Sirvi Autor "Preeden, Ulla" järgi

Nüüd näidatakse 1 - 2 2

Impaktbretšade peenfraktsiooni lõimis Kärdla, Neugrundi, Avike ja Lumparni kraatrites
(2004) Preeden, Ulla; Puura, Väino, juhendaja; Kirs, Juho, juhendaja
Remagnetizations in sedimentary rocks of Estonia and shear and fault zone rocks of southern Finland
(2009-10-20T13:19:55Z) Preeden, Ulla
The present doctoral thesis combines palaeomagnetic, rock magnetic and mineralogical studies of Palaeozoic sedimentary rocks of Estonia and Palaeoproterozoic crystalline rocks of shear and fault zones of southern Finland. The essence of palaeomagnetism is that a record of the ancient magnetic field is locked in a rock. Silurian and Ordovician carbonate samples were collected from twelve Estonian outcrops and Palaeoproterozoic rocks were sampled in five outcrops of southern Finland. The localities in Finland are located along the extensive north-east to south-west trending Porkkala–Mäntsälä shear zone and the north–south trending Vuosaari–Korso shear zone. They were chosen for the study, because these were expected to indicate possible reactivations. In a result of the studies primary magnetizations were found in Ordovician sedimentary rocks of northern Estonia and in Palaeoproterozoic shear and fault zone rocks of southern Finland. Magnetite and titanomagnetite are the carriers of the primary remanence. Secondary magnetizations of different ages were detected as well, implying that the areas have experienced multiple reactivations. A common secondary overprint of late Palaeozoic age characterizes both the studied Ordovician–Silurian sedimentary rocks of Estonia and the Precambrian crystalline shear and fault zone rocks of southern Finland. The main carrier of this remanence is hematite, but the contribution of maghemite is observed besides. The remanence represents chemical remanent magnetization. The origin of this secondary magnetization is postulated to be associated with brines, possibly with meteoric waters, as well as with fluids derived from orogenic belts like Hercynian or Uralian. The late Palaeozoic overprint is quite widespread on several continents and has been observed in different types of rocks of different ages all over the world. For that reason we believe that the formation of Pangea has largely contributed to the formation of remagnetizations in the late Palaeozoic also in the studied region.