The role of crustal buoyancy on generation and emplacement of magmatism during continental collision [dataset]

During continental collision, considerable amounts of buoyant continental crust subduct to depth and subsequently exhume. Whether various exhumation paths contribute to contrasting styles of magmatism across modern collision zones is unclear. Here, we present 2D thermomechanical models of continental collision combined with petrological databases to investigate the effect of the main contrasting buoyancy forces, in the form of continental crustal buoyancy vs oceanic slab age (i.e. its thickness). We specifically focus on the consequences for crustal exhumation mechanisms and magmatism. Results indicate that it is mainly crustal density that determines the degree of steepening of the subducting continent and separates the models parameter space into two regimes. In the first regime, high buoyancy values (∆ρ>500 kg/m3) steepen the slab most rapidly (to 45-58), leading to opening of a gap in the subduction channel through which the subducted crust exhumes ('subduction channel crustal exhumation'). A shift to a second regime ('underplating') occurs when the density contrast is reduced by 50 kg/m3. In this scenario, the slab steepens less (to 37-50), forcing subducted crust to be placed below the overriding plate. Importantly, the magmatism changes in the two cases: crustal exhumation through the subduction channel is mainly accompanied by a narrow band of mantle melts, while underplating leads to widespread melting of mixed sources. Finally, we suggest that the amount (or density) of subducted continental crust, and the resulting buoyancy forces, could contribute to contrasting collision styles and magmatism in the Alps and Himalayas/Tibet.

在大陆碰撞（continental collision）过程中，大量具有浮力的大陆地壳会俯冲至深部，随后发生折返。目前学界尚未明确，现代碰撞带中不同的地壳折返路径是否会引发岩浆作用样式的显著差异。
本研究构建了结合岩石学数据库（petrological databases）的大陆碰撞二维热力学模型（thermomechanical models），以探究两种核心对立浮力的影响效应：大陆地壳浮力与洋板片年龄（即其厚度）。研究重点聚焦于地壳折返机制与岩浆作用的相关响应。
结果表明，地壳密度是决定俯冲大陆板片陡化程度的核心因素，并将模型参数空间划分为两种机制状态。第一种机制状态下，高浮力值（密度差Δρ>500 kg/m³）可使板片快速陡化（至45°~58°），进而在俯冲通道（subduction channel）中形成空隙，俯冲地壳可通过该空隙完成折返，即‘俯冲通道地壳折返’。当密度差降低50 kg/m³时，模型将切换至第二种机制状态——‘底侵作用（underplating）’。在此情景中，板片陡化程度更低（仅至37°~50°），迫使俯冲地壳被安置于仰冲板块下方。
值得注意的是，两种机制下的岩浆作用特征存在显著差异：通过俯冲通道完成的地壳折返主要伴随窄带状地幔熔体生成，而底侵作用则会引发混合源区的广泛熔融。
最后，本研究提出，俯冲大陆地壳的总量（或密度）及其产生的浮力，可能是导致阿尔卑斯造山带与喜马拉雅-青藏高原造山带出现碰撞样式与岩浆作用差异的关键诱因。