Onset of Plate Tectonics and Thermochemical Evolution of the Early Earth

板块构造代表了下伏地幔对流系统的表面表现，关于我们的太阳系是地球独有的，但它的开始仍然是一个悬而未决的问题。例如，据推测，板块运动是在太古代开始的，可能是由于大陆边缘的俯冲过程，通过地壳拆沉或由于致密的基底层。因此，太古代板块(大陆)和致密物质的相互作用，以及后来的相互作用，是令人感兴趣的。今天的地震学观测到的核幔边界的大的低剪切速度区(LLSVP)也被认为是由致密的基底层形成的热化学储集层(桩)，可能起源于基岩浆海洋。然而，化学密度高的物质的存在不仅仅是一种被动的特征。致密的物质与热对流重新耦合，起到恢复力的作用。因此，它对对流流动本身有着深刻的影响。上升流的浮力较小，可能无法分解板块，这可能会导致板块构造的起步较晚。这一建议的目的是研究板块启动和成桩的机制，并对致密储层的板块运动和形成的开始时间以及这些储层的存活时间进行约束。因此，计划用具有板块特征的热化学地幔对流数值模式进行广泛的参数研究。特别要研究流变学参数和初始条件对早期板幔耦合系统的影响。

Plate tectonics represents the surface expression of the underlying mantle convection system and with regard to our solar system is unique to the Earth but its onset still remains an open question. For example, it is speculated that plate motion initiated during the Archaean, maybe due to subduction processes at the edges of continents, by crustal delamination or due to a dense basal layer. Therefore, the interaction of plates (continents) and dense material in the Archaean, and also later, is of interest. Today’s seismologically observed large low shear velocity provinces (LLSVPs) at the core-mantle boundary are also regarded as thermochemical reservoirs (piles) formed from a dense basal layer that possible originates from a basal magma ocean. The presence of chemically dense material is, however, not just a passive feature. The dense material rather recouples with the thermal convection and acts as restoring force. Therefore it has profound impact on the convective flow itself. Upwellings have less buoyancy and might not be able to break up the plates which could lead to a late onset of plate tectonics. The aim of this proposal is to study the mechanisms of plate initiation and pile formation and to give constraints on the onset time of plate motion and formation of dense reservoirs as well as the survival time of these reservoirs. Therefore an extensive parameter study with numerical thermochemical mantle convection models featuring plates is planned. In particular, the effect of rheological parameters and initial conditions on the early coupled plate-mantle system shall be investigated.