The crustal structure of Norway from inversion of teleseismic receiver functions     

L. Ottemöller  V. Midzi 《Journal of Seismology》2003,7(1):35-48

Teleseismic body waves from seismic broadband and short periodstations were used to investigate the crustal structure of Norwaythrough inversion of the receiver functions. The Moho depths ofthe Baltic Shield are quite well known from previous studiesincluding seismic experiments and spectral ratio technique.However, the results on the details of the crustal structure areinconsistent. This study provided more detailed crustalstructure information at 16 locations than previously known andgenerally confirmed Moho depth results obtained in earlier studies. Significant differences are seen at a few sites. The Moho for the various sites was found at depths between28 and 44 km. In summary, the crustal thicknessincreases from the West Coast of Norway, away from thecontinental margin, towards the centre of the Baltic Shield andfrom Southwest to the Northeast. This corresponds to theincreasing age of the crust. The P velocities in the crust atmost sites show a gradual increase from about 6.0 to 7.1 km/s, withoutclear layering.  相似文献   

Upper lithospheric seismic velocity structure across the Pripyat Trough and the Ukrainian Shield along the EUROBRIDGE'97 profile   总被引：1，自引：0，他引：1  

H. Thybo  T. Janik  V. D. Omelchenko  M. Grad  R. G. Garetsky  A. A. Belinsky  G. I. Karatayev  G. Zlotski  M. E. Knudsen  R. Sand  J. Yliniemi  T. Tiira  U. Luosto  K. Komminaho  R. Giese  A. Guterch  C. -E. Lund  O. M. Kharitonov  T. Ilchenko  D. V. Lysynchuk  V. M. Skobelev  J. J. Doody 《Tectonophysics》2003,371(1-4):41-79

We present new results on the structure resulting from Palaeoproterozoic terrane accretion and later formation of one of the aulacogens in the East European Platform. Seismic data has been acquired along the 530-km-long, N–S-striking EUROBRIDGE'97 traverse across Sarmatia, a major crustal segment of the East European Craton. The profile extends across the Ukrainian Shield from the Devonian Pripyat Trough, across the Palaeoproterozoic Volyn Block and the Korosten Pluton, into the Archaean Podolian Block. Seismic waves from chemical explosions at 18 shot points at approximately 30-km intervals were recorded in two deployments by 120 mobile three-component seismographs at 3–4 km nominal station spacing. The data has been interpreted by use of two-dimensional tomographic travel time inversion and ray trace modelling. The high data quality allows modelling of the P- and S-wave velocity structure along the profile. There are pronounced differences in seismic velocity structure of the crust and uppermost mantle between the three main tectonic provinces traversed by the profile: (i) the Pripyat Trough is a ca. 4-km-deep sedimentary basin, fully located in the Osnitsk–Mikashevichi Igneous Belt in the northern part of the profile. The velocity structure is typical for a Precambrian craton, but is underlain by a ca. 5-km-thick lowest crustal layer of high velocity. The development of the Pripyat Trough appears to have only affected the upper crust without noticeable thinning of the whole crust; this may be explained by a rheologically strong lithosphere at the time of formation of the trough. (ii) Very high seismic velocity and Vp/Vs ratio characterise the Volyn Block and Korosten Pluton to a depth of 15 km and probably also the lowest crust. The values are consistent with an intrusive body of mafic composition in the upper crust that formed from bimodal melts derived from the mantle and the lower crust. (iii) The Podolian Block is close to a typical cratonic velocity structure, although it is characterised by relatively low seismic velocity and Vp/Vs ratio. A pronounced SW-dipping mantle reflector from Moho to at least 70 km depth may represent the Proterozoic suture between Sarmatia and Volgo–Uralia, the structure from terrane accretion, or a later shear zone in the upper mantle. The sub-Moho P-wave seismic velocity is high everywhere along the profile, with the exception of the area above the dipping reflector. This velocity change further supports a plate tectonic origin of the dipping mantle reflector. The profile demonstrates that structure from Palaeoproterozoic plate tectonic processes are still identifiable in the lithosphere, even where younger metamorphic equilibration of the crust has taken place.  相似文献   

High-resolution body wave tomography beneath the SVEKALAPKO array: I. A priori three-dimensional crustal model and associated traveltime effects on teleseismic wave fronts   总被引：3，自引：0，他引：3  

Senén Sandoval  Edi Kissling  Jörg Ansorge  the SVEKALAPKO Seismic Tomography Working Group 《Geophysical Journal International》2003,153(1):75-87

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盾构砂性土层所加泡沫剂替代品的工地试验研究     

黄留新  唐汉  盛国新 《江苏地质》2007,31(3):262-267

以上海地铁M8线盾构掘进施工为实例,对掘进过程中所用的进口和国产泡沫剂的性能和效果进行了分析,从中选择有效、经济的泡沫代品,为以后的泡沫法盾构施工提供借鉴和参考。  相似文献   

Decomposition analysis of the BEAR magnetotelluric data: implications for the upper mantle conductivity in the Fennoscandian Shield   总被引：1，自引：0，他引：1  

I. Lahti  T. Korja  P. Kaikkonen  K. Vaittinen  BEAR Working Group 《Geophysical Journal International》2005,163(3):900-914

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加拿大拉布拉多铀矿化类型和铀矿勘探潜力     

王永春  谭亮  李猛猛  刘行  王龙  张熹鹏 《世界地质》2015,34(1):127-134

拉布拉多(Labrador)地处加拿大地盾东部边缘,其U矿化类型多样,但最重要的是赋存于变质火山岩和沉积岩内的矿化,主要分布于Makkovik省中心矿带区(CMB)的古元古代表壳岩和侵入岩中。该区矿化有岩浆型(伟晶岩和酸性火山岩)、后生--热液型(有些类似于Fe氧化物--Cu--Au(IOCG)型矿床)、剪切带型(可能是变质--交代成因)和砂质沉积岩中的层状矿化,但未发现典型的不整合型。根据其矿化类型,结合已发现矿床的成矿地质特征和矿化地质资料分析,得出该区的一些成矿远景区有较大的勘探潜力,圈定White Bear湖U矿勘查战略选区和Nash湖U矿勘查战略选区。  相似文献   

Broad-scale spatial pattern of forest landscape types in the Guiana Shield     

Valéry Gond  Vincent Freycon  Jean-François Molino  Olivier Brunaux  Florent Ingrassia  Pierre Joubert  Jean-François Pekel  Marie-Françoise Prévost  Viviane Thierron  Pierre-Julien Trombe  Daniel Sabatier 《International Journal of Applied Earth Observation and Geoinformation》2011

Detecting broad scale spatial patterns across the South American rainforest biome is still a major challenge. Although several countries do possess their own, more or less detailed land-cover map, these are based on classifications that appear largely discordant from a country to another. Up to now, continental scale remote sensing studies failed to fill this gap. They mostly result in crude representations of the rainforest biome as a single, uniform vegetation class, in contrast with open vegetations. A few studies identified broad scale spatial patterns, but only when they managed to map a particular forest characteristic such as biomass. The main objective of this study is to identify, characterize and map distinct forest landscape types within the evergreen lowland rainforest at the sub-continental scale of the Guiana Shield (north-east tropical South-America 10° North-2° South; 66° West-50° West). This study is based on the analysis of a 1-year daily data set (from January 1st to December 31st, 2000) from the VEGETATION sensor onboard the SPOT-4 satellite (1-km spatial resolution). We interpreted remotely sensed landscape classes (RSLC) from field and high resolution remote sensing data of 21 sites in French Guiana. We cross-analyzed remote sensing data, field observations and environmental data using multivariate analysis. We obtained 33 remotely sensed landscape classes (RSLC) among which five forest-RSLC representing 78% of the forested area. The latter were classified as different broad forest landscape types according to a gradient of canopy openness. Their mapping revealed a new and meaningful broad-scale spatial pattern of forest landscape types. At the scale of the Guiana Shield, we observed a spatial patterns similarity between climatic and forest landscape types. The two most open forest-RSLCs were observed mainly within the north-west to south-east dry belt. The three other forest-RSLCs were observed in wetter and less anthropized areas, particularly in the newly recognized “Guianan dense forest arch”. Better management and conservation policies, as well as improvement of biological and ecological knowledge, require accurate and stable representations of the geographical components of ecosystems. Our results represent a decisive step in this way for the Guiana Shield area and contribute to fill one of the major shortfall in the knowledge of tropical forests.  相似文献   

Post-collisional magmatism in the northern Arabian-Nubian Shield: The geotectonic evolution of the alkaline suite at Gebel Tarbush area, south Sinai, Egypt     

Esam Sadek Farahat  Mokhles Kamal Azer 《Chemie der Erde / Geochemistry》2011,71(3):247-266

Post-collisional alkaline magmatism (∼610–580 Ma) is widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield (ANS), i.e. the northern part of the Egyptian Eastern Desert and Sinai. Alkaline rocks of G. Tarbush constitute the western limb of the Katharina ring complex (∼593 ± 16 Ma) in southern Sinai. This suite commenced with the extrusion of peralkaline volcanics and quartz syenite subvolcanics intruded by syenogranite and alkali feldspar granite. The mineralogy and geochemistry of these rocks indicate an alkaline/peralkaline within-plate affinity. Quartz syenite is relatively enriched in TiO₂, Fe₂O₃, MgO, CaO, Sr, Ba and depleted in SiO₂, Nb, Y, and Rb. The G. Tarbush alkaline suite most likely evolved via fractionation of mainly feldspar and minor mafic phases (hornblende, aegirine) from a common quartz syenite parental magma, which formed via partial melting of middle crustal rocks of ANS juvenile crust. Mantle melts could have provided the heat required for the middle crustal melting. The upper mantle melting was likely promoted by erosional decompression subsequent to lithospheric delamination and crustal uplift during the late-collisional stage of the ANS. Such an explanation could explain the absence or scarce occurrence of mafic and intermediate lithologies in the abundant late- to post-collisional calc-alkaline and alkaline suites in the northern ANS. Moreover, erosion related to crustal uplift during the late-collision stage could account for the lack or infrequent occurrence of older lithologies, i.e. island arc metavolcanics and marginal basin ophiolites, from the northern part of the ANS.  相似文献   

Petrogenesis of granitic rocks of the Jabal Sabir area,South Taiz City,Yemen Republic     

Rasmy I.El-Gharbawy 《中国地球化学学报》2011,30(2):193-203

The Tertiary granitic intrusive body(～21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening.This intrusive body occupies the southern sector of Taiz City.It is triangular in shape,affected by two major faults,one of which is in parallel to the Gulf of Aden,and the other is in parallel to the eastern margin of the Red Sea coast.The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.The granitic body of Jabal Sabir belongs to the alkaline or peralkaline suite of A-type granites.It is enriched in the REE.The tight bundle plot of its REE pattern reflects neither tectonism nor metamorphism.This granite body is characterized by high alkali(8.7%-10.13%),high-field strength elements(HFSE),but low Sr and Ba and high Zn contents.The abundance of xenoliths from the neighboring country rocks and prophyritic texture of the Jabal Sabir granite body indicate shallow depths of intrusion.The major and trace elements data revealed a fractional crystallization origin,probably with small amounts of crustal contamination.It is interpreted that the Jabal Sabir intrusion represents an anorogenic granite pertaining to the A-type,formed in a within-plate environment under an extensional tectonic setting pertaining to rift-related granites.  相似文献   

The Neoproterozoic layered mafic–ultramafic intrusion of Gabal Imleih, south Sinai, Egypt: Implications of post-collisional magmatism in the north Arabian–Nubian Shield     

M.K. Azer  R.I. El-Gharbawy 《Journal of African Earth Sciences》2011,60(4):253-272

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