Two major types of late Svecofennian granitoids occur in south central Sweden. Large homogeneous massifs of coarse-grained granite with trace element characteristics typical of granites formed in tensional settings occur along the Central Swedish Gravity Low (CSGL). The other type comprises smaller intrusions of irregular, heterogeneous, locally derived granites (IHLD granites). We present U-Pb zircon ages are presented of one IHLD granite and of three varieties of the homogeneous intrusions. The result for the IHLD granite is 1779+-8 Ma. One of the samples of the homogeneous type yielded an age of 1769.7 +- 3.4 Ma. The remaining two samples have heterogeneous zircon populations. The emplacement age of these rocks is bracketed by the intercept ages of 1770 +- 6 and 1779 +- 23 Ma.The overlapping ages of granite groups of different types show that different types of granites were formed contemporaneously in the same region as a result of melt formation at various depths and from various sources.
Godkänd; 1996; 20070328 (pafi)