On the Evolution and Fate of Sediment Diapirs in Subduction Zones
On the Evolution and Fate of Sediment Diapirs in Subduction Zones
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DOI：
10.1029/2021gc009873
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发表时间：
2021-10
期刊：
影响因子：
3.7
通讯作者：
B. Klein;M. Behn
中科院分区：
文献类型：
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作者：
B. Klein;M. Behn
在俯冲带，大量的沉积物和其他地壳物质被带到下行板块的顶部，穿过海沟进入地幔。这代表了地球表面的物质循环到内部的主要过程。然而，这些回收材料的命运尚不确定。俯冲下来的物质可能随板块一起进入深部地幔，也可能形成底辟，上升到地幔楔体较热的部分，在那里它们可以熔化和/或重新分层到弧形地壳的底部。虽然这种物质可以是沉积物、洋壳和地幔岩石的混合物(或“混杂”)，但这里我们关注的是下行板上最上层沉积物的动力学。我们修改了热力学模型，以准确预测与俯冲带相关的压力和温度条件下一系列俯冲沉积物成分的平衡矿物组合、熔融行为和密度。利用这个热力学模型，我们建立了沉积底辟的耦合动力学模型，并确定了控制底辟行为的主要参数：沉积物厚度和成分，以及俯冲带的热状态。更大的沉积物厚度、更多的长英质成分和更温暖的热条件有利于上升底辟的重新分层。相比之下，底辟作用在较冷的弧区或俯冲沉积层较薄或更镁铁质的地区受到抑制。将这一模型应用于现代俯冲带表明，今天有多个过程活跃，重新分层作用发生在现代弧的一个重要子集上。
At subduction zones, significant volumes of sediments and other crustal material are carried on top of the downgoing plate past the trench and into the mantle. This represents the dominant process by which material from the Earth's surface is recycled to the interior. However, the fate of these recycled materials is uncertain. Subducted material may be carried with the slab into the deep mantle, or it may form diapirs that ascend into the hotter portions of the mantle wedge, where they can melt and/or be relaminated to the base of the arc crust. While this material can be a mixture (or “mélange”) of sediments, oceanic crust and mantle rocks, here we focus on the dynamics of the uppermost layer of sediments on the downgoing slab. We modified a thermodynamic model to accurately predict the equilibrium mineral assemblage, melting behavior, and density of a range of subducted sediment compositions at pressure and temperature conditions relevant to subduction zones. Using this thermodynamic model, we constructed a coupled dynamic model of sediment diapirs and identified the primary parameters that control diapir behavior: sediment thickness and composition, and the thermal state of the subduction zone. Relamination of ascending diapirs is favored by greater sediment thicknesses, more felsic compositions, and warmer thermal conditions. By contrast, diapirism is suppressed in colder arcs, or where subducted sediment layers are thin or more mafic. Applying this model to modern subduction zones suggests that multiple processes are active today, with relamination occurring in a significant subset of modern arcs.