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

在地球深处，地幔的热岩石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所阻挡，这基本上导致了地球上所有的火山活动，尤其是位于地幔异常热点之上的岛屿上的火山活动。本研究解决了地球动力学中的两个主要问题：岩石圈基底的起源和地幔热点处的地幔对流性质。冰岛是一个巨大的火山岛，它是由一个热点形成的，热地幔在那里上升，撞击岩石圈板块。从遥远的地震传到冰岛记录下来的地震波以前所未有的细节揭示了冰岛地下地幔的结构。由于温度过高和岩浆的存在，这种波穿过地幔的速度会减慢，在对流优先排列地幔矿物的地区，这种波的传播方向不同。一方面，冰岛的记录表明，冰岛地下有一层厚（150公里）和宽（600公里）的部分熔融的热地幔，这表明热地幔上涌在很深的地方被由成分分层形成的岩石圈基底偏转。另一方面，地震波速度的明显方向依赖性揭示了矛盾的证据，这表明上涌的地幔在更浅的深度被由温度分层形成的岩石圈基底偏转。本研究旨在解决这一矛盾，利用数值模型对冰岛地下地幔对流、岩浆生成和晶体排列进行三维模拟。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测到的记录进行定量比较。对许多这样的计算进行不同地幔性质的测试，将用于确定冰岛地下最不可能和最可能的条件。确定冰岛地下岩石圈和地幔对流最浅深度的成因，将推进我们对这个系统的基本理解，以及对地球上其他环境和其他有活跃对流和岩浆活动的行星的基本理解。

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.