Abstract A wide variety of magmas entrain, transport and erupt mantle material in the form of xenoliths and xenocrysts. The host magmas are often low viscosity in nature and range from basalt to more esoteric compositions such as kimberlite, nephelinite and basanite. Here we focus on kimberlite magmas which are particularly successful at transporting deep mantle cargo to the surface, including economically important quantities of diamond. Collections of mantle-derived xenoliths and xenocrysts are critical to our understanding of the structure, stability, composition, thermal state, age, and origin of the lithosphere. However, they also inform on magma transport conditions. Through a series of scaled analogue experiments, we document the relative mechanical stability of olivine, garnet, orthopyroxene, clinopyroxene and diamond xenocrysts during magma ascent. Our experiments fluidized these mantle minerals at a constant gas flux for variable amounts of time approximating transport in a high velocity, turbulent, fluid-rich (supercritical fluid or gas, depending on depth) magma. The evolution of mineral surface features, morphology and grain size distributions is analyzed as a function of residence time. We show that on timescales consistent with magma ascent, each mantle mineral is subject to mechanical modification resulting in mass loss and reshaping (rounding) by grain size reduction and surface pitting. We further discuss the chemical consequences of producing fine particle chips that are highly susceptible to dissolution. Lastly, we utilize an empirical model that relates textural observations (e.g. impact pit size) on xenocrysts to differential particle velocities. Our approach applied to natural kimberlitic olivine and garnet xenocrysts indicates differential velocities of ∼ 4 m s − 1 – the first direct estimate for velocity in an ascending kimberlite magma.

中文翻译：

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捕虏体和异种晶体从源头到地表的运输、存活和改性

摘要 种类繁多的岩浆以包体和包晶的形式夹带、运输和喷发地幔物质。宿主岩浆在性质上通常是低粘度的，范围从玄武岩到更深奥的成分，如金伯利岩、霞石和玄武岩。在这里，我们专注于金伯利岩浆，这些岩浆在将深层地幔货物运输到地表方面特别成功，其中包括具有重要经济意义的数量的钻石。地幔来源的捕虏体和异种晶体的收集对于我们了解岩石圈的结构、稳定性、成分、热状态、年龄和起源至关重要。然而，它们也告知岩浆运输条件。通过一系列按比例缩放的模拟实验，我们记录了橄榄石、石榴石、斜方辉石、岩浆上升过程中的单斜辉石和金刚石异晶。我们的实验使这些地幔矿物以恒定的气体通量流化，持续不同的时间，近似于在高速、湍流、富含流体（超临界流体或气体，取决于深度）岩浆中的输运。矿物表面特征、形态和粒度分布的演变被分析为停留时间的函数。我们表明，在与岩浆上升一致的时间尺度上，每个地幔矿物都会受到机械改性，导致质量损失和通过晶粒尺寸减小和表面点蚀而重塑（圆化）。我们进一步讨论了生产极易溶解的细颗粒碎片的化学后果。最后，我们利用一个与纹理观察相关的经验模型（例如 影响坑大小）对异种晶体的不同粒子速度。我们应用于天然金伯利岩橄榄石和石榴石异种晶体的方法表明，差分速度约为 4 ms - 1——这是对上升的金伯利岩岩浆速度的首次直接估计。