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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >The interaction of fissure swarms and monogenetic lava shields in the rift zones of Iceland
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The interaction of fissure swarms and monogenetic lava shields in the rift zones of Iceland

机译：冰岛裂谷带的裂隙群与单相熔岩盾构的相互作用

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摘要

The divergent plate boundaries of Iceland are marked by rift zones that consist of fissure swarms, i.e. areas with a high density of fractures, faults and eruptive fissures, generally considered to be the surface expressions of dikes. Monogenetic lava shields are common within the rift zones. They are gently sloping, circular cones created by eruptions from a single vent. Many of the shields were emplaced in the early Holocene in response to increased mantle melting when the Pleistocene glacier load on the crust was reduced. In our studies of Icelandic fissure swarms we have established that in most cases where a fissure swarm transects a lava shield there is an inverse correlation between surface elevation and the density of fractures. The summit area of a shield is generally less fractured than the flanks. Fracture densities are also highest on one site of the lava shield, but much lower and even approaching zero values on the other side. This phenomenon is most clearly seen within early-Holocene lava shields (i.e. between similar to 4500 and similar to 13,600 years BP of age). Lava shields younger than 4500 years BP of age have low fracture densities or are not fractured at all. The lower fracture densities within Holocene lava shields suggest that dike intrusions stop or remain deeper in the crust when they approach a lava shield. Various mechanisms may explain this. The topographic load of the lava shield adds to the lithostatic stress, thus increasing the strength, and may affect the depth of a propagating dike. A long-lived eruption of a lava shield may also affect the stress field in the surrounding crust, increase the horizontal compressive stress and thus create a stress barrier for propagating dikes for some time period following the eruption. (C) 2015 Elsevier B.V. All rights reserved.
机译：冰岛发散的板块边界以裂隙带为标志，该裂隙带由裂隙群组成，即具有高密度的裂缝，断层和喷发性裂隙的区域，通常被认为是堤防的表面表现。在裂谷带中，单相熔岩盾牌很常见。它们是由单个喷口喷发而形成的缓缓倾斜的圆锥形。当地壳上的更新世冰川负荷减少时，由于地幔融化的增加，许多盾构都放置在全新世早期。在我们对冰岛裂隙群的研究中，我们发现，在大多数情况下，裂隙群横穿熔岩盾构的情况下，地表高度与裂缝密度之间存在反比关系。盾构的顶端区域通常不如侧面破裂。熔岩护层的一个部位的裂缝密度也最高，而另一侧的裂缝密度低得多，甚至接近零值。在全新世早期的熔岩盾构中（即大约BP年龄为4500至13600年之间），这一现象最为明显。年龄小于4500岁BP的熔岩护盾的骨折密度低或根本没有破裂。全新世熔岩护层内部较低的裂缝密度表明，当接近熔岩护层时，堤坝侵入停止或保持在地壳深处。各种机制可以解释这一点。熔岩护层的地形载荷会增加岩石静应力，从而增加强度，并可能影响传播的堤坝的深度。熔岩保护层的长期喷发还可能影响周围地壳的应力场，增加水平压应力，从而在喷发后的一段时间内为传播堤防创建应力屏障。 （C）2015 Elsevier B.V.保留所有权利。

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