LAURENTIA 2020: WHAT HAVE WE LEARNED IN THE PAST DECADE?

In 2007 the author of this abstract co-authored a synthesis of the current knowledge about the Precambrian tectonic evolution of Laurentia. At that time the Canadian Lithoprobe project was finishing and the US EarthScope project was starting. Thus, it was an appropriate time to document what we thought we knew about the tectonic history of Laurentia and to be provocative about what we might discover in the coming decade. More than a decade has passed, the EarthScope project and two major northern Canada mapping programs have concluded, and it is again time to assess current knowledge about Laurentia tectonics, and perhaps also time for another provocative look at potential future discoveries and interpretations.

Whitmeyer and Karlstrom (2007) presented a sequence of images that illustrated the growth and development of Laurentia at time slices from the Paleoproterozoic to the Cambrian. The GSA 2020 “Assembling Laurentia” Pardee session and associated theme sessions take a similar approach and focus on key periods of tectonic activity (“turning points”) that had significant impacts on Laurentia. Highlighted examples of turning points that encompass important changes in the character, rate, or style of tec­tonic processes and/or fundamental changes in global tectonics processes include: formation of crust and cratonization in the Neoarchean, development of modern tectonics and secular changes in the Paleoproterozoic, crustal evolution and accellerated tectonics in the early Mesoproterozoic, the role of Laurentia within the Proterozoic supercontinent of Rodinia, rifting and continental margin evolution during the Neoproterozoic breakup of Rodinia and transition to Pannotia and Gondwana, Paleozoic closure of the Iapetus and Rheic oceans and growth of the Appalachian-Caledonian oro­gen, and the Mesozoic growth of the western continental margin by subduction processes. Although certainly not the only important time periods in the evolution of Laurentia, these turning points highlight the collaborative inte­gration of data sets across geologic disciplines and illustrate how discontinuities at all lev­els of the crust, lithosphere, and deeper mantle can be integrated with the surface record in order to develop a truly four dimensional model of Earth tectonics.