U-Pb isotope analyses of zircons from a Precambrian gneiss area in northern Sweden and their chronostratigraphic implications
作者:
Torbjörn Skiöld,
期刊:
Geologiska Föreningen i Stockholm Förhandlingar
(Taylor Available online 1981)
卷期:
Volume 103,
issue 1
页码: 17-25
ISSN:0016-786X
年代: 1981
DOI:10.1080/11035898109455199
出版商: Taylor & Francis Group
关键词: U-Pb;dates;absolute age;chronostratigraphy;zircon;crystal form;overgrowths;gneiss;para-gneiss;granodiorite;metamorphism;supracrustals;Svecokarelian;Proterozoic;northern Lapland;northern Norrbotten;northern Sweden;N6745 N6825 E2330 E2240
数据来源: Taylor
摘要:
A zircon study has been made on folded, conformable gneisses and an intrusive igneous rock from the northeastern part of Sweden. U-Pb ages of size and colour fractions of zircon concentrates from the gneisses show complex distributions on the concordia plot. This is related to varying degrees of secondary overgrowth on zircon cores and the formation of new zircons during the Svecokarelian (early Proterozoic) orogeny. Detrital zircons from a very pure quartzite have a maximum age of about 2700 Ma. They almost completely lack overgrowth textures and indicate an age close to that of the Archaean, conceivably igneous, source material. Zircons from the mica and amphibole gneisses have subhedral and rounded cores which, together with the observed layering, imply a sedimentary origin. They have apparent ages of less than 2063 Ma and close to the main metamorphic event, about 1850 Ma ago. Because of the low overgrowth/core volume ratios observed, one may suspect that the zircon core material in the mica and amphibole gneisses was in part derived from Proterozoic volcanic rocks. Thus, the recorded zircon ages favour Proterozoic deposition for all para-gneisses investigated, which is not consistent with other recent investigations. The minimum age of deposition is marked by an intrusive, foliated granodiorite with an age of 1873 ± 23 Ma (2 δ).
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