Rb-Sr mineral ages for the Grenvillian metamorphic development of spilites from the Dalsland Supracrustal Group,SW Sweden |
| |
| Authors: | H P Zeck B T Hansen |
| |
| Institution: | (1) Present address: Geological Institute, Copenhagen University, Øster Voldgade 10, 1350 Copenhagen K, Denmark;(2) Present address: Institute for Mineralogy, Westfälische Wilhelms-Universität, Münster, 4400 Corrensstraße 24, W-Germany |
| |
| Abstract: | Rb-Sr isotope systematics have been investigated of epidote, actinolite, albite and biotite concentrates from 4 spilite samples from the Precambrian basement directly W of lake Vänern in SW Sweden. The rocks belong to the Dalsland Supracrustal Group whose basal conglomerate was deposited on an erosion surface with a maximum age of c. 1,200 Ma. Epidote-WR and actinolite-WR tie lines in a Nicolaysen diagram give ages with an average of 990±10 (la) Ma, which is thought to represent the metamorphic culmination. Biotite-WR lines yield an average age of 900±15 (1σ) Ma, which indicates the time at which the rock complex cooled through the isotopic closure temperature of biotite, estimated at c. 250° C. The average cooling rate in this period was very low, 1–2° C/Ma. Initial Sr isotopic ratios of the 4 spilite samples vary from 0.7040 to 0.7080 and are thought to reflect interaction of mantle-derived basalts with seawater. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
