Universität zu Köln

Fassmer, Kathrin ORCID: 0000-0002-4598-7457, Obermueller, Gerrit, Nagel, Thorsten J., Kirst, Frederik, Froitzheim, Nikolaus, Sandmann, Sascha, Miladinova, Irena ORCID: 0000-0002-2808-0378, Fonseca, Raul O. C. ORCID: 0000-0002-0897-4884 and Muenker, Carsten (2016). High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy). Lithos, 252. S. 145 - 160. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1872-6143

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Abstract

The Etirol-Levaz Slice in the Penninic Alps (Valtournenche, Italy) is a piece of eclogite-facies continental basement sandwiched between two oceanic units, the blueschist-facies Combin Zone in the hanging wall and the eclogite-facies Zermatt-Saar Zone in the footwall. It has been interpreted as an extensional allochthon from the continental margin of Adria, emplaced onto ultramafic and mafic basement of the future Zermatt-Saar Zone by Jurassic, rifting-related detachment faulting, and later subducted together with the future Zermatt-Saas Zone. Alternatively, the Etirol-Levaz Slice could be derived from a different paleogeographic domain and be separated from the Zermatt-Saas Zone by an Alpine shear zone. We present Lu-Hf whole rock-garnet ages of two eclogite samples, one from the center of the unit and one from the border to the Zermatt-Saas Zone below. These data are accompanied by a new geological map of the Etirol-Levaz Slice and the surrounding area, as well as detailed petrology of these two samples. Assemblages, mineral compositions and garnet zoning in both samples indicate a clockwise PT-path and peak-metamorphic conditions of about 550-600 degrees C/20-25 kbar, similar to conditions proposed for the underlying Zermatt-Saas Zone. Prograde garnet ages of the two samples are 61.8 +/- 1.8 Ma and 52.4 +/- 2.1 Ma and reflect different timing of subduction. One of these is significantly older than published ages of eclogite-facies metamorphism in the Zermatt-Saar Zone and thus contradicts the hypothesis of Mesozoic emplacement. The occurrence of serpentinite and metagabbro bodies possibly derived from the Zermatt-Saas Zone inside the Etirol-Levaz Slice suggests that the latter is a tectonic composite. The basement slivers forming the Etirol-Levaz Slice and other continental fragments were subducted earlier than the Zermatt-Saar Zone, but nonetheless experienced similar pressure-temperature histories. Our results support the hypothesis that the Zermatt-Saas Zone and the overlying continental slivers do not represent a coherent paleogeographic unit but rather formed by successive, in sequence subduction and accretion of different fragments. (c) 2016 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Fassmer, Kathrin UNSPECIFIED orcid.org/0000-0002-4598-7457 UNSPECIFIED Obermueller, Gerrit UNSPECIFIED UNSPECIFIED UNSPECIFIED Nagel, Thorsten J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kirst, Frederik UNSPECIFIED UNSPECIFIED UNSPECIFIED Froitzheim, Nikolaus UNSPECIFIED UNSPECIFIED UNSPECIFIED Sandmann, Sascha UNSPECIFIED UNSPECIFIED UNSPECIFIED Miladinova, Irena UNSPECIFIED orcid.org/0000-0002-2808-0378 UNSPECIFIED Fonseca, Raul O. C. UNSPECIFIED orcid.org/0000-0002-0897-4884 UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-277092
DOI:	10.1016/j.lithos.2016.02.019
Journal or Publication Title:	Lithos
Volume:	252
Page Range:	S. 145 - 160
Date:	2016
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1872-6143
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language ZERMATT-SAAS OPHIOLITE; SESIA-LANZO ZONE; LAGO-DI-CIGNANA; LU-HF GARNET; BLANCHE TECTONIC SYSTEM; RAPID EXHUMATION; TAUERN WINDOW; SM-ND; PROGRADE METAMORPHISM; SCHISTES LUSTRES Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/27709