The origin of Pangea

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Over the last 20 years, evidence has been amassing that Pangea, a supercontinent that formed 300 million years ago, is just the latest in a series of supercontinents that have formed repeatedly since the early Precambrian, only to break up and reform again. Although the mechanisms responsible are controversial, many geoscientists agree that repeated cycles of supercontinent amalgamation and dispersal have had a profound effect on the evolution of the Earth's crust, atmosphere, climate, and life. The existence of Pangea, which broke up about 200 million years ago, is a cornerstone of plate tectonics, and its assembly and fragmentation have governed the evolution of the Earth's crust for the past 500 million years. To a first order, we know where and when Pangea formed, but not why. Over the next grant cycle, I intend to investigate why Pangea formed. My approach is to combine field work with laboratory analyses of samples selected from sites that expose critical relationships between rock units. Graduate students are directly involved in each stage of the research program. I will continue to work on the evolution of the Rheic Ocean, an ocean that formed about 500 million years ago between dispersing continents (an interior ocean), and whose closure 200 million years later resulted in the amalgamation of Pangea. However, to obtain a global view, I also need to study rocks that document the evolution of the Paleopacific ocean, an "exterior" ocean that surrounded the dispersing continents. If the evolution of these oceans is dynamically linked, then contraction of the interior ocean, which began about 440 million years ago should be coeval with expansion of the exterior ocean. The dual approach of field work augmented by laboratory analysis will allow me to test the potential geodynamic connection between interior and exterior oceans and to test various hypotheses (including some of my own) that have been proposed for the amalgamation of Pangea.