In Japan there have been only few contributions to the so-called “granite-tectonics”, that is, the structural petrology of granite plutons. In these fifteen years, however, a number of structural studies accompanied by geophysical researches have been made by the staffs of our institute. Among them, mesozonal plutons in the Kitakami mountain-lands including Tono, Senmaya, Hitokabe, and Goyosan masses, are described in this paper.
Generally a granitic pluton shows the concentric structure composed of the acid central core and the basic marginal shell. The internal structure reproduced by foliation and lineation is usually in harmony with such structure, though the inclination of the contact with the walls is diversely. It is inward-dipped in the Tono mass, and outward-dipped in the Senmaya mass.
On the other hand, according to the gravimetric investigation, a granite pluton has generally a comparatively large negative anomaly beneath itself. But the locus of the negative center is not neccessarily corresponding to the locus of the center of the surface structure. Both centers perfectly coincide in the Tono pluton, but it is not the case in the Senmaya and the Goyosan plutons.
Thus it is assumed that the emplacement shape of the Tono pluton is a symmetric “drop”-like form, whereas those of the Senmaya and the Goyosan plutons are asymmetric in form. In other words, the inclined “shallot”-form may be more suitable for the latter two plutons.
Different from the above three massive plutons, the Hitokabe pluton is characterized by “beads” structure in which at least three subdomes and one subbasin are linked together.
In conclusion, a magmato-tectonic model of the emplacement of granitic plutons in the Kitakami mountainlands is presented in Fig. 33, where the P-types are the mesozonal plutons emplaced in the lower Paleozoic terrain and the M-types are the epizonal plutons in the upper Paleozoic and Mesozoic terrains. It is important that the P-type plutons are entirely distributed in the geanticlinal uplifted area including both Setamai and Tobigamori domes, whereas the M-type plutons are developed in the surrounding areas and closely associated with the Cretaceous volcanic formation.

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