Abstract
Geological and volcanological data in and around the Hida Mountain Range (northern Japanese Alps) have been compiled to elucidate the relationship between uplift and volcanism in this area.
The age and volume data of volcanics in this area were compiled using volcano-stratigraphy, tephrochronology, and radiometric dating. This study revealed two periods of intense igneous activity: 2.5-1.5Ma (Stage I) and 0.8-0Ma (Stage III). Less abundant igneous activity is found in Stage II. Volume of erupted magma at Stage I and Stage III are 1, 300 and 300km3, respectively. Stage I is characterized by enormous volcanic activity. The uplifting timing of the Hida Range is indicated by the ages of the gravel sediments in the Matsumoto, Takayama, and Toyama basins at the foot of the Hida Range. The gravel sediments in these basins were divided into the two major stages of 2.5-1.5Ma and 0.8-0Ma. Therefore, major uplifting ages of the Hida Range correspond well to the two major igneous stages, namely Stage I and Stage III, suggesting a good temporal relationships between volcanism and uplift in the Hida Range.
Although the state of the regional stress field in Stage I was tensional, the Hida Range uplifted at this stage. Therefore, the mechanism of uplifting at Stage I was isostatic uplift caused by magmatic intrusion. On the other hand, the regional stress field in Stage III was compressional, and the state of the elastic crust of this area might be thin due to continuous magma intrusion into the upper crust. Therefore, the possible mechanism of uplifting in Stage III is a buckling fold in the thin elastic crust. In short, the process of uplifting of the Hida Range after 3Ma can be interpreted as a combination of two different mechanisms: magma accumulation rate in the upper crust and changes in the regional stress field.
