Zircon Characteristics of Transscandinavian Igneous Belt Rocks in Southern Sweden

• The 1.81-1.66 Ga Transscandinavian Igneous Belt (TIB) is one of the major geological entities of Scandinavia. It is sub-divided into three age-groups based on zircon U-Pb-datings of rocks within the terrane. Zircons from nine rocks in the TIB and its neighbour to the west, the Eastern Segment, have been examined with scanning electron microscope, using backscatter electron and cathodeluminescence imaging techniques. The purpose of the study has been to test the reliability of the ages obtained by the previous datings following the method of Krogh (1973), through interpretations of the morphology and texture of the zircons. All samples showed more or less complex textures. The most complex textures appeared in the samples in and about the Protogine Zone, the major shear zone roughly located between the Transscandinavian Igneous Belt and the Eastern Segment. Recrystallized and metamict grains were common and should have led to Pb-loss of different amounts, and hence some discordance when analysed. Due to in some cases several overgrowths and asymmetric textures, the method of Krogh (1973) is probably an unsatisfying way if one whish to obtain more accurate ages. It is suggested that the zircons of this study are to be examined by ion-microprobe, in order to obtain these data. This is important for the future view on the Transscandinavian Igneous Belt and its surroundings.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

zircon

scanning electron microscope

TIB

Eastern Segment

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)