Do continental collisions cause major dimensional changes in the impacted continents?

Tuesday, March 22, 2016 - 4:10pm

Major changes in continental dimensions are suggested to occur after continental collisions. In a paper recently published in the December issue of Geology, considered the number one Earth Science journal for provocative research, Professor Emeritus Henry Halls advocates that about a billion years ago the North American continent was shortened by about 4000 km in a NW-SE direction during a mountain-building episode, caused by the collision of Laurentia (ancestral North America) and a part of South America (Amazonia). The result of this collision is seen in the Grenville Province, a belt of highly deformed rocks, now largely transformed from their original state under high pressures and temperatures, and repeatedly thrust towards the NW along a stack of southeast - dipping faults.  These rocks form a now deeply-eroded former mountain chain that runs for several thousand kilometers down the eastern seaboard of North America. Key evidence for the crustal shortening  includes newly-acquired  paleomagnetic data obtained from the Paleomagnetism Laboratory of UTM’s Department of Chemical and Physical Sciences. The Grenville Province is of a scale comparable to the Himalaya Mountains which are presently being formed as a result of India’s collision with Asia. Across the Himalayas at least 1600 km of crustal shortening has been documented over the last 50 my, but India continues to move northwards with respect to Asia at almost 4cm/yr so further shortening can be expected. Since the Grenville mountain-building episode has developed to completion, a shortening of 4000 kilometres may not be unreasonable or excessive.  For the Himalayas the shortening is accompanied at deeper, hotter crustal levels by lateral extrusion of the crust. If lateral extrusion has occurred in Laurentia, its area may have remained substantially the same and only the shape changed.  The implications of the study are that following major continental collisions, significant changes in the dimensions of the impacted continents might be expected. This in turn will impact paleogeography, paleoclimate and also the fitting together of continents in the geological past. Full Article Here