Teton Range, Wyoming: An Uplift Recording Two Distinct Archean Histories

The Archean basement of the Teton Range contains evidence of domains with two distinct histories: an area in the northeast that was involved in high-pressure metamorphism (P~12kb) at 2690 Ma, and an area in the southwest that never experienced high-pressure metamorphism. The boundary between these two blocks is mostly obscured by the intrusion of the 2547 Ma Mount Owen Quartz Monzonite.

The northern domain consists of pelitic gneisses and amphibolites that were partially melted during granulite facies metamorphism at 2690 Ma. These rocks contain zircon as old as 3.45 Ga, negative initial εNd (-1 to -6), and Nd model ages 3.2-3.6 Ga. These rocks were thrust onto layered gneisses that have positive initial εNd and younger Nd model ages (2.8-3.2 Ga). Both gneisses were intruded by leucogranites at 2685 to 2675 Ma; the older leucogranites are more deformed than the younger.

The southern domain consists of 2800 Ma orthogneiss, layered ortho- and paragneisses, and the Rendezvous metagabbro. The Rendezvous metagabbro was intruded before 2695 ±10 Ma yet shows no evidence of the intense deformation and high P granulite metamorphism that affected the northern domain at this time. The orthogneiss is interfolded with a biotite-rich paragneiss that has a slightly positive initial εNd and zircons with an age spectrum with peaks at 2710 Ma; 2663 and 2630 Ma. Therefore the paragneiss was deposited and the southern domain metamorphosed no earlier than 2630 Ma, long after the metamorphism and intrusive events in the northern block.

These data suggest that there are two Archean domains in the Tetons, a northern one with high P metamorphism and abundant 2.68 Ga leucogranites and a southern one that was metamorphosed after 2630 Ma. These blocks were amalgamated after 2630 Ma but before the Mount Owen Quartz Monzonite was intruded at 2547 Ma.