Tectono-stratigraphic terranes in Archaean gneiss complexes as evidence for plate tectonics: The Nuuk region,southern West Greenland |
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| Institution: | 1. Glendale, Tiddington, Thame, Oxon OX9 2LQ, UK;2. GeoQuEST Research Centre, School of Earth & Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia;1. Department of Geosciences, Biogeology, University of Tübingen, Hölderlinstrasse 12, 72074 Tübingen, Germany;2. Senckenberg Research Centre for Human Evolution and Paleoenvironment, University of Tübingen, Hölderlinstrasse 12, 72076 Tübingen, Germany;3. Instituto de Investigaciones Arqueológicas y Paleontológicas del Cuaternario Pampeano (INCUAPA-CONICET), Universidad Nacional del Centro de la provincia de Buenos Aires, Del Valle 5737, B7400JWI Olavarría, Buenos Aires, Argentina;4. Museo Municipal de Ciencias Naturales Pachamama, Santa Clara del Mar, Argentina;5. Universidad Nacional de Mar del Plata, Argentina;6. Div. Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque, 1900 La Plata, Argentina;7. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET, Entre Ríos y Mendoza s/n, 5301 Anillaco, La Rioja, Argentina;1. School of Earth Science and Resources, Chang''an University, Xi''an 710054, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Guangdong Provincial Key Laboratory of Mineral Physics and Materials, 511 Kehua Street, Guangzhou 510640, China;4. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;5. Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B5E1, Canada;1. Key Lab of Submarine Geosciences and Prospecting Techniques, MOE, Institute for Advanced Ocean Study, College of Marine Geosciences, Ocean University of China, Qingdao 266100, China;2. Laboratory for Marine Geology and Environment, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China;3. State Key Laboratory of Continental Dynamics, Northwest University, Xi''an 710069, China;4. Tianjin North China Geological Exploration Bureau, Tianjin 300170, China;5. UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland;1. School of Earth Sciences and Resources, China University of Geosciences, Beijing, 29 Xueyuan Road, Beijing 100083, China;2. Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia;3. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea |
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| Abstract: | Prior to 1970 grey gneiss complexes were interpreted as partially-melted sedimentary sequences. Once it was recognised from the Nuuk region that they comprised calc-alkaline igneous complexes, it was understood that such complexes world-wide were dominated by TTG (trondhjemite-tonalite-granodiorite) initially found to have juvenile Sr, Nd and, subsequently, Hf isotopic signatures. Between 1970 and 1985 the Nuuk region gneiss complex was interpreted by the non-uniformitarian ‘super-event’ model of crust formation which proposed occasional but extensive crust formation, with craton-wide correlation of granulite facies metamorphism and deformational phases. The igneous rocks formed in a late- Meso- to early Neoarchaean super-event engulfed crust formed in an Eoarchaean super-event. Mapping and reinterpretation at Færingehavn showed there are three TTG gneiss domains, each with different early accretionary, metamorphic and tectonic histories, separated by folded meta-mylonites. This established the key feature of the tectono-stratigraphic terrane model; that each terrane has an early intra-terrane history of crust formation, deformation and metamorphism, upon which is superimposed a later deformation and metamorphic history common to several terranes after they were juxtaposed. Remapping and >250 U-Pb zircon age determinations have refined the geological evolution of the entire Nuuk region, and has confirmed at least four main crust formation events and two collisional orogenies with associated transient high pressure metamorphism within clockwise P-T-t loops. Via independent corroborative studies the tectono-stratigraphic terrane model has been accepted for the Nuuk region and, through the discovery of similar relations across other gneiss complexes, its mode of evolution is found to be applicable to Archaean high-grade gneiss complexes worldwide. The TTG and mafic components that dominate each terrane have geochemistry interpreted to indicate subduction-related magmatism at convergent plate boundaries. Each terrane is thus dominated by juvenile additions to the crust. Intra-terrane sedimentary rocks show near unimodal age distributions in contrast to those near the boundaries which are more diverse and complex. The combined geochronological, metamorphic and structural evidence of convergence of these terranes leading to collisional orogeny, this indicates that plate tectonic processes operated throughout the Archaean. |
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