Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA.
GEOTOP, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada.; Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA.
Sci Adv. 2016 Dec 23;2(12):e1601107. doi: 10.1126/sciadv.1601107. eCollection 2016 Dec.
Earth's tectonic plates are generally considered to be driven largely by negative buoyancy associated with subduction of oceanic lithosphere. In this context, mid-ocean ridges (MORs) are passive plate boundaries whose divergence accommodates flow driven by subduction of oceanic slabs at trenches. We show that over the past 80 million years (My), the East Pacific Rise (EPR), Earth's dominant MOR, has been characterized by limited ridge-perpendicular migration and persistent, asymmetric ridge accretion that are anomalous relative to other MORs. We reconstruct the subduction-related buoyancy fluxes of plates on either side of the EPR. The general expectation is that greater slab pull should correlate with faster plate motion and faster spreading at the EPR. Moreover, asymmetry in slab pull on either side of the EPR should correlate with either ridge migration or enhanced plate velocity in the direction of greater slab pull. Based on our analysis, none of the expected correlations are evident. This implies that other forces significantly contribute to EPR behavior. We explain these observations using mantle flow calculations based on globally integrated buoyancy distributions that require core-mantle boundary heat flux of up to 20 TW. The time-dependent mantle flow predictions yield a long-lived deep-seated upwelling that has its highest radial velocity under the EPR and is inferred to control its observed kinematics. The mantle-wide upwelling beneath the EPR drives horizontal components of asthenospheric flows beneath the plates that are similarly asymmetric but faster than the overlying surface plates, thereby contributing to plate motions through viscous tractions in the Pacific region.
地球的构造板块通常被认为主要是由大洋岩石圈俯冲引起的负浮力驱动的。在这种情况下，大洋中脊（MOR）是被动板块边界，其离散可以容纳俯冲海洋板块在海沟处的流动。我们表明，在过去的 8000 万年中，地球主要的大洋中脊（EPR）的特征是有限的脊垂直迁移和持续的、不对称的脊增生，这与其他 MOR 相比是异常的。我们重建了 EPR 两侧板块与俯冲相关的浮力通量。一般来说，更大的板块拉力应该与更快的板块运动和 EPR 更快的扩张相关。此外，EPR 两侧的板块拉力不对称应该与板块迁移或在更大的板块拉力方向上增强的板块速度相关。根据我们的分析，没有一个预期的相关性是明显的。这意味着其他力量对 EPR 的行为有显著贡献。我们使用基于全球积分浮力分布的地幔流动计算来解释这些观察结果，这需要地核-地幔边界热通量高达 20 TW。时变地幔流动预测产生了一个长期存在的深部上升流，其在 EPR 下具有最高的径向速度，并被推断为控制其观测运动学。EPR 下的全球上地幔上升流驱动了板块下的软流圈流动的水平分量，这些流动同样不对称，但比上覆的表面板块更快，从而通过太平洋地区的粘性牵引力对板块运动做出贡献。
