ISSN:
0016-7835
Keywords:
Key words Eastern Alps
;
Magmatism
;
Alkaline rocks
;
Geochronology
;
U
;
Pb
;
Zircon
;
Cadomian
;
Pan-African
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Two orthogneiss suites dominate the Silvretta nappe. Primary crystallization of the larger suite ('younger orthogneisses') is assumed to be Ordovician in age. The second, adjacent magmatic suite consists of older, alkaline to calc-alkaline, ultrabasic, basic to intermediate and granitic rocks known as 'older orthogneisses'. U–Pb data of multigrain zircon fractions, as well as single zircon stepwise evaporation 207Pb/206Pb results suggest a latest Proterozoic to early Cambrian intrusion age for the protoliths of the 'older orthogneisses' as both dating methods yield early Cambrian crystallization ages of 526±7 and 519±7 Ma for an alkaline granite gneiss; similar results were obtained for two neighbouring calc-alkaline orthogneisses (207Pb/206Pb ages of 533±4 and 568±6 Ma, respectively). The crystal habitus corresponds to P5, S19 and S9 zircons of magmatic origin. Whole-rock initial Sr isotope ratios indicate a primitive source. The igneous protoliths of these 'older orthogneisses' represent a fragment of a Cadomian (Pan-African) crust found in places within the basement of the European Hercynides.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00284513
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