ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The effect of Alpine (∼40 my) low amphibolite facies metamorphism on strontium isotopes in the Variscan (∼250–300 my) granitic complex of the Zentralgneis was investigated by analysing samples of a leucogranite which forms small intrusions into a tonalite. The leucogranite has Rb/Sr ratios up to 30. Two muscovites and three biotites underwent complete reequilibration during the metamorphism. The ages of 12–20 my are consistent with published K-Ar ages on micas from the same area, and reflect post-metamorphic cooling. Six whole-rock samples define an isochron with an age of 244±7 my (λ=1.47×10−11yr−1). Three further samples, collected within 30 cm of contacts with the tonalite, plus 1 cm sawn slabs of leucogranite and tonalite from either side of a contact fit a line with 10% greater slope; this line is interpreted as a mixing line, resulting from contamination of the leucogranite, near its contacts, with strontium from the enclosing tonalite. The time of contamination is uncertain but petrological evidence suggests it is the result of the metamorphism. Neither leucogranite whole rocks nor minerals from the tonalite, at contacts and in a xenolith, show any evidence for preferential mobilisation of radiogenic strontium in the course of metamorphism.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373345
