Near-liquidus growth of feldspar spherulites in trachytic melts: 3D morphologies and implications in crystallization mechanisms
Near-liquidus growth of feldspar spherulites in trachytic melts: 3D morphologies and implications in crystallization mechanisms
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DOI：
10.1016/j.lithos.2014.12.003
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发表时间：
2015-02-01
期刊：
影响因子：
3.5
通讯作者：
Carroll, Michael R.
中科院分区：
文献类型：
--
作者：
Arzilli, Fabio;Mancini, Lucia;Carroll, Michael R.
利用X射线显微层析和电子背散射衍射（EBSD）数据研究了球晶碱性长石的成核和生长过程。本文首次报道了碱长石球晶的形状择优取向（SPO）和晶体择优取向（CPO）。同步辐射X射线显微层析成像和EBSD数据集的分析，使我们能够研究的粗面质熔体中的球晶的形态特征，在定量的方式，突出的三维形状，择优取向，分支片晶和晶体孪晶，提供有关的成核机制的球晶结晶的见解。成核从异质核（预先存在的晶体或气泡）开始，随后它演变形成“蝴蝶结”形态，在几个小时内达到径向球晶形状。由于球晶内的每个片层也是孪生的，这些合成球晶不能被认为是单核，而是由异相成核产生的晶体聚集体。孪晶边界可以具有比一般晶体-晶体边界更低的能量，并且许多孪晶晶粒显示出强的局部弯曲的证据，其与孪晶平面结合，研究表明，层状晶体的生长速率（10（-6）-10（-7）cm/s）在球晶中的结晶度与单晶相似或略高一个数量级。此外，最高的体积生长速率（10（-11）-10（-12）cm（3）/S）表明，球晶内的碱性长石可以快速生长，在1 s内达到接近10 μ m（3）的体积尺寸。(C)2014爱思唯尔有限公司版权所有。
The nucleation and growth processes of spherulitic alkali feldspar have been investigated in this study through X-ray microtomography and electron backscatter diffraction (EBSD) data. Here we present the first data on Shape Preferred Orientation (SPO) and Crystal Preferred Orientation (CPO) of alkali feldspar within spherulites. The analysis of synchrotron X-ray microtomography and EBSD datasets allowed us to study the morphometric characteristics of spherulites in trachytic melts in quantitative fashion, highlighting the three-dimensional shape, preferred orientation, branching of lamellae and crystal twinning, providing insights about the nucleation mechanism involved in the crystallization of the spherulites. The nucleation starts with a heterogeneous nucleus (pre-existing crystal or bubble) and subsequently it evolves forming "bow tie" morphologies, reaching radially spherulitic shapes in few hours. Since each lamella within spherulite is also twinned, these synthetic spherulites cannot be considered as single nuclei but crystal aggregates originated by heterogeneous nucleation. A twin boundary may have a lower energy than general crystal-crystal boundaries and many of the twinned grains show evidence of strong local bending which, combined with twin plane, creates local sites for heterogeneous nucleation.This study shows that the growth rates of the lamellae (10(-6)-10(-7) cm/s) in spherulites are either similar or slightly higher than that for single crystals by up to one order of magnitude. Furthermore, the highest volumetric growth rates (10(-11)-10(-12) cm(3)/S) show that the alkali feldspar within spherulites can grow fast reaching a volumetric size of similar to 10 mu m(3) in 1 s. (C) 2014 Elsevier B.V. All rights reserved.