Titanite-rutile thermochronometry across the boundary between the Archaean Craton in Karelia and the Belomorian Mobile Belt,eastern Baltic Shield |
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| Institution: | 1. Department of Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, AL, USA;2. Division of Biostatistics and Epidemiology, Cincinnati Children''s Hospital Medical Center, Cincinnati, OH, USA;3. Department of Obstetrics and Gynecology, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA;4. Biosciences Division, Center for Cancer & Metabolism, SRI International, USA;5. Department of Nutrition Sciences, School of Nutrition, University of Alabama at Birmingham, Birmingham, AL, USA;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;3. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia |
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| Abstract: | U–Pb isotopic dating has been carried out on titanites and rutiles from the Karelian Protocraton, the Belomorian Mobile Belt and the intervening junction zone. These are some of the principal Archaean crustal units in the Baltic Shield which have undergone regeneration to various degrees during the Palaeoproterozoic. Palaeoproterozoic resetting of U–Pb titanite ages was complete in the Belomorian Belt and almost complete in the junction zone, while it hardly affected the Karelian Protocraton. In the latter, major crustal cooling occurred at 2.71–2.69 Ga after a major igneous event at 2.74–2.72 Ga, but a tectonothermal event at 2.65–2.64 Ga was less comprehensive. In the Belomorian Belt, a northeastern marginal zone immediately underlying the collisional-thrusting suture of the Lapland-Kola orogen has somewhat higher titanite ages of ca. 1.94–1.87 Ga than the central zone where these ages range between 1.87 and 1.82 Ga. Comparison between the titanite and rutile U–Pb ages suggests a postorogenic cooling rate between 2 and 4°/Ma in these parts of the Belt. The Neoarchaean junction zone between the Karelian and Belomorian provinces was a zone of particularly intense tectonic, magmatic and hydrothermal activity during or after the Palaeoproterozoic Lapland-Kola orogeny. Dominant, newly grown titanites in that zone have ages as young as 1.78–1.75 Ga, and the age differences between the titanite and rutile U–Pb ages are substantially smaller than elsewhere. |
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