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

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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.