Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads
Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads
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不平衡纹理与平衡建模：十字路口的地质年代学
DOI：
10.1144/sp332.1
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
I. Villa
中科院分区：
文献类型：
--
作者：
I. Villa
摘要矿物中的亚微观化学不平衡现象极为普遍。在变质地体及其附近的花岗岩、接触光环和断层中，水促进了不平衡再结晶。再结晶几乎在任何温度下都比扩散再平衡成本低。放射性同位素(4He除外)的再平衡扩散速度永远不会快于形成矿物结构的主要元素。锆石、独居石、角闪石、钾长石、黑云母和白云母均与残留物有关。在自然界中，重置同位素记录的机制更多地取决于促进再结晶的水的可用性，而不是达到预设的温度。含水矿物的实验室扩散实验在一定程度上受到溶解-再沉淀的困扰，但总是在很大程度上。矿物地质计时仪应该被视为“地质湿度计”，基本上可以确定流体循环的时间。由于亚微观岩石学，同位素不平衡可以与岩石成因不平衡联系在一起。分析技术的进步使每一代矿物的成功测年成为可能。这打开了关于岩石P-T-A-X-d历史的更丰富的数据，从长远来看，这也将提高我们开发可信数值模型的能力。
Abstract Submicroscopic microchemical disequilibrium in minerals is extremely widespread. Disequilibrium recrystallization is promoted by water in metamorphic terranes and near granites, contact aureoles, and faults. Recrystallization is energetically less costly at almost any temperature than diffusive re-equilibration. Radiogenic isotopes (except 4He) never diffusively re-equilibrate faster than major elements forming the mineral structure. Isotopic inheritance tied to relicts was demonstrated for zircon, monazite, amphibole, K-feldspar, biotite and muscovite. The mechanism for resetting the isotope record in nature depends more on the availability of recrystallization-enhancing water than on reaching a preset temperature. Laboratory diffusion experiments on hydrous minerals were plagued, to a variable but always large extent, by dissolution–reprecipitation. Mineral geochronometers should be viewed as ‘geohygrometers’ that essentially date the fluid circulation episodes. Thanks to submicroscopic petrology, isotopic disequilibria can be put into context with petrogenetic disequilibria. Analytical advances allow the successful dating of each mineral generation. This has opened up a much richer wealth of data on the P–T–A–X–d history of rocks, which in the long run will also improve our ability to develop credible numeric models.