K–Ar ages of the Ohmine Granitic Rocks, south‐west Japan
K–Ar ages of the Ohmine Granitic Rocks, south‐west Japan
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日本西南部 Ohmine 花岗岩的 K-Ar 年龄
DOI：
10.1046/j.1440-1738.2003.00401.x
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发表时间：
2003
期刊：
影响因子：
1.5
通讯作者：
H. Shinjoe
中科院分区：
文献类型：
--
作者：
T. Sumii;H. Shinjoe
大峰花岗岩是沿纪伊半岛中轴线呈沿着分布的一系列花岗岩。它们的精确年龄尚未确定，尽管分布在半岛的早中新世至中新世中期的其他地质单元的精确年龄已被报道。本文对大峰花岗质岩石中的六个主要花岗岩体Dorogawa、Shirakura、Kose、Asahi、Tenguyama和Shiratani进行了黑云母K-Ar年龄测定。大部分年龄为14.8 ~ 14.6Ma。 虽然一个岩体较老（15.4 ± 0.2Ma），两个岩体较年轻（14.0 ± 0.2Ma和13.4 ± 0.1Ma），但由于它们的年龄存在一些不确定性，因此在讨论岩体之间的相互关系时，不考虑它们的年龄。 最南端的Katago-Mukuro岩脉的年龄因其强烈的蚀变而无法确定，但地层限制表明它的年龄小于16.1 Ma。 大部分的Ohmine花岗岩集中在一个狭窄的年龄窗口约14.8-14.6 Ma，虽然他们的地球化学/岩石学特征表明，他们是由多个岩浆批次。 本研究结果还揭示了大峰花岗岩的主要活动与纪伊半岛巨大的长英质火成岩活动，如熊野酸性岩和室吕火山碎屑流存款同时发生。
Abstract The Ohmine Granitic Rocks are a series of granitic rocks that are distributed in a chain stretching along the central axis of the Kii Peninsula. Their precise ages have not been determined, although precise ages have been reported for other geological units of the early to middle Miocene distributed over the peninsula. In this study, biotite K–Ar ages were obtained for the six major granitic plutons of the Ohmine Granitic Rocks: Dorogawa, Shirakura, Kose, Asahi, Tenguyama and Shiratani. Most are aged from 14.8 to 14.6 Ma. Although one pluton is older (15.4 ± 0.2 Ma) and two are younger (14.0 ± 0.2 Ma and 13.4 ± 0.1 Ma), these ages are excluded from the discussion of the mutual correlation among the plutons because some ambiguities exist in their ages. The age of the southernmost unit, the Katago–Mukuro Dykes, was not determined because of its intense alteration, but stratigraphic constraints suggest that it is younger than 16.1 Ma. The majority of the Ohmine Granitic Rocks concentrate within a narrow age window of approximately 14.8–14.6 Ma, although their geochemical/petrographical characteristics suggest that they were generated by multiple magma batches. The results of this study also reveal the simultaneous occurrence of the major activities of the Ohmine Granitic Rocks and the gigantic felsic igneous activities in the Kii Peninsula, such as the Kumano Acidic Rocks and the Muro Pyroclastic Flow Deposit.