THE 2.68 – 2.67 TETON – WIND RIVER DOMAIN: EVIDENCE FOR ACTIVE-MARGIN TECTONICS AND CONTINENT-CONTINENT COLLISION ON THE WESTERN MARGIN OF THE WYOMING PROVINCE

The Archean gneisses of the Teton and Wind River ranges were deformed in a 2.68 – 2.67 Ma event that has all the hallmarks of modern plate tectonics. These include: 1) Emplacement of calc-alkalic magmas with juvenile Nd characteristics in the Wind River Range (Bridger batholith 2670 ±13 Ma) and Teton Range (Rendezvous Gabbro 2672 ± 2 Ma). 2) Tholeiitic dike swarm emplaced at 2680 in the western Owl Creek Mountains and eastern Wind River Range. 3) Westward thrusting of deep crustal block in the Wind River Range after 2680 but before 2657 Ma. 4) High pressure (T > 950°C, P > 11 kbar) pelitic granulites in the Teton Range that at 2676 Ma were deformed and hydrated at T = 700°C and P > 10 kbar. 5) The presence of paragneisses with juvenile Nd isotopic signatures in the Teton Range that could represent sediments that accumulated in a fore-arc or accretionary prism environment. The linear nature of this belt, the high-P metamorphism in the Teton Range, the distinct contractional tectonic style in the Wind River range and probably in the Teton Range, the calc-alkalic magmatism with juvenile components, and the juvenile paragneisses in the Teton Range are all consistent with modern plate tectonics and not with vertical tectonic patterns seen in other Archean terranes at this time. We contend that the features described above could have formed during eastward or northeastward subduction beneath the western margin of the Wyoming province around 2.68 to 2.67 Ga. This would have formed a magmatic arc on the 2.95 - 2.84 Ga basement of the Wyoming province in the present site of the Wind River Range and back-arc rifting farther east in the Owl Creek Mountains. This orogenic event was terminated around 2.676 Ma by a continent-continent collision that is recorded in the high-pressure rocks in the northern Teton Range. The 2.95 – 2.84 Ga plutonic rocks that dominate the center of the Wyoming province have characteristics similar to TTG suites found in other Archean cratons and we see no compelling reason to ascribe their formation to a plate tectonic process. If this is so, then modern plate tectonics began in the Wyoming province around 2.68 Ga.