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of Laurentia. These continental nuclei form 190–70 Ma Growth of the Western appropriate time to think about the tectonic
Laurentia’s core. Continental Margin by Subduction, record in the broadest possible terms.
With or Without Terrane Accretion Geophysical data sets are now widely avail-
1.9–1.7 Ga: Turning Points in This 190–70 Ma time slice saw the forma- able, and workers are processing and inte-
Paleoproterozoic Tectonic Evolution tion of the wide North America Cordillera grating the data in new ways to gain insight
The Paleoproterozoic time interval saw and the opening of the Gulf of Mexico, into 3D implications of surface observations.
the formation of the first recognizable pas- involving a number of processes, including Actualistic models of plumes, drips, slabs,
sive margins, formation and accretion of extension, shortening, lateral translation, slab tears, mantle wind, Moho variation, and
oceanic crust, arcs, back-arc basins, foreland subduction, magmatism, metamorphism, discontinuities at all levels of the crust, litho-
basins, and other environments arguably erosion, and sedimentation. sphere, and deeper mantle can be integrated
characteristic of modern plate tectonics. The choice of time slices is based, at least with the surface record in order to build a
in part, on the current literature and recent truly 4D model of Earth tectonics.
1.5–1.4 Ga: GEON 14 Enigmas meeting symposia that have highlighted new The second reason is more specifically
and Advances in Understanding insights and interpretations, as well as unre- related to the current time and environment
the Crustal Evolution and solved questions about Laurentia’s geologic in which we are living—itself a distinct
Paleogeography of the Early history. The selection of particular time “Turning Point.” As we write this article, we
Mesoproterozoic North America slices and the duration of the time windows are all sequestered in our homes in the hope
Mesoproterozoic Laurentia was dominated will certainly be debated, but it is hoped that that we can help mitigate the current pan-
by an Andean-scale active, but still very enig- the discussion will articulate critical ques- demic threat. We are also unsure whether the
matic margin, spanning ~5000 km, from east- tions or outstanding problems and foster 2020 GSA Montréal meeting will happen,
ern Canada to the southwestern United States future collaboration and innovation across and if so, in what form. This gathering of
and Mexico. the geological and geophysical research
communities. One aim is to gather momen- many geoscience disciplines under the
1.2–1.0 Ga: Mesoproterozoic to tum for developing new tools for open- framework of Laurentia’s evolution will be a
Early Neoproterozoic Tectonic source, widely available, collaborative inte- celebration of the creative, collaborative, and
Evolution of Laurentia and Its Role gration of time-slice data sets across geologic international efforts that have made the sci-
within the Supercontinent Rodinia disciplines and across the continent. As indi- entific advances possible. Plate tectonics is
The late Mesoproterozoic to early Neo- cated previously, we hope to distinguish our unifying theory, and as such, inherently
proterozoic spans the rise and fall of the times when Laurentia’s plate tectonic setting involves all the fields of the geological sci-
Grenville orogen at the center of the super- led to major changes in tectonic style from ences. Moreover, understanding the evolu-
continent Rodinia, the formation of the times when the controlling tectonic pro- tion of Laurentia has always required an
Midcontinent Rift, and the initial breakup of cesses themselves may have shifted. international effort, although most critically
Rodinia. Two or three session proposers/organiz- engaging people located in North America.
ers—including Canadian, U.S., and Mexican We are not just “in it together,” but with
700–540 Ma Neoproterozoic to researchers—have volunteered to chair and respect to Laurentia, we are “on it together.”
Cambrian Rifting and Continental coordinate the individual topical sessions. Our individual research programs have
Margin Evolution during Breakup of The goal is to solicit the broadest range of always benefitted from the research of col-
Rodinia and Pannotia researchers, research areas, and research dis- leagues, working in other places and on dif-
The Neoproterozoic to Cambrian time ciplines (including sedimentology, structural ferent problems in their respective subfields,
interval marked the breakup of Rodinia and geology, petrology, geophysics, geobiology, leading us to insights and discoveries that
Pannotia, and formation of the margins of etc.) in order to capture all aspects of the would have otherwise been out of reach. It
Laurentia. The Neoproterozoic was also a evolving continent (including now external has become more important than ever to
time of profound climatic and biologic Laurentian fragments and traces) and its assemble (whether in person or virtually),
change, which may have been related to consequent implications during a particular make new connections across our fields, and
these changing tectonic conditions. time slice. The Pardee Symposium and the together establish our collective understand-
seven associated topical sessions have been ing of the place we all share.
420–340 Ma Paleozoic Mobile endorsed by several GSA Divisions as well
Margins as the Mineralogical Society of America. REFERENCE CITED
The Silurian–Carboniferous closure of the There are two reasons that this is a particu- Barton, K.E., Howell, D.G., and Vigil, J.F., 2003,
Iapetus and Rheic oceans and the progressive larly opportune time to take such an adventur- The North America Tapestry of Time and Ter-
growth of the Appalachian-Caledonian oro- ous approach at a national meeting. First, the rain: U.S. Geological Survey, Geologic Investi-
gen along eastern Laurentia marked the onset conclusion of the EarthScope project in the gations Series I-2781.
of a series of tectonic events that propagated U.S., the LITHOPROBE project in Canada, Manuscript received 3 Apr. 2020
around Laurentia between the Devonian and and many other more regional geology- Revised manuscript received 15 Apr. 2020
Permian. geophysics collaborations make this an Manuscript accepted 24 Apr. 2020

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