長崎県野母半島樺島花崗岩産ジルコンのU-Pb年代

Abstract

The Kabashima Granite has intruded the pre-Cretaceous geological unit in Kabashima Island near the southern tip of the Nomo (Nagasaki) Peninsula, Nagasaki Prefecture, western Kyushu, Japan. Although previous studies have reported Late Cretaceous (ca. 93-77 Ma) muscovite and biotite K-Ar dates from this granite body, we obtained only Early Cretaceous (ca. 125-110 Ma) zircon U-Pb dates; the dates were calculated from all the ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U data sets with the error-ellipse (2σ) intersecting the concordia curve on the concordia diagram. The difference between the muscovite and biotite K-Ar and zircon U-Pb dates is between 25 million and 40 million years.