High‐Resolution Mantle Flow Models Reveal Importance of Plate Boundary Geometry and Slab Pull Forces on Generating Tectonic Plate Motions
High‐Resolution Mantle Flow Models Reveal Importance of Plate Boundary Geometry and Slab Pull Forces on Generating Tectonic Plate Motions
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DOI：
10.1029/2022jb025877
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发表时间：
2023-07
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通讯作者：
Arushi Saxena;J. Dannberg;Rene Gassmöller;M. Fraters;T. Heister;R. Styron
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作者：
Arushi Saxena;J. Dannberg;Rene Gassmöller;M. Fraters;T. Heister;R. Styron
基于地球物理约束的地幔对流模型使我们对地球上驱动和抵制板块运动的力量有了基本的了解。然而，现有的计算潜在力平衡的研究是相互矛盾的，并且板块边界几何形状对地表变形的影响尚不清楚。我们通过发展具有非均匀密度和粘性分布的全球瞬时三维地幔对流模型和使用不同几何形状规定的弱板块边界来解决这些问题。我们发现，全球地震模型(GEM，Pagani等人，2018年，https://doi.org/10.1177/8755293020931866)，)的板块边界几何特征是开放的板块边界，在海洋中具有离散的岩石圈深度薄弱带，在大陆内分布的地壳断层与观测数据达到最好的拟合，方向相关性为95.1%，全球点向速度残差为1.87厘米/年。一个好的拟合还需要板块边界比周围的岩石圈弱3~4个数量级，软流圈粘度在5×10~(17)~5×10~(18)PaS之间，没有软流圈和下地幔不均质性的模型平均分别保持30%和70%的板块速度。我们的结果表明，地球的板块边界并不均匀，可以用海洋中更离散的板块边界和大陆内分布的断层来更好地描述。此外，它们强调了板块边界几何形状对板块运动方向和速度的影响，并重申了最上部地幔中的板块拉力作为主要板块驱动力的重要性。
Mantle convection models based on geophysical constraints have provided us with a basic understanding of the forces driving and resisting plate motions on Earth. However, existing studies computing the balance of underlying forces are contradicting, and the impact of plate boundary geometry on surface deformation remains unknown. We address these issues by developing global instantaneous 3‐D mantle convection models with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different geometries. We find that the plate boundary geometry of the Global Earthquake Model (GEM, Pagani et al., 2018, https://doi.org/10.1177/8755293020931866), featuring open plate boundaries with discrete lithospheric‐depth weak zones in the oceans and distributed crustal faults within continents, achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point‐wise velocity residual of 1.87 cm/year. A good fit also requires plate boundaries being 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5 × 1017 and 5 × 1018 Pa s. Models without asthenospheric and lower mantle heterogeneities retain on average 30% and 70% of the plate speeds, respectively. Our results show that Earth's plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents. Furthermore, they emphasize the impact of plate boundary geometry on the direction and speed of plate motions and reaffirm the importance of slab pull in the uppermost mantle as a major plate driving force.