Abstract
The serpentinization of peridotitic rocks which constitute the main part of the Miyamori ultrabasic rock mass, Iwate prefecture, was studied in the field and also under the microscope with the result summarized as follows: In the eastern part of the mass (C-type area), the original peridotite is replaced by network veinlets of chrysotile serpentine, resulting in a mesh structure (C-type replacement), while in the western part (A-type area) by fiblous antigorite serpentine (A-type replacement)., In the C-type and also in the eastern border zone of the A-type area, some of the rocks have been subjected first to the C-type replacement and second to the A-type replacement (C-A type replacement)., It is concluded that the C-type replacement took place at a higher temperature than the A-type., The eastern part of the mass had been kept at a high temperature for some time as compared with the western, because the Palaeozoic sediments bordering the mass on its east had already been heated by the intrusion of granodiorite prior to the serpentinization of the peridotite., There is an indications that some of SiO 2, H 2O and CO 2 were migrated from the western eastern to the part of the peridotite mass during the serpentinization, which facilitated the replacement.,
