Timing of activity of the Yusubaru Granite and petrogenetical relationship with the Leucocratic Granite, Cretaceous Granitic rocks in northern Kyushu, Southwest Japan

<p>The Yusubaru Granite and Leucocratic Granite from the eastern part of northern Kyushu, Southwest Japan were investigated with respect to major and trace element analyses, U-Pb zircon dating, rare-earth element (REE) analysis and Sr-Nd isotope analysis. The Yusubaru Granite is divided into two facies in terms of petrographical features: the main and melanocratic porphyritic facies. The main facies are composed of fine-grained biotite granite and two-mica granite. The melanocratic porphyritic facies, which are composed of hornblende -biotite granodiorite and granite, are scattered in the main facies. The Leucocratic Granite is mainly composed of fine- and coarse-grained muscovite granite and two-mica granite. Variations of the whole-rock chemical compositions of the main facies of the Yusubaru Granite and Leucocratic Granite overlap with those of the Masaki Granite, although the REE patterns differ. The initial Sr and Nd isotopic ratios of the main facies also differ from those of the Masaki Granite. The main facies of the Yusubaru Granite and Leucocratic Granite are considered to be derived from a single magma chamber based on petrochemical investigations, and the Leucocratic Granite magma was activated after the Yusubaru Granite main facies magma. U-Pb dating of zircons separated from the main facies gives an age of 98.6 ± 0.9 Ma, which is considered to be the timing of the magma activity that produced this granite. Newly determined Sr and Nd isotopic ratios corrected to 98.6 Ma for the two main facies samples from theYusubaru Granite are within the range of isotopic compositions for the North Zone defined by Kagami (2005). </p>