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Geodynamics of generation of oceanic crust-an example of the Oman ophiolite

洋壳生成的地球动力学——以阿曼蛇绿岩为例

基本信息

批准号：
09041101
负责人：
MIYASHITA Sumio
金额：
$ 11.33万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09041101/
关键词：
ophiolite oceanic crust Oman mantle layered gabbro

项目摘要

The results obtained from this research project are summarized for each group.Mantle group clarified an interaction between melt and mantle in the mantle-crust transition zone. Also they round the interaction was quite hetrogenous palce to place. Analyses of spinel using river sand show that the mantle peridotites of the Oman ophiolite are highly depleted compared to oceanic mantle, suggesting that signiricant modification or the mantle peridotite occured during later island arc stage.Gabbro group round two series of gabbros previously regarded as successive complex, which were formed at advancing and dying magma chambers beneath ocean ridges, respectively. This is explained by overlapping ocean ridges where propagation and retreating or ridges appeared. The central part of ridge segment where thick Moho transition zone occurs was determined through regional detailed geological mapping in the northern Oman ophiolite. From the central part to the tip or ridge segmenl, mineral compositions or layered gabbro varies systematically from less evolved to more evolved compositions.Upper crust group measured direction and thickness of dikes from extensive area in the northern Oman ophiolite. They found that the direction of dikes varies for each several km length, indicating the smallest order of segmentation of ocean ridges. The thickness of dikes increases from the central part to tip of the ridge segment in more large scale which is presumed from the petrological features of gabbro and mantle peridotite.Structural group found two different mineral lineations on foliation plane in the metamorphic sole beneath the Oman ophiolite. Also they clarified that the degree of preferred orientation is quite various even in one outcrop.

地幔群阐明了地幔-壳过渡带中熔体与地幔的相互作用。而且他们之间的互动是相当异质的地方。河砂尖晶石分析表明，阿曼蛇绿岩中地幔橄榄岩相对于大洋地幔而言亏损严重，表明地幔橄榄岩在岛弧晚期发生了明显的改造作用。辉长岩群围绕着两个系列的辉长岩，它们分别形成于洋脊下的进岩浆房和退岩浆房。这是因为洋脊重叠，在那里出现了传播和后退或洋脊。通过对阿曼北方蛇绿岩区的区域地质填图，确定了中脊段的中部存在厚层莫霍面过渡带。从中部到脊端或脊段，层状辉长岩的矿物成分从低演化到高演化有系统的变化。上地壳组测量了阿曼北方蛇绿岩大面积脉岩的方向和厚度。他们发现，堤坝的方向每隔几公里长度就发生变化，这表明洋脊的分割顺序最小。从辉长岩和地幔橄榄岩的岩石学特征推测，脉岩的厚度从脊段中部向脊端有较大幅度的增加，构造组在阿曼蛇绿岩下的变质基底中发现了两种不同的矿物线理面理。他们还阐明了即使在一个露头中，优先取向的程度也是相当不同的。