島根半島およびその周辺地域における飛騨隠岐変成帯の分布についての考察

Basic to intermediate intrusive bodies intruded into the Miocene formation, are known in the green tuff region of Shimane prefecture and its adjacent areas, the coast of the Sea of Japan.
From the petrochemical point of view, these rocks are classified into the following three types ; tholeiitic, high almina, and alkali basalt type. The first type occurs in the Oda Miocene sedimentary basin underlain by Sangun metamorphic rocks. The second one occurs in the Izumo Miocene sedimentary basin and the eastern part of Shimane peninsula district. Both districts are Miocene sedimentary basin underlain by Paleogene granite batholith. The last one occurs in the western part of Shimane peninsula district. The basement rocks of the Miocene sediments are infered to be related with the Hida-Oki Metamorphic rocks in judgment from the rock type of this intrusive rock and geological relation.
On the other hand, a finding of the gravels of gneissic rocks from the Miocene Koura formation is a important matter to solve the relation between Hida-Oki metamorphic belt and Chugoku belt.
It implies the presence of mountain land composed of gneissic rocks of Hida-Oki metamorphic belt in and around the Shimane peninsula district at the dawn of the Miocene. The gravels of gneissic rocks were derived from island left behind in the progress of sinking to the basin of Koura formation.
In addition to above mentioned facts, it is of much interest that the green tuff alteration in Shimane peninsula district as compared with the mainland district are remarkable.
Olivine hyperite inclusion in the Miocene pyroxene andesite lava from Oda city, western district of San'in-Hokuriku green tuff subregion of Japan, is characterized by having high calcic plagioclase, relatively high content of <Al>_2O_3, CaO and MgO, and low content of SiO_2. From the above mentioned characters, it is likely that it is derived from the layer produced by the remelt of the Precambrian oceanic basalt layer embedded at the basement of the crust.
Based on the above mentioned geological relations, the writer concludes that the southern limit of the Hida-Oki metamorphic belt exist around Shimane peninsula district.