Partial convective overturn basins: A qualitative model based on salt minibasins

Abstract

Early Earth tectonic processes remain enigmatic. One proposed regime that does not exist on Earth today is partial convective overturn (PCO), where dominantly vertical tectonism is driven by density instabilities. Predicted effects of PCO on the rock record focus on structural, igneous, and metamorphic evidence, many of which are non-unique. To supplement this, we propose a qualitative model of PCO basin sedimentology, stratigraphy, and architecture based on characteristics of salt minibasins. We argue that halotectonics provide an appropriate analogue for PCO surface processes as both have density-driven diapirism resulting in surficial patterns of domal relief and inter-diapir accommodation. Our PCO basin model is characterized by the combination of (1) paleohighs over domes, (2) syn-depositional diapirism, and (3) diapir-influenced basin shape. We propose several lines of evidence for each of these characteristics, including an unroofing provenance sequence, reduced depositional energy away from domes, paleoflow shedding off of the domes, and progressive angular unconformities observed on multiple sides of a dome or basin. We compare our model to previously proposed features of PCO basins and demonstrate that the most optimistic assessment of prior sedimentological studies that suggest PCO formed specific Archean basins often lack evidence of all three characteristics or provide observations from only one side of a dome or basin, leaving ambiguity about whether the basin is truly shaped by diapirism.