Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland
Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland
复制标题
侵入性片群和冰岛地壳第三层的身份
DOI：
10.1144/gsjgs.131.2.0143
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发表时间：
1975
影响因子：
2.7
通讯作者：
G. Walker
中科院分区：
文献类型：
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作者：
G. Walker
在冰岛东南部被深度切割的部分发现的倾斜的基性侵入岩席群被认为是一个广泛分布的层的一部分，在该国的其他地区，该层出现在海平面以下，作为地震折射研究揭示的6.35 km s−1地壳层。根据地壳和上升岩浆的密度梯度差异，提出了席状岩群形成的一个简单机制：当基性岩浆的密度处处小于其切割岩石的体积密度时，它上升到地表，否则它往往被侧向转向，形成一个侵入席状岩群，其密度与围岩的密度相等。一旦开始，地壳中的密度关系是这样的，群是强烈的自我永存的性质。据信，冰岛一半以上的岩浆已经转移到形成席状群。一个推论是，冰岛的地壳“过滤”了进入其中的岩浆，只有较轻的或以高体积速率上升的岩浆才能成功地通过地表。当岩浆批次上升频率较高时，可发育合流式席状辉长岩侵入体。在中央火山也会出现片状的火山群或栖息的火山群，其中低密度的酸性火山岩“捕获”了上升的岩浆。
The remarkable swarm of inclined basic intrusive sheets found in the deeply dissected part of SE Iceland is believed to constitute part of a widespread layer which, in other parts of the country, occurs below sea level as the 6.35 km s−1 crustal layer revealed by seismic refraction studies. A simple mechanism for the generation of the sheet swarm is proposed, based on the contrasted density gradients of crust and uprising magma: basic magma rises to the surface when its density is everywhere less than the bulk density of the rocks it cuts, otherwise it is often diverted laterally to form an intrusive sheet where its density equals that of the country rock. Once initiated, density relations in the crust are such that the swarm is strongly self-perpetuating in nature. It is believed that more than half of the uprising magma in Iceland has been so diverted to form the sheet swarm. One corollary is that the crust in Iceland “filters” the magmas entering it so that only the lighter or those which rise at a high volumetric rate succeed in passing through to the surface. Confluent sheet gabbro intrusions may develop when the frequency of uprise of magma batches is high. Sheet swarm cupolas or perched swarms also occur in central volcanoes, in which the low-density acid volcanic rocks “capture” uprising magmas.