High-Temperature Contact Metamorphism Around the Marble Canyon Intrusion, Texas

位于德克萨斯州范霍恩附近的大理石峡谷侵入体被一个接触光环所包围，其中出现了闪长岩相组合。初步相平衡计算表明，接触附近达到了异常高的温度(925-1025摄氏度)。然而，热流考虑表明，如果对侵入的几何形状有合理的假设，对于接触光环来说，这个温度太高了。一项研究计划将仔细检查大理石峡谷光环的地球化学，定量评估热光环和流体的性质，并试图解释这种明显的差异。大理石峡谷光环含有大量的矿物物种(表1)，因此特别有利于高温接触变质作用的研究。这里提出的研究将结合岩石学和地球化学方法，对形成高温接触光环的过程有一个综合的理解，特别是大理石峡谷光环。数据将允许对温度和流体成分的变化、交代作用和反应进程进行定量评估，这些变化随着距离侵入体的距离增加而增加。地球化学研究将集中于碳/氧稳定同位素变化和常量元素和微量元素随距离的变化的整体化学评价。将检查从不同来源获得的类似数据(例如，从热模拟和相平衡获得的温度以及从反应进度和同位素计算获得的流体/岩石比)的内部一致性，并将根据所涉及的数据库、假设和实际误差来评估观察到的任何差异。将特别注意这样一种可能性，即流体/岩石比的概念本身可能是错误的，需要对变质流体和岩石之间的相互作用进行另一种描述。

The Marble Canyon intrusions, located near Van Horn, Texas is surrounded by a contact aureole in which sanidinite facies assemblages occur. Preliminary phase equilibrium calculations suggest that unusually high temperatures (925 - 1025 C) were reached near the contact. Heat flow considerations suggest, however, that this temperature is too high for a contact aureole given reasonable assumptions about the geometry of the intrusion. A research program is outlined that will carefully examine the geochemistry of the Marble Canyon aureole, quantitatively evaluate the thermal aureole and the nature of the fluid and attempt to explain this apparent discrepancy. The Marble Canyon aureole contains a large number of mineral species (Table 1), and thus is especially conducive to a study of contact metamorphism at high temperatures. The study proposed here will combine petrological and geochemical approaches to yield a combined understanding of the processes which form high temperature contact aureoles in general, and the Marble Canyon aureole in particular. Data will allow a quantitative evaluation of temperature and fluid compositions changes, metasomatism and reaction progress with increasing distance from the intrusion. Geochemical studies will concentrate on C/O stable isotopic variations and bulk chemical evaluation of changes in major and trace elements with distance from the intrusion. Similar data obtained from different sources (e.g. temperatures from thermal modelling and phase equilibria and fluid/rock ratios from reaction progress and isotopic calculations) will be examined for internal consistency, and any observed differences will be evaluated in terms of the data bases, assumptions, and real errors involved. Particular attention will be given to the possibility that the concept of fluid/rock ratios may itself be erroneous and that alternative descriptions of the interactions between metamorphic fluids and rocks are needed.