Extensional origin of ductile fabrics in the Schist Belt, Central Brooks Range, Alaska—II. Microstructural and petrofabric evidence

• Published in: Journal of Structural Geology
• Main Authors: Law, Richard D., Miller, Elizabeth L., Little, Timothy A., Lee, Jeffrey
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 1994
• Subjects: Brooks Range; Alaska
• Online Access: https://authors.library.caltech.edu/85350/; https://resolver.caltech.edu/CaltechAUTHORS:20180316-154525787

A regional system of S-dipping faults is exposed in the Florence and Fall Creeks area of the south-central Brooks Range. This fault system has previously been mapped as the ‘root zone’ of a N-vergent fold-and-thrust belt of Jurassic-Cretaceous age, although individual faults juxtapose lower grade on higher grade metamorphic rocks suggesting apparent extensional geometries. The structurally highest of these faults places rocks of the oceanic Paleozoic-Mesozoic Angayucham terrane, together with unconformably overlying Cretaceous clastic rocks, on Devonian metagreywacke and phyllite. This metagreywacke-phyllite (MP) unit in turn structurally overlies Devonian (?) and older basement rocks of the Brooks Range Schist Belt along a S-dipping structural contact previously mapped as the Florence Creek fault. The Schist Belt and MP units are both characterized by a regionally developed, S-dipping greenschist facies foliation that displays a pronounced N-S-trending, down-dip elongation lineation which earlier workers regarded as being associated with N-vergent thrusting. While only one foliation (S_d) is recognized in the MP unit, in the underlying Schist Belt this foliation (S_2) overprints an earlier blueschist facies mineral assemblage and associated foliation (S_1).