K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska
Open-File Report
78-254
By: Donald L. Turner, R. B. Forbes, and C.F. Mayfield
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Abstract
We report 76 previously unpublished K-Ar mineral ages from 47 metamorphic and igneous rocks in the southwestern Brooks Range. The pattern of radiometric ages is complex, reflecting the complex geologic history of this area. Local and regional radiometric evidence suggests that the southern Brooks Range schist belt has, at least in part, undergone a late Precambrian metamorphism and that the parent sedimentary and igneous rocks for the metamorphic rocks dated as late Precambrian are at least this old (Precambrian Z).
This schist terrane experienced a major thermal event in mid-Cretaceous time, causing widespread resetting of nearly all K-Ar mica ages. A series of apparent ages intermediate between late Precambrian and mid-Cretaceous are interpreted as indicating varying amounts of partial argon loss from older rocks during the Cretaceous event. The schist belt is characterized by dominant metasediments and subordinate metabasites and metafelsites. Blueschists occur within the schist belt from the Chandalar quadrangle westward to the Baird Mountains quadrangle, but geologic evidence does not support the existence of a fossil subduction zone.
Suggested Citation
Turner, D.L., Forbes, R.B., Mayfield, C., 1978, K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska: U.S. Geological Survey Open-File Report 78-254, Report: 41 p.; 3 Plates: 30.18 × 22.68 inches or smaller, https://doi.org/10.3133/ofr78254.
ISSN: 2331-1258 (online)
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska |
| Series title | Open-File Report |
| Series number | 78-254 |
| DOI | 10.3133/ofr78254 |
| Year Published | 1978 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Description | Report: 41 p.; 3 Plates: 30.18 × 22.68 inches or smaller |
| Country | United States |
| State | Alaska |
| Other Geospatial | Survey Pass, Ambler River, and eastern Baird Mountains quadrangles |
| Scale | 250000 |