Monazite stability, composition and geochronology as tracers of Paleoproterozoic events at the eastern margin of the East European Craton (Taratash complex, Middle Urals) Sven Sindern a, ⁎, Axel Gerdes b , Yuri L. Ronkin c , Annika Dziggel a , Ralf Hetzel d , Bernd Aloys Schulte e a Institute of Mineralogy and Economic Geology, RWTH Aachen University, Wüllnerstr. 2, 52056 Aachen, Germany b Institute of Geosciences, Johann Wolfgang Goethe University, Altenhöferallee 1, 60438 Frankfurt a.M., Germany c Institute of Geology and Geochemistry, Russian Academy of Sciences, Ekaterinburg, Russia d Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, 48149 Münster, Germany e Ruffinistr. 12, 80634 Munich, Germany abstract article info Article history: Received 9 May 2011 Accepted 16 November 2011 Available online 1 December 2011 Keywords: Ural mountains Taratash complex LA-ICP-MS Geochronology Monazite The Precambrian Taratash complex (Middle Urals) is one of the rare windows into the Palaeoproterozoic and earlier history of the eastern margin of the East European Craton. Monazite from intensively deformed rocks within a major amphibolite-facies shear zone in the Taratash complex has been investigated by means of electron-probe microanalysis and laser-ablation SF-ICP-MS. Metamorphic and magmatic cores of monazite from metasedimentary and metagranitoid rocks yield U–Pb ages of 2244 ± 19 and 2230 ± 22 Ma (± 2 σ) and record a previously unknown pre-deformational HT- metamorphic event in the Taratash complex. Subsequent dissolution–reprecipitation of monazite, during shear zone formation under amphibolite-facies conditions, caused patchy zonation and chemical alteration of the recrystallised monazite domains, leading to higher cheralite and huttonite components. This process, which was mediated by a probable (alkali + OH)-bearing metamorphic fluid also caused a total resetting of the U–Pb-system. The patchy domains yield concordant U–Pb-ages between 2052 ± 16 and 2066 ± 22 Ma, interpreted as the age of the shear zone. In line with previously published ages of high grade metamorphism and migmatisation, the data may point to a Palaeoproterozoic orogenic event at the eastern margin of the East European Craton. Post-deformational fluid-induced greenschist-facies retrogression caused partial to complete breakdown of monazite to fluorapatite, REE + Y-rich epidote, allanite and Th-orthosilicate.The retrograde assemblages ei- ther form coronas around monazite, or occur as dispersed reaction zones, indicating that the REE, Y, and Th were mobile at least on the thin section scale. The greenschist-facies metamorphic fluid was aqueous and rich in Ca. Monazite affected by advanced breakdown responded to the retrogression by incorporating the cheralite or huttonite components during a fluid-induced dissolution–reprecipitation process. This event did not reset the U–Pb-system but caused partial Pb loss reflected by discordant U–Pb-dates. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Monazite is an abundant accessory mineral in many igneous and metamorphic rocks. Due to the incorporation of Th and U but not Pb during crystallisation, monazite is now used as a standard geochron- ometer (Harrison et al., 2002; Williams et al., 2007). Monazite has been shown to record magmatic (Broska et al., 2000; Kelts et al., 2008), metamorphic (Bingen et al., 1996; Fitzsimons et al., 2005; Foster et al., 2000, 2002; Franz et al., 1996; Krenn et al., 2009; Iizuka et al., 2010; Schulz, 2009; Spear and Pyle, 2002), and metasomatic or hydrothermal events (Ayers et al., 2006; Catlos et al., 2008; Kempe et al., 2008; Rasmussen et al., 2006; Schandl and Gorton, 2004). Monazite is resistant to radioactive damage (Seydoux-Guillaume et al., 2004). Depending on the bulk rock chemistry, and the presence and composition of a fluid phase, it can be stable over a large PT-range (Budzyn et al., 2011; Harlov et al., 2011; Hetherington et al., 2010; Janots et al., 2008; Spear, 2010; Spear and Pyle, 2002; Wing et al., 2003). In rocks with complex P–T–t-histories, monazite growth is often reflected by the formation of distinct monazite generations or compositional subdomains within the monazite grains (Mahan et al., 2006a; Williams et al., 2007). Complex and irregularly distributed, chemically distinct monazite subdomains with sharp boundaries indi- cate that coupled dissolution–reprecipitation to be a common process Lithos 132-133 (2012) 82–97 ⁎ Corresponding author. Tel.: + 49 241 8095778; fax: + 49 241 8092341. E-mail address: sindern@rwth-aachen.de (S. Sindern). 0024-4937/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2011.11.017 Contents lists available at SciVerse ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos