Xd. Wang et al., U-Pb and Sm-Nd dating of high-pressure granulite- and upper amphibolite facies rocks from SW Sweden, PRECAMB RES, 92(4), 1998, pp. 319-339
Geochronological data from different radiometric systems on high-grade meta
morphic rocks in the Southwest Swedish Granulite Region, southwestern Swede
n, are generally analytically precise but sometimes in conflict with each o
ther. Age data from seven samples on which a variety of radiometric methods
have been applied are presented. The age of peak metamorphism is determine
d by metamorphic zircons from two garnet amphibolites at c. 975 Ma using th
e conventional U-Pb isotope and Pb-Pb evaporation methods. Titanites from t
he same type of rocks give ages of c. 923 +/- 3 Ma and 945 +/- 2 Ma. The Sm
-Nd data on malic granulites and garnet amphibolites yield surprisingly you
ng ages between 945 and 900 Ma, similar to previous Sm-Nd ages. These ages
are comparable to, or even younger than, the Ar-40-Ar-39 hornblende ages th
at range between 1030 and 930 Ma. Assuming that the Sm-Nd systematics are e
ntirely controlled by volume diffusion, the closure temperature of the Sm-N
d system in minerals from these rocks would be comparable to, or lower than
, that of Ar diffusion in hornblende, i.e. around 500 degrees C. (C) 1998 E
lsevier Science B.V. All rights reserved.