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Constraints on incipient charnockite formation from zircon geochronology and rare earth element characteristics

Author:
  • Andrius Rimsa
  • Leif Johansson
  • M. J. Whitehouse
Publishing year: 2007
Language: English
Pages: 357-369
Publication/Series: Contributions to Mineralogy and Petrology
Volume: 154
Issue: 3
Document type: Journal article
Publisher: Springer

Abstract english

We present high spatial resolution ion-microprobe U-Th-Pb geochronology and rare earth element (REE) data combined with cathodoluminescence (CL) and back-scattered electron (BSE) imaging for complex zircons in incipient charnockites from Sondrum, SW Sweden. Examination of closely paired samples across the dehydration zone demonstrates that incipient charnockite formation at Sondrum is a zircon-forming process. We determined the age of the dehydration event (i.e. charnockitisation) to 1,397 +/- 4 Ma (2 sigma, MSWD = 1.7). This is the first successful attempt to date incipient charnockite formation using U-Pb systematics of zircon. Internal structure, chemical and isotopic characteristics of zircon indicate that the granitic pegmatite in the core of the incipient charnockite is a melting zone. Commonly observed bulk rock HREE depletion in incipient charnockites is not caused by zircon dissolution but by involvement of garnet as a reactant in the dehydration reactions. Moreover, REE patterns of the newly formed zircon are HREE-enriched, indicating non-concurrent growth and suggesting that the degree of charnockite depletion in HREE might be controlled by the volume of newly formed zircon.

Keywords

  • Geology
  • REE
  • zircon
  • (incipient) charnockite
  • Sondrum
  • geochronology

Other

Published
  • ISSN: 0010-7999
Leif Johansson
E-mail: leif [dot] johansson [at] geol [dot] lu [dot] se

Professor

Lithosphere and Biosphere Science

+46 46 222 98 87

+46 70 530 76 73

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