Global trench migration velocities and slab migration induced upper mantle volume fluxes: Constraints to find an Earth reference frame based on minimizing viscous dissipation
Global trench migration velocities and slab migration induced upper mantle volume fluxes: Constraints to find an Earth reference frame based on minimizing viscous dissipation
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DOI：
10.1016/j.earscirev.2008.01.005
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发表时间：
2008-05
影响因子：
12.1
通讯作者：
W. Schellart;D. Stegman;J. Freeman
中科院分区：
文献类型：
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作者：
W. Schellart;D. Stegman;J. Freeman
自从板块构造学出现以来，不同的全局参考系已被用来描述板块和海沟的运动。不同参考系之间的板块运动和沟渠迁移差异可能很大（高达 4 厘米/年）。这项研究概述了地球上所有成熟和初期俯冲带的海沟迁移速度，这些速度是在八个不同的全球参考系中计算的。计算表明，无论参考系如何：（1）战壕后退始终主导战壕前进，244 个战壕段中有 62-78% 后退； (2) 平均和中值海沟速度始终为正（后退），并且分别在 1.3–1.5 厘米/年和 0.9–1.3 厘米/年范围内； (3) 仅在靠近侧板边缘（<1500 km）处观察到沟槽快速后退； (4) 远离板块边缘（>2000 公里）的沟渠后退总是缓慢的。这些计算是通过具有不同板片宽度的地球动力学模型进行预测的，其中板块运动、海沟运动和地幔流是由致密板片俯冲引起的，这表明海沟运动确实主要由板片浮力驱动，并且靠近横向板片边缘对海沟迁移速度具有主要控制作用。尽管有这四个一般性结论，这些参考系之间的速度仍然存在显着差异。因此，重要的是确定哪个参考系最有可能描述真实的绝对速度，以了解驱动板块构造和地幔对流的力。这里提出，基于流体动力学考虑和地球动力学模型的预测，最佳候选方案是优化后退海沟段的数量，最小化宽（> 4000 km）俯冲带中心的海沟-垂直海沟迁移速度（vT⊥），最大化位于最近侧板片边缘2000 km内的后退海沟段数量，最小化海沟-垂直海沟迁移的绝对平均值。地球上所有俯冲带的速度（|vT⊥|），并最大限度地减少由海沟迁移和相关的横向板片迁移（即板片后滚或板片前滚）引起的全球上地幔环形体积通量（phiTo）。计算表明，这些条件在一个特定的印度-大西洋热点参考系中得到了最好的满足，其中 75% 的俯冲带后退，宽俯冲带中心的 vT⊥ 范围在 -3.5 至 1.8 厘米/年之间，83% 的海沟段位于最近的横向板片边缘后退的 2000 公里范围内，|vT⊥| 的平均值为 2.1 cm/yr， phiTo=456 km3/yr（下限）和 539 km3/yr（上限）。包含地球上所有初期俯冲带会导致通量略高，分别为 465 平方公里/年（下限）和 569 平方公里/年（上限）。研究还发现，该参考系接近于最小化与位于主要克拉通下方的大陆龙骨运动相关的岩石圈下上地幔总体积通量（ΦK）。然而，需要强调的是， ΦK 比 ΦTo 小一个数量级，因此重要性较低。总之，印度-大西洋热点参考系似乎更适合计算板块速度和板块边界速度。
Since the advent of plate tectonics different global reference frames have been used to describe the motion of plates and trenches. The difference in plate motion and trench migration between different reference frames can be substantial (up to 4 cm/yr). This study presents an overview of trench migration velocities for all the mature and incipient subduction zones on Earth as calculated in eight different global reference frames. Calculations show that, irrespective of the reference frame: (1) trench retreat always dominates over trench advance, with 62–78% of the 244 trench segments retreating; (2) the mean and median trench velocity are always positive (retreating) and within the range 1.3–1.5 cm/yr and 0.9–1.3 cm/yr, respectively; (3) rapid trench retreat is only observed close to lateral slab edges (<1500 km); and (4) trench retreat is always slow far from slab edges (>2000 km). These calculations are predicted by geodynamic models with a varying slab width, in which plate motion, trench motion and mantle flow result from subduction of dense slabs, suggesting that trench motion is indeed primarily driven by slab buoyancy forces and that proximity to a lateral slab edge exerts a dominant control on the trench migration velocity. Despite these four general conclusions, significant differences in velocities between such reference frames remain. It is therefore important to determine which reference frame most likely describes the true absolute velocities to get an understanding of the forces driving plate tectonics and mantle convection. It is here proposed that, based on fluid dynamic considerations and predictions from geodynamic modelling, the best candidate is the one, which optimises the number of trench segments that retreat, minimizes the trench–perpendicular trench migration velocity (vT⊥) in the centre of wide (>4000 km) subduction zones, maximizes the number of retreating trench segments located within 2000 km of the closest lateral slab edge, minimizes the average of the absolute of the trench–perpendicular trench migration velocity (|vT⊥|) for all subduction zones on Earth, and minimizes the global upper mantle toroidal volume flux (ϕTo) that results from trench migration and associated lateral slab migration (i.e. slab rollback or slab roll-forward). Calculations show that these conditions are best met in one particular Indo-Atlantic hotspot reference frame, where 75% of the subduction zones retreat, vT⊥in the centre of wide subduction zones ranges between −3.5 and 1.8 cm/yr, 83% of the trench segments located within 2000 km of the closest lateral slab edge retreat, the average of |vT⊥| is 2.1 cm/yr, and ϕTo=456 km3/yr (lower limit) and 539 km3/yr (upper limit). Inclusion of all the incipient subduction zones on Earth results in slightly greater fluxes of 465 km3/yr (lower limit) and 569 km3/yr (upper limit). It is also found that this reference frame is close to minimizing the total sub-lithospheric upper mantle volume flux (ϕK) associated with motion of continental keels located below the major cratons. It is stressed, however, that ϕKis an order of magnitude smaller than ϕTo, and thus of subordinate importance. In conclusion, the Indo-Atlantic hotspot reference frame appears preferable for calculating plate velocities and plate boundary velocities.