The active period of the Ayu Trough estimated from K-Ar ages:the southeastern spreading center of Philippine Sea Plate.

Abstract

In order to estimate the active period of the Ayu Trough, which lies at the boundary between the Philippine Sea Plate and the Caroline Plate, we measured K-Ar ages of submarine rocks dredged from the region. Samples recovered from the trough axis are similar to typical MORB and/or BABB in chemical and petrological features and show K-Ar ages of around 1 Ma. This suggests that the Ayu Trough might have been a spreading center at least during the last 1 million years. While, samples recovered at a site 62 km east of the axial rift valley show K-Ar ages of 20–25 Ma, and they are high-alkali andesites. If these samples indicate that an island arc existed there at 25 Ma, the activity of the Ayu Trough might have started at 25 Ma or later.