Zircon U–Pb and Hf – isotopes from the eastern part of the Sveconorwegian Orogen, SW Sweden: implications for the growth of Fennoscandia
Andreas Petersson, Anders Scherstén, Jenny Andersson, Charlotte Möller, 2015. "Zircon U–Pb and Hf – isotopes from the eastern part of the Sveconorwegian Orogen, SW Sweden: implications for the growth of Fennoscandia", Continent Formation Through Time, N. M. W. Roberts, M. Van Kranendonk, S. Parman, S. Shirey, P. D. Clift
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Current models for the growth of Fennoscandia, including the eastern part of the Sveconorwegian Province, are largely based on U–Pb data and do not discriminate between juvenile and reworked crust. Here we present new combined U–Pb and Hf isotopic data, from the Eastern Segment and the Idefjorden terrane of the Sveconorwegian Province, and suggest a revised model of crustal growth. Most of the crystalline basement in this part of the shield formed by mixing of a 2.1–1.9 Ga juvenile component and Archaean crust. Archaean reworking decreases between 1.9 and 1.7 Ga and a mixed Svecofennian crustal reservoir is generated. Succeeding magmatism between 1.7 and 1.4 Ga indicates reworking of this reservoir with little or no crust generation. At c. 1.2 Ga, an influx of juvenile magma is recorded by granite to quartz-syenite magmatism with mildly depleted (ɛHf 1.18 Ga of c. 3) signatures. The amount of recycled crust in the 1.9–1.7 Ga arc system is in contrast to previously proposed models for the growth of the southwestern part of the Fennoscandian Shield. This model agrees with long-term subduction along the western margin of Fennoscandia, but suggests substantial reworking of existing crust and decreasing amounts of <1.9 Ga crustal growth.
The analytical method, U–Pb SIMS table, U–Pb LA-SF-ICP-MS table and Lu–Hf table are available at www.geolsoc.org.uk/SUP18648
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The continental crust is our archive of Earth history, and the store of many natural resources; however, many key questions about its formation and evolution remain debated and unresolved:
What processes are involved in the formation, differentiation and evolution of continental crust, and how have these changed throughout Earth history?
How are plate tectonics, the supercontinent cycle and mantle cooling linked with crustal evolution?
What are the rates of generation and destruction of the continental crust through time?
How representative is the preserved geological record?
A range of approaches are used to address these questions, including field-based studies, petrology and geochemistry, geophysical methods, palaeomagnetism, whole-rock and accessory-phase isotope chemistry and geochronology. Case studies range from the Eoarchaean to Phanerozoic, and cover many different cratons and orogenic belts from across the continents.