Renggli Christian J, Wiesmaier Sebastian, De Campos Cristina P, Hess Kai-Uwe, Dingwell Donald B
1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany.
2Research School of Earth Sciences, Australian National University, Canberra, Australia.
Contrib Mineral Petrol. 2016;171(11):96. doi: 10.1007/s00410-016-1305-1. Epub 2016 Oct 15.
A time series of experiments at high temperature have been performed to investigate the influence of particle settling on magma mixing. A natural rhyolite glass was held above a natural basalt glass in a platinum crucible. After melting of the glasses at superliquidus temperatures, a platinum sphere was placed on the upper surface of the rhyolitic melt and sank into the experimental column (rhyolitic melt above basaltic melt). Upon falling through the rhyolitic-basaltic melt interface, the Pt sphere entrained a filament of rhyolitic melt in its further fall. The quenched products of the experiments were imaged using X-ray microCT methods. The images of our time series of experiments document the formation of a rhyolite filament as it is entrained into the underlying basalt by the falling platinum sphere. When the Pt particle reached the bottom of the crucible, the entrained rhyolitic filament started to ascend buoyantly up to the initial rhyolitic-basaltic interface. This generated a significant thickness increase of a comingled "melange" layer at the interface due to "liquid rope coiling" and piling up of the filament. As a consequence, the basalt/rhyolite interface was greatly enlarged and diffusive hybridisation greatly accelerated. Further, bubbles, originating at the interface, are observed to have risen into the overlying rhyolite dragging basalt filaments with them. Upon crossing the basalt/rhyolite interface, the bubbles have non-spherical shapes as they adapt to the differing surface tensions of basaltic and rhyolitic melts. Major element profiles, measured across the rhyolite filaments, exhibit asymmetrical shapes from the rhyolite into the basalt. Na and Ti reveal uphill diffusion from the rhyolite towards the interface in the filament cross sections. These results reveal the potential qualitative complexity of the mingling process between rhyolitic and basaltic magmas in the presence of sinking crystals. They imply that crystal-rich magma mingling may be expected to be accelerated with respect to crystal-poor systems. We urge the further fluid dynamic analysis of these phenomena, obtainable for the first time using detailed tomographic imaging.
已进行了一系列高温实验，以研究颗粒沉降对岩浆混合的影响。在铂坩埚中，将天然流纹岩玻璃置于天然玄武岩玻璃上方。在高于液相线温度下使玻璃熔化后，将一个铂球放置在流纹岩熔体的上表面，铂球沉入实验柱中（流纹岩熔体在玄武岩熔体上方）。铂球穿过流纹岩 - 玄武岩熔体界面时，在其进一步下落过程中夹带了一缕流纹岩熔体。实验的淬火产物使用X射线显微CT方法成像。我们的实验时间序列图像记录了流纹岩细丝被下落的铂球夹带进入下层玄武岩时的形成过程。当铂颗粒到达坩埚底部时，夹带的流纹岩细丝开始向上浮力上升至初始流纹岩 - 玄武岩界面。由于“液绳盘绕”和细丝堆积，这在界面处产生了混合“混熔体”层的显著厚度增加。结果，玄武岩/流纹岩界面大大扩大，扩散混合大大加速。此外，观察到起源于界面的气泡带着玄武岩细丝上升到上覆的流纹岩中。穿过玄武岩/流纹岩界面时，气泡呈现非球形，因为它们适应了玄武岩和流纹岩熔体不同的表面张力。在流纹岩细丝上测量的主要元素剖面显示从流纹岩到玄武岩呈不对称形状。钠和钛在细丝横截面中显示出从流纹岩向界面的上坡扩散。这些结果揭示了在下沉晶体存在下流纹岩和玄武岩岩浆混合过程潜在的定性复杂性。它们意味着相对于贫晶体系统，富晶体岩浆混合可能会加速。我们敦促对这些现象进行进一步的流体动力学分析，这首次可通过详细的断层成像获得。
