Metamorphism of Ultrabasic Rocks Caused by Intrusion of Granodiorite in Miyamori District, Iwate Prefecture : Metamorphism of serpentine Rock

The Miyamori ultrabasic mass in Iwate Prefecture is metamorphosed, at its western side, by intrusion of granodioritic rocks., The zone of metamorphism (maximum width about 4km) developed in the serpentine and serpentinized dunite may be divided, geologically as well as petrographically, into the following subzones from west to east; 1st zone: enstatite-cummingtonite-spinel zone and spinel-hornblende zone., 2st zone: tremolite-(actinolite)-anthophylite-chlorite zone., 3rd zone: tremolite-antigorite zone., 4th zone: antigorite zone., The rocks which characterize the 1st to 3rd subzones were probably formed simultaneously according to the differece in physice-chemical conditions depending on their distances from the granodiorite mass., This was immediately followed by retrogressive metamorphism during which the rocks of each of the three subzones were successively replased by minerels characteristic of the subzone directly on its east (lower grade one) and finally by antigorite., This mineral first appears as veins through the rocks of the 1st to 3rd subzones, but is finally collected togerther to form large masses which are designated as the 4th zone., There is no evidence to show that the rocks of these subzones were formed progressively from lower grade one.