Feldspar in felsic orthogneiss as indicator for UHT crustal processes

• HOKADA Tomokazu

  National Institute of Polar Research Department of Polar Science, The Graduate University for Advanced Studies

• SUZUKI Satoko

  Center for Chronological Research, Nagoya University

Abstract

Felsic orthogneisses with tonalitic and granodioritic compositions are dominant in the ultrahigh-temperature (UHT) metamorphic terrane of the Archaean-early Proterozoic Napier Complex, East Antarctica. Antiperthitic or mesoperthitic ternary feldspar occurs in addition to Qtz, Opx with/without Cpx in these felsic orthogneisses. Such feldspar grains commonly display zonal structure with respect to the volume of exsolution lamella; lamellae-enriched core and lamellae-free rim. Pre-exsolution one-phase compositions have been recovered separately for the feldspar core (an:ab:or = 20-28:53-56:17-28 in tonalitic samples and an:ab:or = 15-17:37-48:36-48 in granodioritic samples) and for the whole feldspar grain (an:ab:or = 24-29:58-63:13 in tonalitic samples and an:ab:or = 18-20:45-56:24-37 in granodioritic samples). Application of feldspar thermometry for these recovered one-phase compositions and the feldspar cores yield a temperature range of 940-1100 °C, which is relatively higher temperatures than the whole feldspar grain giving > 850-1070 °C. These compositional differences between core and rim of single feldspar grains are probably due to either sub-solidus or melt-related processes. The compositional and textural information of ternary feldspars in felsic orthogneisses can be therefore potential tools for understanding UHT crustal processes.

Journal

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 101 (5), 260-264, 2006

  Japan Association of Mineralogical Sciences

Keywords

• Antarctica
• Feldspar
• Napier Complex
• Orthogneiss
• Ultrahigh temperature/UHT

Details

• CRID: 1390282681522248704
• NII Article ID: 10018106142
• NII Book ID: AA11460926
• DOI: 10.2465/jmps.101.260
• ISSN: 13493825
• ISSN: 13456296
• Text Lang: en
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed