Metamorphic grade and gradient from white K-micas of Na-mica bearing sedimentary rocks in the Mosquito Creek Basin,East Pilbara Craton,Western Australia |
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| Authors: | Hanan J Kisch Wouter Nijman |
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| Institution: | 1. Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel;2. Department of Sedimentology, Faculty of Geosciences, Utrecht University, Postbus 80021, 3508TA, The Netherlands;1. Department of Geology, Aksum University, P. O. B 314, Axum, Ethiopia;2. School of Earth Sciences, Addis Ababa University, P. O. B 1176, Addis Ababa, Ethiopia;3. Institute of Archaeology, The Hebrew University of Jerusalem, Mt. Scopus, Jerusalem, 91905 Israel;1. Universidade Federal do Rio de Janeiro, Depto. De Geologia, IGEO, Rio de Janeiro, RJ, 21949-900, Brazil;2. Instituto de Geociências, UnB, Brasília, Distrito Federal, Brazil;3. Serviço Geológico do Brasil, Brasília, Distrito Federal, Brazil;4. Universidade Estadual do Rio de Janeiro, Faculdade de Geologia, Rio de Janeiro, Brazil;5. Federal University of Rio de Janeiro, (UFRJ), Universidade Federal do Rio de Janeiro, Brazil;1. Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China;2. Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany;3. Dept. of Geoscience, Aarhus University, Høegh Guldbergs Gade 2, 8000 Åarhus, Denmark;4. Institut für Geologische Wissenschaften, Freie Universität Berlin, Abt. Geochemie, Gebäude B, Malteserstr. 74-100, 12249 Berlin, Germany;5. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China;6. Dept. of Earth Sciences, University of Hong Kong, Pukfalam Road, Hong Kong, China;7. Department für Geo- und Umweltwissenschaften und GeoBio Center, Universität München, 80333 München, Germany;8. Dept. of Geology and Mineralogy, University of Cologne, 50674 Cologne, Germany;9. Dept. of Geology, University of Johannesburg, Auckland Park, South Africa;1. Universidade Federal do Rio de Janeiro, Dep. de Geologia, IGEO, Rio de Janeiro, Brazil;2. Universidade Estadual do Rio de Janeiro, TEKTOS, Faculdade de Geologia, Rio de Janeiro, Brazil;3. Petrobras CENPES, Av. Horácio de Macedo, 950 Cidade Universitária, Ilha do Fundão, Rio de Janeiro, Brazil;1. Institut für Geographie und Geologie der Universität Würzburg, Am Hubland, 97074 Würzburg, Germany;2. Instituto de Ciencias Geológicas, Facultad de Ciencias, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. Department of Geological Sciences, University of Cape Town, Rondebosch, 7701, South Africa |
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| Abstract: | Shales and phyllites from the turbidite sequences of the 2.9 Ga Mosquito Creek Formation of the East Pilbara, Western Australia contain varying amounts of paragonite and mixed Na–K micas (MNKMs), the 0 0 l X-ray diffraction reflections of which are unresolved from the 10-Å reflections, and only partly resolved from the 5-Å reflections of white K-mica (WKM). The Kübler index (‘crystallinity’), the full width at half maximum (FWHM) of the WKM, obtained from these composite reflections by applying a three-peak deconvolution procedure, reveals a metamorphic zoning of the Mosquito Creek Formation. The highest, “epimetamorphic”, grade occurs in the — largely Na-mica free — southern part, with lower, medium- to high-anchimetamorphic, grades in the central part, notably in a WSW-ENE anticlinal zone extending from Nullagine to the Blue Spec Mine. The Na-mica free metasediments of the Glen Herring Shale of the Fortescue Group, overlying the Mosquito Creek Formation to the W, show only a slightly lower metamorphic grade. The low b0 lattice parameter of the WKMs indicates a very low metamorphic P/T gradient. The Na-mica bearing metasediments of the Mosquito Creek Formation correspond to a kaolinite-bearing protolith, strongly Al-enriched and K-depleted with respect to the presumably granitic-tonalitic source rock. |
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