The tertiary magmatic sweep, Nevada, and early proterozoic tholeiitic/alkaline/peralkaline plutonism, Northwest Territories

该项目的目标是：a)更好地了解美国西部过去4000万年形成的火成岩的来源；b)调查与加拿大西北地区南部一个古老超大陆分裂有关的火成岩活动。在过去的4000万年里，美国西南部，特别是内华达州的火山活动非常剧烈，伴随着地壳的伸展和断裂。火山活动有条不紊地从东北向西南横扫内华达州，这可能是法拉龙板块在北美下方俯冲的结果。对于火山活动是如何与俯冲板块或地壳伸展联系起来的，火山岩的来源是什么，以及这种火成岩活动在多大程度上导致了内华达州同时期的金矿化，我们知之甚少。我们试图确定岩浆的来源，无论是在地幔还是在地壳（或两者兼而有之），并更好地描述火山活动横扫内华达州北部和西部的时间。在西北地区，大约20亿年前，沿大奴湖东岸形成了一个火成岩侵入杂岩，携带着富含铌、钽和稀土元素的岩石，这些元素对工业都很重要。这些侵入标志着该地区历史上的一个新时期，在经历了长时间的地质静止之后，一个古老的大陆被分裂成碎片，使这些侵入物得以浮出水面。了解这些侵入体的地球化学特征、成因以及它们之间的关系，将有助于改进具有重要经济意义的稀土矿物的成因模式，并为该区寻找更多矿化提供帮助。

The goals of this project are to a) better understand the sources of igneous rocks emplaced during the last 40 million years in the western United States, and b) investigate igneous activity associated with breakup of an old supercontinent in the southern Northwest Territories of Canada. The past 40 million years has been a time of intense volcanic activity in the southwestern United States, particularly Nevada, accompanied by stretching and faulting of the crust. Volcanism swept methodically from northeast to southwest across Nevada, presumably a result of the subduction of the Farallon Plate beneath North America. We understand very little of how volcanism was linked to the subducting plate or crustal stretching, what the sources for the volcanic rocks were, and to what degree this igneous activity was responsible for contemporaneous gold mineralization in Nevada. We seek to identify the sources of magmas, either in the mantle or in the crust (or both), and better describe the timing of the sweep of volcanism across northern and western Nevada. In the Northwest Territories, an igneous intrusive complex was emplaced along the East Arm of Great Slave Lake around 2 billion years ago, carrying with it rocks rich in Nb, Ta, and rare earth elements, all important to industry. The intrusions mark a new period in the history of the region, where, after a long period of geological quiescence, an old continental landmass was split into fragments that allowed these intrusions to rise to the surface. Understanding the geochemistry and origin of the intrusions and the relationships between them will improve models for the origin of the economically important rare earth minerals and add to the exploration effort for more mineralization in the area.