抄録
The Tamadare Amphibolite Complex in the western Hitachi district, which is mainly composed of amphibolite group derived from gabbroic-quartzdioritic plutonics with a small amount of biotite schist and siliceous schist, is regarded as a basement complex lying under the Hitachi metamorphic rocks fomed by the Abean erogenic movements. The amphibolite group can be devided into three facies: (1) gneissose facies, (2) schistose facies, and (3) boundary facies. The structural revolutionary trend of basement complex, field occurrence of the abovementioned facies and textural changes of hornblende in the light of petrofabric investigation suggest that two stages of metamorphism should have been superimposed in the Tamadare Amphibolite Complex. One of the metamorphism (pre-Abean event probably) which made up gneissose facies characterized by coarse-grained relict minerals and relict textures of plutonics origin, together with marked microfolding structure. The other is the tectonic event (possibly Abean orogenic movement) which converted the gneissose facies into schistose facies characterized by fine-grained secondary minerals, together with preferred orientation of hornblende and strikingly schistose texture. The first metamorphism (formation of gneissose facies) is presumably correspondent to the metamorphism which concerned with the formation of the Nishidohira metamorphic complex, whilst the second one (formation of schistose facies) is identical with the tectonic event which formed the Hitachi metamorphic rocks.
