Petrochemistry of the Sakainokami plutonic body, Kitakami mountains, northeastern Japan.

Sakainokami plutonic body is one of the many Cretaceous intrusive bodies in the northern Kitakami mountains. The present study revealed that the plutonic body is composed of three rock types, namely: type A, type B and type C, which have been emplaced successively in that order. Types A and C are further subdivided into three and two subtypes, respectively, as follows: Type A Subtype A-1: Biotite-bearing olivine augite hornblende gabbro Subtype A-2: Biotite, hypersthene-bearing augite hornblende gabbro Subtype A-3: Augite-bearing biotite hornblende gabbro Type B: Augite-bearing biotite hornblende gabbro—diorite Type C Subtype C-1: Biotite hornblende monzodiorite—granodiorite Subtype C-2: Biotite hornblende granodiorite. Within subtypes A-2 and A-3, two groups differing in the crystallization sequence of plagioclase and hornblende are identified. In one group, hornblende has crystallized earlier than plagioclase and there is an accumulation of more hornblende than normally. In the other group, plagioclase has crystallized earlier than hornblende and there is an accumulation of opaque minerals in certain portions. The former group is designated as group h and the latter is designated as group p. Without considering the presence of these groups the plots of type A rocks are segregated in accordance with these groupings three different trends emerge. These trends are designated as trend I, trend II and trend III. Trend I represents the case where there is accumulation of hornblende; trend II, where there is accumulation of opaque mineral; and trend III, representing the calc-alkaline trend.