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。地幔对流被覆盖的岩石圈板块阻挡，导致地球上几乎所有的火山活动，特别是覆盖在地幔异常热点上的岛屿上的火山活动。这项研究解决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热区的地幔对流性质。冰岛是一个巨大的火山岛，它是由一个热点形成的，在这个热点下，热地幔在下面上升，并冲击着岩石圈板块。冰岛记录的远距离地震产生的地震波，以前所未有的细节揭示了冰岛地幔的结构。这种波穿过地幔的速度因过高的温度和岩浆的存在而变慢，在对流优先排列地幔矿物的地区，不同的传播方向是不同的。一方面，有关冰岛的记录表明，冰岛下面有厚(150公里)和宽(600公里)的高温地幔和部分熔融的地幔，这表明由成分分层形成的岩石圈基底在很深的地方偏转了热地幔上涌。另一方面，地震波速的明显方向依赖性揭示了相互矛盾的证据，这表明上升地幔在更浅的深度被温度分层形成的岩石圈底部偏转。这项研究旨在解决这一矛盾，通过使用数值模型来模拟冰岛下面的地幔对流、岩浆生成和晶体排列。然后，研究人员将计算地震波在模型地幔结构中的传播，并将预测的地震记录与观测记录进行定量比较。对许多具有不同地幔性质的此类计算进行测试，将被用来确定冰岛地下最不可能和最可能的条件。确定冰岛之下岩石圈和地幔对流最浅深度的原因，将有助于我们对这一系统以及地球和其他具有活跃对流和岩浆活动的行星上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.