Uncovering the origins of continents
Until recently, the development of the first real continental crust on Earth was something of a mystery. However, research within the Earth Ocean and Atmospheric Science Department (EOAS) at UBC, published last week in Nature Communications marks a breakthrough in current understanding of the origins of the modern lithosphere.
On modern Earth, the production of new continental crust is driven by plate tectonics and, in particular, within subduction zones. Yet, plate tectonics is likely to have worked very differently, or not at all, during the first few billion years of Earth’s history. This presents a chicken and the egg problem for scientists: Did the first crust result from the start of plate tectonics or did plate tectonics start as a result of the continents developing? If not for plate tectonics, how else may the continental crust have developed?
Dr. Matthijs Smit, EOAS associate professor and Canada Research Chair, used specific chemical tracers that are unaffected by geological alteration processes to identify the source of the rocks that made up most of the newly formed continental crust during the Archaean: tonalite-trondhjemite-granodiorites (TTGs). By studying the chemical composition of TTGs across the globe, using data amassed in an international database, Dr. Smit and coauthors Kira Musiyachenko and Jeroen Goumans, were able to tease out large scale patterns. Trends in TTG compositions indicate that these rocks formed during slow burial, thickening and melting of precursor oceanic plateau crust. Their discovery provides a novel explanation of how continental crust may have originated without requiring an external driver, such as a meteorite impact. The findings published last week are a paradigm shift in the way geoscientists have understood the origins of continental crust and plate tectonics during the Archean era.