Pacific plate apparent polar wander and Pacific-Farallon spreading rates bracketing the age of the Hawaiian-Emperor Bend

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Within the framework of plate tectonics, hotspots are hypothesized to be the surface manifestation of an underlying rising plume of hot rock that comes from deep in Earth's mantle to intersect the plate and create a chain of volcanoes as the plate moves laterally relative to the hotspot. Hotspots can be sites of mid-plate volcanism such as Hawaii and Yellowstone or sites of excessive volcanism as seen along plate boundaries as in Iceland on the Mid-Atlantic Ridge. This project focuses on the Hawaiian hotspot, which has produced the Hawaiian-Emperor chain of volcanoes that extends 5800 kilometers from the youngest and currently active volcano Loihi, just southeast of the big island of Hawaii, through the Hawaiian Islands to the 80 million year old Meiji seamount near the Aleutian trench. The Hawaiian chain, which is the younger part of the Hawaiian-Emperor chain, is oriented west-northwest from Loihi for a distance of 3500 km where it changes in orientation by almost 60° to the north-northwest and becomes the Emperor seamount chain. This change in orientation is called the Hawaiian-Emperor bend and is estimated to be about 50 million years old. This project is aimed at understanding what causes this bend in the Hawaiian-Emperor chain. The two basic hypotheses are (1) that the plume stood still and the Pacific plate changed its direction of motion relative to the plume 50 million years ago, or (2) that the plume moved rapidly southward during formation of the Emperor chain, but has moved little since 50 million years ago as the Hawaiian chain was formed. To distinguish between these hypotheses the project will analyze existing magnetic field data collected by ship and aeromagnetic surveys to determine the direction of magnetization locked into the ocean crust and uppermost mantle of the plate during a time interval spanning the Hawaiian-Emperor bend. The time-averaged geomagnetic field varies predictably with latitude, so that ancient magnetization directions will provide the paleolatitude and paleo-orientation of the Pacific plate and the plume-related Hawaiian-Emperor volcanoes. Understanding these fundamental processes will permit a better understanding of hazards posed by volcanoes and by earthquakes within the Pacific Ocean basin and the surrounding "ring of fire". The proposed work will give valuable research experience and transferable quantitative skills to graduate and undergraduate students. The methods and results will be incorporated into university lectures. The subject of hotspots and plate tectonics is popular with the broader public and the results will be disseminated as widely as possible.Magnetic anomaly skewness data are an established source of reliable paleomagnetic poles. In addition to existing marine magnetic data, this project will utilize Project MAGNET vector aeromagnetic data from low paleolatitudes to obtain poles with greater accuracy than alternative methods. Reliable poles will be determined with compact confidence limits for chrons between 20r (44 Ma) and 26r (60 Ma), which bracket the Hawaiian-Emperor bend and a shift in the pole relative to Pacific hotspots of about 8°. The project will determine when and how rapidly this shift occurred and evaluate how much is due to motion of the Hawaiian hotspot relative to a mantle reference frame and how much is due to true polar wander. Particular attention will be paid to any accelerations in plate motion that are recorded in the time span from 65 Ma to 32 Ma which may provide evidence for or against a change in Pacific plate motion coincident with the Hawaiian-Emperor bend. The project will also complete the analysis of data from time periods 68 Ma, 79 Ma, and 81 Ma to better estimate Pacific plate and Hawaiian hotspot apparent polar wander during the formation of the northern Emperor chain.