Under Pressure: Strain and Stress Constraints on the Longevity of Modern Plate Tectonics Inferred From 3.5 Ga Intrusions in Isukasia, Southwest Greenland

Abstract:

Constraining the longevity of modern plate tectonics is essential for understanding Archean crustal thickening and the processes that formed the existing cratons. The 3.7 - 3.8 Ga rock record preserved in the Isua Supracrustal Belt (ISB) has been debated as evidence for temporally isolated subduction, the initiation of continuous, modern-day plate tectonics, or as stagnant-lid dynamics. Assessment of a slightly younger regional event, such as the 3.5 Ga Ameralik dike swarm, for evidence of modern-style plate tectonics could assess if any subduction related to the ISB was temporally isolated, or the start of modern, continuous plate tectonics. Previous research has not confirmed the number of intrusive events comprising the Ameralik dike swarm, nor has it quantitatively analyzed the dominant stress directions during emplacement. Thus, we focus on the relatively undeformed Ameralik dike swarm north of the ISB to constrain the regional tectonic history of the Isua region. We utilize remote sensing data from ArcticDEM and optical imagery from Sentinel-2 to map and quantitatively interpret the northern Ameralik dikes. First, we analyze these datasets at specific key localities that correspond to outcrop observations on the ground, and develop criteria for identifying dikes in the full area. We then expand our analysis to the entire region north of the ISB to quantitatively assess dike lengths and orientations. We determine the number of intrusive events and the dominant stress orientations for each event, and test for the extent of folding of the ISB post-dike emplacement. Ongoing analysis is focused on testing the previously published hypothesis that modern plate tectonics, rather than stagnant-lid dynamics, operated 3.5 Ga. Our findings may help constrain the longevity of modern plate tectonics on Earth.