Using the long-lived Mesoproterozoic Laurentia-Baltica (NENA) connection to test the geocentric-axial-dipole (GAD) model at 1.46 Ga

The geocentric-axial-dipole (GAD) model is fundamental for paleomagnetism, which is considered broadly valid for the last 2 billion years but still always worthy of rigorous testing. One way to test the GAD model in deep time is to utilize the rock records that have independent paleogeographic indications (e.g., evaporites) and see if the GAD model could give consistent paleolatitudinal estimates. Another approach is to take advantage of a robust plate reconstruction model and see if the spatial distribution of paleomagnetic directions is compatible with the GAD model. Recently, Sears (2021) questioned the robustness of the GAD model in the Mesoproterozoic, and proposed a normal-tesseral quadrupole as the predominant field. However, his proposal faces some problems. First, his reconstruction model places Siberia against southwest Laurentia, which is not widely accepted within the tectonics community. Second, in Sears (2021)s model, some paleomagnetic directions are at odds with a distribution predicted by a normal-tesseral quadrupole field. We propose to use the long-lived connection between Laurentia and Baltica (a.k.a. NENA reconstruction) in the Mesoproterozoic to directly test the field geometry at 1.46 Ga. Our approach has several advantages. For instance, the NENA reconstruction is well constrained by paired geology as well as paleomagnetic data on a several-hundred-million-year time scale. In addition, the data we carefully chose from Baltica and Laurentia are closely matched and precisely dated at 1.46 Ga, with age uncertainties less than ~20 million years. In this presentation, we make comparisons to see whether the 1.46 Ga data from Laurentia and Baltica could be satisfyingly explained by a GAD field, or whether a normal-tesseral quadrupole field needs to be invoked. Results from this study could help us better understand the evolution of Earths geodynamo since Mesoproterozoic time.