| 英文摘要: | The seismically active Mackenzie Mountains are an enigmatic range in the Canadian Subarctic spanning the Yukon and Northwest Territories. Unlike most mountain ranges, the Mackenzies lie far away from the nearest (Pacific-North American) plate boundary where mountain-building stresses originate. Somehow, stress is being transferred for hundreds of miles across the relatively undeformed Yukon Territory to cause this actively uplifting range to fold up against the ancient and rigid heart of interior North America. This region is one of the most geophysically unexplored in all of North America, and understanding it is a key to a broader understanding of the whole Alaskan/Canadian tectonic system and how it forms mountains (including the highest in North America) and generates earthquakes. The Mackenzie Mountain range is the only actively deforming range in of its type in North America today, but its deep interior uplift style has similarities to important past mountain building events that formed the Rocky Mountain Cordillera that runs through much of the North American West, including major provinces of the U.S. Rocky Mountains in Colorado, Wyoming, and Montana. The project will produce new insight into the past and present mountain-building processes of the region by imaging the deep geological and seismic structure and measuring the ongoing surface deformation, and by interpreting these new data in a full geological context. To do this, students and faculty from Colorado State University and the University of Alaska?Fairbanks will deploy an array of forty broadband seismometers, and 3 new continuous GPS instruments augmented with campaign surveys at 25 more sites, transecting the wilderness heart of the Mackenzie Mountains for over 1000 km. This project will be undertaken in partnership with Yukon College, a two-year college, to engage undergraduates in research and fieldwork, and to expose them to new research opportunities and career insights beyond which are common for students in the Yukon and Northwest Territories. Furthermore, we will, for the first time, be able to emplace seismometers and GPS instruments near the zones of active seismicity, to better locate regions of active faulting. While this area is sparsely populated, understanding seismic risk here is essential for protecting critical infrastructure such as oil and gas pipelines and mine waste impoundments.
The Mackenzie Mountains are actively deforming in a zone far inboard from the main plate boundary (Yakutat terrane), while the region between the plate boundary and the mountains is relatively aseismic. Early uplift of the Mackenzie Mountains suggests that inherited lithosphere-scale terrane boundaries may also play a role in their location. A prevailing hypothesis (Mazzotti and Hyndman, 2002) to explain the anomalous characteristics of the Mackenzie Mountains is that lateral transport in the relatively aseismic zone occurs along a crustal or lithospheric-scale detachment, with little deformation between the Yakutat indentor and the eventual inboard collision with the craton. Constraining surface strain from GPS in association with seismic tomography and anisotropy studies will enable us to test/refine/refute this hypothesis for intraplate stress transfer and to understand the geometry and nature of interaction between mobile lithosphere and the craton in much more detail than has been previously possible in this remote area. This project will test a number of predictions based on this prevailing model, related to: viscosity, lithosphere-scale structure, evidence for crustal/lithosphere scale detachment, the transition between mobile and cratonic lithosphere, the partitioning of strain between the mobile belt and craton, and the influences and depth extent of major faults (i.e., the Tintina fault), and the associations between high heat flow and volcanism and lithosphere through upper mantle structure. As an integral part of the project, the research team will partner with Yukon College to incorporate First Nations and other local students in fieldwork, research and outreach, and to contribute to geophysical career and scientific opportunities and broad awareness for students at that institution. We will involve an undergraduate student at University of Alaska Fairbanks with fieldwork and encourage the student to follow this up with undergraduate research using the data. Other institutional broader impacts include links to Canadian, French, and Australian research partners, as well as linking to an ongoing (IRIS (Incorporated Research Institutions for Seismology) undergraduate intern-associated) seismicity analysis partnership with the United State Geologic Survey, where the intern is also a possible candidate for eventual graduate student engagement in this project, and the education of two graduate students. Furthermore, the new instrumentation will provide first-order constraints on regions of active faulting and seismic hazard, important for preventing industrial accidents and their associated environmental impacts. Finally, we will integrate our surface wave research into classroom materials for use at our institutions and to be made publically available as part of an IRIS Education and Public Outreach initiative. |