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Assembling Laurentia—Integrated Theme

Sessions on Tectonic Turning Points

Michael L. Williams, Dept. of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA, mlw@geo.umass.edu;
Dawn A. Kellett, Geological Survey of Canada–Atlantic Division, Natural Resources Canada/Government of Canada, 1 Challenger
Drive, Dartmouth, Nova Scotia B2Y 4A2, Canada, dawn.kellett@canada.ca; Basil Tikoff*, Dept. of Geoscience, University of Wisconsin–
Madison, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA, basil@geology.wisc.edu; Steven J. Whitmeyer, Dept. of Geology and
Environmental Science, James Madison University, 801 Carrier Drive, MSC 6903, Harrisonburg, Virginia 22807, USA, whitmesj@jmu.edu

The North American continent records the headlined by a Pardee Symposium, which and the broader implications of, these changes,
evolution of tectonic processes and tectonic will provide an overview of the tectonic evo- and to widen the scope of investigation
environments from the earliest Archean to lution of Laurentia and an introduction to the beyond a particular boundary or regional geo-
modern times. The continent hosts a rich concept of key “Turning Points.” Seven logical event to the scale of Laurentia itself.
Archean (and possibly Hadean) record, at related topical sessions, under the general The time slices for the topical sessions are as
least three great Proterozoic orogenic belts, heading “Assembling Laurentia,” will span follows (with brief explanations from each
and a wide range of Phanerozoic tectonic, the GSA meeting. Each session will scruti- session proposal):
sedimentary, and paleobiologic environ- nize key periods in the long history of the con-
ments, including active plate boundaries. In tinent when the character, rate, or style of tec- 2.8–2.5 Ga: Neoarchean Crust
many ways, Laurentia (ancestral North tonic processes may have changed or when Formation and Cratonization
America) might be thought of as the proto- the plate tectonic process itself may have The Neoarchean time interval was the last,
typical continent, with a little—if not a lot— changed in some fundamental way. The ulti- great episode of Precambrian crust forma-
of everything. With its long record of chang- mate goal is to identify potential drivers for, tion prior to the Paleoproterozoic assembly
ing tectonic settings, supercontinent cycles,
and geologic outcomes, one question per-
sists: Does Laurentia preserve a record of
fundamental, relatively short duration
changes in tectonic processes on Earth, or
rather, a gradually changing configuration of
continents in a slowly evolving plate tectonic
system? The resolution of this question
requires a continent-wide perspective on tec-
tonics through time, and it requires the inte-
gration of many fields of geoscience. One
way to approach the question is to ask (1)
what is the holistic geological character of
Laurentia at particular times in Earth his-
tory?; and (2) what are the apparent control-
ling factors at those times, from mantle
dynamics to plate interactions, to surface
weathering, to biological evolution?
The GSA 2020 Annual Meeting provides
an opportunity to address the tectonic evolu-
tion of Laurentia and the evolution of tectonic
processes in general as an international geo-
science community. A meeting-long series of Figure 1. The tapestry of North
American geology, showing regions
topical sessions have been organized that will of exposed Archean and Protero-
focus on important times—which we call zoic rocks in red-orange colors,
Paleozoic rocks in purple-blue col-
“Turning Points”—in the assembly, disas- ors, Mesozoic rocks in green col-
sembly, modification, and growth of North ors, and Cenozoic rocks and sedi-
ments in yellow colors. After Barton
America (Fig. 1). These sessions will be et al. (2003).
GSA Today, v. 30, https://doi.org/10.1130/GSATG459GW.1. Copyright 2020, The Geological Society of America. CC-BY-NC.

*Corresponding author.

36 GSA Today | July 2020