GEOLOGY AND U-PB GEOCHRONOLOGY OF ARCHEAN BASEMENT AND PROTEROZOIC COVER IN THE PRIEST RIVER COMPLEX, NORTHWESTERN UNITED-STATES, AND THEIRIMPLICATIONS FOR CORDILLERAN STRUCTURE AND PRECAMBRIAN CONTINENT RECONSTRUCTIONS
Pt. Doughty et al., GEOLOGY AND U-PB GEOCHRONOLOGY OF ARCHEAN BASEMENT AND PROTEROZOIC COVER IN THE PRIEST RIVER COMPLEX, NORTHWESTERN UNITED-STATES, AND THEIRIMPLICATIONS FOR CORDILLERAN STRUCTURE AND PRECAMBRIAN CONTINENT RECONSTRUCTIONS, Canadian journal of earth sciences, 35(1), 1998, pp. 39-54
Precambrian basement rocks exposed within tectonic windows in the Nort
h American Cordillera help to define the Precambrian crustal structure
of western North America and possible reconstructions of the Late Pro
terozoic supercontinent Rodinia. New geologic mapping and U-Pb dating
in the infrastructure of the Priest River metamorphic complex, norther
n Idaho, documents the first Archean basement (2651 +/- 20 Ma) north o
f the Snake River Plain in the North American Cordillera. The Archean
rocks are exposed in the core of an antiform and mantled by a metaquar
tzite that may represent the nonconformity between basement and the ov
erlying Hauser Lake gneiss, which is correlated with the Prichard Form
ation of the Belt Supergroup. A structurally higher sheet of augen gne
iss interleaved with the Hauser Lake gneiss yields a U-Pb zircon cryst
allization age somewhat greater than 1577 Ma. The slivers of augen gne
iss were tectonically interleaved with the surrounding Hauser Lake gne
iss near the base of the Spokane dome mylonite zone, which arches acro
ss this part of the Priest River complex. We conclude that the Spokane
dome mylonite zone lies above the Archean basement-cover contact and
that it was, in part, equivalent to the basal decollement of the Rocky
Mountain fold and thrust belt. New U-Pb dates on metamorphic monazite
and xenotime reveal peak metamorphism at ca. 72 Ma, compatible with m
ovement along the Spokane dome mylonite zone at that time. The Archean
basement could be interpreted as the western extension of the Hearne
province, or a new Archean basement terrane separated from the Hearne
province by an Early Proterozoic suture. The unique assemblage of 2.65
Ga basement, similar to 1.58 Ga felsic intrusive rocks, and the Middl
e Proterozoic Belt Supergroup can be used as a piercing point for the
identification of the conjugate margin to Laurentia. Our new dating su
pports previous correlations of Australia's Gawler craton (2.55-2.65 G
a) and its 1590 Ma plutons with the Priest River complex basement gnei
sses. The Priest River complex basement may be a piece of eastern Aust
ralia stranded during rifting of the supercontinent Rodina in the Late
Proterozoic.