Granitic rocks in the central and northern Abukuma Mountains, containing abundant pegmatite, are known to produce various pegmatite minerals. Granitic rocks in the Uzumine area, one of pegmatite-producing spots in the central Abukuma Mountains, are described from the geological and petrological view points.
The granitic rocks are divided into the older foliated granodioritic rocks, the younger medium-grained two-mica granodioritic rocks, and the younger porphyritic two-mica granitic rocks. The younger porphyritic two-mica granitic rocks have been considered to be intimately related with pegmatite bearing rare element minerals, such as euxenite, monazite and xenotime etc.. The two-mica granitic rocks are the richest in potash feldspar and the highest in SiO
2 content (73-76%), and also contain biotites with low Mg/(Mg+Fe) ratio. They exhibit characteristics of S-type in mineral assemblage and normative corundum content, but are plotted in an I-type area in an ACF diagram. Moreover, their REE concentrations and strong light REE enrichment patterns, are positively comparable to those of I-type plutonic rocks.
The younger porphyritic two-mica granitic rocks may be formed either through the fractional crystallization of an I-type granodioritic magma, or from an independent granitic magma. In the latter case, the granitic magma may be originated from a parental material different from that of the I-type granodioritic magma, but the two magmas have a common residue of garnet and hornblende during partial melting of parental materials.
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