Some chemical and magnetic properties of rock samples from Matsukawa-ura drillhole, Soma city, Fukushima Prefecture, north-east Japan

—— Granitic rocks of Matsukawa-ura drillhole ——

Abstract

Granitic rocks, collected 327-850 meters below the surface near Matsukawa-ura, were chemically and magnetically investigated. The main phase is medium-grained tonalite, but one interval (565-675 meters) contains fine-grained tonalite and weakly shistose medium-grained tonalite.
      Microscopic observations show that many samples are affected by weathering and alteration.
     Twelve major elements of 26 samples were analyzed, as were trace elements Rb, Sr, Y, Zr, Ba, Th and U. Magnetic susceptibility, saturation magnetization, and Curie temperature of the same samples were also measured.
     The results of the chemical analysis demonstrate the homogenity of medium-grained tonalite but magnetic properties varies widely in each sample.
     In comparing the abundance of chemical elements with the Miyako and Senmaya granitic bodies, in Kitakami Mountains and the granitic rocks in the Onikobe area (eastern area), western area of Kitakami Mountains, the medium-grained tonalite samples from the Matsukawa-ura drillhole are characterized by low K₂O, Rb, Zr, Th and U content and high MgO, Na₂O and Sr content relative to the averages of other granites with similar silica content.