0191-8141/94 $07.00+0.00 Extensional origin of ductile fabrics in the Schist Belt, Central Brooks

• Main Authors: Alaskamii Microstructural, Petrofabric Evidence, Richard D. Law, Elizabeth L. Miller, Timothy A. Liti'le
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1992
• Subjects: Bya; Brooks Range
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.517.6687; http://www.geology.cwu.edu/facstaff/lee/publications/pdf.papers/AL2.JSG.pdf

Abstract--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 uggesting apparent extensional geometries. The structurally highest of these faults places rocks of the oceanic Paleozoic-Mesozoic Angayucham terrane, together with unconformably overlying Creta-ceous 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 bya regionally developed, S-dipping reenschist facies foliation that displays apronounced N-S-trending, down-dip elongation lineation which earlier workers regarded as being associated with N-vergent thrusting. While only one foliation (Sd) is recognized inthe MP unit, in the underlying Schist Belt this foliation ($2) overprints an earlier blueschist facies mineral assemblage and associated foliation ($1). Mylonites with strong asymmetric crystal fabrics are well developed inquartz stringers in the MP unit and in Schist Belt rocks located at less than 250 m beneath the Florence Creek fault. These asymmetric single- and cross-girdle c-axis fabrics indicate atop down-to-the-south shear sense. This shear sense is confirmed in XZ sections by