Geochronology and geochemistry of deeply buried basement along the western Superior Craton and eastern Trans-Hudson Orogen (North America)

The Paleoproterozoic Trans-Hudson Orogen of North America resulted from the amalgamation of the Wyoming, Hearne, Sask, and Superior cratons. Previous work has constrained the timing of terminal collision of the Hearne, Sask, and Superior cratons to ca. 1.83-1.80 Ga (Canadian Shield), and the Wyoming and Superior cratons to 1.78-1.72 Ga (Black Hills, South Dakota, USA). More than 1200 km separate the Canadian Shield and Black Hills, between which there is no crystalline basement exposure due to Phanerozoic sedimentary cover, and limited data exist. This study presents U-Pb zircon geochronologic, major and trace element geochemical, and isotopic (epsilon (sub Hf) zircon and epsilon (sub Nd) whole-rock) data from two basement drill cores approximately 3000 m deep collected along the western edge of the Superior Craton and eastern margin of the Trans-Hudson Orogen overprint, between the Canadian Shield and Black Hills. The western core contains ca. 1.83 Ga mafic gneiss with juvenile isotopic [epsilon (sub Hf(i)) and epsilon (sub Nd(i)) ] geochemical signatures and an amphibolite-grade metamorphic overprint. The eastern core contains ca. 2.7 Ga granitic gneiss with trace element and juvenile isotopic geochemical signatures that are consistent with granitoids from the western Superior Craton. Paleoproterozoic (ca. 1.79-1.77 Ga) granitoid intrusions occur in both cores that display trace element signatures suggestive of origination in a continental arc setting. Isotope geochemistry plus inherited zircon populations indicate that intrusive granitoids are mixtures of juvenile Paleoproterozoic mantle and recycled crustal material. The ca. 1.79-1.77 Ga granitic magmatism observed falls chronologically between the terminal Hearne, Sask, and Superior collision and the Wyoming and Superior collision, and the data presented herein represent a step toward better understanding the buried southern Trans-Hudson Orogen.