K-Ar年代測定に基づく両白山地の鮮新; 更新世火山活動の時空分布

Temporal-spatial variations of Plio-Pleistocene volcanic activity in the Ryohaku Mountains, cental Japan; Evidences from K-Ar ages

棚瀬 充史*; 及川 輝樹*; 二ノ宮 淳; 林 信太郎*; 梅田 浩司

Tanase, Atsushi*; Oikawa, Teruki*; Ninomiya, Atsushi; Hayashi, Shintaro*; Umeda, Koji

中部日本、両白山地の鮮新-更新世火山は、東南東-西北西方向の九頭竜火山列と南北方向の白山火山列をなす。両白山地における鮮新-更新世火山活動の時空分布を石基試料のK-Ar年代に基づいて検討した。初期(3.51.5Ma)には、二つの火山列の交点付近での火山活動が見られる。1.20.7Maには、九頭竜火山列で東南東端の烏帽子・鷲ヶ岳火山から西北西端の法恩寺火山へ火山活動が移動する。その後、白山火山列の活動が0.4Maに始まり、現在まで継続している。

Temporal and spatial variations on Plio-Pleistocene volcanism in the Ryohaku Mountains, central Japan, have been investigated by newly obtained K-Ar ages on 38 groundmass samples separated from volcanic rocks. The volcanoes in the Ryohaku Mountains form two volcanic rows of the Kuzuryu and hakusan Volcanic Chains which have ESE-WNW and N-S alignments, respectively. Early volcanic activity occurred intermittently from 3.6 Ma to 1.5 Ma, and the volcanoes near the junction of the two volcanic chains were active. The volcanic activity in the ESE-WNW trending Kuzuryu Volcanic Chain was restricted in the age range from 1.2 Ma to 0.7 Ma with migration from Eboshi-Washigatake Volcano (ESE end) to Hoonji Volcano (WNW end). The N-S trending Hakusan Volcanic Chain was active from 0.4 Ma to the present.