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The Rocky Mountain chain is a fascinating geologic formation, as it (at least, at first glance) defies some basic geological rules, including that most mountain ranges form subduction zones.<\/p>\n
A new study further complicates the formation of the Canadian Rockies by using seismic tomography to show that the North American craton\u2014the geologic heart of the continent\u2014actually dips six degrees westward near the Rockies rather than forming a sharp vertical step as previously believed.<\/p>\n
Better understanding of the Cordillera-craton boundary (CCB) will help scientists discover answers about this perplexing geologic formation.<\/p>\n
In Geology 101, you learn that mountain ranges form near subduction zones. Take, for example, the famous Himalayas<\/a>, or the Cascades<\/a> in North America. These mountains ranges were formed by two tectonic plates crashing into each other and one slipping under, or subducting, the other. The result of these geologic pile-ups is towering, majestic mountaintops that serve as reminders of our tectonic history.<\/p>\n And then, there are the Rocky Mountains<\/a>.<\/p>\n Although this mountain range\u2014which stretches from northern Canada to New Mexico\u2014provides some of the most stunning views on the continent, the range is hundreds of miles away from any subduction zone<\/a>. This makes the Rockies a bit of a conundrum when piecing together its formation history, and a new study published in the journal Nature Communications<\/a> shows that geologists are still learning new things about the range to this day.<\/p>\n In this study, scientists from the University of Alberta relied on seismic analysis to glimpse the boundary between two plates\u2014the Cordilleran layer (75 kilometers deep) and the craton layer (180 kilometers deep)\u2014in the Canadian Rockies. A Cordillera (Spanish for \u201clittle rope\u201d) describes the thin, hot lithosphere<\/a> that makes up mountain chains, such as the Rockies and the Andes, whereas a craton is the geologic core of a continent.<\/p>\n The most effective method for examining geological structures so deep beneath the Earth\u2019s crust is to rely on seismic measurements that pass through the region. This method, known as \u201cseismic tomography,\u201d tracks the speed and direction of seismic waves as they pass through certain materials, providing a snapshot of the complex geology beneath our feet. By analyzing this Cordillera-craton boundary (CCB), the authors discovered new characteristics of the geologically dynamic region.<\/p>\n For one, the North American craton\u2014which terminates in Alberta in the Canadian Rockies\u2014actually dips 6 degrees westward. This is in contrast to the previously held belief that this boundary was actually a sharp, vertical step. Secondly, the bottom of the craton is being eroded by the hot mantle rock<\/a> located beneath it.<\/p>\n \u201cOur study offers compelling evidence for a multi-layered lithospheric architecture beneath the eastern Cordillera,\u201d the authors wrote, \u201c[and] provide[s] an impetus for a better understanding of the Cordillera-craton boundary evolution, especially when aided by improved constraints from seismic tomography, geological sampling and geodynamic modelling.\u201d<\/p>\n