40Ar39Ar ages of igneous rocks recovered from Daiichi-Kashima and Erimo Seamounts during the Kaiko project
Abstract Ten igneous rocks recovered from the Daiichi-Kashima Seamount, the Erimo Seamount and near the Japan Trench with the use of the submersible “Nautile” were dated by the 40 Ar 39 Ar and KAr methods. The Daiichi-Kashima Seamount is estimated to have been formed about 120 Ma based on the 40 Ar 39 Ar plateau ages of recovered rocks. This result is consistent with the fossil age estimated from the limestone covering the top of the seamount. A plateau age of 103.9 Ma was obtained for a sample of the Erimo Seamount. Comparing the 40 Ar 39 Ar ages of these seamounts and the ages of the surrounding ocean floors based on magnetic anomaly patterns, these seamounts are supposed to have been formed by the off-ridge volcanism. Ages of rocks near the Japan Trench were determined to be 56, 59 and 80 Ma. Considering the reported age data and the circumstances of the sampling site, these rocks are inferred to have not extruded at the sampling site.