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| Titel |
Continental crust subducted deeply into lithospheric mantle: the driving force of Early Carboniferous magmatism in the Variscan collisional orogen (Bohemian Massif) |
| VerfasserIn |
Vojtěch Janoušek, Karel Schulmann, Ondrej Lexa, František Holub, Jan Franek, Stanislav Vrána |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091865
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| Publikation (Nr.) |
 EGU/EGU2014-6179.pdf |
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| Zusammenfassung |
| The vigorous Late Devonian–Early Carboniferous plutonic activity in the core of the
Bohemian Massif was marked by a transition from normal-K calc-alkaline, arc-related
(~375–355 Ma), through high-K calc-alkaline (~346 Ma) to (ultra-)potassic (343–335 Ma)
suites, the latter associated with mainly felsic HP granulites enclosing Grt/Spl mantle
peridotite bodies. The changing chemistry, especially an increase in K2O/Na2O and
87Sr/86Sri with decrease in 143Nd/144Ndi in the basic end-members, cannot be reconciled by
contamination during ascent. Instead it has to reflect the character of the mantle sources,
changing over time.
The tectonic model invokes an oceanic subduction passing to subduction of the attenuated
Saxothuringian crust under the rifted Gondwana margin (Teplá–Barrandian and Moldanubian
domains). The deep burial of this mostly refractory felsic metaigneous material is evidenced
by the presence of coesite/diamond (Massonne 2001; Kotková et al. 2011) in the detached
UHP slices exhumed through the subduction channel and thrusted over the Saxothuringian
basement, and by the abundance of felsic HP granulites (> 2.3 GPa), some bearing
evidence for small-scale HP melt separation, in the orogen’s core (Vrána et al.
2013). The subduction channel was most likely formed by ‘dirty’ serpentinites
contaminated by the melts/fluids derived from the underlying continental-crust
slab (Zheng 2012). Upon the passage through the orogenic mantle, the continental
crust-slab derived material not only contaminated the adjacent mantle forming
small bodies/veins of pyroxenites (Becker 1996), glimmerites (Becker et al. 1999)
or even phlogopite- and apatite-bearing peridotites (Naemura et al. 2009) but the
felsic HP–HT granulites also sampled the individual peridotite types at various
levels.
Eventually the subducted felsic material would form an (U)HP continental wedge under
the forearc/arc region, to be later redistributed under the Moldanubian crust by channel flow
and crustal relamination mechanisms. The presence of refractory light material rich in
radioactive elements under the denser upper plate would eventually result in gravity-driven
overturns in the thickened crust. The contaminated lithospheric mantle domains
yielded, soon thereafter, ultrapotassic magmas whose major- and compatible-trace
element signatures point to equilibration with the mantle peridotite, while their LILE
contents and radiogenic isotope signatures are reminiscent of the subducted continental
crust.
This research was financially supported by the GAÄR Project P210-11-2358
(to VJ) and Ministry of Education of the Czech Republic program LK11202 (to
KS).
Becker, H. 1996. Journal of Petrology 37, 785–810.
Kotková, J. et al. 2011. Geology 39, 667–670.
Massonne, H.–J. 2001. European Journal of Mineralogy 13, 565–570.
Naemura, K. et al. 2009. Journal of Petrolology 50, 1795–1827.
Schulmann, K., et al., 2014. Geology, in print.
Vrána, S. 2013. Journal of Geosciences 58, 347–378.
Zheng, Y. F. 2012. Chemical Geology 328, 5–48. |
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