Universität zu Köln

Sandmann, Sascha, Nagel, Thorsten J., Herwartz, Daniel ORCID: 0000-0003-3604-8295, Fonseca, Raul O. C. ORCID: 0000-0002-0897-4884, Kurzawski, Robert M., Muenker, Carsten and Froitzheim, Nikolaus (2014). Lu-Hf garnet systematics of a polymetamorphic basement unit: new evidence for coherent exhumation of the Adula Nappe (Central Alps) from eclogite-facies conditions. Contrib. Mineral. Petrol., 168 (5). NEW YORK: SPRINGER. ISSN 1432-0967

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Abstract

The Adula Nappe in the Central Alps is a mixture of various pre-Mesozoic continental basement rocks, metabasics, ultrabasics, and Mesozoic cover rocks, which were pervasively deformed during Alpine orogeny. Metabasics, ultrabasics, and locally garnet-mica schists preserve eclogite-facies assemblages while the bulk of the nappe lacks such evidence. We provide garnet major-element data, Lu profiles, and Lu-Hf garnet geochronology from eclogites sampled along a north-south traverse. A southward increasing Alpine overprint over pre-Alpine garnets is observed throughout the nappe. Garnets in a sample from the northern Adula Nappe display a single growth cycle and yield a Variscan age of 323.8 +/- 6.9 Ma. In contrast, a sample from Alpe Arami in the southernmost part contains unzoned garnets that fully equilibrated to Alpine high-pressure (HP) metamorphic conditions with temperatures exceeding 800 degrees C. We suggest that the respective Eocene Lu-Hf age of 34.1 +/- 2.8 Ma is affected by partial re-equilibration after the Alpine pressure peak. A third sample from the central part of the nappe contains separable Alpine and Variscan garnet populations. The Alpine population yields a maximum age of 38.8 +/- 4.3 Ma in line with a previously published garnet maximum age from the central nappe of 37.1 +/- 0.9 Ma. The Adula Nappe represents a coherent basement unit, which preserves a continuous Alpine high-pressure metamorphic gradient. It was subducted as a whole in a single, short-lived event in the upper Eocene. Controversial HP ages and conditions in the Adula Nappe may result from partly preserved Variscan assemblages in Alpine metamorphic rocks.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Sandmann, Sascha UNSPECIFIED UNSPECIFIED UNSPECIFIED Nagel, Thorsten J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Herwartz, Daniel UNSPECIFIED orcid.org/0000-0003-3604-8295 UNSPECIFIED Fonseca, Raul O. C. UNSPECIFIED orcid.org/0000-0002-0897-4884 UNSPECIFIED Kurzawski, Robert M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Froitzheim, Nikolaus UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-424344
DOI:	10.1007/s00410-014-1075-6
Journal or Publication Title:	Contrib. Mineral. Petrol.
Volume:	168
Number:	5
Date:	2014
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-0967
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language METAMORPHIC FIELD GRADIENTS; P-T EVOLUTION; HIGH-PRESSURE; SM-ND; PERIDOTITE BODY; LEPONTINE ALPS; WESTERN ALPS; PRE-ALPINE; SWISS ALPS; MC-ICPMS Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/42434