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

在板块构造的框架内，热点被假设为地下上升的热岩羽流的表面表现，这些热岩来自地球地幔深处，与板块相交，并在板块相对于热点横向移动时产生一系列火山链。热点可以是板块中火山活动的地点，如夏威夷和黄石公园，也可以是沿板块边界看到的火山过度活动的地点，如冰岛的中大西洋山脊。该项目的重点是夏威夷热点，该热点产生了夏威夷-帝王火山链，从夏威夷大岛东南最年轻和目前最活跃的洛伊希火山延伸5800公里，穿过夏威夷群岛，一直延伸到阿留申海沟附近有8000万年历史的明治海山。夏威夷链是夏威夷-帝王链中较年轻的部分，它从洛伊希向西北偏西方向延伸3500公里，向西北偏北方向变化近60°，形成皇帝海山链。这种朝向的变化被称为夏威夷-帝王弯，据估计约有5000万年的历史。这个项目旨在了解是什么导致了夏威夷-帝王链条的这种弯曲。两个基本假设是(1)5,000万年前烟柱静止不动，太平洋板块相对于烟柱的运动方向发生了变化；(2)在皇帝岩链形成过程中，岩柱快速南移，但自5,000万年前夏威夷岩链形成以来几乎没有运动。为了区分这些假设，该项目将分析由船舶和航磁调查收集的现有磁场数据，以确定在跨越夏威夷-帝王弯的一段时间间隔内锁定在洋壳和板块最上面地幔的磁化方向。时间平均的地磁场随纬度的变化是可以预测的，因此古代磁化方向将提供太平洋板块和与羽流相关的夏威夷-帝王火山的古纬度和古方位。了解这些基本过程将有助于更好地了解火山和太平洋盆地及其周围“火环”内的地震所造成的危险。这项拟议的工作将为研究生和本科生提供宝贵的研究经验和可移植的量化技能。这些方法和结果将被纳入大学讲课。热点和板块构造这一主题在更广泛的公众中很受欢迎，其结果将尽可能广泛地传播。磁异常偏斜度数据是可靠的古地磁极点的可靠来源。除了现有的海洋磁学数据外，该项目还将利用来自低古纬度的项目磁矢量航磁数据，以比其他方法更准确的方式获取极点。可靠的极点将在20R(44 MA)到26R(60 MA)之间确定可靠的极点，这包括夏威夷-帝王弯曲和极点相对于太平洋热点约8°的偏移。该项目将确定这种变化发生的时间和速度，并评估夏威夷热点相对于地幔参考系的运动有多少是由于真正的极地漂移造成的。将特别注意在65 Ma至32 Ma期间记录到的任何板块运动的加速，这可能为与夏威夷-帝王弯曲一致的太平洋板块运动的变化提供证据。该项目还将完成68 Ma、79 Ma和81 Ma时间段的数据分析，以更好地估计太平洋板块和夏威夷热点在北部帝王链形成期间的极地漂移。

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.