THE KINETICS OF NUCLEATION AND CRYSTAL-GROWTH AND SCALING LAWS FOR MAGMATIC CRYSTALLIZATION
THE KINETICS OF NUCLEATION AND CRYSTAL-GROWTH AND SCALING LAWS FOR MAGMATIC CRYSTALLIZATION
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DOI：
10.1007/bf00375522
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发表时间：
1987-01-01
影响因子：
3.5
通讯作者：
JAUPART, C
中科院分区：
文献类型：
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作者：
BRANDEIS, G;JAUPART, C
岩浆结晶依赖于成核和晶体生长的动力学。它发生在一个被称为结晶区间的有限厚度区域，该区间进入未结晶岩浆。我们提出了一个量纲分析，它允许一个简单的了解结晶特性。我们使用标度来表示成核速率和晶体生长速率，分别用ImandYm表示。晶化时间尺度τ分别由(Ym~3/Im)−_(1/4)和(κ·τ)_1/2给出，其中κ为热扩散率。结晶间隔的厚度与该长度尺度成正比。晶体尺寸的标度由(ym/Im)1/4给出。我们使用数值计算来推导所有感兴趣的参数之间的无量纲关系：结晶前沿位置与时间、结晶间隔厚度与时间、晶体尺寸与边缘距离、温度与时间。我们评估了结果对动力学函数形式的敏感性。生长函数的形式对结晶行为的影响不大，而形核函数的影响则相反。由此可见，成核是关键过程。在自然情况下，岩浆结晶在不断演化的条件下进行。局部标度定律适用，时间和尺寸为τ=(Y3/I)−1/4和R=(Y/I)1/4，其中Y和I是晶体在局部生长和形核的速率。τ是实现结晶的时间，R是平均晶体尺寸。我们结合岩石学观察，利用这些定律来推断成核速率和生长速率的原位数值。定义了两个结晶区。在玄武岩侵入岩边缘普遍存在的高瞬变条件下，过冷度高，峰值形核和生长速率必须接近1 cm−3·−1和10−7 cm/S，这与实验室测量结果一致。在大型侵入体内部普遍存在的准平衡条件下，过冷度很小。在10−7~10−3 cm−3s−1和10−10~10−8 cm/S的范围内，我们得到了局部形核和生长的速率。
Magmatic crystallization depends on the kinetics of nucleation and crystal growth. It occurs over a region of finite thickness called the crystallization interval, which moves into uncrystallized magma. We present a dimensional analysis which allows a simple understanding of the crystallization characteristics. We use scales for the rates of nucleation and crystal growth, denoted byImandYmrespectively. The crystallization time-scaleτcand length-scaledcare given by (Ym3/Im)−1/4and (κ·τ)m1/2respectively, whereκis thermal diffusivity. The thickness of the crystallization interval is proportional to this length-scale. The scale for crystal sizes is given by (Ym/Im)1/4. We use numerical calculations to derive dimensionless relationships between all the parameters of interest: position of the crystallization front versus time, thickness of the crystallization interval versus time, crystal size versus distance to the margin, temperature versus time. We assess the sensitivity of the results to the form of the kinetic functions. The form of the growth function has little influence on the crystallization behaviour, contrary to that of the nucleation function. This shows that nucleation is the critical process. In natural cases, magmatic crystallization proceeds in continously evolving conditions. Local scaling laws apply, with time and size given byτ=(Y3/I)−1/4andR=(Y/I)1/4, whereYandIare the rates at which crystal are grown and nucleated locally.τis the time to achieve crystallization andRthe mean crystal size. We use these laws together with petrological observations to infer the in-situ values of the rates of nucleation and growth. Two crystallization regimes are defined. In the highly transient conditions prevailing at the margins of basaltic intrusions, undercoolings are high and the peak nucleation and growth rates must be close to 1cm−3·−1and 10−7cm/s, in good agreement with laboratory measurements. In quasi-equilibrium conditions prevailing in the interior of large intrusions, undercoolings are small. We find ranges of 10−7to 10−3cm−3s−1and of 10−10to 10−8cm/s for the local rates of nucleation and growth respectively.