Generation of Archean Granitoids and the Onset of Plate Tectonics.

大陆地壳的形成对地球的宜居性产生了一级影响，它与生命的出现直接相关，并使生命得以迁移到陆地上。与海洋相比，大陆的海拔较高，因为大陆地壳岩石的成分是花岗质，与地幔岩石相比密度相对较低。人们普遍认为，这些岩石一定是在玄武岩和含水阶段存在的多步骤过程中由地幔熔融形成的。在今天的地球上，这种情况发生在俯冲带。然而，在太古代地球，地幔温度更高，地幔中产生了更多的熔体，海洋地壳明显更厚。模型表明，如果地幔电位温度比现在的温度高150-250K，那么俯冲作用就不可能发生。相反，部分地壳可能已经滴入地幔，这一过程被称为凹陷。因此，板块构造是否在太古宙起作用的问题取决于两个关键点：1)太古宙上地幔的温度如此之高，以至于海洋板块无法俯冲；2)太古宙花岗岩的形成过程与俯冲作用无关。花岗岩是如何形成的还不完全清楚，特别是对于一个更温暖的地球。在这个建议中，我们将使用岩石学约束来建立一个厚洋壳模型；一种是与下部超镁铁质堆积和上部限制的水合玄武岩强烈分化的。我们还将重新评估确定太古代环境地幔温度的岩石学约束和冷却模型。然后，我们将使用2D和3D数值模型模拟该地壳内的脱水、熔融和变形，并将结果与现有的岩石学/地球化学约束条件进行比较。通过在热力学数值模型中加入最近开发的热力学熔融模型和熔体的化学演化，我们可以使用模型预测来测试俯冲或俯冲是否是一个更有效的形成花岗岩的过程。此外，我们将推导参数化，描述俯冲和俯冲对地球冷却的影响，并将其包括在参数化冷却模型中。这将为这些过程如何影响地球的热演化、如何影响地壳生长以及我们星球上板块构造开始的时间提供新的见解。

The formation of the continental crust had a first order impact on the habitability of the Earth, being directly linked to the emergence of life and later allowing life to migrate onto land. Continents have a high elevation compared to oceans, because continental crustal rocks are granitic in composition and have a relatively low density compared to mantle rocks. It is generally accepted that these rocks must have formed by melting the mantle in a multi-step process that requires basalt and hydrous phases to be present. On the present-day Earth this occurs in subduction zones. Yet, in the Archean Earth, mantle temperatures were higher, more melt was produced in the mantle, and oceanic crust was significantly thicker. Models suggest that if mantle potential temperatures were 150-250K higher than present-day values, subduction could not have operated. Instead, parts of the crust may have dripped down into the mantle, a process known as sagduction. The question of whether plate tectonics operated in the Archean therefore depends on two key points: 1) that temperatures in the Archean upper mantle were so high that oceanic plates were unsubductable; 2) that Archean granitoids were produced by a process independent of subduction. How granites formed is incompletely understood, particularly for a warmer Earth. In this proposal, we will use petrological constraints to build a model of thick oceanic crust; one that is strongly differentiated with ultramafic cumulates in the lower half and hydrated basalt restricted to upper layers. We will also re-evaluate petrological constraints and cooling models that define temperatures in Archean ambient mantle. Then we will use 2D and 3D numerical models to simulate dehydration, melting and deformation within this crust and compare the results with available petrological/ geochemical constraints. By including recently developed thermodynamic melting models and the chemical evolution of melts in the thermomechanical numerical models, we can use model predictions to test whether sagduction or subduction is a more efficient process to create granites. In addition, we will derive parameterizations that describe the effect of both subduction and sagduction on the cooling of the Earth and include these in parameterized cooling models. This will give new insights in how such processes affect the thermal evolution of the Earth, how this affected crustal growth and on the timing of the onset of plate tectonics on our planet.