The diversity of Tanohata granitic mass, northern Kitakami mountains, Iwate Prefecture

Abstract

The Tanohata granitic mass, northern Kitakami mountains, Iwate Prefecture, shows various rock facies. The granitic mass is classified into six types by the rock facies as follows. 1) Moichi type - hornblende biotite granodiorite 2) Hagiu type - hornblende biotite granodiorite 3) Otomo type - biotite granodiorite 4) Kawaguchi type - biotite hornblende granodiorite 5) Otanabe type - hornblende biotite quartz monzonite 6) Shimoakuka type - hornblende biotite quartz monzonite It is concluded that the Tanohata granitic mass is the composite one, being the product of successive intrusions of the above-mentioned types and the order of intrusions is as follows, that is, at first the Kawaguchi body occurred during the last period of orogeny, the second is the Moichi and then the Hagui and the Otomo intruded successively. The Otanabe erupted in the north contemporaneously with the Otomo, and at last the Shimoakuka occurred as a separated minor body intruding into the Otanabe with very sharp boundary between both of them.