Podrobnosti záznamu

    Sm-Nd isotope tracer study of UHP metamorphic rocks : implications for continental subduction and collisional tectonics
Údaj o odpovědnosti
    Bor-Ming Jahn
    Jahn, Borming, 1940-
Zdrojový dokument - monografie
    Ultrahigh pressure metamorphism and geodynamics in collision-type orogenic belts
    s. 245-271
    11 diagr., 6 tab.
    Obsahuje bibliografické odkazy
Klasifikační znak
Skupina konspektu
Předmětová skupina
    datování Sm/Nd
    krystalinikum Českého masivu
    metamorfóza vysokotlaká
    podmínky P-T
    vrásnění alpinské
    vrásnění kaledonské
    vrásnění panafrické
    vrásnění variské
Geografické jméno
    Česká republika
Klíčové slovo
Abstrakt (anglicky)
   Sm-Nd isotope tracer techniques are powerful tools in identification of the protolith nature of UHP and HP rocks and can be used to constrain modeling of tectonic processes of continental collision. UHP rocks may have diverse origins, and not all of them carry the same significance for subduction of continental blocks. In this paper, Sm-Nd isotopic data are compiled for UHP and HP rocks, mostly represented by eclogites and garnet peridotites, from the Alpine, Hercynian (Variscan), and Caledonian belts of western Europe; the Pan-African belts of northern Africa; and the Ross belt of Antarctica. These data then are compared with the isotopic characteristics of the UHP rocks from the Dabie orogen of central China.
   Except for the coesite-bearing quartzitic metasediments of Dora-Maira (Western Alps), which are clearly of continental origin, all HP and UHP rocks (eclogites and ultramafic rocks) from the Alpine, Hercynian, and Pan-African belts have oceanic affinities with the characteristic positive "epsilon"Nd/(T) values (= metamorphic initial 143Nd/144Nd ratios). They represent segments of oceanic lithosphere that were subducted, underwent eclogite-facies metamorphism, and later were tectonically transported into orogenic zones during continental collisions. By contrast, the majority of UHP rocks from the European Caledonide and the Dabie orogen have negative "epsilon"Nd/(T) values, indicating continental affinity.
   This suggests that these mafic and ultramafic rocks have had a long crustal residence time and that their UHP metamorphism is indicative of subduction of ancient and cold continental blocks, as represented by some Precambrian gneiss terranes containing mafic components including greenschists, amphibolites, or basic granulites. In the Dabie orogen, none of the UHP eclogites analyzed thus far have shown oceanic affinity; thus they do not represent subducted Tethys Ocean crust. The preservation of ultrahigh "epsilon"Nd/(0) values (+170 to +260) in eclogites of very low Nd concentrations (average 0.5 ppm) from the Weihai region and of the extraordinarily low "sigma"180 in many eclogites and gneisses, the general absence of syntec-tonic granites in the Dabie Shan, and the available age data obtained by different techniques all point to a rapid rate of exhumation and the absence of a pervasive aqueous fluid phase during the entire process of subduction and exhumation of the Dabie UHP terrane
    Česká geologická služba
Kód přispěvatele
    ČGS (UNM)
Zdrojový formát
Datum vložení
    26. 9. 2007
Datum importu
    8. 8. 2012