Laurentia: Turning Points in the Evolution of a Continent
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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.
Pre-Pangean evolution of central southern Laurentia: Insights from zircon U/Pb geochronology, Marathon-Solitario fold-and-thrust belt, west Texas
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Published:January 23, 2023
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CiteCitation
Patricia W. Dickerson*, Blaine R. Hall, Daniel F. Stockli, Lisa D. Stockli, Richard E. Hanson, C. Mark Fanning, Paul O'Sullivan, 2023. "Pre-Pangean evolution of central southern Laurentia: Insights from zircon U/Pb geochronology, Marathon-Solitario fold-and-thrust belt, west Texas", 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
Upper Cambrian through Middle Ordovician sedimentary strata of the Marathon/Solitario Basin (west Texas), which were folded and thrust-faulted during late Paleozoic Appalachian-Ouachita orogenesis, preserve evidence of the pre-Pangean history of the central southern Laurentian margin. New detrital zircon analyses reported here are from three Marathon Basin/Solitario formations: the upper Cambrian Dagger Flat Sandstone; the Lower Ordovician Marathon Formation, including the Rodrigues Tank Sandstone Member; and the Middle Ordovician Ft. Peña Formation. The far-southwestern outcrops of those Iapetus margin strata are within the Solitario dome (Presidio and Brewster Counties, Texas).
Solitario zircon U/Pb geochronological results (laser ablation–inductively coupled plasma–mass spectrometry [LA-ICP-MS], sensitive high-resolution ion microprobe [SHRIMP]) expand the record of Cryogenian rifting as the Cuyania terrane separated from Laurentia. We evaluated these new data along with earlier geochronological and geochemical results from rift-related lava clasts in Lower–Middle Ordovician sedimentary subaqueous debris-flow deposits in the northwestern Marathon Basin. Deepening of the Iapetus seaway near the Laurentian margin (late Cambrian–Middle Ordovician) stimulated headward erosion of drainages, reflected in the systematic north-northwestward shift in zircon provenance from the west Texas Grenvillian and Southern Granite-Rhyolite Provinces to Yavapai-Mazatzal and Cheyenne Belt sources.
The Cuyania rifted terrane underwent subduction at the western Gondwanan margin of the Iapetus Ocean in mid-Ordovician time (486 ± 7 Ma to 463 ± 4 Ma), and the resulting volcanism in the Famatina complex (Argentina) was most intense from ca. 472 to 468 Ma. Magmatic zircons from Ft. Peña bentonitic layers have identical U/Pb (488–468 Ma) and biostratigraphic (Darriwilian) ages to those from Famatinian bentonites at Talacasto (470 ± 5 Ma) in the Precordillera of Cuyania. Geologically constrained paleomagnetic reconstructions for 470 Ma depict the proximity of the Famatina arc, the rifted Cuyania terrane, and southern Laurentia at low southern latitudes (equator to ~30°S). These first U/Pb geochronological data from the Marathon/Solitario depocenter of western Iapetus appear to be compatible with such a configuration and can serve as test data for emerging tectonic interpretations.
