Abstract. The nature of compositional heterogeneity in Earth’s lower mantle remains a long-standing puzzle that can inform about the long-term thermochemical evolution and dynamics of our planet. Here, we use global-scale 2D models of thermochemical mantle convection to investigate the coupled evolution and mixing of (intrinsically-dense) recycled and (intrinsically-strong) primordial heterogeneity in the mantle. We explore the effects of ancient compositional layering of the mantle, as motivated by magma-ocean solidification studies, and of the physical parameters of primordial material. Depending on these physical parameters, our models predict various regimes of mantle evolution and heterogeneity preservation over 4.5 Gyrs. Over a wide parameter range, primordial and recycled heterogeneity are predicted to coexist with each other in the lower mantle of Earth-like planets. Primordial material usually survives as mid-to-large scale blobs (or streaks) in the mid-mantle, around 1000–2000 km depth. This preservation is largely independent on the initial primordial-material volume. In turn, recycled oceanic crust (ROC) persists as large piles at the base of the mantle and as small streaks everywhere else. In models with a dense FeO-rich layer that is initially present at the base of the mantle, the FeO-rich material partially survives at the top of ROC piles, causing the piles to be compositionally stratified. Moreover, the addition of an ancient FeO-rich basal layer in the lowermost mantle significantly aids the preservation of the viscous domains in the mid-mantle. Primordial blobs are commonly (but not always) directly underlain by thick ROC piles, and aid their longevity and stability. The preservation of primordial domains along with recycled piles is relevant for Earth as it may reconcile geophysical and geochemical constraints on lower mantle heterogeneity.

中文翻译：

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地球下地幔原始和再生异质性的耦合动力学和演化

摘要。地球下地幔的组成非均质性仍然是一个长期存在的难题，它可以告知我们地球的长期热化学演化和动力学。在这里，我们使用热化学幔对流的全球二维模型研究地幔中（本征密）循环和（本征强）原始异质性的耦合演化和混合。我们探讨了由岩浆-海洋凝固研究激发的地幔古代成分分层的影响，以及原始物质的物理参数的影响。根据这些物理参数，我们的模型预测了4.5 Gyrs以上的地幔演化和异质性保存的各种机制。在较宽的参数范围内，原始和循环异质性预计将在类地球行星的下地幔中共存。原始物质通常以大约1000-2000 km深度的地幔中部的中大型斑点（或条纹）幸存。这种保存在很大程度上与原始原始材料的体积无关。反过来，可回收的海洋地壳（ROC）则在地幔底部以大堆的形式存在，而在其他地方则以小条状形式存在。在最初存在于地幔底部的致密富FeO层的模型中，富FeO的材料部分保留在ROC桩的顶部，导致桩在成分上分层。此外，在最下部的地幔中添加古老的富FeO基底层，可显着帮助保留地幔中部的粘性区域。原始团块通常（但并非总是）直接被厚厚的ROC桩置于基底之下，并有助于它们的寿命和稳定性。原始区域的保存以及回收桩对地球来说是重要的，因为它可以调和对较低地幔非均质性的地球物理和地球化学约束。