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| Titel |
Albitization as Record of the Triassic Paleosurface in the Sudetic Crystalline Massif (Poland) |
| VerfasserIn |
Kouakou Fulgence Eric Yao, Christine Franke, Medard Thiry, Pawel Aleksandrowski, Adam Szuszkiewicz, Krzysztof Turniak |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050807
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| Zusammenfassung |
| Although paleogeographic time markers are available in sedimentary basin, where all strata
are chronologically stacked, there is still a lack of such markers for the crystalline basement.
This limits the knowledge about the temporal evolution of the continental basement areas.
The alteration process of albitization affects both, crystalline and sedimentary rocks, and
seems to be highly abundant in the European Palaeozoic basement. Therefore, it could
probably be use as a tool to develop time markers for the reconstruction of basement
erosion.
Albitization consists in the replacement of the primary igneous feldspars (K, Ca-Na) by
secondary albite, the chloritization of the ferromagnesian minerals, and the development of
accessory minerals such as hematite, maghemite, sericite, calcite, and apatite. In the
crystalline context albitization is conventionally considered as the result of deep metasomatic
alteration, while in sedimentary deposits it is interpreted as resulting from diagenetic
alteration processes. Nevertheless, recent studies showed that albitization affecting both
sedimentary and crystalline rocks are linked to the Triassic paleosurface (Yerle and
Thiry, 1979; Schmitt, 1986; Parcerisa et al., 2009). This has been also confirmed by
paleomagnetic studies that date the associated iron oxide minerals to Triassic ages (Ricordel
et al., 2007; Franke et al., 2009).
Albitized rocks are frequent in the Polish Sudetes. So to prove their probable link with the
Triassic paleosurface, we study their petrology and spatial distribution. The sections show
three albitization facies: (1) pervasively albitized facies, reddish and highly fractured,
(2) less intense albitization restricted to fractures walls, (3) a weakly albitization
restricted to fractures and to some milimetric spots within the rocks. As the most
albitized facies are situated close to the surface, and the less albitized facies are found
deeper down the profile, the different albitization level observed here correspond to a
nearly 200 meter albitization profile with decreasing intensity from the surface to the
depth.
Furthermore, the significant occurrence of iron oxides in the albitized facies supports the
assumption of the presence of oxidizing conditions during the development of these facies.
The most albitized facies are the most oxidized ones. Moreover, the paleomagnetic dating of
these iron oxides formed during the albitization process indicates a Triassic remagnetization
(Edel et al., 1997; Franke et al., 2010).
The Triassic paleosurface can be reconstructed by matching the different sites of the
albitized facies. This correlation shows that the remnants of the Triassic paleosurface are
preserved in the center of the Sudetes crystalline massif. The paleosurface rises from the
basin edge in the NW to the inner zones of the crystalline massif in the SE. The preservation
of the Triassic paleosurface proves that the post-Triassic erosion of the basement has been
weak, in the order of less than the albitization profile thickness. In some places, non-albitized
facies seem contiguous to the albitized facies along the paleosurface. These discontinuities
may point to fault zones that previously haven’t been noticed due to the lack of reliable
benchmarks.
The mapping of the different facies and the Triassic overprints allow to reconstruct the
geometry of the Triassic paleosurface. A better understanding of the geomorphology of the
paleosurface is a useful tool to date strain events and to clarify the post-Triassic structural
history of the Sudetic crystalline massif as well as providing tie points for geodynamical
modeling.
REFERENCES
Edel J.-B., Aifa T., Jelenska M., Kadzialko-Hofmokl M., Zelazniewicz A. (1997).
Réaimantations des formations paléozoïques des Sudètes polonaises et courbe de dérive des
pôles géomagnétiques d’Europe du Carbonifère moyen au Jurassique moyen. Comptes
Rendus de l’Académie des Sciences - Séries IIA - Earth and Planetary Science Letters, 325:
479-486.
Franke C., Thiry M., Jelenska M., Kodzialko-Hofmokl M., Lagroix F., Parcerisa D.,
Szuszkiewicz A., Turniak K. (2009). Remagnetization of Variscan massifs and reconstruction
of the Triassic paleosurface in Europe, AGU Fall Meeting 2009, San Francisco,
USA.
Franke C., Thiry M., Gomez-Gras D., Jelenska M., Kadzialko-Hofmokl M., Lagroix F.,
Parcerisa D., Spassov S., Szuszkiewicz A., Turniak K. (2010). Paleomagnetic age constrains
and magneto-mineralogic implications for the Triassic paleosurface in Europe. Geophysical
Research Abstracts, vol. 12, EGU 2010-7858.
Parcerisa D., Thiry M., Schmitt J. M. (2009). Albitisation related to the Triassic
inconformity in igneous rocks of the Morvan Massif (France). International Journal of Earth
Science 99: 527-544.
Ricordel C., Parcerisa D., Thiry M., Moreau M.-G., Gómez-Gras D. (2007). Triassic
magnetic overprints related to albitization in granites from the Morvan massif (France).
Palaeogeography Palaeoclimatology Palaeoecology 251: 268-282.
Schmitt J. M. (1986). Albitisation triasique, hydrothermalisme jurassique et altération
supergène récente : métallogénie des gisements uranifères du Rouergue. Doct. ès Sciences
Thesis, Strasbourg, Louis Pasteur University: p. 240.
Yerle J. J., Thiry M. (1979). Albitisations et minéralisations uranifères dans le socle et les
sédiments permo-houillers du bassin de Brousse-Broquiès (Aveyron, France). Bulletin
BRGM 4: 275-290. |
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