Dynamics of dyke intrusion in the mid-crust of Iceland
Dynamics of dyke intrusion in the mid-crust of Iceland
复制标题
冰岛中地壳堤坝侵入动力学
DOI：
10.1016/j.epsl.2011.02.038
复制
发表时间：
2011
影响因子：
5.3
通讯作者：
S. Jakobsdóttir
中科院分区：
文献类型：
--
作者：
R. White;Julian Drew;H. Martens;Janet Key;H. Soosalu;S. Jakobsdóttir
我们已经捕获到一个显着的序列的微震显示渐进的熔融侵入岩墙向上移动的岩床在18公里深的中地壳的冰岛北方火山裂谷带。三分之二的地壳是在海洋中的裂缝中形成的。三分之二的地壳是由侵入和冻结形成的，然后由下面的地幔中产生的熔融岩石喷发而成。在这里，我们显示了地震活动伴随着熔体侵入从17.5至13.5公里的深度沿着在冰岛裂谷带的中地壳倾斜50°的堤坝。虽然在这些深度的地壳通常是平静的，高应变率熔融侵入产生高达2.2级的微震。力矩张量的解决方案显示占主导地位的双力偶故障，与故障机制，有时翻转之间的正常和反向断层在几分钟内在同一位置，但打破沿着断层面具有相同的方向。我们提出了翻转断层机制的几种可能原因：随着更多熔融物侵入，岩脉内的凝固玄武岩塞破裂;沿着亚平行裂缝或岩脉指状体沿着侵入传播岩脉尖端附近产生的局部应力场;或相邻梯队岩脉之间的小凹凸或偏移运动。虽然断层最终是由熔体运动引起的，但在矩张量解中没有可分辨的体积分量。从微地震推断的断层面与震源所描绘的堤坝的整体平面精确对齐。熔体注射以2- 3米/分钟的速度沿通道c沿着传播的脉冲串形式发生。0.2米厚，产生了持续数小时的微震群。中间的静止期持续数十至数百小时。
We have captured a remarkable sequence of microearthquakes showing progressive melt intrusion of a dyke moving upward from a sill at 18km depth in the mid-crust of the northern volcanic rift zone in Iceland. Two-thirds of the earth's crust is created at mid-ocean rifts. Two-thirds of that crust is formed by intrusion and freezing before it erupts of molten rock generated within the underlying mantle. Here we show seismicity accompanying melt intrusion from 17.5 to 13.5km depth along a dyke dipping at 50° in the mid-crust of the Icelandic rift zone. Although the crust at these depths is normally aseismic, high strain rates as melt intrudes generate microearthquakes up to magnitude 2.2. Moment tensor solutions show dominantly double-couple failure, with fault mechanisms sometimes flipping between normal and reverse faulting within minutes in the same location, but breaking along fault planes with the same orientations. We suggest several possible reasons for the flipping fault mechanisms: the breakage of solidified plugs of basalt within the dyke itself as more melt intrudes; intrusion along sub-parallel fractures or dykelet fingers into the local stress field created near the tip of a propagating dyke; or movement on small jogs or offsets between adjacent en echelon dykes. Although the faulting is caused ultimately by melt movement, there is no resolvable volumetric component in the moment tensor solutions. The inferred fault planes from microearthquakes align precisely with the overall plane of the dyke delineated by hypocentres. Melt injection occurs in bursts propagating at 2–3m/min along channels c. 0.2m thick, producing swarms of microearthquakes lasting several hours. Intervening quiescent periods last tens to hundreds of hours.