K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska

Turner, Donald L.; Forbes, R. B.; Mayfield, C. F.

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We report 76 previously unpublished K-Ar mineral ages from 47 metamorphic and igneous rocks in the southwestern Brooks Range.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.

Genre:

USGS Numbered Series

ProdID:

7270

Citation Author:

Turner, Donald L.; Forbes, R. B.; Mayfield, C. F.

Citation Contributing Office:

Citation Datum:

Citation Day:

Citation Edition:

Citation Editor:

Citation End Page:

Citation Issue:

Citation Keywords:

Citation Language:

ENGLISH

Citation Larger Work Title:

Citation LatN:

Citation LatS:

Citation LonE:

Citation LonW:

Citation Month:

Citation No Pagination:

Citation Number Of Pages:

Citation Online Only Flag:

Citation Phsyical Description:

41 leaves, 3 leaves of plates :ill., fold. maps ;scale 1:250,000; 28 cm.

Citation Projection:

Citation Public Comments:

Citation Publisher:

U.S. Geological Survey,

Citation Series:

Open-File Report

Citation Series Code:

OFR

Citation Series Number:

78-254

Citation Search Results Text:

K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska; 1978; OFR; 78-254; Turner, Donald L.; Forbes, R. B.; Mayfield, C. F.

Citation Start Page:

Citation Volume:

Citation Year:

1978

Type:

citation/reference

Text:

K-Ar geochronology of the Survey Pass, Ambler River and Eastern Baird Mountains quadrangles, southwestern Brooks Range, Alaska; 1978; OFR; 78-254; Turner, Donald L.; Forbes, R. B.; Mayfield, C. F.