PROVENANCE PATTERNS AND TECTONIC STYLES OF CA. 2.3–1.8 GA METASEDIMENTARY STRATA IN NORTHERN MICHIGAN BASED ON REGIONAL MAPPING AND DETRITAL ZIRCON U-PB GEOCHRONOLOGY

Detrital zircon U-Pb data from ca. 2.3–1.8 Ga metasedimentary successions in northern Michigan are used to test regional stratigraphic correlations and yield key insights into provenance and tectonic styles along the southern Superior craton. Circa 2.3–2.2 Ga Chocolay Group turbiditic strata and quartzite record initial rifting and basin formation along the southern Superior margin. Unimodal ca. 2.7–2.6 Ga age populations were derived from abundant Archean batholiths in the surrounding region. Distinctive ca. 2.3 Ga populations are rare but present in some samples, but the source(s) of these grains is not well understood. Chocolay Group detrital zircon data are very similar to upper Huronian Supergroup strata to the east and with other global ca. 2.3–2.2 Ga glaciogenic successions. The ca. 2.1 Ga Dickinson Group contains bimodal ca. 2.9 and 2.7 Ga age populations in the East Branch Arkose and Solberg Schist­­­ that are distinctive in the region and suggest a mixture of recycled 2.3 Ga Chocolay Group quartzite and more diverse regional Archean basement sources. Minor ca. 2.1 Ga grains indicate derivation from nearby plutonic sources or eroded volcanic equivalents of the same age, consistent with magmatism, regional uplift, and final rifting of the southern Superior craton ca. 2.1. After a ca. 100 Ma hiatus, the Ajibik and Siamo Formations of the ca. 1.90–1.85 Menominee Group have unimodal ca. 2.7–2.6 Ga age populations that suggest continued derivation from ca. 2.7–2.6 Ga batholiths and (or) recycling of older underlying strata. The Goodrich Formation of the basal Baraga Group (ca. 1.85–1.83 Ga) shows similar patterns. A provenance shift to prominent ca. 1.85 Ga populations occurs in turbiditic strata of the Michigamme Formation (upper Baraga Group), indicating arrival of the outboard Wisconsin magmatic terrane to the south. Michigamme strata record basin evolution between the southern Superior Province and the exotic terrane as it approached and collided during the ca. 1.87–1.83 Ga Penokean orogeny, but the relative role of Penokean versus younger ca. 1.78–1.76 Ga tectonism in regional folding and metamorphism remains uncertain. Additional mapping and geochronology focused on Michigamme strata will better constrain regional depositional ages, facies relationships, and tectono-metamorphic patterns.