Laurentia: Turning Points in the Evolution of a Continent

The North American continent has a rich record of the tectonic environments and processes that occur throughout much of Earth history. This Memoir focuses on seven “turning points” that had specific and lasting impacts on the evolution of Laurentia: (1) The Neoarchean, characterized by cratonization; (2) the Paleoproterozoic and the initial assembly of Laurentia; (3) the Mesoproterozoic southern margin of Laurentia; (4) the Midcontinent rift and the Grenville orogeny; (5) the Neoproterozoic breakup of Rodinia; (6) the mid-Paleozoic phases of the Appalachian-Caledonian orogen; and (7) the Jurassic–Paleogene assembly of the North American Cordillera. The chapters in this Memoir provide syntheses of current understanding of the geologic evolution of Laurentia and North America, as well as new hypotheses for testing.
The Ordovician South Mayo Trough, a basin that recorded the passage of a triple junction along the Laurentian margin Available to Purchase
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Published:January 23, 2023
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CiteCitation
Paul D. Ryan*, John F. Dewey, 2023. "The Ordovician South Mayo Trough, a basin that recorded the passage of a triple junction along the Laurentian margin", Laurentia: Turning Points in the Evolution of a Continent, Steven J. Whitmeyer, Michael L. Williams, Dawn A. Kellett, Basil Tikoff
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ABSTRACT
Tectonic models for arc-continent collision can be overly complex where, for example, diachronous sedimentation and deformation along a single plate boundary are attributed to separate tectonic events. Furthermore, continuous sedimentation in a single basin recording a diachronous collision along a plate margin makes it difficult to use classical unconformable relationships to date an orogenic phase. In this chapter, we describe the Ordovician South Mayo Trough of western Ireland, a remarkable example of such a basin. It originated in the late Cambrian–Early Ordovician as a Laurentia-facing oceanic forearc basin to the Lough Nafooey arc. This arc was split by a spreading ridge to form a trench-trench-ridge triple junction at the trench. The basin remained below sea level during Grampian/Taconic arc-continent collision and, following subduction flip, received sediment from an active continental margin. Sedimentation ended during Late Ordovician Mayoian “Andean”-style shortening, broadly coeval with a marked fall in global sea level. These major tectonic events are traced through the nature of the detritus and volcanism in this basin, which is preserved in a mega-syncline. The Grampian orogen is not recorded as a regional unconformity, but as a sudden influx of juvenile metamorphic detritus in a conformable sequence.