Failed rifting and fast drifting: Midcontinent Rift development, Laurentia’s rapid motion and the driver of Grenvillian orogenesis

Abstract

The late Mesoproterozoic was a time of large-scale tectonic activity both in the interior and on the margins of Laurentia-most notably the development of the Midcontinent Rift and the Grenvillian orogeny. Volcanism within the North American Midcontinent Rift between ca. 1109 and 1083 Ma, as well as other contemporaneous volcanism within Laurentia, has provided an opportunity to develop extensive paleomagnetic data sets spanning this time period. These data result in an apparent polar wander path (APWP) for Laurentia that goes from a high latitude apex known as the Logan Loop into a swath known as the Keweenawan Track. A long-standing challenge of these data was the appearance of asymmetry between relatively steep reversed polarity directions from older rift rocks and relatively shallow normal polarity directions from younger rift rocks. This asymmetry was used to support an interpretation that there were large non-dipolar components to the geomagnetic field at the time. Recent data sets support the interpretation that this directional change was progressive and therefore a result of very rapid motion of Laurentia from high to low latitudes rather than a stepwise change across non-dipolar reversals. We present high precision U-Pb dates from Midcontinent Rift volcanics that result in an improved chronostratigraphic framework for rift volcanics and unconformities that improves correlations as well as constraints on rift development. We use these dates in volcanostratigraphic context to temporally constrain a new compilation of Midcontinent Rift paleomagnetic poles. 1 These paleomagnetic poles include new data from the North Shore Volcanic Group and the Osler Volcanic Group. The U-Pb dates constrain the rate of implied plate motion more precisely than has previously been possible. We apply a novel Bayesian approach to assess the rate of implied plate motion through inverting for paleomagnetic Euler poles. If the path is to be explained by a single Euler pole these inversions reveal that motion of the continent exceeded 27 cm/year. The path is particularly well-explained by a model wherein there is continuous true polar wander in addition to rapid plate motion that changes direction and slows at ca. 1096 Ma. Laurentia's movement from high to low latitudes resulted in collisional tectonics on its leading margin which could be associated with such a change in plate motion. We propose that upwelling of the Keweenawan mantle plume was associated with an avalanche of subducted slab material with downwelling that drove fast plate motion. This fast plate motion was followed by the Grenvillian orogeny from ca. 1090 to ca. 980 Ma. Prolonged collisional orogenesis could have been sustained due to this strong convective cell that therefore played an integral role in the assembly of the supercontinent Rodinia.

Primary and Secondary Red Bed Magnetization Constrained by Fluvial Intraclasts

“…As in our results, their data revealed a distinct mid‐temperature component with a shallow upward inclination and a high‐temperature component with a near horizontal inclination. A progression from horizontal to upward inclinations is consistent with the expected change through time if the movement along the Keweenawan Track persisted past the end of rift magmatism (Fairchild et al, ; Swanson‐Hysell et al, ) and is consistent with a later age of remanence acquisition for the mid‐temperature component. While the inclination of the mid‐temperature and high‐temperature components are indistinguishable between our data and that of Henry et al (), the declinations are different such that their declinations are ~24° more northerly than those obtained for BRa.…”

“…The direction of this chemical remanence is distinct, but similar, to that of the detrital remanence with a change in both declination and inclination. This result suggests that the chemical remanence was acquired as plate motion continued at the end of the Keweenawan Track (Swanson‐Hysell et al, ). This chemical remanent magnetization direction is well‐grouped (Figure ) suggesting that the hematite that carries the remanence formed at a similar time rather than over a protracted period (which could lead to a streaked distribution; Beck et al, ).…”

Evaluating the Shinumo-Sespe drainage connection: Arguments against the “old” (70–17 Ma) Grand Canyon models for Colorado Plateau drainage evolution

“…Laurentia's apparent polar-wander path during Mesoproterozoic to Cambrian time is shown in Figure 3B (Swanson-Hysell et al, 2019). Data sets from North America support the conclusion by Sabbeth et al (2019) that Mesoproterozoic source rocks would contain moderate primary inclinations and Neoproterozoic and Cambrian source regions would contain shallow inclinations.…”

Oxygenated Mesoproterozoic lake revealed through magnetic mineralogy

“…The Re-Os date for the Nonesuch Formation is shown in italics with 2σ uncertainty(11). The U-Pb dates(10,12) are shown with 2σ uncertainties (X/Y) that include analytical uncertainty alone (X) and include tracer and decay constant uncertainty (Y) for comparison with the Re-Os date. Cores studied in this work from the Ashland Syncline (DO-8 and WC-9) are shown with red stars.A B (A and B) Rock magnetic and iron speciation data from the DO-8 (A) and WC-9 (B) cores through the Nonesuch Formation.…”