Timing of Palaeoproterozoic intra-orogenic sedimentation in the central Fennoscandian Shield; evidence from detrital zircon in metasandstone

Detrital zircon U-Pb SIMS data on quartz-rich metasandstone units presumed to belong to the upper part of the Svecofennian stratigraphy in southeastern Finland and east-central Sweden suggest the existence of clastic sedimentary basins between the two main orogenic phases at 1.89-1.86 Ga and 1.83-1.79 Ga, during a period referred to as the intra-orogenic phase (1.86-1.83 Ga). Stratigraphically below the metasandstone at Hamrange, east-central Sweden, is a metadacite with an U-Pb zircon TIMS age of 1888 +/- 6 Ma, which indicates the maximum age of sedimentation. It also indicates that an earlier proposed correlation of Hamrange metavolcanic rocks and 1.86Ga equivalents at Los to the northwest must be rejected. Instead, there is a temporal affinity to the metavolcanic rocks in the Bergslagen Province to the south or Southern Finland to the east. Quartz-rich metasandstone samples from four localities, Luukkola, Pyhantaka and Tiirismaa in Finland and Hamrange in Sweden, yield multimodal detrital zircon age distributions with main populations at 2.95-2.60 Ga, 2.10-1.95 Ga and 1.92-1.85 Ga. The groups are similar in all four samples, and they are comparable to previously reported detrital ages in this part of the Fennoscandian Shield. The oldest zircon analysed gave an age of 3.32 Ga (Tiirismaa). The maximum ages of sedimentation (and of subsequent deformation and metamorphism), indicated by the youngest detrital zircon, from the four localities are 1842 10 Ma (Luukkola), 1865 +/- 11 Ma (Pyhantaka), 1848 +/- 13 Ma (Tiirismaa), and 1855 10 Ma (Hamrange), respectively. Possible source rocks for these zircon grains are found within and around the vast Ljusdal Batholith in Sweden, and in the Arc Complexes of Western and Southern Finland. It is concluded that several intra-orogenic sedimentary basins existed during the time interval 1.86-1.83 Ga ago, between two major orogenic events in the Fermoscandian Shield

Vitrified hillforts as anthropogenic analogues for nuclear waste glasses : project planning and initiation

Nuclear waste must be deposited in such a manner that it does not cause significant impact on theenvironment or human health. In some cases, the integrity of the repositories will need to sustain fortens to hundreds of thousands of years. In order to ensure such containment, nuclear waste is frequentlyconverted into a very durable glass. It is fundamentally difficult, however, to assure the validity ofsuch containment based on short-term tests alone. To date, some anthropogenic and natural volcanicglasses have been investigated for this purpose. However, glasses produced by ancient cultures for thepurpose of joining rocks in stonewalls have not yet been utilised in spite of the fact that they might offersignificant insight into the long-term durability of glasses in natural environments. Therefore, a projectis being initiated with the scope of obtaining samples and characterising their environment, as well asto investigate them using a suite of advanced materials characterisation techniques. It will be analysedhow the hillfort glasses may have been prepared, and to what extent they have altered under in-situconditions. The ultimate goals are to obtain a better understanding of the alteration behaviour of nuclearwaste glasses and its compositional dependence, and thus to improve and validate models for nuclearwaste glass corrosion. The paper deals with project planning and initiation, and also presents some earlyfindings on fusion of amphibolite and on the process for joining the granite stones in the hillfort walls.Keywords: ageing, amphibolite, analogue, anthropogenic, Broborg, glass, hillfort, hill-fort, leaching,long-lived, nuclear, rampart, waste.Konferensartikel i tidskrift</p