Toward an understanding of Neogene plate dynamics: Completion of a high-resolution, closure-enforced chronology of global plate motions since 20 Ma

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Motivated by work to date, which documents changes in the motions of all the major tectonic plates during the Neogene period (~23-2.5 million years ago), the proposed effort will systematically quantify the geographic scope, nature, and timing of global plate motion changes since 20 million years ago. The Principle Investigators will create a first-ever kinematic framework that will be broadly useful for understanding the relationship of instantaneous plate movements measured by geodetic techniques to movements over millions of years, as well as for modeling the forces that have determined plate motions during the Neogene. The results will be broadly useful to geoscientists, particularly geodesists, paleomagnetists, seismologists, structural geologists, and plate dynamicists. Key papers published on this topic over the past few decades have been cited thousands of times and provide an essential conceptual and quantitative framework for teaching and understanding the Neogene tectonic and geologic evolution of the ocean basins and nearly all the continents. The Principle Investigators will complete a high-resolution chronology of global plate motions since 20 million years ago, comprising most of the Neogene period. Sequences of closure-enforced plate rotations, at ~1 million year intervals, will describe the relative motions since 20 million years ago of all the major plates. The path to completing the study is well defined and consists of (1) new identifications of magnetic reversals from the southern Mid-Atlantic Ridge and Southeast Indian Ridge, as well as compilation of suitable fracture zone and transform fault flow lines along these and other spreading centers, (2) updates to largely complete sets of magnetic anomaly identifications from the southern Central Indian Ridge and Gulf of Aden, (3) compilations of existing reversal identifications from Pacific Basin spreading centers, if suitable, or new identifications for some Pacific Basin spreading centers, (4) methodological upgrades to estimate rotations consistent with plate circuit closures, to search more efficiently for best solutions, to include random and systematic data errors and the influence of the data geometry in rotation uncertainties, and to use a Bayesian methodology to suppress random noise in the rotation sequences. Half or more of the work needed to build the Neogene model has already been accomplished, partly by the Principle Investigator and a Russian collaborator via two NSF-funded projects that have spanned the past decade and partly by other investigators who have worked on the Neogene plate tectonics of the Pacific Basin. The existing data already include nearly 40,000 magnetic reversal identifications interpreted by the Principle Investigator for existing projects and 15,000 crossings of oceanic fracture zones and transform faults. Abundant data are available for completing the proposed analysis, including high-quality aeromagnetic data from the southern Mid-Atlantic Ridge that were previously unavailable for this kind of work.