Using electromagnetic geophysics to understand global tectonics and resource distribution

在地质历史的过程中，板块构造塑造了地球的表面。许多重要的过程都发生在构造板块相对运动的边界上。当两个板块会聚，一个大洋板块被迫向下进入地幔时，就形成了俯冲带。俯冲带之所以重要，是因为它们将水输送到地幔中，产生形成火山的熔融岩石，引起大地震，也形成重要类型的矿物存款。俯冲带存在于加拿大西部温哥华岛下面，是火山和地震危险的原因。俯冲带随着时间的推移而变化，有时下沉的板块会向外移动，阻止火山爆发并改变变形模式。这种行为发生在今天的安第斯山脉下面，纳斯卡板块在那里俯冲到南美洲板块之下。在秘鲁有一个扁平的板块，并向南生长。在哥伦比亚，以前平坦的板块最近变得陡峭，火山再次活跃。 这项研究计划将通过使用地球物理成像来调查俯冲带，以绘制水和部分熔体等流体的位置。绘制地球内部的流体分布图需要使用在地表测量的地球物理数据来确定深部岩石的性质。地震成像使用声波，但在对低浓度流体成像时无效。然而，流体会极大地改变岩石的电阻率，这种特性可以用大地电磁法（MT）来确定，大地电磁法是一种地球物理勘探方法，它使用低频无线电波对地下超过200公里的深度进行成像。 在这项建议中，MT将被用来研究发生在加拿大和南美洲的俯冲带的过程。对自然无线电波的测量将转换成地球电阻率的三维图像。根据这些3D模型，将确定水和熔融岩石的分布。在加拿大，这将有助于了解温哥华岛下的俯冲带中哪里有水，以及加里波第带火山喷发的熔融岩石起源于哪里。在秘鲁和哥伦比亚，三维模型将显示当板块变平和变陡时地球结构的变化。 在相关研究中，MT方法将用于调查过去北美大陆形成时发生的构造事件。由此产生的模型将用于研究这些过去的事件如何形成矿床。这一过程正被用来改进矿物勘探方法，不仅要寻找矿床，而且要寻找矿物系统中过去流体流动的区域。 研究计划的一个主要重点将是培养本科生和研究生谁将有资格在学术研究，减少灾害和矿产勘探工作。

Plate tectonics has shaped the surface of the Earth over the course of geological history. Many important processes occur at the boundaries where tectonic plates move relative to each other. Subduction zones are formed when two plates converge and an oceanic plate is forced downwards into the mantle. Subduction zones are important because they transport water into the mantle, generate molten rock that forms volcanoes, cause large earthquakes and also form important types of mineral deposit. A subduction zone is present in Western Canada beneath Vancouver Island and is responsible for both volcano and earthquake hazards. Subduction zones vary over time and sometimes the down going plate flattens out, stopping the volcanoes from erupting and changing the pattern of deformation. This behaviour occurs today beneath the Andes mountains where the Nazca Plate subducts beneath the South American Plate. In Peru a flat slab is present and grows southward. In Colombia, a previously flat slab has recently steepened, with volcanoes becoming active once again. This research program will investigate subduction zones by using geophysical imaging to map the location of fluids such as water and partial melt. Mapping fluid distribution within the Earth requires the use of geophysical data measured at the surface to determine the properties of rocks at depth. Seismic imaging uses acoustic waves but is not effective at imaging low concentrations of fluids. However, fluids dramatically change the electrical resistivity of a rock and this property can be determined with magnetotellurics (MT) a geophysical exploration method that uses low frequency radio waves to image the subsurface to depths in excess of 200 km. In this proposal, MT will be used to study the processes that occur in subduction zones in Canada and South America. Measurements of the natural radio waves will be converted into 3-D images of the electrical resistivity of the Earth. From these 3-D models the distribution of water and molten rock will be determined. In Canada this will improve understanding of where water is present in the subduction zone beneath Vancouver Island and where the molten rock originates that is erupted in the volcanoes of the Garibaldi Belt. In Peru and Columbia the 3-D models will show how Earth structure changes when slabs flatten and steepen. In related research, the MT method will be used to investigate the tectonic events that occurred in the past as the North American continent was formed. The resulting models will be used to investigate how these past events formed mineral deposits. This process is being used to improve the methods used in mineral exploration by searching not just for mineral deposits, but regions of past fluid flow in the mineral systems approach to exploration. A major emphasis of the research program will be to train undergraduate and graduate students who will be qualified to work in academic research, hazard reduction and mineral exploration.