Open File Report 1989-04

Open File Report 1989-04

OFR 1989-04

Proposal for Scientific Drilling on the Steen River Structure, Northwestern Alberta

Author(s) Wilson, J.A. Langenberg, C.W. Date 1989-01-01

The Steen River Structure (SRS) is located in northwestern Alberta, approximately 115 km NNW of the town of High Level and 710 km from Edmonton. The structure has no surface expression, but was intersected by chance during petroleum exploration drilling in the 1960's. Regionally, the SRS lies predominantly within the Great Bear magmatic arc basement terrain. It is cut by the fault which separates the Great Bear from the Hottah accreted terrain and lies very close to the subsurface extension of the Great Slave Lake shear zone.

The structure itself consists of a central uplift surrounded by a rim syncline and an outer raised rim. The outer diameter of the SRS is approximately 25 km. The central block consists of basement upthrust 1100 m above the regional level. The rim syncline is downthrust 200 to 600 m below regional levels, and the outer raised rim is upthrust 20 to 50 m. Thus, there is a relative throw of 1700 m between the center and parts of the rim syncline. The structure is surrounded by an irregular disturbed zone extending up to 30 km from the raised rim. This disturbed zone appears to be the result of doming and is cut by normal faults producing local horsts and grabens.

Published work on the SRS is sparse and is primarily concerned with the evidence for shock metamorphism seen in basement core from the central uplift. The unaltered basement is not cored but probably is an amphibolite, biotite gneiss or granitoid. The altered basement has a gneissic texture and is cut by breccia zones. In this section, quartz, amphibole, feldspar and biotite all show evidence of shock metamorphism. In addition to fragments of the country rock, the breccia zones contain both devitrified and fresh glassy fragments. Zones of partly devitrified, glassy rock are also common.