A record of Neoarchaean cratonisation from the Storø Supracrustal Belt, West Greenland

Abstract

During the late Archaean, exotic juvenile continental (TTG) terranes assembled into stable cratons leading to continental emergence and deposition of shallow-marine sedimentary sequences. This period of cratonisation coincided with crustal reworking and maturation driving the production of granites sensu stricto on most cratons, and may mark a final transition to mobile-lid tectonics. We investigate the relative timing of continental assembly, stabilization, emergence, and maturation, during the formation of the North Atlantic Craton (NAC) in West Greenland from its constituent terranes, using geochemical data from zircon and monazite extracted from its oldest mature metasedimentary unit, the Storø quartzite. Zircons form two U-Pb age groups: (i) an older >2820Ma group with juvenile (elevated) ϵHf(t) and δ18O, derived from weathering surrounding Mesoarchaean terranes; and (ii) a younger <2700Ma group with less radiogenic (lower) ϵHf(t) and elevated δ18O that record post-burial metamorphism peaking ca. 2620 Ma. The quartzite protolith has a maximum depositional age of ca. 2830 Ma, and was deposited after final TTG formation but prior to granite magmatism at ca. 2715 Ma, during which time terranes had sufficiently assembled, stabilized, and emerged to form a common watershed. Cratons form via lateral accretion which requires strong continental lithosphere, for which one agent is crustal reworking and maturation. However, for the NAC, terrane assembly and emergence commenced prior to granite formation, and crustal reworking may be a response to lithospheric thickening. Cratonisation involves a series of complex, intertwined processes operating over 100's of millions of years, which together lead to the development of thick, stable, continental lithosphere. Studies of ancient mature metasediments such as the Storø quartzite can help build timelines for these processes to ultimately better understand their choreography and co-dependencies, that together produced Earth's enduring cratons.