Geochronology of carbonatites from the Canadian and Baltic Shields, and the Canadian Cordillera: clues to mantle evolution

U-Pb ID-TIMS age of the Tiksheozero carbonatite: expression of 2.0 Ga alkaline magmatism in Karelia, Russia

“…Together with the 800 Ma lower intercept age of the line, the deviation to the left suggests that the grains were affected by an early Pb loss event in the Proterozoic before undergoing new Pb loss in the Paleozoic. Therefore the 800 Ma lower intercept age is considered to be geologically meaningless and simply reflect the effect of superimposed disturbances, the type of events that affected much more strongly the isotopic data from previous studies [ [7,18] and references therein].…”

“…The results are variable, showing that it is Paleoproterozoic, but many isotopic systems were affected by disturbances after emplacement, both in the Paleoproterozic and in the Paleozoic [ [7,18], and references therein]. For example, the zircon U-Pb data reported by [7] demonstrate both types of disturbances, one set of data showing 50-70% discordance towards a Paleozoic event. A Devonian U-Pb age has also been reported for perovskite by [19], which relates it to a metasomatic overprint possibly related to the alkaline activity in Kola and Karelia.…”

“…By contrast, baddeleyite yielded concordant U-Pb ion probe data giving an average 207 Pb/ 206 Pb age of 1995 ±10 Ma [20]. Apatite preserves the primary signature fitting a 1.98 Ga isochron in a 207 Pb/ 204 Pb-206 Pb/ 204 Pb diagram [14] although its UPb system was clearly disturbed [7]. In this paper, we report ID-TIMS U-Pb results on zircon and baddeleyite from carbonatite that provide a reliable age for emplacement of the Tiksheozero complex.…”

“…The majority, including the economically most important ones, formed in the Paleozoic but there are also several older generations reaching into the Paleoproterozoic and the Neoarchean [1][2][3][4][5][6][7][8]. Al- * E-mail: fernando.corfu@geo.uio.no kalic complexes witness episodes of mantle activity, generally related to extensional tectonic processes in the crust [e.g.…”

Evidence for the Multi-Stage Petrogenetic History of the Oka Carbonatite Complex (Québec, Canada) as Recorded by Perovskite and Apatite

“…In North America, carbonatite and alkaline magmatism spans ~2.7 Ga [8,9], and Oka ( Figure 1) is one of the youngest carbonatite complexes on the basis of available geochronological data for various minerals and/or rock types. Apatite fission track ages reported for Oka vary between 118 ± 4 and 133 ± 11 Ma [10], whereas Shafiquall et al [11] document K-Ar ages that range between 107 and 119 Ma for the intrusive alnöites associated with the complex.…”