Matrix rheology effects on reaction rim growth I: evidence from orthopyroxene rim growth experiments
Matrix rheology effects on reaction rim growth I: evidence from orthopyroxene rim growth experiments
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基质流变学对反应边缘生长的影响 I：来自斜方辉石边缘生长实验的证据
DOI：
10.1111/j.1525-1314.2008.00804.x
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发表时间：
2009
影响因子：
3.4
通讯作者：
P. Ulmer
中科院分区：
文献类型：
--
作者：
R. Milke;R. Abart;K. Kunze;M. Koch‐Müller;D. Schmid;P. Ulmer
边缘形成反应石英 + 橄榄石 = 邻辉石用于研究基质流变性对边缘生长速率的影响。将石英基质中橄榄石颗粒周围的斜方辉石边缘生长与橄榄石基质中石英颗粒周围的边缘生长进行比较。在恒定的 P-T 条件下，在一个胶囊内，橄榄石基质中的石英碎屑周围的斜方辉石边缘比石英基质中的橄榄石碎屑周围生长得更快。傅里叶变换红外光谱表明，由于水吸附在反应物颗粒表面，整个样品都是水饱和的。与石英基质相比，橄榄石基质中斜方辉石生长速率的增加可以用基质流变学来解释，其中在两种不同的基质包裹体排列中，橄榄石基质表现得“更软”，石英基质“更坚硬”。与橄榄石基质相比，石英与调节负反应体积相关的应变能更高，并且减少了驱动斜方辉石边缘生长的自由能。两种斜方辉石边缘的生长结构表明，MgO 的扩散率略高于 SiO2 的扩散率。在给定的 P、T、fH2O 下，MgO 和 SiO2 的相对迁移率似乎受压缩 Ol/Opx 界面处斜方辉石生长过程中能量最小化的控制。我们的实验为变质岩中与边缘生长反应相关的两个先前被忽视的效应提供了证据：（i）沿化学势梯度到反应位点的扩散率是流变学的函数，（ii）反应边缘或日冕生长过程中组分的相对扩散率是边缘界面处局部体积变化的函数。
The rim‐forming reaction quartz + olivine = orthopyroxene is used to investigate the effect of matrix rheology on rim growth rates. Orthopyroxene rim growth around olivine grains in quartz matrix is compared to rim growth around quartz grains in an olivine matrix. At constant P–T, within one single capsule, orthopyroxene rims grow faster around quartz clasts in olivine matrix than around olivine clasts in quartz matrix. Fourier transform infra‐red spectra indicate that the entire samples are water saturated because of water adsorption on the reactant grain surfaces. The increased orthopyroxene growth rates in olivine matrix as opposed to quartz matrix are interpreted in terms of matrix rheology, where in the two different matrix‐inclusion arrangements the olivine matrix behaves ‘softer’ and the quartz matrix ‘more rigid’. The strain energy associated with accommodation of the negative reaction volume is higher for the quartz than the olivine matrix and reduces the free energy that drives orthopyroxene rim growth. Growth textures in both kinds of orthopyroxene rims indicate that the diffusivity of MgO slightly exceeds the diffusivity of SiO2. The relative mobility of MgO and SiO2 at given P, T, fH2O seems to be controlled by energy minimization during orthopyroxene growth at the compressive Ol/Opx interface. Our experiments provide evidence for two previously overlooked effects relevant to rim growth reactions in metamorphic rocks: (i) diffusivity along chemical potential gradients to reaction sites is a function of rheology and (ii) the relative diffusivity of components during reaction rim or corona growth is a function of local volume changes at the rim’s interfaces.