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Study on the Process of Island Arc Formation Inferred from the Bonin Islands

小笠原群岛推断岛弧形成过程研究

基本信息

批准号：
07404027
负责人：
SHIRAKI Keiichi
金额：
$ 25.47万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07404027/
关键词：
Island arc Izu-Bonin-Mariana arc Japanese Islands Boninite Sanukite High-Mg andesite Bronzite andesite Intra-plate basalt 小笠原諸島プレート内玄武岩

项目摘要

The purpose of the study is to know how the silicic continental crust forms from the mafic oceanic crust. comparing volcanic rocks from the immature Bonin Islands with those from the mature Japanese arcs. The important results in fiscal year 1998 are as follows.1.Mikadukiyama volcanic rocks in Chichi-jima, Bonin Islands, were summarized : the Mikadukiyama volcanics are richer in incompatible elements except for Rb and K than the boninite series rocks, suggesting that the former have formed under less hydrous conditions from less depleted sources than the latter.2.Picrite basalts with more than 16 % MgO were discovered from the lowest of the Pliocene Uegusukudake formation on the north coast of Kume-jima, Ryukyu Islands. Their highest Fo of olivine is 92.2 and Cr2O3 of chromite is 56.5 %, indicating refractory nature of their magmas. 1 suggested that the picrite basalts were generated by high temperature mantle plume causing Okinawa Trough back-arc spreading.3.The high-Mg andesites from … More Ou-jima, immediately east of Kume-jima, have bahaitic affinities with high Sr/Y and Sr/Rb. This is the first finding of bahaite from the Japanese Islands.4.Sanukitic rocks around Mt. Oninohana-yama, central Saga Prefecture, were investigated. The sanukites have high Nb contents (29-36 ppm) and contain bronzite with Mg^# 84.7 and Cr203 0.58 %. They represent the easternmost occurrence of high-Nb bronzite andesites in northwest Kyushu.5.Sanukites from Hario-jima, northern Nishisonogi Peninsula and Arita, western Saga Prefecture, have moderately high Nb (16-21 and 17-18 ppm, respectively), and bronzite andesites from the southern Nishisonogi Peninsula are low in Nb (<10 ppm). The Nb contents of sanukitoids in northwest Kyushu decrease from sanukites (39-64 ppm) in the northern Kitamatsuura Peninsula to the south.6.Preliminary investigation was carried out on the volcanic rocks of the Palau Islands, Micronesia ; samples were collected first from the inner part of Baberudaob Island since World War II.High-Mg andesites were discovered from the Baberndaob volcanic rocks representing the lowest sequence of the Palau Islands. The volcanic rocks from the Palau Islands are similar in chemical composition to tholeiites and calc-alkali rocks from Haha-jima in the Bonin Islands. Less

研究的目的是了解镁铁质洋壳是如何形成陆壳的。将小笠原群岛未成熟的火山岩与成熟的日本岛弧的火山岩进行比较。1998年度的重要成果如下：1.小笠原群岛秩知岛三渡山火山岩的研究结果：三渡山火山岩比玻安岩系列岩石富含Rb和K以外的不相容元素，表明前者是在含水量较低的条件下形成的，其来源比后者少。MgO是在琉球群岛久米岛北岸上新世Uegusukudake组的最低层发现的。橄榄石的Fo最高为92.2，铬铁矿的Cr_2O_3最高为56.5%，表明岩浆具有耐火性质。1表明苦橄玄武岩是由高温地幔柱引起的冲绳海槽弧后扩张形成的 ...更多信息位于久米岛以东的欧岛具有高Sr/Y和Sr/Rb的巴哈伊质亲合性。这是在日本列岛首次发现的巴哈伊岩。鬼之花山，中央佐贺县，进行了调查。sanukite具有高Nb含量（29-36 ppm），并且包含具有84.7%的Mg和0.58%的Cr2 O3的古铜色岩。5.西索木半岛北方播落岛和佐贺县西部有田的赞岐岩中Nb含量较高（分别为16-21和17-18 ppm），西索木半岛南部的青铜安山岩中Nb含量较低（<10 ppm）。九州西北部的sanukitoids的Nb含量从sanukites减少（39-64 ppm）。6.对密克罗尼西亚帕劳群岛火山岩进行了初步调查;自第二次世界大战以来，首次从巴伯鲁道布岛内部收集样本。高-镁安山岩是从代表帕劳群岛最低层序的巴本道布火山岩中发现的。帕劳群岛火山岩的化学成分与小笠原群岛哈哈岛的拉斑玄武岩和钙碱性岩相似。少