Trace element abundances, isotopic compositions and ages for the Tertiary acidic igneous rocks from the coastal areas of the Japan Sea.

日本海沿岸第三纪酸性火成岩的微量元素丰度、同位素组成和年龄。

• 批准号: 02640597
• 负责人: TERAKADO Yasutaka
• 金额: $ 1.09万
• 依托单位: Kobe University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1990
• 资助国家: 日本
• 起止时间: 1990 至 1991
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02640597/
• 关键词: Acidic igneous rocks; Opening of the Japan Sea; REE pattern; Sr isotopic ratio; 希土類元素パタ-ン; ストロニチウム同位体比

Determinations of trace element abundances, Sr isotopic compositions and Rb-Sr ages were performed for the Tertiary acidic as well as related basic to intermediate igneous rocks from the coastal areas of the Japan Sea. The major purpose of this study is to examine the differences in trace element abundances and Sr isotopic compositions between the rocks formed before and after the opening of the Japan Sea which event occurred at about 15 Ma. The summary of the results on the northern Hyogo and Kyoto prefectures is as follows, and the results on Fukui area are consistent with the conclusions below. The initial Sr isotopic ratios for the igneous rocks of ages ca. 62, 43, 17 - 13, 5 - 3 Ma are 0.7073 - 0.7080, 0.7058, 0.7070 - 0.7091, and 0.7058 - 0.7076, respectively. These values are indistinguishable from those of Cretaceous acidic rocks in the surrounding areas (0.707 - 0.708 for Hyogo; 0.7054 - 0.7075 for eastern Tottori; 0.708 - 0.7104 for Kyoto and eastern ones). Moreover, it would … More be important that rather high Sr isotopic ratios of about 0.7060 - 0.7065 for some Quaternary basic rocks were reported. The REE patterns for all of the Tertiary acidic rocks show light REE enrichment, though size of Eu anomaly is variable: some samples seem to have no Eu anomaly. With respect to trace element abundances and Sr isotopic ratios, any clear differences between the acidic rocks formed before and after the opening of the Japan Sea were not found in this study. Moreover, the acidic rocks have almost identical Sr isotopic ratios to those of basic to intermediate ones, though the acidic rocks may tend to have higher Sr isotopic ratios. In conclusion, it was considered that the Sr isotopic compositions of the Tertiary acidic magmas may reflect those of mantle values, though some effect of crustal processes might have changed them in some extent. The author speculated that the uppermost mantle beneath Southwest Japan had been rotated together with the crust of Southwest Japan. In order to clarify the above conclusions, more data, especially Nd isotopic data, is necessary and mantle metasomatic processes or the role of fluid in the mantle would be important for producing those magmas. Less

本文对日本海沿岸第三纪酸性及相关基性-中性火成岩进行了微量元素丰度、Sr同位素组成和Rb-Sr年龄测定。本研究的主要目的是检查的微量元素丰度和Sr同位素组成的差异之间形成的岩石之前和之后的日本海的事件发生在大约15 Ma。关于北方兵库县和京都县的结果总结如下，关于福井地区的结果与以下结论一致。岩浆岩的初始Sr同位素比值约为1.25。62、43、17 - 13、5 - 3 Ma的平均年龄分别为0.7073 - 0.7080、0.7058、0.7070 - 0.7091、0.7058 - 0.7076。这些值与周边地区白垩纪酸性岩石的值难以区分（兵库县为0.707 - 0.708;鸟取县东部为0.7054 - 0.7075;京都和东部为0.708 - 0.7104）。而且， ...更多信息 一些第四纪基性岩的Sr同位素比值高达0.7060 - 0.7065。所有第三系酸性岩石的稀土配分模式均表现为轻稀土富集，但Eu异常的大小不一，有些样品似乎没有Eu异常。在微量元素丰度和Sr同位素比值方面，本研究未发现日本海开海前后形成的酸性岩石之间存在明显差异。此外，酸性岩石具有几乎相同的Sr同位素比值的基性到中间的，虽然酸性岩石可能倾向于具有较高的Sr同位素比值。认为第三纪酸性岩浆的Sr同位素组成可能反映了地幔的Sr同位素组成，但地壳作用的某些影响可能使其发生了一定程度的变化。作者推测，日本西南部下方的最上层地幔与日本西南部的地壳一起旋转。为了阐明上述结论，需要更多的数据，特别是Nd同位素数据，地幔交代过程或地幔中流体的作用对这些岩浆的产生很重要。少

项目成果

Y.Terakado and S.Nohda: "Rb-Sr dating of acidic rocks from the middle part of the Inner Zone of Southwest Japan:tectonic implications for the migration of the Cretaceous to Paleogene igneous activity." Chemical Geology. (1993)

Y.Terakado 和 S.Nohda：“日本西南内区中部酸性岩石的 Rb-Sr 测年：对白垩纪到古近纪火成岩活动迁移的构造意义”。

Y.Terakado and S.Nohda: "Rb-Sr dating of acidic rocks from the middle part of the Inner Zone of Southwest Japan: tectonic implications for the migration of the Cretaceous to Paleogene igneous activity." Chemical Geology. (1993)

Y.Terakado 和 S.Nohda：“日本西南内区中部酸性岩石的 Rb-Sr 测年：对白垩纪到古近纪火成岩活动迁移的构造意义”。