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)多个冰缘岩墙的形成条件(2)多个岩墙的形成条件(3)多个岩墙在弧形火山和缓慢扩展的山脊中很常见，而在快速扩张的山脊中可能很少见。多个冰缘岩墙：对Izu Oshima的Fudeshima火山、Yatsugatake火山北部的更老的火山和塞浦路斯的Troodos蛇绿岩进行的实地研究揭示了一种多重岩墙的存在，这些岩墙的倍增冰冷边缘仅在离岩墙边缘几十厘米的范围内1-20厘米厚。这种岩脉表明岩浆侵入的脉冲在短时间间隔内重复。多岩墙形成的条件：在特罗多斯蛇绿岩中，多个岩墙的存在局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是简单的岩墙。这表明，形成多重岩脉的条件是：1)岩浆侵入的重复，2)岩浆侵入频率/岩墙固化时间的大比例(F/S比值)。这表明在Smail中，1)岩浆没有以脉冲形式侵入，或2)F/S比值很高。此外，岩浆脉冲的产生还受岩浆充注体积与岩浆室体积之比的控制。

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.