Carol D. Frost*
Dept. of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA
Paul A. Mueller
Dept. of Geological Sciences, University of Florida Gainesville, Gainesville, Florida 32611, USA
David W. Mogk
Dept. of Earth Sciences, Montana State University, Bozeman, Montana 59717, USA
B. Ronald Frost
Dept. of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA
Darrell J. Henry
Dept. of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
Abstract
The record of the first two billion years of Earth’s history (the Archean) is notoriously incomplete, yet
crust of this age is present on every continent. Here we examine the Archean record of the Wyoming craton in
the northern Rocky Mountains, USA, which is both well-exposed and readily accessible. We identify three
stages of Archean continental crust formation that are also recorded in other cratons. The youngest stage is
characterized by a variety of Neoarchean rock assemblages that are indistinguishable from those produced by
modern plate-tectonic processes. The middle stage is typified by the trondhjemite-tonalite-granodiorite
(TTG) association, which involved partial melting of older, mafic crust. This older mafic crust is not
preserved but can be inferred from information in igneous and detrital zircon grains and isotopic
compositions of younger rocks in Wyoming and other cratons. This sequence of crust formation characterizes
all cratons, but the times of transition from one stage to the next vary from craton to craton.
*Corresponding author: Carol Frost, frost@uwyo.edu
Manuscript received 30 Mar. 2022. Revised manuscript received 27 June 2022.
Manuscript accepted 28 June 2022. Posted 4 Aug. 2022.
© The Geological Society of America, 2022. CC-BY-NC.
https://doi.org/10.1130/GSATG541A.1