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The complex age of orthogneiss protoliths exemplified by the Eoarchaean Itsaq Gneiss Complex (Greenland): SHRIMP and old rocks |
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| Authors: | Kenji Horie Allen P Nutman Clark RL Friend Hiroshi Hidaka |
| Institution: | 1. National Institute of Polar Research, 10-3, Midori-cho, Tachikawa 190-8518, Japan;2. Department of Earth and Planetary Systems Sciences, University of Hiroshima, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan;3. School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia;4. Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia;5. 45 Stanway Road, Headington, Oxford, OX3 8HU, UK |
| Abstract: | Field studies integrated with cathodoluminescence petrography and SHRIMP U–Pb dating of zircons from >150 orthogneisses and metatonalites from the Eoarchaean Itsaq Gneiss Complex (southern West Greenland) shows that only a minority contain ≥3840 Ma zircons, whereas the majority carry only younger ones. Rocks containing ≥3840 Ma zircons vary from very rare single-phase metatonalites to more common complexly banded tonalitic migmatites. The former metatonalites have simple oscillatory-zoned ≥3840 Ma zircon with limited recrystallisation and overgrowth, whereas the more common migmatites have much more complicated zircon populations with both ≥3840 Ma and 3650–3600 Ma oscillatory-zoned zircon, more extensive recrystallisation and widespread complex core-rim multiple growth relationships. |
| Keywords: | Greenland Itsaq Gneiss Complex Geological mapping Eoarchaean Gneiss complexes U&ndash Pb zircon dating Zircon petrography |
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