论文标题
对流及其对大陆岩石圈的影响
Heat-blanketed convection and its implications for the continental lithosphere
论文作者
论文摘要
地球大陆的特征是在长寿命的放射性同位素中强烈富集。最近的估计表明，它们在地面表面释放的热量的33％，同时占据了地幔的1 \％。这种独特的特征通过影响其热结构和传热对基础地幔具有深远的影响。然而，尚未系统地研究富含产生热量元素的大陆地壳对基础披风的影响。在这里，我们通过考虑由混合加热流体组成的简化对流系统进行初步研究，其中所有内部加热都集中在厚度的顶层$ d_ {hl} $（称为“热式对流”）。我们在3D笛卡尔几何形状中对四个特定的设置和$ d_ {hl} $的各种值执行24个数值模拟。我们的结果表明，加热层的影响很大程度上取决于其厚度相对于均质加热情况中热边界层（$δ_{tbl} $）的厚度（$ d_ {hl} = 1.0 $）。更具体地说，对于$ d_ {hl}>δ_{tbl} $，由加热层引起的效果非常适度，而对于$ d_ {hl}<δ_{tbl} $，对流系统的属性被强烈改变为$ d_ {hl} $降低。特别是，与$ d_ {hl} = 1.0 $相比，非常薄的加热层的表面热通量和对流活力显着增强。因此，产生热量的垂直分布可能在地幔动力学上起关键作用。然而，对于地球，大陆的存在不应显着影响表面热通量，因此不应显着影响地球的冷却速率。
Earth's continents are characterized by a strong enrichment in long-lived radioactive isotopes. Recent estimates suggest that they contribute to 33\% of the heat released at the surface of the Earth, while occupying less than 1\% of the mantle. This distinctive feature has profound implications for the underlying mantle by impacting its thermal structure and heat transfer. However, the effects of a continental crust enriched in heat-producing elements on the underlying mantle have not yet been systematically investigated. Here, we conduct a preliminary investigation by considering a simplified convective system consisting in a mixed heated fluid where all the internal heating is concentrated in a top layer of thickness $d_{HL}$ (referred to as "heat-blanketed convection"). We perform 24 numerical simulations in 3D Cartesian geometry for four specific set-ups and various values of $d_{HL}$. Our results suggest that the effects of the heated layer strongly depend on its thickness relative to the thickness of the thermal boundary layer ($δ_{TBL}$) in the homogeneous heating case ($d_{HL} = 1.0$). More specifically, for $d_{HL} > δ_{TBL}$, the effects induced by the heated layer are quite modest, while, for $d_{HL} < δ_{TBL}$, the properties of the convective system are strongly altered as $d_{HL}$ decreases. In particular, the surface heat flux and convective vigour are significantly enhanced for very thin heated layers compared to the case $d_{HL} = 1.0$. The vertical distribution of heat producing elements may therefore play a key role on mantle dynamics. For Earth, the presence of continents should however not affect significantly the surface heat flux, and thus the Earth's cooling rate.
