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An inverted metamorphic field gradient in the central Brooks Range, Alaska and implications for exhumation of high-pressure/low-temperature metamorphic rocks

LITHOS

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, , and
DOI: 10.1016/0024-4937(94)90054-X

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Abstract

During exhumation of the Brooks Range internal zone, amphibolite-facies rocks were emplaced atop the blueschist/greenschist facies schist belt. The resultant inverted metamorphic field gradient is mappable as a series of isograds encountered as one traverses up structural section. Amphibolite-facies metamorphism occurred at ??? 110 Ma as determined from 40Ar 39Ar analysis of hornblende. This contrasts with 40Ar 39Ar phengite cooling ages from the uderlying schist belt, which are clearly older (by 17-22 m.y.). Fabrics in both the amphibolite-facies rocks and schist belt are characterized by repeated cycles of N-vergent crenulation and transposition that was likely associated with out-of-sequence ductile thrusting in the internal zone of the Brooks Range orogen. Contractional deformation occurred in an overall environment of foreland-directed tectonic transport, broadly synchronous with exhumation of the internal zone, and shortening within the thin-skinned fold and thrust belt. These data are inconsistent with a recently postulated mid-Cretaceous episode of lithospheric extension in northern Alaska. ?? 1994.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
An inverted metamorphic field gradient in the central Brooks Range, Alaska and implications for exhumation of high-pressure/low-temperature metamorphic rocks
Series title:
LITHOS
DOI:
10.1016/0024-4937(94)90054-X
Volume
33
Issue:
1-3
Year Published:
1994
Language:
English
Publisher:
Elsevier
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
LITHOS
First page:
67
Last page:
83