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首页> 外文期刊>Contributions to Mineralogy and Petrology >Heterogeneous nucleation as the predominant mode of crystallization in natural magmas: numerical model and implications for crystal-melt interaction
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Heterogeneous nucleation as the predominant mode of crystallization in natural magmas: numerical model and implications for crystal-melt interaction

机译：异质成核是天然岩浆结晶的主要模式：数值模型及其对熔体结晶的影响

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摘要

Crystallization of natural magmas is inherently a disequilibrium process, which involves nucleation and growth kinetics, melt-crystal mechanical interactions and subsolidus modifications, which are all recorded in the resulting rock texture. We use a new high-resolution three-dimensional numerical model to address the significance and consequences of homogeneous versus heterogeneous crystal nucleation in silicate magmas. With increasing amount of heterogeneous nuclei during crystallization, initially equigranular textures evolve to porphyritic, bimodal and spherulitic types. The corresponding crystal size distributions (CSDs) become concave-up curved, the clustering index progressively decreases, and the grain contact relationships record increased clustering. Concave-up curved CSDs previously interpreted as resulting from multistage crystallization, mixing of crystal populations, grain agglomeration, or size-dependent growth are now predicted, consistently with other size, spatial and clustering parameters, to form by heterogeneous crystal nucleation. Correlation relationships between various textural parameters and the fraction of heterogeneous nuclei are calibrated and used on representative volcanic and plutonic rocks, including cumulate rocks, to deduce the fraction of heterogeneous nuclei. The results indicate that similar to 60 to similar to 99 % of all nuclei are heterogeneous. For plutonic and cumulate rocks, the estimate of the heterogeneous nuclei fraction based on the clustering index is significantly lower than other estimates. Such discrepancies, in general, point to the occurrence of other processes, and here, the results imply that crystal-mush compaction and interstitial melt extraction were involved during the magma solidification. Formation of crystals in clusters, implicit for heterogeneous nucleation, implies that greater efficiency of crystal-melt separation is expected in these situations.
机译：天然岩浆的结晶本质上是一个不平衡过程，涉及成核和生长动力学，熔体晶体机械相互作用和亚固相线变质，所有这些都记录在形成的岩石质地中。我们使用一种新的高分辨率三维数值模型来解决硅酸盐岩浆中均相和异质晶体成核的意义和后果。随着结晶过程中异质核数量的增加，最初的等粒织构演变为斑状，双峰和球状类型。相应的晶体尺寸分布（CSD）变为凹向上弯曲，聚集指数逐渐降低，并且晶粒接触关系记录了增加的聚集。现在预测凹凹弯曲的CSD是由多阶段结晶，晶体种群混合，晶粒团聚或尺寸依赖性生长所导致的，与其他尺寸，空间和聚类参数一致，是由异质晶体成核形成的。校准了各种质地参数与非均质核分数之间的相关关系，并在包括堆积岩在内的代表性火山岩和深成岩上将其用于推断非均质核的分数。结果表明，所有核中有相似的60％至相似的99％是异质的。对于深成岩和堆积岩，基于聚类指数的非均质核分数的估计显着低于其他估计。通常，这种差异指出了其他过程的发生，并且这里的结果暗示了在岩浆凝固过程中涉及了晶体糊状压实和间隙熔体提取。簇中晶体的形成，对于异质成核是隐含的，这意味着在这些情况下，期望晶体-熔体分离的效率更高。

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