected to the development of the Labrador-Baffin-Makarov spreading branch that ceased to function in the Eocene. The third generation pertains to the formation of the spreading system of interrelated ultraslow Mohna, Knipovich, and Gakkel mid-ocean ridges that has functioned until now in the Norwegian-Greenland and Eurasia basins. The interpretation of the available geological and geophysical data shows that after the formation of the Canada Basin, the Arctic region escaped the geodynamic influence of the Paleopacific, characterized by spreading, subduction, formation of backarc basins, collision-related processes, etc. The origination of the Makarov Basin marks the onset of the oceanic regime characteristic of the North Atlantic (intercontinental rifting, slow and ultraslow spreading, separation of continental blocks (microcontinents), extinction of spreading centers of primary basins, spreading jumps, formation of young spreading ridges and centers, etc., are typical) along with retention of northward propagation of spreading systems both from the Pacific and Atlantic sides. The aforesaid indicates that the Arctic Ocean is in fact a hybrid basin or, in other words, a composite heterogeneous ocean in respect to its architectonics. The Arctic Ocean was formed as a result of spatial juxtaposition of two geodynamic systems different in age and geodynamic style: the Paleopacific system of the Canada Basin that finished its evolution in the Late Cretaceous and the North Atlantic system of the Makarov and Eurasia basins that came to take the place of the Paleopacific system. In contrast to traditional views, it has been suggested that asymmetry of the northern Norwegian-Greenland Basin is explained by two-stage development of this Atlantic segment with formation of primary and secondary spreading centers. The secondary spreading center of the Knipovich Ridge started to evolve approximately at the Oligocene-Miocene transition. This process resulted in the breaking off of the Hovgard continental block from the Barents Sea margin. Thus, the breakdown of Wegener’s Pangea and its Laurasian fragments with the formation of young spreading basins was a staged process that developed nearly from opposite sides. Before the Late Cretaceous (the first stage), the Pangea broke down from the side of Paleopacific to form the Canada Basin, an element of the Amerasia Basin (first phase of ocean formation). Since the Late Cretaceous, destructive pulses came from the side of the North Atlantic and resulted in the separation of Greenland from North America and the development of the Labrador-Baffin-Makarov spreading system (second phase of ocean formation). The Cenozoic was marked by the development of the second spreading branch and the formation of the Norwegian-Greenland and Eurasia oceanic basins (third phase of ocean formation). Spreading centers of this branch are functioning currently but at an extremely low rate.  相似文献   

9.
Multichannel seismic reflection data acquired by Marine Arctic Geological Expedition (MAGE) of Murmansk, Russia in 1990 provide the first view of the geological structure of the Arctic region between 77–80°N and 115–133°E, where the Eurasia Basin of the Arctic Ocean adjoins the passive-transform continental margin of the Laptev Sea. South of 80°N, the oceanic basement of the Eurasia Basin and continental basement of the Laptev Sea outer margin are covered by 1.5 to 8 km of sediments. Two structural sequences are distinguished in the sedimentary cover within the Laptev Sea outer margin and at the continent/ocean crust transition: the lower rift sequence, including mostly Upper Cretaceous to Lower Paleocene deposits, and the upper post-rift sequence, consisting of Cenozoic sediments. In the adjoining Eurasia Basin of the Arctic Ocean, the Cenozoic post-rift sequence consists of a few sedimentary successions deposited by several submarine fans. Based on the multichannel seismic reflection data, the structural pattern was determined and an isopach map of the sedimentary cover and tectonic zoning map were constructed. A location of the continent/ocean crust transition is tentatively defined. A buried continuation of the mid-ocean Gakkel Ridge is also detected. This study suggests that south of 78.5°N there was the cessation in the tectonic activity of the Gakkel Ridge Rift from 33–30 until 3–1 Ma and there was no sea-floor spreading in the southernmost part of the Eurasia Basin during the last 30–33 m.y. South of 78.5°N all oceanic crust of the Eurasia Basin near the continental margin of the Laptev Sea was formed from 56 to 33–30 Ma.  相似文献   

10.
Tectonics and petroleum potential of the underexplored East Arctic area have been investigated as part of an IPY (International Polar Year) project. The present-day scenery of the area began forming with opening of the Amerasia Ocean (Canada and Podvodnikov—Makarov Basins) in the Late Jurassic—Early Cretaceous and with Cretaceous—Cenozoic rifting related to spreading in the Eurasia Basin. The opening of oceans produced pull-apart and rift basins along continental slopes and shelves of the present-day Arctic fringing seas, which lie on a basement consisting of fragments of the Hyperborean craton and Early Paleozoic to Middle Cretaceous orogens. By analogy with basins of the Arctic and Atlantic passive margins, the Cretaceous—Cenozoic shelf and continental slope basins may be expected to have high petroleum potential, with oil and gas accumulations in their sediments and basement.  相似文献   

11.
Seismic data on the southern (Laptev Sea) extremity of the Lomonosov Ridge were used to develop a new structural model for the sedimentary cover. It permitted a correlation between the seismic cross-sections of the ridge crest and two deep-sea basins: the Podvodnikov Basin and the Amundsen Plain. It is the first time that a seismic model has taken into account both regional seismic-reflection profiles obtained from NP drifting ice stations and recent high-resolution CDP data. Our seismic model agrees both with geological data on the Laptev Sea continental margin and the data obtained from deep-sea drilling into the Lomonosov Ridge under the IODP-302 project. The sedimentary cover of the southern Lomonosov Ridge and adjacent parts of the Amundsen Plain and Podvodnikov Basin was dated at the Aptian–Cenozoic. The sedimentary section is divided by two main unconformities, of Campanian–Paleocene and Oligocene–Early Miocene ages. The cover contains a structurally complicated graben system, which is an extension of the New Siberian system of horsts and grabens, recognized in the shelf. Sedimentation began in the grabens in the Aptian–Albian and ended with their complete compensation in the Paleocene.  相似文献   

12.
Opening of the Fram Strait gateway: A review of plate tectonic constraints   总被引：1，自引：0，他引：1  
We have revised the regional crustal structure, oceanic age distribution, and conjugate margin segmentation in and around the Lena Trough, the oceanic part of the Fram Strait between the Norwegian–Greenland Sea and the Eurasia Basin (Arctic Ocean). The Lena Trough started to open after Eurasia–Greenland relative plate motions changed from right-lateral shear to oblique divergence at Chron 13 times (33.3 Ma; earliest Oligocene). A new Bouguer gravity map, supported by existing seismic data and aeromagnetic profiles, has been applied to interpret the continent–ocean transition and the influence of Eocene shear structures on the timing of breakup and initial seafloor spreading. Assuming that the onset of deep-water exchange depended on the formation of a narrow, oceanic corridor, the gateway formed during early Miocene times (20–15 Ma). However, if the initial Lena Trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep-water circulation, the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around Chron 5 times (9.8 Ma; Late Miocene). Paleoceanographic changes at ODP Site 909 (northern Hovgård Ridge) are consistent with both hypotheses of gateway formation. We cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the Lena Trough. The gravity, seismic and magnetic observations question the prevailing hypotheses on the Yermak Plateau and the Morris Jesup Rise as Eocene oceanic plateaus and the Hovgård Ridge as a microcontinent.  相似文献   

13.
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   

14.
The tectonic evolution of the Arctic Region in the Mesozoic and Cenozoic is considered with allowance for the Paleozoic stage of evolution of the ancient Arctida continent. A new geodynamic model of the evolution of the Arctic is based on the idea of the development of upper mantle convection beneath the continent caused by subduction of the Pacific lithosphere under the Eurasian and North American lithospheric plates. The structure of the Amerasia and Eurasia basins of the Arctic is shown to have formed progressively due to destruction of the ancient Arctida continent, a retained fragment of which comprises the structural units of the central segment of the Arctic Ocean, including the Lomonosov Ridge, the Alpha-Mendeleev Rise, and the Podvodnikov and Makarov basins. The proposed model is considered to be a scientific substantiation of the updated Russian territorial claim to the UN Commission on the determination of the Limits of the Continental Shelf in the Arctic Region.  相似文献   

15.
A thorough examination of geophysical data from the Greenland-Norwegian Sea, Eurasia Basin and southern Labrador Sea shows significant asymmetry of several parameters (basement topography adjusted for sediment loading, free-air gravity anomaly, spreading half-rate and seismicity) with respect to crustal age:
1. (1) Average zero-age depth (0–57 m.y. B.P.), depth of highest rift mountain summits, and depth to magnetic basement (10–30 km from axis of Mohns and Knipovich ridges) is less on the North American plate flanks. The zero-age depth asymmetry is 400–500 m for the Eurasia Basin (0–57 m.y. B.P.) and for Mohns Ridge (57-22 m.y. B.P.), and 150–200 m for younger Mohns Ridge crust (22-0 m.y. B.P.) and for the extinct Aegir Ridge (57-27 m.y. B.P.). There is little or no asymmetry in the Labrador Sea except near the extinct rift valley, where the east flank is 150–300 m shallower. Magnetic depth-to-source computations provide an independent confirmation of basement asymmetry: The belts 10–30 km from the axis of Mohns and Knipovich ridges are 100–150 m shallower on the west flank of these ridges. The shallower ridge flank is topographically rougher, so that average rift mountain summits are 300 m shallower on the west flanks of the Mohns-Knipovich ridges, a larger asymmetry than for average zero-age depth. The amount of topographic asymmetry is greatest near the Mohns-Knipovich bend. Asymmetry appears to be greatest for ridges oriented normal to the spreading direction, and less for oblique spreading.
2. (2) Free-air gravity anomaly asymmetries of +5 to +20 mGal ( + sign indicates west flank is more positive) are associated with topographic asymmetry at least within 10–15 m.y. of the axis of Mohns and Knipovich ridges. Gravity is reduced on the older flanks west of the extinct Mid-Labrador Ridge and east of Mohns Ridge; asymmetric crustal layer thicknesses or densities provide one possible explanation, although deep-seated sources (e.g., mantle convection), unrelated to the crust, cannot be excluded.
3. (3) Spreading half-rate was about 5–15% lower on the North American plate flanks of Mohns Ridge (57-35 m.y.) and in the Eurasia Basin (0–57 m.y.); thus the fast-spreading flank tends to produce deeper, smoother crust. However, topographic asymmetry cannot relate only to spreading-rate asymmetry, since for the young Mohns Ridge crust (<9 m.y. B.P.) faster spreading and higher topography are both associated with the west flank.
4. (4) Mid-plate seismicity is higher on the Eurasia (eastern) flank of Mohns and Knipovich ridge, but this effect may be unrelated to the other three.
The fluid-dynamical model of Stein et al. correctly explains the sense of spreading-rate asymmetry (the North American plate, moving faster over mantle, is growing more slowly). However, the other asymmetries and their causal relationships remain theoretically unexplained.  相似文献   

16.
A combined analysis of the recently collected aeromagnetic data from the Eurasian Basin with the magnetic data from the Labrador Sea, the Norwegian-Greenland Sea and the North Atlantic yields a plate kinematic solution for the Eurasian Basin which is consistent with the solution for the North Atlantic as a whole. It shows that the Eurasian Basin and Norwegian-Greenland Sea started to evolve at about anomaly 25 time, though active seafloor spreading did not start in either of these regions until anomaly 24 time. It further shows that the spreading in the Eurasian Basin has been a result of motion only between the North American and Eurasian plates since the beginning, with the Lomonosov Ridge remaining attached to the North American plate. The relative motion among the North American, Greenland and Eurasian plates as obtained from the plate kinematics of the North Atlantic shows that from Late Cretaceous to Late Paleocene (anomaly 34 to 25) Greenland moved obliquely to Ellesmere Island. It is suggested that most of this motion was taken up within the Canadian Arctic Islands resulting in little or no motion along Nares Strait between Greenland and Ellesmere Island. From Late Paleocene to mid-Eocene (anomaly 25-21) Greenland continued to move obliquely, resulting in a displacement of 125 km along and of 90 km normal to the Nares Strait. From mid-Eocene to early Oligocene another 100 km of motion took place normal to the Strait, which correlates well with the Eurekan Orogeny in the Canadian Arctic Island. During these times the relative motion between Greenland and Svalbard (Eurasian plate) was mainly strike-slip with a small component of compression. The implication of the resulting motion between the North American and the Eurasian plates onto the Siberian platform are discussed.  相似文献   

17.
合肥盆地基底构造属性   总被引：33，自引：4，他引：29       下载免费PDF全文
根据合肥盆地及周边地表地质、地震剖面、同位素测年及MT等新资料的综合研究,提出中-新生代合肥盆地的基底是一个不同构造类型基底的叠合与复合.上古生界以前的基底以六安断裂为界,其北为华北板块陆壳型-过渡壳型结晶基底及其上的华北克拉通-被动大陆边缘盆地沉积的上元古-下古生界基底;其南为大别型结晶基底及其上的北淮阳弧后盆地沉积的上元古-下古生界变质基底,而上古生界基底属于弧后前陆盆地型沉积.六安断裂是合肥盆地部位北大别弧、北淮阳晚元古-早古生代弧后盆地在早古生代晚期-晚古生代早期与华北板块的弧-陆碰撞缝合线.  相似文献   

18.
柴达木盆地北缘地区在泛非-祁连期经历了复杂的洋陆转化阶段,于寒武纪-奥陶纪发育了汇聚板块边缘的沟-弧-盆体系,形成了NWW-SEE向展布的柴北缘构造带早古生代岛弧及弧后盆地,沉积了一套碳酸盐岩-碎屑岩-火山岩建造。在此期间,柴北缘古洋壳的俯冲消减作用及欧龙布鲁克微地块和柴达木地块的汇聚作用与欧龙布鲁克微地块南缘沉积类型的发展演化之间存在有机的联系,构成了完整的盆-山耦合体系,引发了一系列构造事件、火山喷发事件及多种类型的事件沉积等。其中欧龙布鲁克微地块整体位于滩间山岛弧北部,在早古生代发生构造背景的转变,由被动大陆边缘转为活动大陆边缘,并诱发了多期火山喷发事件,在柴北缘构造带内形成多套火山岩、火山碎屑岩以及变碎屑岩夹层,同时陆-弧碰撞造山导致的陆壳基底的隆升及大量岛弧物质为稍后期的盆地内部碎屑岩沉积提供了重要物源。与此同时,欧龙布鲁克微地块由稳定型浅水碳酸盐岩台地沉积陷落为深水斜坡环境,在盆地内早奥陶世晚期系有规律地集中发育碳酸盐岩滑塌沉积及重力流沉积（海底扇,浊积岩等）。在此之后,由于岛弧物质向盆地内部提供大量碎屑物质,且陆-弧碰撞触发的火山及地震活动导致了同时期大量的碎屑重力流沉积的发育,并触发相对深水区沉积物向更深水区移动,使得其沉积类型转化为浊流沉积。统计表明上述事件沉积发育的时间与柴北缘地区构造活动相对活跃期基本一致,因此这些早奥陶世晚期厚层、多期次、非稳定性的重力流砂体为柴北缘洋陆俯冲及陆-弧碰撞背景下形成的,它们之间存在耦合关系。  相似文献   

19.
Transient mid-Cretaceous thermal uplift induced by lateral heating from passing oceanic lithosphere is often invoked as a mechanism for the formation of the Côte d'Ivoire–Ghana basement ridge in the Equatorial Atlantic. This heating event should have affected mid-Cretaceous sedimentary rocks along the ridge. However, organic maturity and clay mineral data on the thermal evolution of these rocks suggest that burial temperatures did not exceed 80 °C and that palaeo–geothermal gradients are not anomalous. Optical petrography and the stratigraphic pattern of temperature-sensitive parameters indicate that higher palaeotemperature estimates are related to admixtures of preheated, detrital organic and inorganic matter. Erosion brought the sediments to their present shallow burial depths. Lack of evidence for significant thermal alteration implies that either thermal exchange between oceanic and continental lithosphere along the Côte d'Ivoire–Ghana Transform Margin was negligible, or that lateral heating by oceanic lithosphere was not strong enough to affect the sedimentary cover of the basement ridge.  相似文献   

20.
The seafloor off the Otway/West Tasmanian Basins has an east‐west magnetic lineation attributable to seafloor spreading and notionally identified with the set of seafloor spreading anomalies A8‐A20. Anomaly A20 (45 Ma) lies immediately south of a magnetic quiet zone that extends northward past the continent‐ocean boundary (COB). The Southeast Indian Ocean has a constant angular width between the formerly conjugate margins of Australia and Antarctica, consistent with spreading that started along the entire margin about 96 Ma.The proximity of A20 to the Australian COB in some spreading ridge segments is therefore postulated as due to jumps of the spreading ridge to Australia with concomitant transfer of the older oceanic part of the Australian Plate to the Antarctic Plate. Accordingly, the age of the oldest seafloor at the COB in seven original ridge segments is estimated to step from about 96 to 82, 79, and 75 Ma. Break‐up marks a change in the subsidence of the margin from rapid, during rifting by continental extension, to slow during thermal subsidence of the seafloor. Subsequent ridge jumps to the COB are expected to cause uplift or at least still‐stand of the adjacent continental margin. The subsidence history of the Otway/West Tasmanian margin, as indicated by oil exploration wells, is sympathetic with the timing of the postulated ridge jumps in the adjacent seafloor, as is that of the Great Australian Bight Basin with adjacent seafloor to the west, and of the Bass and Gippsland Basins with the Tasman Sea adjacent to the east. The growth of structure at 80 Ma in the outer Gippsland Basin corresponds with a jump to Australia of the Tasman Sea ridge at 82 and 75 Ma, and at 65 Ma in the Great Australian Bight and Otway Basins to a ridge jump to Australia of the adjacent seafloor. The growth of structure at 60 Ma in the Bass Basin and at 55 Ma in the Gippsland Basin corresponds with the abandonment of the Tasman Sea ridge at A24 (55 Ma) during a re‐organization of spreading in the southwest Pacific.  相似文献   

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