Phase Relations, Reaction Sequences and Petrochronology
Phase Relations, Reaction Sequences and Petrochronology
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DOI：
10.2138/rmg.2017.83.2
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发表时间：
2017-02
影响因子：
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通讯作者：
C. Yakymchuk;C. Clark;R. White
中科院分区：
文献类型：
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作者：
C. Yakymchuk;C. Clark;R. White
岩石年代学的核心是地质年代学与主要矿物组合的岩石学演化之间的关系。本章的重点是概述一些可用的策略，将变质岩中推断的反应序列和微观结构与从副矿物和可数据主要矿物的地质年代学中获得的年龄联系起来。变质岩中的反应序列和矿物组合主要是压力 ( P )、温度 ( T ) 和整体成分 ( X ) 的函数。几种主要的造岩矿物对 P-T 的变化特别敏感（例如石榴石、十字石、黑云母、斜长石），但它们的直接地质年代学具有挑战性，并且在许多情况下目前是不可能的。石榴石是一个例外，它可以使用 Sm-Nd 和 Lu-Hf 地质年代学来测定年代（例如，Baxter 等人，2013 年）。锆石、独居石、磷钇矿、钛铁矿和金红石等辅助矿物计时器在相对较宽的 P-T 条件范围内保持稳定，并且可以包含足够的 U 和/或 Th，以便使用 U-Th-Pb 地质年代学进行测年。因此，将 P-T 敏感主要矿物的生长与辅助和/或主要矿物计时器联系起来对于确定变质 P-T-t 历史至关重要，这本身对于理解变质岩和产生变质岩的地球动力学过程至关重要（例如，England 和 Thompson 1984；McClelland 和 Lapen 2013；Brown 2014）。将从副矿物和主要矿物获得的年龄与重要 P-T 敏感矿物的生长和分解联系起来，需要了解特定块体岩石成分沿良好约束的 P-T 演化的变质反应序列。幸运的是，最广泛研究的变质原岩（例如泥岩、杂砂岩、玄武岩）的相关系和反应序列可以使用定量相平衡正演模型来确定（例如，Powell 和 Holland 2008）。大型化学系统中主要变质矿物的综合活性-成分模型（例如，White 等人，2014a）允许……
At the core of petrochronology is the relationship between geochronology and the petrological evolution of major mineral assemblages. The focus of this chapter is on outlining some of the available strategies to link inferred reaction sequences and microstructures in metamorphic rocks to the ages obtained from geochronology of accessory minerals and datable major minerals. Reaction sequences and mineral assemblages in metamorphic rocks are primarily a function of pressure ( P ), temperature ( T ) and bulk composition ( X ). Several of the major rock-forming minerals are particularly sensitive to changes in P–T (e.g., garnet, staurolite, biotite, plagioclase), but their direct geochronology is challenging and in many cases not currently possible. One exception is garnet, which can be dated using Sm–Nd and Lu–Hf geochronology (e.g., Baxter et al. 2013). Accessory mineral chronometers such as zircon, monazite, xenotime, titanite and rutile are stable over a relatively wide range of P–T conditions and can incorporate enough U and/or Th to be dated using U–Th–Pb geochronology. Therefore, linking the growth of P–T sensitive major minerals to accessory and/or major mineral chronometers is essential for determining a metamorphic P–T–t history, which is itself critical for understanding metamorphic rocks and the geodynamic processes that produce them (e.g., England and Thompson 1984; McClelland and Lapen 2013; Brown 2014). Linking the ages obtained from accessory and major minerals with the growth and breakdown of the important P–T sensitive minerals requires an understanding of the metamorphic reaction sequences for a particular bulk rock composition along a well-constrained P–T evolution. Fortunately, the phase relations and reaction sequences for the most widely studied metamorphic protoliths (e.g., pelites, greywackes, basalts) can be determined using quantitative phase equilibria forward modelling (e.g., Powell and Holland 2008). Comprehensive activity–composition models of the major metamorphic minerals in large chemical systems (e.g., White et al. 2014a) allow …