Constraints on emplacement and timing of the Steen River impact structure, Alberta, Canada

Abstract

The Steen River impact structure (SRIS) is a buried, complex crater located in NW Alberta, Canada. It was discovered in the mid 1900’s and was initially thought to be an endogenic igneous intrusion. With the growth of impact studies on Earth and other planets, the SRIS was recognized as such in the 1960’s. Since then, numerous exploratory wells have been drilled in and around the structure to assess its economic potential. While many of these wells are proprietary, three cores collected in 2000 are available for research and have been the focus of the most recent SRIS studies. A ubiquitous product of impact events is impact breccia, which may contain clasts of target material and melt. At the well-studied Ries impact structure in Germany, this breccia is classified as suevite. The impact breccia observed at the SRIS is similar to the Ries suevite; however, the term “suevite” has been applied to many impact structures and its formation mechanism is still debated. In previous studies, three cores from the SRIS (ST001, ST002, and ST003) were logged by hand and characterized in detail using thin sections; however, a representative, yet detailed, mineralogical overview of the core was lacking. In this thesis, hyperspectral imaging was used to quickly scan the three cores and make detailed mineralogical maps of each. Results highlight hydrothermal and ammoniated minerals in the SRIS impact breccia, and aid in refining the emplacement model for the suevite-like breccia. The only published age of the crater is poorly constrained and conflicts with the stratigraphy overlying the crater. To better constrain the SRIS age, zircons were extracted from the core samples and characterized using secondary ion mass spectrometry. Zircons are commonly used for U-Pb geochronology because they can withstand most geological disturbances and may incorporate radiogenic isotopes into their crystal structure. By analyzing both granite- and melt-derived zircons, this study aimed to constrain the age of the SRIS impact event and compare it to the known age of the Proterozoic basement rocks.