Collaborative Research: Geodynamic Solutions for Seismic Observations of Iceland Hotspot-Ridge Interaction

在地球深处，地幔的热岩像对流流体一样伸展和变形。 地幔对流被覆盖在上面的岩石圈板块阻挡，并导致了地球上基本上所有的火山活动，特别是覆盖在地幔中异常热点上的岛屿上的火山活动。 本文主要讨论了地球动力学中的两个主要问题：岩石圈底部的起源和地幔对流的性质。热点？ 冰岛是一个巨大的火山岛，是由一个热点形成的，热地幔在下面上升，并撞击岩石圈板块。 冰岛地幔的结构被记录下来的地震波以前所未有的细节揭示出来，这些地震波来自遥远的地震。 这种波穿过地幔的速度因温度过高和岩浆的存在而减慢，并且在对流优先排列地幔矿物的区域中，不同的行进方向是不同的。 一方面，冰岛的记录表明，在冰岛之下有一个厚（150公里）和宽（600公里）的部分熔融的热地幔层，这表明热地幔上涌在很深的地方被岩石圈基底偏转，岩石圈基底是由成分分层形成的。 另一方面，矛盾的证据是揭示了一个明确的方向依赖性的地震波的速度，这表明，上涌地幔被偏转在更浅的深度由岩石圈的基础上形成的温度分层。 本研究的目的是解决这个矛盾，通过使用数值模型来模拟，在3D，地幔对流，岩浆生成，和冰岛下面的结晶排列。 然后，研究人员将计算地震波通过模型地幔结构的传播，并将预测的地震记录与观察到的记录进行定量比较。 许多这样的计算与不同的地幔属性的测试将被用来确定最不可能和最可能的条件下冰岛。确定岩石圈的成因和冰岛下方地幔对流的最浅深度将促进我们对这个系统以及地球和其他行星上具有活跃对流和岩浆活动的其他环境的基本理解。

Deep in the Earth, the hot rock of the mantle stretches and deforms like a convecting fluid. Mantle convection is blocked by the overriding lithospheric plates and causes essentially all volcanism on Earth, in particular, the volcanism on islands that overlie unusually hot spots in the mantle. This study addresses two major problems in geodynamics: the origin of the base of the lithosphere and the nature of mantle convection at mantle ?hotspots?. Iceland is a huge volcanic island that is formed by a hotspot where hot mantle is rising beneath, and impinging on the lithospheric plates. The structure of the mantle beneath Iceland is revealed in unprecedented detail by seismic waves that traveled from distant earthquakes to be recorded on Iceland. The speed that such waves traverse the mantle is slowed by excess temperature and the presence of magma, and is different for different travel directions in regions where convection preferentially aligns the minerals of the mantle. On the one hand, the records on Iceland show evidence for a thick (150 km) and broad (600 km) layer of hot and partially molten mantle beneath Iceland, which suggests that the hot mantle upwelling is being deflected at great depths by a lithospheric base formed by a stratification in composition. On the other hand, contradictory evidence is revealed by a clear directional dependence of seismic wave speeds, which suggest that the upwelling mantle is being deflected at much shallower depths by a lithospheric base formed by a stratification in temperature. This study aims to resolve this contradiction by using numerical models to simulate, in 3D, the mantle convection, magma generation, and crystallographic alignment beneath Iceland. The investigators will then compute seismic wave propagation through the model mantle structure and quantitatively compare the predicted seismic records with the observed records. Tests of many of such calculations with different mantle properties will be used to identify the least and most likely conditions beneath Iceland. Determining the cause of the lithosphere and the shallowest depths of mantle convection beneath Iceland will advance our basic understanding of this system as well as other settings on Earth and other planets with active convection and magmatism.