Gravity profiles across the Cheyenne Belt, a precambrian crustal suture in southeastern Wyoming

R. A. Johnson, K. E. Karlstrom, S. B. Smithson, R. S. Houston

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

Geologic discontinuities across the Cheyenne Belt of southeastern Wyoming have led to interpretations that this boundary is a major crustal suture separating the Archaean Wyoming Province to the north from accreted Proterozoic island arc terrains to the south. Gravity profiles across the Cheyenne Belt in three Precambrian-cored Laramide uplifts show a north to south decrease in gravity values of 50-100 mgal. These data indicate that the Proterozoic crust is more felsic (less dense) and/or thicker than Archaean crust. Seismic refraction data show thicker crust (48-54 km) in Colorado than in Wyoming (37-41 km). We model the gravity profiles in two ways: 1) thicker crust to the south and a south-dipping ramp in the Moho beneath and just south of the Cheyenne Belt; 2) thicker crust to the south combined with a mid-crustal density decrease of about 0.05 g/cm3. Differences in crustal thickness may have originated 1700 Ma ago because: 1) the gravity gradient is spatially related to the Cheyenne Belt which has been immobile since about 1650 Ma ago; 2) the N-S gradient is perpendicular to the trend of gravity gradients associated with local Laramide uplifs and sub-perpendicular to regional long-wavelength Laramide gradients and is therefore probably not a Laramide feature. Thus, gravity data support the interpretation that the Cheyenne Belt is a Proterozoic suture zone separating terrains of different crustal structure. The gravity "signature" of the Cheyenne Belt is different from "S"-shaped gravity anomalies associated with Proterozoic sutures of the Canadian Shield which suggests fundamental differences between continent-continent and island arc-continent collisional processes.

Original languageEnglish (US)
Pages (from-to)445-472
Number of pages28
JournalJournal of Geodynamics
Volume1
Issue number3-5
DOIs
StatePublished - Dec 1984
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes

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