Rheological structure and dynamical response of the DSS profile BALTIC in the SE Fennoscandian Shield     

K. Moisio  P. Kaikkonen  F. Beekman   《Tectonophysics》2000,320(3-4):175-194

Numerical modelling was applied to study the present-day state of stress and deformation under different tectonic loading conditions at the seismic BALTIC–SKJ profile in south-eastern Finland and in Estonia. The finite element method was used to solve the numerical problem. The two-dimensional model was constructed using the results from both seismic and thermal studies along the profile. The model is 700 km long and 200 km deep, and is roughly divided into an inhomogeneous, laterally layered crust and a homogeneous mantle lithosphere. Both the linear elastic and non-linear elasto-plastic rheologies were used. Elasto-plasticity was achieved by calculating a rheological strength as a function of depth along the profile. Different tectonic load cases were analysed with displacement, force and pressure type boundary conditions. Also, the effect of different strain rates was investigated. The results suggest that even with relatively low compressive stress levels the lower crust deforms in a plastic manner for a wet crustal rheology. When applying a dry crustal rheology, plastic yielding is attained only with much higher stress fields.  相似文献   

Airborne geophysical characterization of geotectonic relationships in the southern Ribeira Belt,Luís Alves Craton,and northern Dom Feliciano Belt,Brazilian Shield     

《International Geology Review》2012,54(4):471-488

ABSTRACT

In many Precambrian provinces, the understanding about the tectonic history is restrained by the limited exposure of rocks so that aerogeophysical data can provide information below the surface cover of sediments, soil, and water to build a tectonic model of the region. However, the tectonic evolution of cratons and shear zones is very complex due to scarce aerogeophysical and geological data. The integrated observation of geology, aerogammaspectrometry, and aeromagnetometry of the Brazilian Shield, states of Santa Catarina, Paraná, and southern São Paulo, is enhanced by a 2011 high-resolution aerogeophysical survey. The Ponta Grossa and Florianópolis dike swarms show two sets of linear high magnetic signal. Peralkaline–carbonatitic complexes are observed in all images, e.g. Jacupiranga, Tunas, and Anitápolis. Three main geotectonic provinces are apparent in the shield. The Dom Feliciano Belt has two domains in terms of radioelements K, Th, and U. This belt includes granitic rocks of the Florianópolis Batholith, Brusque Group schists, and Itajaí Basin of sedimentary and volcanic rocks. The Luís Alves Craton has mostly the Santa Catarina Granulitic Complex and other gneisses. The craton has patches of high emission rates and extends to the northeastern extreme of the studied area with a high-contrast magnetic signal in most of the unit. The Ribeira Belt also has high in gammaspectrometric images, although less homogeneous than the Dom Feliciano Belt. This belt contains granitic complexes, gneisses, and schists and has a low magnetic signal with patches of high analytical signal amplitude. Shear zones delimit different geotectonic units, but are also significant in the Ribeira Belt. The Luís Alves Craton is the most complex unit, as seen in ternary K + eTh + eU images, requiring the future discrimination of small features. This novel study of the Brazilian Shield based on new geophysical data supports the classification of the proposed main geotectonic units.  相似文献   

Magma Source and Evolution of the Late Neoproterozoic Gabbros in the Arabian-Nubian Shield: Geochemical, Mineralogical and Sr–Nd Isotopic Constraints     

Mohamed M. ABU ANBAR  Bassam A. ABU AMARAH 《《地质学报》英文版》2013,87(Z1):191-191

  相似文献   

Paleoclimate record in the Nubian Sandstone Aquifer,Sinai Peninsula,Egypt     

Abdou Abouelmagd  Mohamed Sultan  Neil C. Sturchio  Farouk Soliman  Mohamed Rashed  Mohamed Ahmed  Alan E. Kehew  Adam Milewski  Kyle Chouinard 《Quaternary Research》2014

Sixteen groundwater samples collected from production wells tapping Lower Cretaceous Nubian Sandstone and fractured basement aquifers in Sinai were analyzed for their stable isotopic compositions, dissolved noble gas concentrations (recharge temperatures), tritium activities, and ¹⁴C abundances. Results define two groups of samples: Group I has older ages, lower recharge temperatures, and depleted isotopic compositions (adjusted ¹⁴C model age: 24,000–31,000 yr BP; δ¹⁸O: − 9.59‰ to − 6.53‰; δ²H: − 72.9‰ to − 42.9‰; < 1 TU; and recharge T: 17.5–22.0°C) compared to Group II (adjusted ¹⁴C model age: 700–4700 yr BP; δ¹⁸O: − 5.89‰ to − 4.84‰; δ²H: − 34.5‰ to − 24.1‰; < 1 to 2.78 TU; and recharge T: 20.6–26.2°C). Group II samples have isotopic compositions similar to those of average modern rainfall, with larger d-excess values than Group I waters, and locally measurable tritium activity (up to 2.8 TU). These observations are consistent with (1) the Nubian Aquifer being largely recharged prior to and/or during the Last Glacial Maximum (represented by Group I), possibly through the intensification of paleowesterlies; and (2) continued sporadic recharge during the relatively dry and warmer interglacial period (represented by Group II) under conditions similar to those of the present.  相似文献   

Geochemistry and petrogenesis of the Ediacaran post-collisional Jabal Al-Hassir ring complex,Southern Arabian Shield,Saudi Arabia     

Asaad M.B. Moufti  Kamal A. Ali  Martin J. Whitehouse 《Chemie der Erde / Geochemistry》2013

The Jabal Al-Hassir ring complex is located between latitudes 19°21′ and 19°42′ N,  and longitudes 42°55′ and 4312′ E, Southern Arabian Shield. It is an alkaline to highly fractionated calc-alkaline granite complex consisting of an inner core of biotite granite followed outward by porphyritic sodic-calcic amphibole (ferrobarroisite) granite. U–Pb zircon geochronology indicates that the Jabal Al-Hassir ring complex was emplaced at ca. 620 Ma. The granites display highly fractionated geochemical features (i.e., Eu/Eu* = 0.05–0.35; enrichment of K, Rb, Th, U, Zr, Hf, Y and REE; depletion of Ta, Nb, Ba, Sr, P, Eu, and Ti). Jabal Al-Hassir granites are post-collisional plutonic rocks and contain abundant microcline perthite and sodic-calcic amphibole, sharing the petrological and chemical features of A₂-type granites. Sr_i values range from 0.70241 to 0.70424, are similar to those expected for magmas extracted from a Neoproterozoic depleted source and much lower than what would be expected, if there was minor involvement of pre-Neoproterozoic continental crust. The geochemical characteristics indicate that their magma was most plausibly represented by partial melting of juvenile lower crust following the collision between East and West Gondwana at the final stage of the Arabian Shield evolution. The data presented in this study are therefore consistent with an intraplate, post-collisional magmatism formed at the beginning of a transition from convergent to extensional tectonics.  相似文献   

Thermochronological data from Sudan in the frame of the denudational history of the Nubian Red Sea margin     

M. L. Balestrieri  E. Abbate  G. Bigazzi  Omer El Bedri Ali 《地球表面变化过程与地形》2009,34(9):1279-1290

Low‐temperature thermochronology provides information on the timing of rifting and denudation of passive margins, and the Red Sea with its well‐exposed, young rift margins is a suitable setting for its application. Here we present new apatite fission‐track (AFT) data from Sudan northern hinterland and Red Sea coastal areas. From the former region we obtained ages between 270 ± 2 Ma ad 253 ± 53 Ma, and from the coastal belt between 83 ± 8 Ma and 39 ± 7 Ma. These data prompted a review and comparison with low‐temperature thermochronological data from the whole Nubian Red Sea Margin, and a discussion on their implication in assessing the margin evolutionary style. AFT data are available for Egypt and Eritrea as well as apatite (U‐Th)/He (AHe) ages for two transects transversal to the margin in Eritrea. Both in Egypt and Eritrea AFT data record a cooling event at about 20–25 Ma (Early Miocene) and an earlier, more local, cooling event in Egypt at about 34 Ma (Early Oligocene). The thermal modeling of the Sudan samples provides an indication of a rapid cooling in Miocene times, but does not support nor rules out an Early Oligocene cooling phase. The re‐assessment of new and existing thermochronological data within the known geological framework of the Nubian and conjugate Arabian margins favours the hypothesis that early rifting stages were affecting the whole Gulf of Suez–Red Sea–Gulf of Aden system since the Oligocene. These precocious, more attenuated, phases were followed by major extension in Miocene times. As to the mode of margin evolution, AFT age patterns both in Egypt and Eritrea are incompatible with a downwarp model. The distribution of AHe ages across the Eritrean coastal plain suggests that there the escarpment was evolving predominantly by plateau degradation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

利比里亚金矿成矿地质背景与资源潜力     

陈冲  陈开旭  严永祥  张继纯  徐景银  郑国权 《地质通报》2022,(1):72-84

西非地区比里姆(Birimian)岩系经历了伊本尼(Eburnean)造山运动,成为全球金矿商业投资的主要含矿岩系之一,该岩系在利比里亚覆盖约36％国土面积.通过对西非尤其是利比里亚地质背景分析,初步建立了利比里亚区域地质构造格架,梳理出比里姆岩系中33处重要意义的岩金矿点,其分布与比里姆绿岩带、区域剪切构造带密切相关...  相似文献   

The 1.90–1.88 Ga magmatism in the southernmost Guyana Shield, Amazonas, Brazil: Geology, geochemistry, zircon geochronology, and tectonic implications     

Cristvo da Silva Valrio  Valmir da Silva Souza  Moacir Jos Buenano Macambira 《Journal of South American Earth Sciences》2009,28(3):304-320

The southernmost Guyana Shield-Uatumã subdomain, northeastern Amazonas State, Brazil is dominantly formed by granitoid and volcanic rocks from the Água Branca Suite (ABS), undivided Granite Stocks (GS) and São Gabriel volcano–plutonic system (SGS). The ABS is characterized by a granite series that exhibits comparatively low Fe/(Fe + Mg) ratio, low (Nb/Zr)_N, high Sr values and high Rb/Zr ratio. Its rocks display metaluminous to weakly peraluminous (A/CNK 0.94–1.06), high-K calc-alkaline, I normal-type character and have moderately to strongly fractionated rare earth elements (REE) pattern. The SG granites and SGS effusive–ignimbrite–granite association is metaluminous to weakly peraluminous (A/CNK 0.84–1.18), high-K calc-alkaline, has moderately to weakly fractionated REE trend, higher Fe/(Fe + Mg) ratio, lower Sr content and lower Rb/Zr ratio. The ABS geochemical signature is consistent with formation from volcanic arc rocks and small participation of collisional setting rocks, whereas the SG and SGS have post-collisional tectonic rocks-related geochemical signature. This model is in harmony with a post-collisional extensional regime, started with the 1.90–1.89 Ga Água Branca magmatism, and culminated with the 1.89–1.88 Ga São Gabriel system at an early stage of intracratonic reactivation, which included intrusion of mafic dikes. The Uatumã subdomain was related to mantle underplating with continental uplift and its origin involved contributions of 2.3–2.44 Ga Archean-contaminated Trans-Amazonian, 2.13–2.21 Ga Trans-Amazonian, 1.93–1.94/2.0 Ga Tapajós-Parima. Foliation styles point out that part of the Água Branca granitoids recorded later deformational effects, likely related to the Rio Negro Province formation.  相似文献   

Source rocks and provenances of the Ladoga Group siliciclastic metasediments (Svecofennian Foldbelt, Baltic Shield): Results of geochemical and Sm-Nd isotopic study     

L. N. Kotova  A. B. Kotov  V. A. Glebovitskii  V. N. Podkovyrov  V. M. Savatenkov 《Stratigraphy and Geological Correlation》2009,17(1):1-19

Siliciclastic metasediments of the Ladoga Group that is the Kalevian stratotype in Karelia correlative with the Kalevian siliciclastic succession in Finland are studied in terms of geochemistry and Sm-Nd isotopic systematics. The results obtained show that rocks in the Ladoga Group lower part are enriched, as compared to rocks of the upper part, in TiO₂, Fe₂O₃, MgO, Cr, Co, Ni, and Sc, being comparatively depleted in Al₂O₃ and Th that is a result of compositional changes in provenances. The Sm-Nd isotopic data evidence that siliciclastic sediments of the Ladoga Group have accumulated during the erosion of rocks, which originated at the time of the Archean and Early Proterozoic crust-forming processes. Siliciclastic material with the Archean and Early Proterozoic T_Nd(DM) values, which are characteristic of metasediments in the group lower part, was derived respectively from granite gneisses of the Archean basement in the Karelian megablock of the Baltic Shield and from volcanic rocks of the Sortavala Group. Volcanic rocks of island-arc terranes of the Svecofennian foldbelt represented main source of siliciclastic material that accumulated in upper part of the succession.  相似文献   

华北基性岩墙群的古地磁极及其哥伦比亚超大陆重建意义   总被引：5，自引：4，他引：1  

侯贵廷  Henry HALLS  Don DAVIS  黄宝玲  杨默函  王传成 《岩石学报》2009,25(3):650-658

从华北克拉通的中西部和东部发育的基性岩墙群获得三个精确定年的实际古地磁极位置(VGPs)。华北克拉通中西部恒山GU岩墙的斜锆石U-Pb年龄为1769±3Ma,该岩墙的古地磁给出古地磁极位置在北纬36°,东经247° (dp=2, dm=4); 华北克拉通东部DY岩墙的斜锆石U-Pb年龄为1620.8±6.9Ma, 获得的古地磁极位置为北纬6.9°东经81.9°(dp=4.31, dm=6.09); 东部另一条岩墙LW4的SHRIMP U-Pb 年龄为1157±18Ma, 获得的古地磁极位置为北纬27.1°东经162°(dp=15.8, dm=18.7)。通过将这三个从基性岩墙获得的华北克拉通古地磁极位置与加拿大地盾的中元古代视极移曲线对比,在中元古代早期（1800~1600Ma）,华北克拉通与加拿大地盾一起同属哥伦比亚超大陆,而在中元古代晚期（1600~1200Ma）,华北克拉通与加拿大地盾分离,响应哥伦比亚超大陆的最终裂解事件。  相似文献