Abstract
Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and zircon fission-track (FT) dating were performed on granitic rocks from the Nojima Fault and its vicinity on northern Awaji Island, Hyogo Prefecture, Japan. The analyses yielded zircon FT ages of 52-78 Ma, which are in agreement with previously reported zircon FT ages. Zircon U-Pb (238U-206Pb) ages of 83-88 Ma were also determined. By combining these results with existing radiometric age data, we estimated the entire cooling history of the granitic basement on northern Awaji Island, spanning the period from the time of intrusion to the present. U-Pb ages were determined from zircons that were prepared for FT dating. Moreover, U-Pb ages were corrected based on analyses of Fish Canyon Tuff zircons as a standard material. As a result, a precise and accurate age of 16.3±0.1 Ma was obtained for the Buluk Member Tuff. This result demonstrates that the effect of common Pb is minimal even when analyzing zircons that are chemically etched, and that the Fish Canyon Tuff, which is a well-known age standard for FT dating, can be used as a standard for U-Pb dating. Many previous studies have reported on zircon FT analyses performed throughout the world. The method applied in the present study should pave the way for adding information on the crystallization age of the studied rocks by analyzing the zircons prepared previously for FT dating.
