Geological studies have proposed collision of the Izu-Mariana arc with the Honshu arc over ten million years. At present, the collision may occur around the base of the Izu Peninsula. This study attempts to detect the uplift by GNSS (Global Navigation Satellite System) data. Using the F3 solution data from January, 2000 to January, 2010 and re-analyzed data by a Precise Point Positioning method from 2006 to 2010, we show spatial distribution of vertical displacement around the Izu Peninsula. As a result, we find the uplift at the base of the Izu Peninsula as well as subsidence on the other sides of the bays beside the Izu Peninsula due to interplate locking. Next, we model the collision of the Izu Peninsula by elastic dislocation and try to reproduce the uplift at the base of the Izu Peninsula. A grid search for the F3 solution data clarifies that elastic collisional sources work at 0.0 mm/yr on the eastern foot of Mt. Hakone, 16 mm/yr on the northern foot, and 13 mm/yr on the western foot. Furthermore, in order to eliminate influences of volcanic activities during the observation period, we remove nonstationary volcanic deformation of Mt. Fuji and Mt. Hakone from the F3 solution data on the basis of previous studies. This examination also reveals the uplift at the base of the Izu Peninsula, although the collision rate on the northern foot of Mt. Hakone turn out to be smaller by an order of magnitude. The present uplift rate revealed by GNSS does not contradict heights of the Tanzawa Mountains, which supports the hypothesis of the collision-derived mountain formation, but the spatial difference between the peak uplift area (present) and the Tanzawa Mountains implies a long-term drift of the collision zone of the Izu Peninsula.
Naticid predatory drill holes on fossil bathyal bivalves were examined in the ancient coldseep site and its surrounding mudstone of the Eocene Poronai Formation, Hokkaido, Japan. Parabolic drill holes in similar sizes were recognized on both chemosynthetic bivalves (Conchocele bisecta and Hubertschenckia ezoensis) and non-chemosynthetic ones (Malletia poronaica, Portlandia watasei, and Cyclocardia tokudai). Drilling intensity (DI) on chemosynthetic bivalves (0.070 to 0.080) is higher than that on non-chemosynthetic bivalves (0.027 to 0059). This suggests that the Eocene naticids could be active in sulfide-rich bottom in the seep site as well as its surroundings, but chi-squared tests did not support any preference on prey bivalve taxa (χ2 = 9.66; df = 5; p > 0.05). Chi-squared tests also did not support that naticid attacks were biased towards in the seep-site against non-seep surroundings (χ2 = 0.43; df = 1; p > 0.05). The naticid attacks on the chemosynthetic bivalves in the seep site were not significantly frequent over the non-chemosynthetic bivalves in the surrounding mud.
High-temperature uniaxial compression experiments were conducted for a rhyolitic obsidian lava from Shirataki, Hokkaido, Japan, under conditions of temperatures from ca. 851 to 733°C, strain rates from ca. 10−2.7 to 10−5.4 s−1 and one atmosphere pressure. The obsidian lava is glassy and almost crystal- and bubble-free. Bulk rock water content is ca. 0.2 wt.%. As temperature decreases, measured viscosity at strain rate of 10−4 s−1 increases from ca. 109.3 to 1010.8 Pa s. Very weak shear thinning behavior is observed and the behavior is well described by power law fluid model. The measured viscosities are consistent with the model of Giordano et al. (2008) within 0.2 log unit error, indicating that the Giordano et al. (2008) model is reliable for estimating viscosity of H2O-poor rhyolitic melt and the present experimental method works well for rhological measurement of highly viscous lava. The temperature conditions at which viscous-brittle transition occurred for the studied lava flow is examined by using Giordano et al. (2008) model combined with the critical Deborah number for silicate melt. The result suggested that the fractured layers in the Akaishidake-jobu lava flow were formed at temperature condition < ca. 680°C.
This paper describes a theoretical outline of the microboudin palaeo-piezometer. The microboudin palaeo-piezometer was recently developed as a practical method for differential stress analysis of metamorphic tectonites. It estimates the far-field differential stress (σ0) on the basis of a theoretical analysis of the proportion of microboudinaged columnar grains in terms of the aspect ratio. We introduce the application of the microboudin palaeo-piezometer with an example from Masuda et al. (2011).