Estimation of time scale for magma intrusion by multiple dykes

结论：通过研究获得的最有意义的知识如下：（1）多个冷缘岩墙（2）多个岩墙形成的条件（3）多个岩墙在弧火山和缓慢扩张的海脊中很常见，而在快速扩张的海脊中可能很少见。对伊豆大岛的Fudeshima火山、八岳火山北方的较老火山岩和塞浦路斯的Troodos蛇绿岩进行了实地研究，揭示了一种多岩脉的存在，这些岩脉仅在距岩脉边缘数十厘米处具有1-20厘米厚的多个冷缘。多脉岩形成的条件：特罗多斯蛇绿岩中，多脉岩的存在仅限于层状辉长岩附近。相反，出现在地层较高层位的席状岩墙则是简单岩墙。这表明有利于多岩墙形成的条件是：（1）岩浆侵入的重复;（2）岩浆侵入频率/岩墙凝固时间的比值（F/S比值）大。Troodos与Semail：Semail蛇绿岩中的席状岩墙都很简单。这说明塞梅尔岩浆不是以脉冲方式侵入的，或F/S比值很高。此外，岩浆脉冲的产生还受再充岩浆体积与岩浆房体积之比的控制。

Conclusions : Most significant knowledge obtained through the research is as follows ;(1) Multiply chilled-margin dykes(2) Conditions of multiple dyke formation(3) Multiple dykes are common in arc volcanoes and slow spreading ridges, while they may be rare in fast spreading ridges.Multiply chilled-margin dykes : Field research done on Fudeshima Volcano, Izu Oshima, Older volcanics of northern Yatsugatake Volcano and Troodos Ophiolite, Cyprus, revealed the existence of a sort of multiple dykes, which have multiply chilled margins 1-20 cm thick only in several tens of centimeters from the dyke selvages. Such dykes indicate that pulse of magma intrusions repeated in a short time interval.Conditions of multiple dyke formation : In Troodos Ophiolite, Presence of multiple dykes are confined to near the layred gabbros. On the contrary, sheeted dykes occurring in stratigraphically higher horizons are of simple dykes. This suggests the conditions which favor the formation of multiple dykes to be 1) repetition of magma intrusion, and 2) large ratios of frequency of magma intrusion/solidification time of dykes (F/S ratio).Troodos vs. Semail : All sheeted dykes examined in the Semail Ophiolite are simple. This suggests that in Semail, 1) magma did not intrude as pulse, or 2) F/S ratio was very high. In addition to this, generation of magma pulse may be controlled by the ratio of volume of recharged magma/that of magma chamber.