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  • 1
    Electronic Resource
    Electronic Resource
    The Darfur Dome, western Sudan: the product of a subcontinental mantle plume (1994)
    Springer
    International journal of earth sciences 83 (1994), S. 614-623 
    Details
    ISSN: 1437-3262
    Keywords: Darfur Dome ; Mantle plume ; Intracontinental volcanism ; Alkaline magmas ; K-Ar age data Bouguer gravity anomaly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194166
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The Darfur Dome, western Sudan: the product of a subcontinental mantle plume (1994)
    Springer
    International journal of earth sciences 83 (1994), S. 614-623 
    Details
    ISSN: 1437-3262
    Keywords: Darfur Dome ; Mantle plume ; Intracontinental volcanism ; Alkaline magmas ; K-Ar age data Bouguer gravity anomaly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01083232
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Post-Variscan sedimentary record of the SW margin of the Bohemian massif: a review (1997)
    Springer
    Geologische Rundschau 86 (1997), S. 178-184 
    Details
    ISSN: 0016-7835
    Keywords: Key words Bohemian massif ; SW margin ; Post-Variscan structural record ; Sedimentary record ; Clastic supply ; Source areas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The late-Palaeozoic to Cenozoic stratigraphic and structural record of the southwestern margin of the Bohemian massif and its extension beneath the southward adjacent Molasse basin shows that it is controlled by a system of basement-involving faults which came into evidence during Stephanian– Autunian times and which were subsequently repeatedly reactivated. Thick Permo-Carboniferous clastics accumulated in fault-bounded transtensional basins aligned with the southwestern Bohemian border zone (SWBBZ). Following late-Autunian deformation of these basins, the SWBBZ was overstepped by late-Permian to Late Jurassic platform sediments, reflecting tectonic stability. During the Early Cretaceous the SWBBZ was strongly reactivated, causing disruption and erosion of its Mesozoic sedimentary cover. Sedimentation resumed in the area of the SWBBZ during late Early and Late Cretaceous with clastic influx from the Bohemian massif reflecting gradually increasing tectonic activity along the SWBBZ. During the Late Senonian and Paleocene transpressional deformations resulted in upthrusting of major basement blocks. In the Molasse basin such structures are sealed by transgressive Late Eocene marine strata. Mio-Pliocene uplift of the Bohemian massif, involving mild reactivation of the SWBBZ, is related to the development of the volcano-tectonic Eger zone. The structural configuration of the SWBBZ is largely the result of Late Senonian–Paleocene compressional intraplate tectonics which play a major role in the structural framework of the northern Alpine and Carpathian foreland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050129
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  • 4
    Electronic Resource
    Electronic Resource
    Rb–Sr and K–Ar mineral data of the KTB and the surrounding area and their bearing on the tectonothermal evolution of the metamorphic basement rocks (1997)
    Springer
    Geologische Rundschau 86 (1997), S. S251 
    Details
    ISSN: 0016-7835
    Keywords: Key words Bohemian Massif ; KTB ; K ; Ar and Rb ; Sr mineral dating ; Middle to post-Variscan tectonothermal evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  K–Ar and Rb–Sr age determinations on muscovites and biotites and K–Ar age determinations on amphiboles are presented for leucocratic gneisses, amphibolites and (meta-)igneous rocks from the Zone of Erbendorf Vohenstrauss (ZEV) and the KTB boreholes located in the northeastern ZEV and leucocratic gneisses from the Erbendorf Greenschist zone (EGZ). The investigations were carried out to contribute to the knowledge of the tectonothermal evolution of the area and to the response of the isotope systems to retrograde processes including recent elevated in- situ temperatures in the boreholes. A memory of an early Ordovician igneous event is given by Rb–Sr ages of 480±5–475±5 Ma obtained on very coarse-grained relic igneous muscovites of metapegmatites from the ZEV. This memory is missing in micas from peg matoids of the drill site. Coarse-grained muscovites of gneisses from ZEV and EGZ surface outcrops and of gneisses and pegmatoids from the boreholes yielded maximum K–Ar ages of 377±3–371±3 Ma related to the end of the Devonian regional metamorphism in both units. Consistent K–Ar and Rb–Sr apparent ages of some muscovites from surface outcrops point to a fast cooling of the metamorphic rocks due to rapid tectonic uplift. The lack of a depth-related gradient in model ages of coarse-grained KTB muscovites is explained by post-Variscan stacking processes. For minerals from intermediate to greater depths of the KTB, a strong age dependence on grain size and disturbances of the isotope systems due to various late- to post-Variscan retrograde processes can be demonstrated. A strong decrease in K–Ar model ages with increasing depth as obtained for biotites from the deepest section of the HB borehole probably indicates time-integrated response of the isotope system to elevated in situ temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00014658
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Comparative K–Ar and Rb–Sr age determinations of retrograde processes on rocks from the KTB deep drilling project (1997)
    Springer
    Geologische Rundschau 86 (1997), S. S272 
    Details
    ISSN: 0016-7835
    Keywords: Key words KTB Bohemian massif ; Retrograde processes ; Fine mineral fractions ; K ; Ar ; Rb ; Sr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Conventional K–Ar and Rb–Sr age determinations were carried out on fine mineral fractions of the KTB rocks and of rocks from the surrounding area in order to get an idea of the timing of retrograde processes which the rocks had suffered in the Late Variscan and afterwards. Coarse-grained mica minerals were used as reference minerals. It can be demonstrated that conventional K–Ar dating on fine mineral fractions is a useful tool to date retrograde processes in crystalline rocks. For methodical reasons the Rb–Sr method is less suitable. A complex age pattern was found which could be divided into different age groups representing different periods of either penetrative retrograde overprint or formation and reactivation of distinct cataclastic fault zones. Whereas the rocks of the KTB have undergone a penetrative retrograde overprint during the Permo-Triassic without any visible deformation, the Jurassic brought a first reactivation of cataclastic fault zones. In Cretaceous time an overprint led to a pronounced second reactivation of cataclastic fault zones. This latter process turned out to be the important one for the stacking and a repetition of the drilled profile in the KTB. The data and interpretations obtained on the fine mineral fractions coincide excellently with fission track data on sphene from the drill site, with sedimentological records concerning a larger regional scale and with hydrothermal alterations and ore-forming events in mid-Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00014660
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