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Leif Johansson

Leif Johansson

Professor

Leif Johansson

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

Author

  • Andrius Rimsa
  • Leif Johansson
  • M. J. Whitehouse

Summary, in 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.

Department/s

  • Lithosphere and Biosphere Science

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

Topic

  • Geology

Keywords

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

Status

Published

ISBN/ISSN/Other

  • ISSN: 0010-7999