THE OREGON TRAIL OROGENY, CA. 2.65 GA COLLISION BETWEEN WYOMING AND SUPERIOR CRATONS DURING ASSEMBLY OF ARCHEAN SUPERCONTINENT KENORLAND

The Oregon Trail structural belt (OTSB) exposed in the Granite Mountains of central Wyoming is a high-grade shear zone that separates two crustal blocks formed from different mantle reservoirs at different times. To the north, the Bighorn tectonic subprovince comprises rocks as old as 3.5 Ga but is dominated by 2.95-2.85 Ga plutonic rocks of the Beartooth-Bighorn magmatic zone derived from a Hadean-aged, high µ (²³⁸U/²⁰⁴Pb) mantle reservoir. The Bighorn crust is 60 km thick with a distinctive 20 km thick, seismically fast (7.x) lower crustal layer. South of the OTSB, the Southern Accreted terrane (SAT) includes greenstone remnants ca. 2.72 to 2.65 Ga, and arc plutonism from 2.81 to 2.63 Ga derived from a low µ mantle reservoir, all characteristics of Superior Province rocks. The SAT is 40 km thick and lacks a 7.x layer. Deformation in the OTSB occurred in multiple pulses with early dip-slip motion over-ridden by later strike-slip; directly dated by U-Pb dates of metamorphic titanite and zircon from 2.66 to 2.63 Ga. A subparallel shear zone in the southern Bighorn Mountains, at Powder River Pass, has similar kinematic history and is a foreland feature related to the OTSB. U-Pb apatite cooling dates indicate that the Bighorn subprovince was tectonically buried ca. 2.65 Ga and progressively unroofed by ca. 2.55 Ga at least 200 km north of the OTSB. Four Archean mafic dike swarms (2.72 to 2.67 Ga) and 7 Proterozoic swarms (2.48 to 1.85 Ga) intrude the Bighorn subprovince; only Proterozoic dikes intrude the SAT. Paleomagnetic data from the mafic dikes and those in the Superior province indicate convergence of the two cratons ca. 2.65 Ga along their present-day southern borders, a reconstruction that persisted 500 myr, with rifting ca. 2.06 Ga. Hydrothermal alteration of mafic rocks in the OTSB and surrounding deformed terrane produced Wyoming jade from ca. 2.51 to 2.43 Ga possibly in response to the Mistassini and Matchewan LIPs. Similar-aged 2.65 to 2.60 Ga sutures between ancient, high µ and younger, low µ blocks occur on 2 other cratons, Superior and Slave. Paleomagnetic data, LIP barcodes, and geologic histories of all high and low µ cratons support a global reconstruction with two large continents colliding ca. 2.65 Ga forming the supercontinent Kenorland, which survived at least 300 myr and progressively rifted apart from 2.35 to 2.06 Ga.