Passive margins in accreting Archaean archipelagos signal continental stability promoting early atmospheric oxygen rise.

Significant changes in tectonic style and climate occurred from the late Archaean to early Proterozoic when continental growth and emergence provided opportunities for photosynthetic life to proliferate by the initiation of the Great Oxidation Event (GOE). In this study, we report a Neoarchaean passive-margin-type sequence (2560-2500 million years ago) from the Precambrian basement of China that formed in an accretionary orogen. Tectonostratigraphic and detrital zircon analysis reveal that thermal subsidence on the backside of a recently amalgamated oceanic archipelago created a quiet, shallow water environment, marked by deposition of carbonates, shales, and shallow water sediments, likely hosts to early photosynthetic microbes. Distinct from the traditional understanding of passive margins generated by continental rifting, post-collisional subsidence of archipelago margins represents a novel stable niche, signalling initial continental maturity and foreshadowing great changes at the Archaean-Proterozoic boundary.

Alpine-style nappes thrust over ancient North China continental margin demonstrate large Archean horizontal plate motions.

Whether modern-style plate tectonics operated on early Earth is debated due to a paucity of definitive records of large-scale plate convergence, subduction, and collision in the Archean geological record. Archean Alpine-style sub-horizontal fold/thrust nappes in the Precambrian basement of China contain a Mariana-type subduction-initiation sequence of mid-ocean ridge basalt blocks in a 1600-kilometer-long mélange belt, overthrusting picritic-boninitic and island-arc tholeiite bearing nappes, in turn emplaced over a passive margin capping an ancient Archean continental fragment. Picrite-boninite and tholeiite units are 2698 ± 30 million years old marking the age of subduction initiation, with nappes emplaced over the passive margin at 2520 million years ago. Here, we show the life cycle of the subduction zone and ocean spanned circa 178 million years; conservative plate velocities of 2 centimeters per year yield a lateral transport distance of subducted oceanic crust of 3560 kilometers, providing direct positive evidence for horizontal plate tectonics in the Archean.