1988 Volume 38 Issue 212 Pages 509-515
To understand the mode of differentiation of granitic magmas of Southwest Japan, neutron activation analyses have been made to measure the trace element abundance of the granitic rocks. During plagioclase-quartzbiotite fractionation, Ba and Rb enrich in successive solids and melt, while Sr is depleted. The incoming of Kfeldspar as a solid phase causes Ba to be depleted along with Sr in successively formed solids, while Rb continues to be enriched. As suggested by MCCARTHY and ROBB (1978), a change in liquidus mineralogy from plagioclase-quartzbiotite to plagioclase-quartz-K-feldspar-biotite during the in situ fractional crystallization of a granitic magma has a marked effect on the abundance of and interrelationships between Ba, Rb and Sr. In general, trace element data from the granitic rocks of Southwest Japan fit the model well, although the observed scatter of the data is somewhat greater than predicted by simple variation in cumulus-intercumulus proportions-possibly due to a diffeence in Ba, Rb and Sr contents of original melts, to the effect of assimilation, and to the change in the Sr partition coefficients for plagioclase during cooling.
