Geochemical study of the Mesoproterozoic Belt-Purcell Supergroup, western North America : implications for provenance, weathering and diagenesis

Provenance in the lower Belt-Purcell Supergroup is constrained based on geochemical systematics and chemical monazite ages of argillites and sandstones. Rare earth element (REE), Cr-Ni, and Th/Sc-Sc systematics is equivalent for both facies and consistent with a dominantly post-Archean source area. Detrital monazite chemical ages restrict major provenance for the Appekunny and Grinnell sandstones and argillites to Paleoproterozoic terranes at ~1800-1600 Ma, minor contributions at ~1600-1500 Ma, and marginal contributions from Archean terranes at ~2600, likely in Laurentia. Similar detrital age spectra for monazites of argillites and sandstones of the Appekunny Formation are consistent with a common provenance for the two facies. The Belt-Purcell sequence records three major diagenetic stages displayed in argillites and sandstones: (1) K-addition and rare earth element post-Archean upper continental crust (PA-UCC)-like pattern; (2) a stage characterized by heavy REE enrichment relative to light REE and HFSE fractionation, and U and Ce mobility; and (3) local dolomitization with REE and high field strenght elements (HFSE) mobility. REE and HFSE mobility are interpreted as the result of oxidized alkaline brines developed by dissolution of evaporites. Monazites from the Appekunny and Grinnell formations differ compositionally and texturally in two groups. Rounded or inclusions with ages >~1400 Ma, interpreted as detrital, have higher Th2O, Y2O3 and lower LREE/HREE contents than euhedral individual monazite grains with chemical age