Collaborative Research: Late Cretaceous and Cenozoic Reconstructions of the Southwest Pacific

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This award, provided jointly by the Antarctic Geology and Geophysics Program of the Office of Polar Programs and the Marine Geology and Geophysics Program of the Division of Ocean Sciences, supports research to develop improved plate rotation models for the Southwest Pacific region (between the Pacific, Antarctic, and Australian plates, and the continental fragments of New Zealand, West Antarctica, Iselin Bank, East Antarctica, and Australia). The improved rotation parameters will be used to address tectonic problems related to motion between East and West Antarctica, and in particular, the questions of relative drift between major hotspot groups and the controversy regarding a possible missing plate boundary in this region. Previous work has documented NNW-striking mid-Tertiary seafloor spreading magnetic anomalies between East and West Antarctica, representing about 150 km of opening of the Adare Trough, north of the Ross Sea. This is not enough motion to resolve the apparent discrepancy between the plate motions and motions inferred from assuming hotspot fixity. Because this motion between East and West Antarctica corresponds to a very small rotation, it points to the need for determination of finite rotations describing motions of the various plates here with a high degree of accuracy, particularly for older times. This is now possible with the datasets that will be used in this project. The work will be accomplished by integrating existing data with analysis and interpretation of other data sets recently made available by Japanese and Italian scientists from their cruises in the region. It will be further augmented by acquisition of new marine geophysical data on selected transits of the R/VIB Nathaniel B. Palmer. Specific objectives of the project include the following:1) improve the rotation model for mid-Tertiary extension between East and West Antarctica by including the plate boundary between the Pacific and Australia plates directly when calculating Australia-West Antarctica motion,2) improve the reconstructions for the Late Cretaceous and Early Tertiary times by including new constraints on several boundaries not previously used in the reconstructions,3) address the implications of new rotation models for the question of the fixity of global hotspots,4) re-examine the geophysical data from the Western Ross Sea embayment in light of a model for substantial mid-Cenozoic extension.