Light Element Investigations of Natural and Experimental Zircon

点击翻译按钮获取中文摘要

The geological events of Earth's past not only shaped the present-day planet, but will also influence the evolution of Earth in the future. In geology, rocks are the key to the past; in many cases they represent the only resource available to study "deep time." However, no known whole rocks exists from before 4 billion years ago. The reservoir of known terrestrial material is limited to very rare "grains of sand" found in only a handful of sediments throughout the world. In the absence of the original rock that hosted these "grains of sand," - or specifically the mineral zircon - there are numerous challenges. This research will address these problems through two complementary approaches. The first involves measurements to deduce the chemical composition of these very rare minerals (zircons), while the second involves the synthesis of the mineral in the controlled environment of a high pressure, high temperature experimental geology laboratory. These experiments - where pressure, temperature, and magma composition can be varied - will serve as a stepping stone to interpret the chemistry of the most ancient known terrestrial samples. The application of these experiments to natural samples will result in new knowledge about the environments and conditions of the earliest Earth (including the composition of magmas), and is therefore a key source of information to understand the evolution of Earth through time. Broader impacts of this work also include the training of undergraduate and graduate students in novel high pressure / high temperature crystal and glass synthesis techniques. Synthetic glasses and crystals make up a component of many consumer products today. Students will also conduct measurements of these materials using modern analytical technology such as a laser ablation inductively coupled plasma mass spectrometer. And finally, secondary school science teachers will benefit from laboratory demonstrations that explain how geologists determine the ages of ancient rocks and minerals; they will also participate in the development of simple diagrams that explain key concepts of geology and geochemistry that they can then use for instruction in their classes. The experimental work for this project will be conducted using a piston cylinder apparatus at the University of Rochester. Zircons will: (i) be synthesized in silicic melts; or (ii) approach equilibrium elemental and isotopic compositions through time series experiments in the presence of fluids. Partition coefficients/isotope compositions of run products will be determined for light stable elements in zircon and co-existing phases. The first goal is to robustly calibrate the incorporation light elements into the zircon lattice as a function of melt composition, melt structure, and temperature. Second, the developed calibrations will be applied to Archean and Hadean zircons. These experiments and the application of the results will play a fundamental role in the quest to link chemical signatures preserved in ancient zircons with early crystal processes. This work will also extend knowledge of the zircon parent rock composition long since gone.