On some fundamentals of igneous petrology
On some fundamentals of igneous petrology
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火成岩岩石学的一些基础知识
DOI：
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发表时间：
2013
影响因子：
3.5
通讯作者：
B. Marsh
中科院分区：
文献类型：
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作者：
B. Marsh
导致火成岩和地球本身多样性的古老晶体分馏过程是岩浆作用和物理化学中众所周知的化学过程。但事实证明，这一过程和相关过程的更广泛的物理方面在许多方面都是难以捉摸的，特别是它与岩石成分、纹理和分层等宏观特征的空间变化的关系。岩浆系统，无论是火山、岩脉、岩岩还是岩体，通常都是在分析当前问题和最终结果的情况下进行的。解决这些问题所采用的过程通常是纯粹的化学过程，每个问题通常都是独特的，几乎没有出现任何一般原则，而这些原则对于理解岩浆过程和问题的更广泛视角至关重要。一开始就试图提供一系列与分析大多数岩浆问题相关的不可违反的岩浆第一原理。这些涉及： 初始条件；临界结晶度；凝固前沿；传输和就位通量；斑晶、异晶、原晶；晶体尺寸；分层和晶体分选；热对流；岩浆过程是物理的。除了这些原则之外，还提出了两个初始条件和结果明确的参考岩浆系统：萨德伯里冲击融化片和夏威夷熔岩湖。萨德伯里是由过热岩浆在大约 5 分钟内结晶成近乎均匀的序列而形成的，而由充满晶体的浆液形成的微小熔岩湖则形成了高度分化的层状序列。主要区别在于形成的初始条件，尤其是输入材料的性质。面临的挑战是使用这些参考端构件和建议的原理构建和分析岩浆系统（即岩浆室、岩床、岩脉和熔岩）。夏威夷 50 万年的火山记录展示了可以预期的输入材料，即岩浆的总体成分变化很大，反映了夹带的橄榄石原晶的丰富性。这些晶体的来源各不相同，并且在任何单个样品中，晶体之间的组成可能高度异质，但化学分馏的总体模式却非常规则且明确。如果类似的输入形成大型侵入体，这些系统无疑将由富含晶体的浆料主导，这些浆料提供了大量促进奇异分层的物理过程，同时，考虑到退火和持续晶体生长的影响，最终的化学记录遵循了晶体分馏的所有历史悠久的效应。长期以来假设的瞬时就位的无晶体岩浆的初始条件无法合理地产生观察到的岩石记录。
The age-old process of crystal fractionation leading to the diversity of the igneous rocks and Earth itself is an exceedingly well-understood chemical process in magmatism and physical chemistry. But the broader physical aspects of this and related processes have proven elusive on many fronts, especially in its relation to the spatial variations in rock composition, texture, and macroscopic features like layering. Magmatic systems, be they volcanic, dikes, sills, or plutons, are generally analyzed with a problem at hand and an end result in mind. The processes invoked to solve these problems, which are most often purely chemical, are often unique to each problem with few if any general principles emerging that are central to understanding the wider perspective of magmatic processes and problems. An attempt is made at the outset to provide a list of inviolate Magmatic First Principles that are relevant to analyzing most magmatic problems. These involve: initial conditions; critical crystallinity; solidification fronts; transport and emplacement fluxes; phenocrysts, xenocrysts, primocrysts; crystal size; layering and crystal sorting; thermal convection; magmatic processes are physical. Along with these principles, two reference magmatic systems are suggested where the initial conditions and outcome are unequivocal: the Sudbury impact melt sheet and the Hawaiian lava lakes. Sudbury formed in ~5 min by superheated magma crystallized to a near uniform sequence, while the tiny lava lakes, formed of crystal-laden slurries, form a highly differentiated layered sequence. The major difference is in the initial conditions of formation, especially the nature of the input materials. The challenge is to construct and analyze magmatic systems (i.e., magma chambers, sills, dikes, and lavas) using these reference end members and the suggested principles. The Hawaiian 500,000 year volcanic record exhibits what can be expected as input materials, namely a highly varied output of magma of an overall composition reflecting the abundance of entrained olivine primocrysts. The provenance of these crystals is varied, and within any single sample, the population may be highly heterogeneous in composition from crystal to crystal, yet the overall pattern of chemical fractionation is exceedingly regular and well defined. If similar inputs go to form large intrusions, these systems will undoubtedly be dominated by crystal-rich slurries, which provide a vast set of physical processes promoting exotic layering and, at the same time, given the effects of annealing and continued crystal growth, a final chemical record adhering to all the time-honored effects of crystal fractionation. The long assumed initial condition of instantaneously emplaced crystal-free magmas cannot reasonably produce the observed rock records.