Variation of plagioclase shape with size in intermediate magmas: a window into incipient plagioclase crystallisation
Variation of plagioclase shape with size in intermediate magmas: a window into incipient plagioclase crystallisation
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中间岩浆中斜长石形状随尺寸的变化：了解斜长石初期结晶的窗口
DOI：
10.1007/s00410-022-01922-9
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发表时间：
2022
影响因子：
3.5
通讯作者：
Mangler M
中科院分区：
文献类型：
--
作者：
Mangler M
火山岩通常表现出复杂的结构，这些结构既来自岩浆储层，也来自上升到地表的过程。虽然通常分析矿物组成、大小和数量密度的变化来重建喷发前的岩浆历史，但晶体形状通常被认为是恒定的，尽管有实验证据表明晶体习性对岩浆条件的敏感性。在这里，我们开发了一个新的程序（ShapeCalc），从二维晶体相交数据计算三维形状，并将其应用于研究中间火山岩中斜长石微岩（l< 100µm）晶体形状随尺寸的变化。最小的晶体趋向于呈现棱柱状的三维形状，而较大的晶体（直径5-10 μ m）则逐渐呈现出更扁平的形状。晶体生长模型和实验约束表明，这一趋势反映了斜长石生长过程中的形状演变，最初生长为棱柱状棒状，随后中间尺寸优先过度生长，形成板状形状。由于非常小的晶体的过度生长会强烈地影响外部形态，斜长石微岩的形状取决于每个晶体的可用生长体积，随着晶体数密度的增加，在减压驱动的结晶过程中，每个晶体的可用生长体积减小。我们提出的生长模型表明，岩浆中发育的晶体形状范围受过冷和总晶体数的时间演化控制，即不同的冷却/减压路径。例如，在缓慢到中等岩浆上升速率和准连续成核的情况下，早期形成的晶体变大并发展成板状，而晚期成核产生较小的棱柱状晶体。相比之下，岩浆的快速上升可能完全抑制成核，或者如果在浅深度停止，可能产生与板状晶体形状相关的单一成核爆发。这种晶体形状的变化具有诊断价值，也是构建csd和涉及岩浆流变学的模型时需要考虑的重要因素。
Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct pre-eruptive magmatic histories, crystal shapes are often assumed to be constant, despite experimental evidence for the sensitivity of crystal habit to magmatic conditions. Here, we develop a new program (ShapeCalc) to calculate 3D shapes from 2D crystal intersection data and apply it to study variations of crystal shape with size for plagioclase microlites (l< 100 µm) in intermediate volcanic rocks. The smallest crystals tend to exhibit prismatic 3D shapes, whereas larger crystals (l> 5–10 µm) show progressively more tabular habits. Crystal growth modelling and experimental constraints indicate that this trend reflects shape evolution during plagioclase growth, with initial growth as prismatic rods and subsequent preferential overgrowth of the intermediate dimension to form tabular shapes. Because overgrowth of very small crystals can strongly affect the external morphology, plagioclase microlite shapes are dependent on the available growth volume per crystal, which decreases during decompression-driven crystallisation as crystal number density increases. Our proposed growth model suggests that the range of crystal shapes developed in a magma is controlled by thetemporal evolutionof undercooling and total crystal numbers, i.e., distinct cooling/decompression paths. For example, in cases of slow to moderate magma ascent rates and quasi-continuous nucleation, early-formed crystals grow larger and develop tabular shapes, whereas late-stage nucleation produces smaller, prismatic crystals. In contrast, rapid magma ascent may suppress nucleation entirely or, if stalled at shallow depth, may produce a single nucleation burst associated with tabular crystal shapes. Such variation in crystal shapes have diagnostic value and are also an important factor to consider when constructing CSDs and models involving magma rheology.
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影响因子：
3.9
作者：
E. Mollard;C. Martel;J. Bourdier
通讯作者：
E. Mollard;C. Martel;J. Bourdier
影响因子：
2.1
作者：
J. Schmelzer;A. Abyzov;E. B. Ferreira;V. Fokin
通讯作者：
V. Fokin
合成玄武岩中斜长石晶体的 3D 重建
影响因子：
3.1
作者：
S. Duchêne;E. Pupier;C. L. C. de Veslud;M. Toplis
通讯作者：
M. Toplis
影响因子：
3.5
作者：
BRANDEIS, G;JAUPART, C
通讯作者：
JAUPART, C
影响因子：
5.3
作者：
La Spina, G.;Arzilli, F.;Mader, H. M.
通讯作者：
Mader, H. M.