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| Titel |
The internal structure of eclogite-facies ophiolite complexes: Implications
from the Austroalpine outliers within the Zermatt-Saas Zone, Western Alps |
| VerfasserIn |
Sebastian Weber, Raul Martinez |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128283
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| Publikation (Nr.) |
 EGU/EGU2016-8261.pdf |
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| Zusammenfassung |
| The Western Alpine Penninic domain is a classical accretionary prism that formed after the
closure of the Penninic oceans in the Paleogene. Continental and oceanic nappes were
telescoped into the Western Alpine stack associated with continent–continent collision.
Within the Western Alpine geologic framework, the ophiolite nappes of the Zermatt–Saas
Zone and the Tsate Unit are the remnants of the southern branch of the Piemonte–Liguria
ocean basin. In addition, a series of continental basement slices reported as lower
Austroalpine outliers have preserved an eclogitic high-pressure imprint, and are tectonically
sandwiched between these oceanic nappes. Since the outliers occur at an unusual
intra-ophiolitic setting and show a polymetamorphic character, this group of continental
slices is of special importance for understanding the tectono-metamorphic evolution of
Western Alps.
Recently, more geochronological data from the Austroalpine outliers have become
available that make it possible to establish a more complete picture of their complex
geological history. The Lu-Hf garnet-whole rock ages for prograde growth of garnet fall
into the time interval of 52 to 62 Ma (Weber et al., 2015, Fassmer et al. 2015), but
are consistently higher than the Lu-Hf garnet-whole rock ages from several other
locations throughout the Zermatt-Saas zone that range from 52 to 38 Ma (Skora et al.,
2015). This discrepancy suggests that the Austroalpine outliers may have been
subducted earlier than the ophiolites of the Zermatt-Saas Zone and therefore have been
tectonically emplaced into their present intra-ophiolite position. This points to the
possibility that the Zermatt-Saas Zone consists of tectonic subunits, which reached
their respective pressure peaks over a prolonged time period, approximately 10-20
Ma.
The pressure-temperature estimates from several members of the Austroalpine outliers
indicate a complex distribution of metamorphic peak conditions, without ultrahigh-pressure
indications. By contrast, the peak conditions derived from the ophiolites of the Zermatt–Saas
Zone are uniform, and close to or inside the coesite stability field. These results
further underline that the oceanic lithosphere, which experienced its geodynamic
evolution as a relatively coherent unit, may contain slices of continental rocks, which in
turn show differences in the metamorphic evolution compared to the surrounding
ophiolites.
Faßmer, K., Obermüller, G., Nagel, T.J., Kirst, F., Froitzheim, N., Sandmann, S.,
Miladinova, I., Fonseca, R.O.C., Münker, C. (2015): Coherent vs. non-coherent subduction of
ophiolite complexes - new insights from the Zermatt-Saas Zone in the Western Alps.
GeoBerlin 2015, Berlin, Germany.
Skora, S., Mahlen, N. J., Johnson, C. M., Baumgartner, L. P., Lapen, T. J., Beard, B. L.,
Szilvagyi, E. T., 2015. Evidence for protracted prograde metamorphism followed by rapid
exhumation of the Zermatt-Saas Fee ophiolite. Journal of Metamorphic Geology, 33,
711-734.
Weber, S., Sandmann, S., Fonseca, R. O. C., Froitzheim, N., Mu¨ nker, C., Bucher, K.,
2015. Dating the beginning of Piemonte-Liguria Ocean subduction: Lu-Hf garnet
chronometry of eclogites from the Theodul Glacier Unit (Zermatt-Saas Zone, Switzerland).
Swiss Journal of Geosciences, 108, 183-199. |
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