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1.
《International Geology Review》2012,54(10):1213-1225
P- and S-wave tomography of the upper mantle beneath the Cape Verde hotspot is determined using arrival-time data measured precisely from three-component seismograms of 106 distant earthquakes recorded by a local seismic network. Our results show a prominent low-velocity anomaly imaged as a continuous column <100 km wide from the uppermost mantle down to about 500 km beneath Cape Verde, especially below the Fogo active volcano, which erupted in 1995. The low-velocity anomaly may reflect a hot mantle plume feeding the Cape Verde hotspot.  相似文献   

2.
The tectonic position of the Kamchatka Cape Peninsula at the junction of the active Kuril–Kamchatka and Aleutian arcs exposes the coastline of the peninsula to strong neotectonic activities. Fracture zones have variable influence on uplift of the Kamchatka Cape Peninsula. Relevant morphologic indicators of neotectonic activity are multilevel, highly uplifted marine terraces and terraces displaced along active faults. Recent uplift rates of coastal sediments are determined by remote sensing via ASTER and SRTM DEM combined with optically stimulated luminescence dating (OSL). On the Kamchatka Cape Peninsula, terraces from the same generation are mapped at different elevations by remote sensing methods. After defining different areas of uplifted terraces, four neotectonic blocks are identified. According to apatite fission track data, the mean differential exhumation rates range from 0.2 to 1.2 mm year?1 across the blocks since Late Miocene. The OSL data presented point to significant higher uplift rates of up to 3 ± 0.5 and 4.3 ± 1 mm year?1, which indicates an acceleration of the vertical movement along the coast of Kamchatka Cape Peninsula in Upper Pleistocene and Holocene times.  相似文献   

3.
Holocene aeolian silts deposited on the Cape Verde Islands provide information about the origin of African palaeodusts that have fallen on the north-eastern Atlantic ocean over the last 10 000 years. Sedimentological composition indicates that most of these aeolian silts are unquestionably of continental origin. Their Sr and Nd isotopic composition identifies a Saharan origin-suggesting transport by Harmattan winds. We estimate that Saharan dust comprises 75–95% of material in these Holocene silts, the rest coming from the weathering of local basaltic bedrock.  相似文献   

4.
The Cadamosto Seamount is an unusual volcanic centre from Cape Verde, characterised by dominantly evolved volcanics, in contrast to the typically mafic volcanic centres at Cape Verde that exhibit only minor volumes of evolved volcanics. The magmatic evolution of Cadamosto Seamount is investigated to quantify the role of magma-crust interaction and thus provide a perspective on evolved end-member volcanism of Cape Verde. The preservation of mantle source signatures by Nd–Pb isotopes despite extensive magmatic differentiation provides new insights into the spatial distribution of mantle heterogeneity in the Cape Verde archipelago. Magmatic differentiation from nephelinite to phonolite involves fractional crystallisation of clinopyroxene, titanite, apatite, biotite and feldspathoids, with extensive feldspathoid accumulation being recorded in some evolved samples. Clinopyroxene crystallisation pressures of 0.38–0.17 GPa for the nephelinites constrain this extensive fractional crystallisation to the oceanic lithosphere, where no crustal assimilants or rafts of subcontinental lithospheric mantle are available. In turn, magma-crust interaction has influenced the Sr, O and S isotopes of the groundmass and late crystallising feldspathoids, which formed at shallow crustal depths reflecting the availability of oceanic sediments and anhydrite precipitated in the ocean crust. The Nd–Pb isotopes have not been affected by these processes of magma-crust interaction and hence preserve the mantle source signature. The Cadamosto Seamount samples have high 206Pb/204Pb (>19.5), high εNd (+6 to +7) and negative Δ8/4Pb, showing affinity with the northern Cape Verde islands as opposed to the adjacent southern islands. Hence, the Cadamosto Seamount in the west is located spatially beyond the EM1-like component found further east. This heterogeneity is not encountered in the oceanic lithosphere beneath the Cadamosto Seamount despite greater extents of fractional crystallisation at oceanic lithospheric depths than the islands of Fogo and Santiago. Our data provide new evidence for the complex geometry of the chemically zoned Cape Verde mantle source.  相似文献   

5.
Reaction zones around minerals in mantle xenoliths have been reported from many localities worldwide. Interpretations of the origins of these textures fall into two groups: mantle metasomatic reaction or reaction during transport of the xenoliths to the surface. A suite of harzburgitic mantle xenoliths from Sal, Cape Verde show clear evidence of reaction during transport. The reactions resulted in the formation of olivine–clinopyroxene and Si- and alkali-rich glass reaction zones around orthopyroxene and sieve-textured clinopyroxene and sieve textured spinel, both of which are associated with a Si- and alkali-rich glass similar to that in the orthopyroxene reaction zones. Reaction occurred at pressures less than the mantle equilibration pressure and at temperatures close to the liquidus temperature of the host magma. In addition, there is a clear spatial relation of reaction with the host lava: reaction is most intense near the lava/xenolith contact. The residence time of the xenoliths in the host magma, determined from Fe–Mg interdiffusion profiles in olivine, was approximately 4 years. Our results cannot be reconciled with a recent model for the evolution of the mantle below the Cape Verde Archipelago involving mantle metasomatism by kimberlitic melt. We contend that alkali-rich glasses in the Sal xenoliths are not remnants of a kimberlitic melt, but rather they are the result of reaction between the host lava or a similar magma and xenolith minerals, in particular orthopyroxene. The formation of a Si- and alkali-rich glass by host magma–orthopyroxene reaction appears to be a necessary precursor to formation of sieve textured spinel and clinopyroxene.  相似文献   

6.
The Cape Verde hotspot, like many other Ocean Island Basalt provinces, demonstrates isotopic heterogeneity on a 100–200 km scale. The heterogeneity is represented by the appearance of an EM1-like component at several of the southern islands and with a HIMU-like component present throughout the archipelago. Where the EM1-like component is absent, a local DMM-like component replaces the EM1-like component. Various source lithologies, including peridotite, pyroxenite and eclogite have been suggested to contribute to generation of these heterogeneities; however, attempts to quantify such contributions have been limited. We apply the minor elements in olivine approach (Sobolev et al. in Nature 434:590–597, 2005; Science, doi: 10.1126/science.1138113, 2007), to determine and quantify the contributions of peridotite, pyroxenite and eclogite melts to the mantle heterogeneity observed at Cape Verde. Cores of olivine phenocrysts of the Cape Verde volcanics have low Mn/FeO and low Ni*FeO/MgO that deviate from the negative trend of the global array. The global array is defined by mixing between peridotite and pyroxenite, whereas the Cape Verde volcanics indicate contribution of an additional eclogite source. Eclogite melts escape reaction with peridotite either by efficient extraction in an area of poor mantle flow or by reaction of eclogite melts with peridotite, whereby an abundance of eclogite can seal off the melt from further reaction. Temporal trends of decreasing Mn/FeO indicate that the supply of eclogite melts is increasing. Modelling suggests the local DMM-like end-member is formed from a relatively peridotite-rich melt, while the EM1-like end-member has a closer affinity to a mixed peridotite–pyroxenite–eclogite melt. Notably the HIMU-like component ranges from pyroxenite–peridotite-rich melt to one with up to 77 % eclogite melt as a function of time, implying that sealing of melt pathways is becoming more effective.  相似文献   

7.
We present new Sr-Nd isotope compositions together with major- and trace element concentrations measured for whole rocks and mineral separate phases (apatite, biotite and calcite) from fifteen Cape Verde oceanic carbonatites (Atlantic Ocean). Trace element patterns of calcio- and magnesio-carbonatites present a strong depletion in K, Hf, Zr and Ti and an overall enrichment in Sr and REE relative to Cape Verde basalts, arguing for distinct source components between carbonatites and basalts. Sr and Nd isotopic ratios show small, but significant variations defining a binary mixing between a depleted end-member with unradiogenic Sr and radiogenic Nd values and a ‘‘enriched’’ end-member compatible with old marine carbonates. We interpret the depleted end-member as the Cape Verde oceanic lithosphere by comparison with previous studies on Cape Verde basalts. We thus propose that oceanic carbonatites are resulting from the interaction of a deep rooted mantle plume carrying a lower 4He/3He signature from the lower mantle and a carbonated metasomatized lithosphere, which by low degree melting produced carbonatite magmas. Sr-Nd compositions and trace element patterns of carbonatites argue in favor of a metasomatic agent originating from partial melting of recycled, carbonated oceanic crust. We have successfully reproduced the main geochemical features of this model using a Monte-Carlo-type simulation.  相似文献   

8.
Parental magmas of the Cape Verde Islands are high-Mg foidites, picrobasalts, and basanites. The rocks can be classified into the following two differentiated series: (1) a high-alkali series, which includes picrites, high-Mg foidites, low-Mg-foidites, and phonolites; and (2) a series of moderate alkalinity, which includes picrobasalts, basanites, tephrites, tephrophonolites, phonotephrites, phonolites, and trachytes.The differentiation of both series is associated with a decrease in the concentrations of Mg, Fe, Ti, and Ca and an increase in the contents of Al, Si, K, and Na. Rare lithophile elements (REE, Zr, Nb, Th, Rb, and U) progressively enrich younger derivatives. The Sr and Ba concentrations pass through a maximum, as is typical of alkaline series, which are characterized by broad crystallization fields of plagioclase and melilite, minerals that have high distribution coefficients of these elements. The analysis of the composition of volcanic rocks from the Cape Verde Islands within the scope of the system olivine-diopside-nepheline shows that the evolution of the parental magmas was controlled by crystallization differentiation in shallow-depth intermediate chambers. This conclusion finds further support in data on inclusions in minerals and a simulated crystallization model in a magmatic chamber.  相似文献   

9.
The structure of anomalously uplifted areas in transverse ridges of the Vema, S o Paulo, and Romanche fracture zones is considered. It is concluded that their formation and eventual development in the present-day structure of the central Atlantic bottom proceeded during two stages. The first stage that corresponds to a short period at the Tortonian-Messinian transition (10 Ma ago) was marked by transportation of deep-seated rocks into the upper part of the lithosphere along thrust faults with mass motion in the meridional direction along the axis of the Mid-Atlantic Ridge. The second stage was characterized by contrasting highamplitude vertical movements from 10 to 3 Ma ago. It is suggested that near-meridional compression in the domains surrounding the Western Tethys in the Tortonian-Messinian resulted in deformation of the upper lithosphere within large transform fracture zones of the central Atlantic. The deformation that occurred 10 Ma ago was a manifestation of the global neotectonic epoch of the Earth.  相似文献   

10.
New lead, strontium and helium isotopic data, together with trace element concentrations, have been determined for basalts from the Cape Verde archipelago (Central Atlantic). Isotopic and chemical variations are observed at the scale of the archipelago and lead to the definition of two distinct groupings, in keeping with earlier studies. The Northern Islands (Santo Antão, São Vicente, São Nicolau and Sal) present Pb isotopic compositions below the Northern Hemisphere Reference Line (NHRL) (cf. Hart, 1984), unradiogenic Sr and relatively primitive 4He/3He ratios. In contrast, the Southern Islands (Fogo and Santiago) display Pb isotopes above the NHRL, moderately radiogenic Sr and MORB-like helium signatures. We propose that the dichotomy between the Northern and Southern Islands results from the presence of three isotopically distinct components in the source of the Cape Verde basalts: (1) recycled ∼1.6-Ga oceanic crust (high 206Pb/204Pb, low 87Sr/86Sr and high 4He/3He); (2) lower mantle material (high 3He); and (3) subcontinental lithosphere (low 206Pb/204Pb, high 87Sr/86Sr and moderately radiogenic 4He/3He ratios). The signature of the Northern Islands reflects mixing between recycled oceanic crust and lower mantle, to which small proportions of entrained depleted material from the local upper mantle are added. Basalts from the Southern Islands, however, require the addition of an enriched component thought to be subcontinental lithospheric material instead of depleted mantle. The subcontinental lithosphere may stem from delamination and subsequent incorporation into the Cape Verde plume, or may be remnant from delamination just before the opening of the Central Atlantic. Basalts from São Nicolau reflect the interaction with an additional component, which is identified as oceanic crustal material.  相似文献   

11.
This research is focused on the composition of the sediments produced in volcanic islands when the climate does not favour weathering. The XRD mineralogy (bulk sample and fraction finer than 63 μm), petrography and geochemistry of a set of bedload stream and beach samples collected in the “old” Maio and the “young” Fogo islands of Cape Verde archipelago are used to investigate the compositional transformations promoted by exogenous processes during island denudation. The main factor responsible for the variability in sediment composition is the incorporation of biogenic material derived from the evolving shelves; it largely exceeds the effects of the exhumation of different volcanic and basement units. Given the arid climate (and steep land surface in Fogo), only the most labile components of basaltic rocks, such as volcanic glass, are decomposed. The incipient weathering and sorting processes are responsible for the depletion of Al in bedload deposits. The same happens with other elements usually regarded as non-mobile (namely, Nb, Th, REE, etc.), while Mg is concentrated. Thus, weathering indices grounded on the premise that “mobile” elements are lost and “non-mobile” elements are enriched via weathering are useless in Cape Verde bedload sediments. With time, weathering is able to promote Na leaching and the formation of secondary minerals, which tend to retain non-mobile elements released in the earlier stages of alteration (e.g., LREE, Th, Y, Nb, Ta etc.). Sorting processes are responsible for the selective removal of less-dense grains, explaining local differences between beach and stream deposits. Beach placers are enriched in augitic clinopyroxene (occasionally also in olivine in the Fogo island), and Sc, Cr and Co. Niobium and Ta must be hosted in fine-grained particles that are easily windblown and their abundances in dusts may reveal Cape Verde as a source of airborne material crossing the Atlantic Ocean.  相似文献   

12.
In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78·8 ± 0·9 ka, which overlaps within error with the 73 ± 7 ka age proposed for Fogo volcano's flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (<78 ka) remains undated. In summary, the geological record of Maio exhibits well-preserved evidence of repeated tsunami inundation, reinforcing the notion that tsunami hazard is not so low at volcanic archipelagos featuring prominent and highly-active volcanoes such as in Cape Verde.  相似文献   

13.
The geological and geophysical data primarily on the structure of the upper sedimentary sequence of the northern Knipovich Ridge (Norwegian-Greenland Basin) that were obtained during Cruise 24 of the R/V Akademik Nikolai Strakhov are considered. These data indicate that the recent kinematics of the northern Knipovich Ridge is determined by dextral strike-slip displacements along the Molloy Fracture Zone (315° NW). This stress field is superimposed by a system related to rifting and latitudinal opening of rifts belonging to the ridge proper. Thus, the structural elements formed under the effect of two stress fields are combined in this district. Several stages of tectonic movements are definable. The first stage (prior to 500 ka ago) is marked by the dominant normal faults, which are overlain by the lower and upper sedimentary sequences. The second stage (prior to 120–100 ka ago) is characterized by development of normal and reverse faults, which displace the lower sequence and are overlain by the upper sequence. Both younger and older structural features reveal peaks of tectonic activity separated by intermediate quiet periods 50–60 ka long. The stress field of the regional strike-slip faulting is realized in numerous oblique NE-trending normal and normal-strike-slip faults that divide the rift valley and its walls into the segments of different sizes. Their strike (20°–30° NE) is consistent with a system of secondary antithetic sinistral strike-slip faults. The system of depressions located 40 km west of the rift valley axis may be considered a paleorift zone that is conjugated at 78°07′ N and 5°20′ W with the NW-trending fault marked by the main dextral offset. The stress field that existed at this stage was identical to the recent one. The rift valley axis migrated eastward to its present-day position approximately 2 Ma ago (if the spreading rate of ～0.7 cm/yr is accepted). The obtained data substantially refine the understanding of the initial breakup of continents with the formation of oceanic structural elements. The neotectonic stage is characterized by combination of different stress fields that resulted in the formation of a complex system of tectonic structural units, including those located beyond the recent extension zone along the rift axis of the Knipovich Ridge. The tectonic deformations occurred throughout the neotectonic stage as discrete recurrent events.  相似文献   

14.
南海具有复杂的地质构造背景,扩张结束以后,新构造运动活跃,但各区域新构造运动发生的时间及运动特征有较大差异。本文综合分析了南海各区域构造演化事件、现今构造格局及新构造运动的基本特征,认为南海新构造运动的起始时间为中中新世（约15 Ma）较合理。在此基础上,收集和整理了南海及邻区最新的地质和地球物理资料,对南海海域新构造期地层差异升降、活动断裂、天然地震以及岩浆活动等新构造表现形式进行了综合分析,系统总结了南海新构造运动特征,并根据活动断裂、天然地震以及岩浆活动等特征和分布规律分析,认为南海海域新构造的表现形式之间存在较大的耦合性。本文根据新构造运动表现形式在空间分布的不平衡性,将南海及邻区划分为1个强构造活动区、3个中等强度构造活动区以及1个弱构造活动区,并结合研究区应力场特征分析,认为南海新构造运动主要受控于东部菲律宾海板块和太平洋板块对东亚大陆边缘的持续俯冲碰撞作用。  相似文献   

15.
The volcanic history of Santo Antão, NW Cape Verde Islands,includes the eruption of basanite–phonolite series magmasbetween 7·5 and 0·3 Ma and (melilite) nephelinite–phonoliteseries magmas from 0·7 to 0·1 Ma. The most primitivevolcanic rocks are olivine ± clinopyroxene-phyric, whereasthe more evolved rocks have phenocrysts of clinopyroxene ±Fe–Tioxide ± kaersutite ± haüyne ± titanite± sanidine; plagioclase occurs in some intermediate rocks.The analysed samples span a range of 19–0·03% MgO;the most primitive have 37–46% SiO2, 2·5–7%TiO2 and are enriched 50–200 x primitive mantle in highlyincompatible elements; the basanitic series is less enrichedthan the nephelinitic series. Geochemical trends in each seriescan be modelled by fractional crystallization of phenocrystassemblages from basanitic and nephelinitic parental magmas.There is little evidence for mineral–melt disequilibrium,and thus magma mixing is not of major importance in controllingbulk-rock compositions. Mantle melting processes are modelledusing fractionation-corrected magma compositions; the modelssuggest 1–4% partial melting of a heterogeneous mantleperidotite source at depths of 90–125 km. Incompatibleelement enrichment among the most primitive magma types is typicalof HIMU OIB. The Sr, Nd and Pb isotopic compositions of theSanto Antão volcanic sequence and geochemical characterchange systematically with time. The older volcanic rocks (7·5–2Ma) vary between two main mantle source components, one of whichis a young HIMU type with 206Pb/204Pb = 19·88, 7/4 =–5, 8/4 0, 87Sr/86Sr = 0·7033 and 143Nd/144Nd= 0·51288, whereas the other has somewhat less radiogenicSr and Pb and more radiogenic Nd. The intermediate age volcanicrocks (2–0·3 Ma) show a change of sources to two-componentmixing between a carbonatite-related young HIMU-type source(206Pb/204Pb = 19·93, 7/4 = –5, 8/4 = –38,87Sr/86Sr = 0·70304) and a DM-like source. A more incompatibleelement-enriched component with 7/4 > 0 (old HIMU type) isprominent in the young volcanic rocks (0·3–0·1Ma). The EM1 component that is important in the southern CapeVerde Islands appears to have played no role in the petrogenesisof the Santo Antão magmas. The primary magmas are arguedto be derived by partial melting in the Cape Verde mantle plume;temporal changes in composition are suggested to reflect layeringin the plume conduit. KEY WORDS: radiogenic isotopes; geochemistry; mantle melting; Cape Verde  相似文献   

16.
在已有调查研究的基础上,通过野外地质调查和剖面测量,重点分析了岷江松潘段的漳腊盆地、斗鸡台盆地地貌特征、第四纪沉积物类型、物质成分、空间分布等特征,并系统测量和研究了松潘段岷江干流及其支流的河流阶地特征。研究表明,新构造运动控制了松潘段第四纪盆地的形态和地貌演化过程,漳腊盆地和斗鸡台盆地形成于中新世末至上新世初,西侧控盆断裂为东倾正断层,东侧为西倾逆断层,盆地为断块发生西降东升的翘板式断块运动过程中形成的,称之为"翘板式箕状盆地"。松潘段岷江河谷地貌呈现出宽谷和窄谷交替出现的特点,岷江干流及其支流中发育多处湖相地层,沉积特征表现为堰塞湖。岷江上游松潘段最多发育6级阶地,以侵蚀阶地和堆积阶地为主,主要形成于中更新世晚期—全新世时期。阶地级数具有分段性特点,不同区段阶地阶面宽窄不一,受区内新构造活动控制明显。岷江上游新构造运动表现为南北条带性和东西向差异掀斜抬升的特点,红桥关以上整体为构造隆升区,至少具有3次构造隆升,岷江上游斗鸡台盆地构造隆升强度整体上大于漳腊盆地。在尕米寺地区可能发生了6次构造抬升,红桥关一带构造抬升明显要强于漳腊盆地。  相似文献   

17.
Fe-Mn deposits for this research were sampled at the floor of the Atlantic Ocean in the Cape Verde Quadrangle, Elena Seamount, and Strakhov Basin. The samples were analyzed for major components and for Ni, Co, Cu, P, S, and other trace elements by ICP-AES. Common features in the distribution of REE (high positive Ce anomalies) were discovered, and trends in the distribution of elements with depths are revealed. As, Pb, Sr, Co, and Pt are prone to accumulate in shallower water areas, whereas Cu and Li are enriched at deeper water territories. The samples are analyzed in compliance with Andreev’s classification, and their noble metal composition is determined.  相似文献   

18.
The 1995 eruption of Fogo (Cape Verde Islands) differed from previous eruptions by the occurrence of evolved lavas, the SW-orientation of vents, and pre-eruptive seismicity between Fogo and the adjacent (~20 km) island of Brava. We have conducted a thermobarometric and chemical study of this eruption in order to reconstruct its magma plumbing system and to test for possible connections to Brava. The bimodal eruption produced basanites (5.2–6.7 wt% MgO) and phonotephrites (2.4–2.8 wt% MgO) that are related by fractional crystallization. Clinopyroxene-melt-barometry of phenocrysts yields pressure ranges of 460–680 MPa for the basanites and 460–520 MPa for the phonotephrites. Microthermometry of CO2-dominated fluid inclusions in olivine and clinopyroxene phenocrysts yields systematically lower pressure ranges of 200–310 MPa for basanites and 270–470 MPa for phonotephrites. The combined data indicate pre-eruptive storage of the 1995 magmas within the lithospheric mantle between 16 and 24 km depth. During eruption, the ascending magmas stalled temporarily at 8–11 km depth, within the lower crust, before they ascended to the surface in a few hours as indicated by zonations of olivine phenocrysts. Our data provide no evidence for magma storage at shallow levels (<200 MPa) or lateral magma movements beneath the Fogo-Brava platform. Sr–Nd–Pb isotope ratios of samples from Brava differ significantly from those of the 1995 and older Fogo lavas, which rules out contamination of the 1995 magmas by Brava material and indicates different mantle sources and magma plumbing systems for both islands.  相似文献   

19.
对藏北长江源地区河谷地貌和新构造变形调查发现,该区具有平行式水系格局,河谷地貌以形态不同的窄谷和宽谷为特点,新近纪以来该区主要经历了早期挤压和晚期伸展构造演化过程,产生了褶皱-逆冲、走滑剪切、正断层和地堑构造3种构造变形样式。长江源区河谷地貌的形成演化明显受新构造运动的影响,新构造运动不仅控制了河谷地貌形态与水系格局,而且影响了河流阶地分布以及洪(冲)积扇的形态、结构。长江源地区主要水系至少自全新世以来是沿新构造运动产生的不同性质断裂构造溯源侵蚀发育而成。  相似文献   

20.
The Knipovich Ridge extends for 550–600 km between the Mohns Ridge and the demarcation Spitsbergen Fracture Zone. The structural features of this ridge are repeatedly mentioned in the literature; however, substantial discrepancies remain in the treatment of its tectonics. New data on the structure of this ridge presented in this paper are based on the results of continuous seismic profiling in the area studied by the expedition of the Geological Institute, Russian Academy of Sciences and the Norwegian Petroleum Directorate on the R/V Akademik Nikolaj Strakhov in 2006; 56 seismic lines allow us to depict zones differing in seismic records that provide insights into their internal tectonic structure. Interpretation of the seismic data makes it possible to compile maps of the acoustic basement surface and sedimentary cover thickness in the studied area. These maps expand our knowledge of the geological history and geodynamics of the Knipovich Ridge at the neotectonic stage of its evolution.  相似文献   

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