Detrital zircon provenance of the Mesoproterozoic Midcontinent Rift, Lake Superior region, U.S.A

We report the ages of detrital zircons (²⁰⁷Pb/²⁰⁶Pb LA-ICPMS; n p 1188) from 12 clastic units that are representative of the Mesoproterozoic Midcontinent Rift System (MRS) of North America. Magmatism of the MRS spanned 1115-1085 Ma. The Puckwunge, Nopeming, and Bessemer basal sandstones and the Oronto and Bayfield Group sandstones received a predominance of Keweenaw Rift-Grenville (1.3-1.0 Ga) zircons but also contributions of Wolf River (1.45 Ga), Yavapai (1.75 Ga), Penokean (1.8 Ga), and Archean (2.6-3.6 Ga) ages. Interflow sedimentary rocks in the North Shore Volcanic Group received only rift-aged zircons. The maximum depositional ages derived from detrital zircons also better constrain the age-stratigraphic relationship of the unfossiliferous rift section, in comparison to the overlying fossiliferous Franconia (n p 99 zircons), Mt. Simon (n p 116), and Munising (n p 110) late Cambrian transgressive sands. We also report the date of a granite xenolith (~1 km³) in the Beaver Bay Complex, which has a rift age (1091 Ma; n p 19) and is therefore not a rafted inclusion of Archean basement as previously suspected.