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首页> 外文期刊>Contributions to Mineralogy and Petrology >Magnetite scavenging and the buoyancy of bubbles in magmas. Part 2: Energetics of crystal-bubble attachment in magmas
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Magnetite scavenging and the buoyancy of bubbles in magmas. Part 2: Energetics of crystal-bubble attachment in magmas

机译：磁铁矿清除和岩浆中气泡的浮力。第2部分：岩浆中晶体气泡附着的能量学

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The fate of pre-emptive bubbles depends largely on their buoyancy, which can be strongly modified by the presence of crystals attached to the bubble-melt interface. We define the attachment energy and attachment force as those resulting from the attachment of a crystal to a bubble. The attachment energy is such that (1) attachment of crystals to bubbles is always favored energetically, and (2) oxide minerals attach to bubbles much more strongly than silicates, because the attachment energy is a strong function of the wetting angle. Attaching crystals to bubbles can cause bubble-crystal pairs to become neutrally buoyant. There is a critical bubble radius below which the attachment force will be strong enough to keep the pair together; we show that crystals as large as 1 mm in diameter can form neutrally buoyant pairs. For early erupted Bishop magma, if all magnetite forms neutrally buoyant pairs with gas bubbles, ca. 0.1-0.2 vol percent gas can be stored in the magma; 2-3 vol percent of gas can be accounted for if all minerals form neutrally buoyant aggregates. These values are an order of magnitude lower than what is inferred from melt inclusions. Hence, both magnetite-free and magnetite-rich bubbles might have existed, but only a very small fraction of them could have been neutrally buoyant. Importantly, an intrinsic association between magnetite crystals and bubbles is expected. However, most magnetite crystals in the early erupted Bishop are free of bubbles; the puzzling conclusion is that nucleation away from crystals is favored over heterogeneous nucleation on crystal substrates.
机译：抢先气泡的命运很大程度上取决于它们的浮力，可以通过附着在气泡-熔体界面上的晶体来强烈改变浮力。我们将附着能和附着力定义为晶体与气泡附着所产生的附着能和附着力。附着能是这样的：（1）总是大力促进晶体附着在气泡上，（2）氧化物矿物比硅酸盐更牢固地附着在气泡上，因为附着能是润湿角的强函数。将晶体附着到气泡上会导致气泡晶体对变为中性浮力。有一个临界气泡半径，在该半径以下，附着力将足以使该对保持在一起;我们表明，直径高达1毫米的晶体可以形成中性浮力对。对于较早爆发的毕晓普岩浆，如果所有磁铁矿形成带有气泡的中性浮力对，则大约为。岩浆中可以储存0.1-0.2％（体积）的气体;如果所有矿物均形成中性浮力聚集体，则可占天然气的2-3％（体积）。这些值比从熔体夹杂物推断的值低一个数量级。因此，可能同时存在无磁铁矿和富磁铁矿的气泡，但其中只有极小部分是中性浮力的。重要的是，磁铁矿晶体和气泡之间存在内在联系。然而，早期爆发的毕晓普的大多数磁铁矿晶体都没有气泡。令人费解的结论是，远离晶体成核比晶体衬底上的异质成核更受青睐。

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