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High Resolution and Three-Dimensional Investigation of Crustal Structure of an Island Arc-Toward the Deliberation of Stratified Llthospheric Tectonices(Stratotectonics)

岛弧地壳结构的高分辨率三维研究--对层状地球圈构造（Stratotectonics）的思考

基本信息

批准号：
02102001
负责人：
TAIRA Asahiko
金额：
$ 134.4万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Specially Promoted Research
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1992
项目状态：
已结题

项目摘要

The investigation conducted in 1992 focused on seismic imaging of deep crustal structure of the Izu-Ogasawara(Bonin) Arc along the latitude 32ﾟ.The field investigation included three vessels: R/V Hakuho-maru and Tansei-maru which belong to Ocean Research Institute of the University of Tokyo and a chartered vessel used for explosive operation. Two ship seismic experiments were conducted. Hakuho-maru being as transmitting ship and Tansei-maru as receiving ship. The experiments enabled us to obtain the data for deeper crustal images. Total fifty ocean bottom seismometers (OBS) were deployed along the line of two-ship seismic experiments. The OBS array recorded various signals including dinamite-generated seismic waves and yielded information on upper mantle seismic velocity structure underneath the island arc crust.The results of preliminary data processing indicate that the Izu-Ogasawara Island Arc crust at this location is composed of four seismic layers: 1)2-3.5km/sec P-wave velocity layer which is dominantly composed of cover volcanicalastic sequences(Layer A1),2)4-5km/sec layer which is interpreted to be sheeted dike complex(Layer A2),3) 6.1-6.3km/sec layer of the upper crust(Layer A3),4)7.1-7.3km/sec layer which corresponds to the lower crust(Layer a4).Layer A3 is 5km thick under the fore arc region and increases thickness under the central rift zone(7-8km thick). Layer A4 shows relatively uniform thickness: about 8km thick under the fore arc and 7km thick under the central rift zone.Layer A3 shows a range of seismic velocity typical to "granitic layer". Taking also account that the Tanzawa pluton in the Izu collision zone could well be an exposed example we interpreted Layer A3 as felsic intrusive layer possibly being composed of tonalite and granodiorite. This felsic layer might be derived from remelting of the lower crust mafic layer (including pre-existed oceanic crust ?) Layer A4 is probably composed of underplated mafic-ultra mafic intrusives.

1992年进行的调查重点是沿北纬32度沿着的伊豆-小笠原（小笠原）弧的地壳深部结构的地震成像。实地调查包括三艘船只：属于东京大学海洋研究所的R/V Hakuho-maru和Tansei-maru以及一艘用于爆破作业的租用船只。进行了两次船舶地震试验。白凤丸作为发送船，丹生丸作为接收船。这些实验使我们能够获得更深地壳图像的数据。共布设了50台海底地震仪（OBS），沿沿着进行了双船地震试验。OBS台阵记录到了包括硅藻土激发的地震波在内的多种信号，并获得了岛弧地壳下上地幔地震速度结构的信息。初步资料处理结果表明，该地点的伊豆-小笠原岛弧地壳由四个地震层组成：1）P波速度层为2-3.5km/s，主要由盖层火山碎屑岩组成（A1层），2）4- 5 km/sec层，解释为席状岩墙复合体（A2层），3）6.1-6.3km/sec的上地壳层（A3）7.1-7.3km/s层，相当于下地壳（A4），A3层在弧前区厚5 km，在中央裂谷带以下增厚（7- 8 km）。A_4层厚度较均匀，弧前下约8 km，中央裂谷带下约7 km，A_3层地震速度范围为典型的“花岗岩层”。考虑到伊豆碰撞带中的Tanzawa岩体很可能是一个出露的例子，我们将A3层解释为长英质侵入层，可能由英云闪长岩和花岗闪长岩组成。这一长英质层可能是下地壳镁铁质层（包括先存洋壳？）A4层可能由底侵的镁铁质-超镁铁质侵入岩组成。