Book excerpt: The Davis Peak area is a ~100 km 2 part of the northern Park Range, Colorado, comprised of a heterogeneous suite of high-grade metamorphic and associated ultramafic/mafic-to-felsic intrusive rocks. These rocks are part of an extensive province of Paleoproterozoic island-arc terranes exposed in basement-involved uplifts that extend southward from the Cheyenne belt in southeastern Wyoming. Modern interpretations contend that the accretion of these terranes began along the Cheyenne belt with the ~1.78-Ga accretion of the Green Mountain arc followed by accretion of the ~1.75-Ga Rawah arc to the southern margin of the Green Mountain arc along the Farwell Mountain-Lester Mountain suture zone. Rocks of the northernmost Park Range are commonly interpreted as part of the Green Mountain arc, however, the affinity of these rocks has not been studied in detail. This study has employed a broad range of techniques including detailed field mapping, petrographic analysis, thermobarometry, and radiometric dating to determine the affinity of high-grade metamorphic rocks and associated intrusive rocks in the Davis Peak area. Detailed geologic field mapping reveals that the Davis Peak area is primarily comprised of a heterogeneous suite of metamorphic rocks (Big Creek gneiss) that have been pervasively intruded by ultramafic/mafic-to-felsic plutonic rocks. This diverse assemblage of metamorphic and igneous rocks is broadly equivalent to lithologic units recognized in the Sierra Madre (southeastern Wyoming), which are interpreted as part of the Green Mountain arc. Thus this correlation suggests that Precambrian rocks of the Davis Peak area are also part of the Green Mountain arc. The penetrative fabric in the Davis Peak area is chiefly a northeast-southwest-striking foliation that has been locally overprinted by younger ductile-to-brittle deformations. This structural history is basically comparable to the deformational history manifested in the Precambrian rocks of the Sierra Madre and Medicine Bow Mountains. This potential correlation suggests that regionally extensive ductile deformation dated at ~1.75 Ga and late cataclastic deformation dated at ~1.6 Ga have affected the entire Green Mountain arc including the northern Park Range. The Big Creek gneiss is characterized by metapelitic garnet-biotite-sillimanite paragneisses, metavolcanic (sometimes garnet-bearing) amphibolites, and intercalated subordinate calc-silicate rocks. Thermobarometric results from these rocks suggest that the Davis Peak area experienced metamorphic P-T conditions of ~6 kb and 675 °C followed by a period of decompression at ~4 kb and ~650 °C. Several U-Pb radiometric ages from metamorphic monazite and titanite have been used to directly date metamorphism and suggest that two phases of metamorphism have affected the Davis Peak area at ~1752 Ma and ~1615-1565 Ma. Microstructural and compositional evidence from high-grade metamorphic rocks suggest that evidence for ~1752-Ma metamorphism is only locally preserved and that thermobarometric results chiefly reflect tectonothermal events at ~1.6 Ga. Furthermore, non-penetrative epidote-bearing slickensided surfaces in the Davis Peak area are comparable with similar surfaces dated at ~1.6 Ga associated with the Cheyenne belt thereby suggesting that late deformation and metamorphism in the Davis Peak area continued under greenschist-facies conditions. Additionally, thermobarometric results from this study are strikingly similar to results obtained south of the proposed Farwell Mountain-Lester Mountain suture zone suggesting that the proposed break in metamorphic grade across this boundary may not exist. If this conclusion is correct, it requires a revised tectonic scenario for this part of the Colorado province.