FOUR BILLION YEAR RECORD OF OCEAN PLATE STRATIGRAPHY IN ACCRETIONARY OROGENS PRESERVE A RECORD OF SEA FLOOR SPREADING, SUBDUCTION, AND ACCRETION THROUGHOUT EARTH HISTORY

Few reliable markers for the operation of plate tectonics in ancient rocks are preserved in Precambrian orogens, and it has become a major debate in the Earth Sciences as to “when did plate tectonics begin?” Ocean plate stratigraphy (OPS) is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust from the time it forms at a spreading center, to the time it is incorporated into an accretionary prism at a convergent margin. In this contribution, we review the major geological characteristics of relict Cenozoic to early Archean oceanic crust and OPS persevered in Alaska, Japan, California (Franciscan Complex), Central Asia, British Isles, Canada (Slave Province), Australia (Pilbara craton), Greenland (Isua and Ivisaartoq belts) and in the circa 4.0 Ga Nulliak greenstone belt of northern Canada. An assessment of OPS in accretionary orogens spanning the duration of Earth's rock record shows remarkable similarities between OPS of all ages in terms of structural style, major rock components, sequence of accretion, and trace element geochemical signatures. Volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts, island arc picrites, mid-ocean ridge basalts, back-arc basalts, oceanic plateau basalts, ocean island basalts, and boninites, with extremely rare komatiites. This demonstrates that sea-floor spreading, lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum, and accretion at convergent margins have been major Earth processes since at least 4.0 Ga ago. There have been some secular changes in the rock types in OPS, such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in Phanerozoic times but absent in the Precambrian, and differences related to slightly higher mantle termperatures, but overall, there have been few changes in the style of OPS accretion with time. Komatiites and banded iron formations occur predominantly in Archean orogenic belts, reflecting higher mantle temperatures and less oxic seawater composition, respectively, before 2.5 Ga. This is clear documentation that plate tectonics, including the lateral movement of oceanic lithosphere, has been a major heat loss mechanism on Earth since the early Precambrian.