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The diversity and geodynamic significance of Late Cambrian (ca. 500 Ma) felsic anorogenic magmatism in the northern part of the Bohemian Massif: A review based on Sm-Nd isotope and geochemical data

By
Christian Pin
Christian Pin
Département de Géologie, UMR 6524 CNRS, Université Blaise Pascal, 5 rue Kessler, 63 038 Clermont-Ferrand, France
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R. Kryza
R. Kryza
Institute of Geological Sciences, University of Wrocław, plac Maxa Borna 9, 50-204 Wrocław, Poland
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T. Oberc-Dziedzic
T. Oberc-Dziedzic
Institute of Geological Sciences, University of Wrocław, plac Maxa Borna 9, 50-204 Wrocław, Poland
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S. Mazur
S. Mazur
Institute of Geological Sciences, University of Wrocław, plac Maxa Borna 9, 50-204 Wrocław, Poland
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K. Turniak
K. Turniak
Institute of Geological Sciences, University of Wrocław, plac Maxa Borna 9, 50-204 Wrocław, Poland
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Jarmila Waldhausrová
Jarmila Waldhausrová
Nad Hercovkow 422, 18200 Prague, Czech Republic
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Published:
January 01, 2007

Ca. 500 Ma orthogneisses and bimodal suites are widespread along the northern part of the Bohemian Massif (central European Variscides) and are interpreted to document intense magmatism during a continental break-up episode along the northern periphery of Gondwana. Based on geological setting, and geochemical and isotopic evidence, these felsic igneous rocks record the generation of: (1) magmas of pure or predominantly crustal derivation, represented by minor extrusives and much more voluminous orthogneisses similar to S-type granitoids; (2) subordinate magmas of exclusively mantle origin (ranging from within-plate alkali trachytes to oceanic plagiogranites) corresponding to felsic derivatives of associated basalts; and (3) magmas of hybrid origin, produced either as a result of large degrees of contamination of mantle-derived magmas ascending through the crust, or alternatively, generated by partial melting of mixed sources, such as interlayered sediments and mafic rocks or graywackes containing a juvenile component. The high-temperature dehydration melting process responsible for the generation of the most abundant rock-types necessitated the advection of mantle heat, in a context of continental lithosphere extension, as documented by broadly coeval basaltic magmatism at the scale of the igneous province. The large volumes of felsic magmas generated during the 500-Ma anorogenic event are interpreted to result from the combination of a hot extensional tectonic regime with the widespread availability in the lower crust of fertile lithologies, such as metagraywackes. This in turn reflects the largely undifferentiated nature of the crustal segment accreted some 50–100 m.y. earlier during the Cadomian orogeny.

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GSA Special Papers

The Evolution of the Rheic Ocean: From Avalonian-Cadomian Active Margin to Alleghenian-Variscan Collision

Ulf Linnemann
Ulf Linnemann
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R. Damian Nance
R. Damian Nance
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Petr Kraft
Petr Kraft
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Gernold Zulauf
Gernold Zulauf
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Geological Society of America
Volume
423
ISBN print:
9780813724232
Publication date:
January 01, 2007

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