What drives and resists plate sinking through the transition zone?

是什么驱动和阻止板块通过过渡区下沉？

基本信息

批准号：
NE/J008028/1
负责人：
Jeroen Van Hunen
金额：
$ 25.51万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FJ008028%2F1
关键词：
What drives resists plate sinking

项目摘要

Mantle circulation is largely driven by the sinking ('subduction') of cold and dense tectonic plates. When these cold slabs reach the transition zone between the upper and lower mantle (from 400 to 800 km depth), their progress is hampered by rapid increases in mantle density and viscosity, as mantle minerals change phase. X-ray type images of the interior of the Earth made using earthquake waves ('seismic tomography') reveal that this zone only forms a barrier for some slabs, while others seem to pass through unhindered. Furthermore, when the seismic images are compared with plate motions through time, it becomes clear that slabs penetrated the lower mantle in the past, where shallower parts of the plate are trapped in the transition zone today. This, as well as evidence of fast and slow subduction phases in plate motions (Goes et al., Nature 2008) indicate that this is a time dependent process, where plate material may pond until a critical mass of material has accumulated, and then flush rapidly into the lower mantle.It is important to understand this fundamental part of mantle circulation as it controls how efficiently the Earth cools and how well heterogeneities like sediments, crust, fluids and CO2 are mixed into it, or brought back up. Furthermore, sudden slab flushing events into the lower mantle have been linked to periods of continental crust formation, changes to the early atmosphere and reorganisations of plate motions. We will investigate slab behaviour in the transition zone using 3D dynamic models of subduction, and evaluate which of the modelled mechanisms are consistent with observational data from the Pacific. Previous numerical models have investigated how individual factors like slab strength, slab density, coupling to the upper plate, and mantle phase transitions affect whether a slab goes straight through the transition zone or stalls there. However, none of these individual parameters can explain the observed variations of plate-transition zone interaction. Nor is it clear for how long slabs may be stalled, and hence on which time scales the upper and lower mantle mix, and on which time scales plate motions and accompanying surface deformation vary. As single properties do not explain the variability of slab-transition-zone interaction, the interplay between mantle, downgoing and upper-plate properties must be crucial. Studying the interaction between these different factors requires 3D dynamic models that let plate motions and slab morphology develop freely, something that is numerically challenging. In recent years, our groups developed such dynamic models and elucidated how combinations of plate density, strength and width control upper-mantle slab morphology. The newest generation of these dynamic models, developed by the group of the PI at Durham, are now capable of modelling all potentially relevant plate and mantle parameters. With these models, we will explore a wide range of parameters to determine which combinations lead to slab ponding and penetration. Next we will compare modelled conditions for stalling and release with those that can be inferred for major subduction zones throughout the last 100-200 million years of Earth history from seismic tomography, plate motion histories and earthquakes in downgoing slab. This will be done using the expertise in model-data comparison in the group of the Co-I at Imperial, in collaboration with partners Prof. Spakman and Prof. Torsvik, leading experts in seismic imaging and plate motion reconstructions, respectively. With these new models and this interdisciplinary team, we will be able to answer the fundamental question of how the transition zone traps and releases subducting slabs, a process that plays a pivotal role in the Earth's internal and plate-tectonic evolution.

地幔循环在很大程度上是由冷和密集的构造板的下沉（“俯冲”）驱动的。当这些冷板到达上层和下地幔之间的过渡区（从400 km的深度到800 km）时，随着地幔矿物质变化相，地幔密度和粘度的迅速增加，它们的进度受到了阻碍。 X射线类型的地球内部使用地震波（“地震层析成像”）表明，该区域仅构成某些平板的障碍，而其他区域似乎不受阻碍地穿过。此外，当将地震图像与板块随着时间的流逝进行比较时，很明显，过去的平板在过去的过渡区中被困在板的较浅部分。这是板块运动中快速和缓慢俯冲阶段的证据（Goes等，自然，2008年）表明，这是一个依赖时间的过程，在该过程中，板块材料可能会池塘池塘直至占据临界材料的积累，然后迅速冲入较低的地幔。二氧化碳被混合在其中，或抬起。此外，突然的平板冲洗事件进入下地幔已与大陆地壳形成时期，早期大气变化和板块运动的重组有关。我们将使用俯冲的3D动态模型研究过渡区中的平板行为，并评估哪些建模机制与太平洋的观察数据一致。以前的数值模型已经研究了单个因素如何等于平板强度，平板密度，耦合到上板以及地幔相变，是否会影响平板是否直线穿过过渡区或摊位。但是，这些各个参数都无法解释观察到的板传输区相互作用的变化。对于可能停滞的平板的时间也不清楚，因此，时间缩放上层和下地幔混合物，并且在哪个时间上，时间缩放了板块的运动和伴随的表面变形。由于单个属性不能解释平板转换区相互作用的可变性，因此地幔，下板和上层属性之间的相互作用必须至关重要。研究这些不同因素之间的相互作用需要3D动态模型，使板运动和平板形态自由发展，这在数字上具有挑战性。近年来，我们的小组开发了这种动态模型，并阐明了板密度，强度和宽度控制上层平板形态的组合。这些动态模型的最新一代是由Durham的PI组开发的，现在能够对所有潜在的相关板和地幔参数进行建模。使用这些模型，我们将探索广泛的参数，以确定哪种组合会导致平板构造和穿透。接下来，我们将将停滞和释放的模型条件与可以推断出的俯冲区域可以推断出的，这些条件可以通过地震层析成像，地震层析成像，板块运动历史和地震中的地球历史上的主要俯冲带来进行比较。这将使用Model-DATA比较的专业知识在帝国的Co-I小组中与合作伙伴Spakman教授和Torsvik教授合作，分别是地震成像和板运动重建的主要专家。借助这些新模型和这个跨学科团队，我们将能够回答过渡区陷阱和释放俯冲板的基本问题，这一过程在地球内部和板块晶体演变的进化中起着关键作用。