Zircon U-Pb Dating and its Applicability toward Engineering Geology

Abstract

U-Pb dating was known as a tool to date the oldest rocks on the earth and was applicable to ages as old as 0.1-1 billion years range. However, the method can now be used to date even Quaternary materials using easily-accessible equipment. Therefore it may be true that U-Pb dating can now be applicable to engineering geology.

This paper deals with a brief introduction to U-Pb dating, showing its principle, experimental procedures using zircon, and some notes on interpreting the age data. It also deals with how the zircon U-Pb method has been used for Quaternary tephras, Quaternary granites, and geothermal exploitations. Finally, this paper shows a new application dealing with landslide. A core drilling was performed at Matsushima, Miyagi Prefecture, where a large landslide is supposed to have happened, creating picturesque small islands in the Matsushima Bay. Zircon U-Pb dating was performed at three points, namely, upper block of the supposed landslide, the supposed landslide layer, and lower block of the supposed landslide, using tuffs and tuffaceous sandstone. All of them yielded ～15 Ma, which indicates there is no geochronological evidence for the supposed landslide.

In conclusion, zircon U-Pb method can now be applicable to a variety of engineering geological aspects（landslide, active faults, etc.）and are expected to be used widely.