The Baric Structures and Exhumation Processes of the Sogauchi Unit in the Sambagawa Belt

The Sogauchi unit is developed as the Sogauchi nappe as a member of primary structure and as the Omogiyama nappe, Terano—Isozu nappe and Saredani—Kabayama—Izushi nappe as members of secondary structure. The baric structures of these nappes have been analyzed on the basis of chemical composition of amphibole in hematite—bearing basic schist. The Sogauchi nappe consists of three subunits as nappes, showing increase of pressure from the lower nappe to the upper nappe and northward increase of pressure for each nappe. The assumed isobaric lines appear to be running in WNW—ESE trend, which is slightly oblique to the general trend of mineral lineation (Lm), and the lower pressure part of each nappe appears to be placed on the western side on the line along Lm. The displacement of the nappes during their subcretion— exhumation appears to have been of westward sense judging from quartz microtextures. The Omogiyama nappe and Saredani—Kabayama —Izushi nappe have been assumed to have been derived as nappes from the northwestern extension (higher pressure parts) of the Sogauchi nappe. However, an alternative model has also been shown for the root of the Saredani — Kabayama —Izushi nappe.