Continental Rifting and Precambrian Tectonics: Insights from Gravity Modeling and Apparent Polar Wander Paths

Elling, Reece Phillip

doi:https://doi.org/10.21985/n2-1q02-1w59

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Continental Rifting and Precambrian Tectonics: Insights from Gravity Modeling and Apparent Polar Wander Paths

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Failed continental rifts provide unique opportunities to study aspects of plate tectonic evolution frozen in time. North America contains three major failed rifts: The Midcontinent Rift (MCR), Southern Oklahoma Aulacogen (SOA), and the Reelfoot Rift (RR). To understand why some rifts fail and why others might succeed to seafloor spreading, this thesis explores details of these rifts and their interactions within the framework of Laurentia’s tectonic history.First, in Chapter 2, I explored aspects of the ~1100 Ma MCR. Although it is exposed along Lake Superior, it is primarily delineated by gravity, magnetic, and seismic data through the central United States. Its structures and evolution, defined by gravity modeling, seismic, and geologic data, tell a story of a sequence of extension, volcanism, subsidence, sedimentation, and subsequent inversion. Near the MCR’s eastern arm also lie orogenic facies related to the Grenville Orogeny, a series of discrete collisions between Laurentia and Amazonia that culminated in the assembly of the supercontinent of Rodinia. I examined the interaction of these juxtaposing tectonic events using their gravity signatures and determined that the lineated gravity highs in the eastern U.S. appear similar to those along the remainder of the MCR, and unlike those along any portion of the Grenville Front (GF) where it is exposed and identified by seismic and potential field data in Canada. However, thrust sheet structures, like those of the southern Canadian GF, are likely present along the MCR’s east arm, as implied by recent seismic data. Next, in Chapter 3, I investigated the similarities and differences of North America’s three major failed rifts – the MCR, SOA, and RR – to gain insight into the rifting process. All three rifts formed in similar tectonic settings as part of Laurentia’s interactions within Rodinia, and followed similar evolutionary paths of extension, magmatism, subsidence, and inversion by later compression, leading to similar widths and architecture. However, differences between the rifts reflect the extent to which these processes occurred. Because no sea floor older than a few hundred million years exists, understanding the tectonics of the Precambrian requires the use of paleomagnetic data to constrain plate motions and model global tectonics. Part of this research, described in Chapters 4 and 5, involved consistent collection and compilation of over 15,000 published paleomagnetic poles to support global plate modeling efforts. The compilation supported a 1.5 Ga plate model that I used to create apparent polar wander (APW) paths for Laurentia, Amazonia, and eleven other major plates. Because cusps in APW paths have long been proposed to be caused by continental rifts or major collisional orogenies, I analyzed this hypothesis by determining the timing of directional changes in the motion of each plate and correlating them to the timing of major tectonic events. Preliminary investigations show promising statistical correlations between the two. This approach can be useful in defining tectonic events in time periods during which paleomagnetic data may be the only constraints.

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