Thermal history of the alteration zones around hot springs at Hongu and Totsukawa area, Southern Kii Peninsula, Southwest Japan

Abstract

The high temperature hot springs such as in Yunomine and Tosenji and the hydrothermal alteration zones of the Hongu area are distributed in the southern part of Kii peninsula, though Quaternary volcanoes which can be their potential heat sources are not distributed in the area. This research has aimed to understand the thermal history of the area by using several dating methods.Thermoluminescence (TL) dating method was applied according to the distance from dykes or gushing out point of the hot springs which thought to be the center of alteration. The results show that the alteration age of Yunomine alteration zone is younger as it approaches the gushing out point of hot spring. No clear tendency was observed in other places. These results suggest that the alteration ages near Yunomine hot spring are controlled by the distance from the gushing out point. However, no clear tendency was observed at other hot springs between the alteration ages and the distance from the center of alteration when two or more activities of alteration have occurred.The results of the TL, Fission Track (FT) and K Ar dating show that after the high temperature hydrothermal alteration (until tens of millions of years ago), relatively low temperature alteration (from at least hundreds of thousands of to tens of thousands of years ago) occurred in Hongu and Totsukawa area.

Detecting thermal anomalies using thermochronometry around hydrothermal alteration zones in the Kii Peninsula, southwest Japan – An attempt

“…8b and 8c). Considering that ZFT ages of ~ 80-70 Ma have been reported for the Southern Shimanto Belt in adjacent areas (Umeda et al, 2007;Hanamuro et al, 2008), the younger ZFT ages in this study may have been partially…”

“…ZFT and AFT thermochronology have been reported in previous studies that investigated the thermal and exhumation history of the accretionary complexes of the Shimanto Belt on the Kii Peninsula (e.g., Tagami et al, 1995;Hasebe and Tagami, 2001;Hasebe and Watanabe, 2004;Umeda et al, 2007;Hanamuro et al, 2008;Ohira et al, 2016), as well as in other regions of the Southwest Japan Arc (Hasebe et al, 1993b(Hasebe et al, , 1997) (Fig. 2).…”

Detecting thermal anomalies using thermochronometry around hydrothermal veins in the Kii Peninsula, southwest Japan – An attempt

“…Considering that ZFT ages of ~ 80-70 Ma were reported in adjacent areas in the Southern Shimanto Belt (Umeda et al, 2007;Hanamuro et al, 2008), the younger ZFT ages in this study may have been partially reset by a reheating episode related to heat in ux in the Miocene (Hasebe and Watanabe, 2004). Considering that the study area is in the northern part of the Southern Shimanto Belt, the AFT ages of ~ 10 Ma reported here are consistent with a southward younging trend, AFT lengths show a unimodal, negatively skewed distribution (Fig.…”

“…The Haroku Formation yielded Eocene radiolarian fossils (Suzuki, 1993), and detrital zircons from a tuffaceous sandstone yielded U-Pb ages of 50.8 ± 1.0 Ma (Tokiwa et al, 2016). Furthermore, many AFT and ZFT dates from the Shimanto Belt of the Kii Peninsula have been reported (e.g., Hasebe and Tagami, 2001;Hasebe and Watanabe, 2004;Umeda et al, 2007;Hanamuro et al, 2008;Ohira et al, 2016) and these reveal a pattern of regional exhumation and expand on local thermal histories (see Section 6.3 for further details).…”