Review of radiometric data from the Yukon Crystalline Terrane, Alaska and Yukon Territory

Abstract

The results of more than 20 years of geochronological studies in the Yukon Crystalline Terrane in east-central Alaska and the western Yukon Territory suggest at least six igneous and thermal (metamorphic?) events. Plutonism during Mississippian, Early Jurassic, mid-Cretaceous, Late Cretaceous, and early Tertiary times is indicated. Evidence also indicates that Mississippian, Early Jurassic, late Early Cretaceous, and late Cretaceous thermal (metamorphic?) events have affected parts of the terrane. The western part of the terrane was affected by a significant regional metamorphic event in late Early Cretaceous time, followed by a terrane-wide mid-Cretaceous plutonic event. The pattern of K-Ar ages allows division of the terrane into domains, bounded by northeast-trending lineaments.L'examen des rksultats de plus de 20 annkes d'ktudes gkochronologiques de la plate-forme cristalline du Yukon rkvkle au moins la prCsence de six kvknements ignks et thermiques (mktamorphiques?). Le plutonisme fut actif durant le Mississippien, le Jurassique infkrieur, le Crktack moyen, le Crktack supkrieur et le Tertiaire infkrieur. On observe que des manifestations thermiques (mktamorphiques?) ont affectk des parties de la plate-forme cristalline du Yukon durant le Mississippien, le Jurassique infkrieur, le CrktacC tardi-infkrieur et le Crktace supkrieur. Durant le Crktack tardi-infkrieur est survenu un important kvknement de mktamorphisme regional qui a affectk la partie occidentale de la plate-forme cristalline, lequel fut suivi au CrktacC moyen par un kvknement plutonique englobant toute la largeur de la plate-forme cristalline. Le motif d'ktalement des Lges K-Ar permet de diviser la plate-forme cristalline en domaines, lesquels sont limitks par des lineaments de direction nord-est.[Traduit par le journal]Can.

Petrology and provenance of the Neogene Usibelli Group and Nenana Gravel; implications for the denudation history of the central Alaska Range

“…A second hypothesis that we considered to account for the subtle changes in sandstone compositions of the Usibelli Group is that they reflect enlargement of fluvial drainage basins into the eastern part of the Yukon-Tanana terrane in Alaska, which contains middle Paleozoic to early Tertiary intrusive and extrusive igneous rocks ( Fig. 1; Wilson et al 1985;Beikman 1994). This hypothesis requires fluvial transport of pebbles and cobbles on the order of ϳ 300 km.…”

Cretaceous reduced granitoids in the Goodpaster Mining District, east central Alaska

“…Felsic and intermediate plutonic rocks intruded the YukonTanana terrane during the Permian (-250 Ma), Late Triassic to Early Jurassic (215-188 Ma), late Early Cretaceous to Late Cretaceous (115-85 Ma) and the Late Cretaceous to early Tertiary (74-50 Ma) (Wilson et al 1985;Foster et al 1994;Hudson 1994;Mortensen et al 2000). Of particular importance for the Goodpaster Mining District is the late Early Cretaceous to Late Cretaceous plutonic event, which is also known throughout most of Yukon and east central Alaska (Aleinikoff et al 2000;Hart et al 2004).…”

“…Mid-Paleozoic, Jurassic, and Early Cretaceous metamorphic events have been proposed (Dusel- Bacon and Aleinikoff 1985;Hudson 1994;Foster et al 1994;Aleinikoff et al 2000;Mair et al 2006). The most recent event began during a Jurassic collisional event, culminating in widespread metamorphism and contractional tectonism in the Early Cretaceous (Aleinikoff and Nokleberg 1985;Wilson et al 1985;Pavlis et al 1993;Dusel-Bacon and Aleinikoff 1996;Day et al 2002). Field relations and U-Pb ages (this study; Day et al 2002) indicate that the youngest metamorphism and deformation in the Goodpaster Mining District was between 130 and 115 Ma, but locally continued to as late as 107 Ma.…”

“…Mantle-derived rocks have low initial Pb concentrations, therefore, the Pb isotopic composition of granite commonly reflects the crust with which it is associated (Farmer and DePaolo 1983;Davidson 1996 Cox et al (1979) modified by Wilson (1989) for plutonic rocks. The thick, curved solid line subdivides the alkalic and subalkalic rocks according to Irvine and Baragar (1971).…”

High‐pressure amphibolite facies dynamic metamorphism and the Mesozoic tectonic evolution of an ancient continental margin, east‐central Alaska

“…1). The eclogite-bearing klippe NE of Fairbanks yields Middle Jurassic K-Ar(Ms) cooling ages (Wilson et al, 1985). A subduction-zone setting is clearly indicated for metamorphism of these bodies, based on P -T conditions of 15*2 kbar at 0 * 2 5 " C for eclogite (Laird el al., 1984;Brown & Forbes, 1986) and the isolated occurrence of glaucophane from the Seventymile terrane north of the study area.…”