ASSEMBLY OF THE KAAPVAAL AND WYOMING CRATONS INTO THE SUPERIA SUPERCONTINENT: KEY EVIDENCE FROM THE BLACK HILLS OF SOUTH DAKOTA AND WYOMING

The supercraton Superia assembled in late Neoarchean time and is envisioned as ~12 cratonic fragments sutured to the margins of the Superior craton (SUP). The Wyoming craton (WY) is a well-established component of Superia that adjoined the SE margin of SUP by 2.6 Ga. The Kaapvaal craton (KAP) as part of the greater Zimvaalbara continent likely adjoined WY in SW Superia. The Black Hills (BH) presently occupy the E margin of the WY craton and new data suggest that its Archean exposures further support a long-lived connection of the WY and KAP cratons. U-Pb age and Lu-Hf isotopic evidence from zircon phenocrysts and xenocrysts from the Neoarchean Missouri Buttes, Bear Lodge, and Little Elk granites define a common crustal evolution line that indicates derivation from juvenile crust at 3.10-3.26 Ga. This is similar to extensive Mesoarchean domains surrounding the KAP craton. We suggest that the BH and similar fragments in the Marshfield-McGrath terranes of the Penokean orogen once formed a contiguous belt of Mesoarchean crust added to the margin of the >3.1 Ga proto WY-KAP craton or alternatively helped to suture these two cratons for the first time between 2.95 and 2.90 Ga. Mesoarchean BH crust was involved during all subsequent magmatic events between 3.15 and 2.56 Ga either by direct internal crust reworking or indirectly by subduction of TTG-derived sediments. Significant magmatic age peaks of 2.95, 2.89-2.86, and 2.74 Ga are indicated by combined xenocrystic and detrital datasets. The BH contain critical evidence of 2.62-2.60 Ga tectonic activity interpreted here to record assembly of the WY-KAP block with SUP that evolved from a juvenile 2.64 Ga arc to an active foreland basin that was rapidly closed, deformed and intruded by 2.6 Ga granites. This history overlaps well with the adjoining Minnesota River Valley terrane (MRV). The 2.52-2.48 Ga Boxelder Fmn in the BH is age equivalent to the Transvaal Supergroup in KAP and contains abundant Meso-Paleoarchean detrital zircons interpreted to have been derived from older crust of the WY and KAP cratons. A tectonic model is proposed that involves the suturing of the WY-KAP cratons to Superia diachronously along a 1,200-km-long margin beginning with early accretion of WY to the Wawa-Abitibi subprovince of SUP at 2.63 Ga and closing with major orogenesis in the BH-MRV and Zimbabwe at 2.60 Ga.