International: US-Germany Doctoral Dissertation Enhancement: High-resolution Laser Ablation ICP-MS Analysis of Metamorphic Rocks from California, Germany, and the Czech Republic

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Subduction zones are one of the primary manifestations of plate tectonics, occuring where two of Earth's plates collide and one slips beneath the other. Subduction of one plate beneath another functions as the primary mechanism for mass transfer between the surface and interior of the Earth. An understanding of fluid-driven chemical cycling in subduction zones provides us with the tools to discover valuable natural resources such as metal ores and natural gas and oil reserves, to develop new resources such as geothermal energy, and to understand the geologic hazards of subduction zones such as earthquakes and volcanic eruptions. This study focuses on the distribution of trace elements in fluids produced in the down-going plate during subduction zone metamorphism. These fluids are responsible for generating the magmas that produce arc volcanoes. In particular, high-pressure metamorphic rocks such as eclogite (subducted oceanic crust) are valuable resources for studying fluid production and transfer within the deeper parts of the subduction zone. In order to track the mobility of trace elements in subduction fluids, this study will examine the geochemistry of individual minerals found in eclogite from the Ring Mountain locality of the Franciscan Complex in California, and the Erzgebirge (Ore Mountains) region of Germany and the Czech Republic. In particular, garnet and rutile will be analyzed in detail to examine the behavior of rare earth and high field strength elements during the production and transport of fluids in eclogitic rocks.The preferred method for analyzing a broad spectrum of trace elements in individual mineral grains is laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Complementary LA-ICP-MS facilities exist at Pennsylvania State University in the US and the University of Mainz in Germany. Faculty at Mainz have developed cutting edge methods that make use of information encoded in minor mineral phases in metamorphic rocks, such as Zr-in-rutile thermometry and U-Pb geochronology. Together these methods can be used to develop a temperature-time history for our samples to help us interpret the conditions under which fluid transport occurred. Penn State PhD student Alicia Cruz-Uribe will spend six weeks at the LA-ICP-MS laboratory in Mainz learning how to implement these specialized analytical techniques from her host and mentor, Dr. Thomas Zack. Cruz-Uribe will return to the US with her knowledge of these techniques to be implemented at the LA-ICP-MS facility at Penn State, under the guidance of advisor Dr. Maureen Feineman. The student will benefit both by direct exposure to new methods and new ways of thinking as well as by teaching those methods to other students upon her return. Both institutes benefit by virtue of the collaborative international research project. This project is funded jointly by the Office of International Science and Engineering and the Division of Earth Sciences.