NWT RESEARCH DATABASE

Tags: physical sciences, geology, remote sensing, paleogeology, magnetic field, meteoritics

Objective(s): To carry out the first detailed study of the newly discovered Tunnunik impact structure, located on Victoria Island, NWT.

Project Description: This project seeks to carry out the first detailed study of the newly discovered Tunnunik impact structure, located on Victoria Island, NWT. The research team will carry out field mapping and conduct gravity, ground magnetic, and seismic surveys, and sample for paleomagnetic studies. They will also ground-truth a remote predictive map generated with Radarsat-2 and other satellite data. The goal of this research and associated research methods are outlined below: Objective 1) Structural geological mapping The structural geology of large multi-km diameter impact craters are poorly constrained. Tunnunik is unique in having a 2 km long river section that offers 100% exposure. This represents the best-exposed slice through a large meteorite impact structure on Earth with the potential to offer a unique glimpse at the internal structure of such geological features. In this project, the research team proposes to create a 3D geological map of the river section, which cuts through the centre of this crater. Detailed geological mapping will be conducted aided by 3D scanning lidar. Faults and fracture surfaces will be mapped and orientations collected. The team will also conduct mapping of the entire crater. Objective 2) Impact-generated hydrothermal alteration The heat generated by impact events typically produces a hydrothermal system. During a reconnaissance visit, PhD student Marion discovered evidence suggesting that the Tunnunik impact generated a hydrothermal system. The research team will search for evidence for this activity in the form of vugs and veins of secondary minerals. In order to prove that this hydrothermal alteration is impact-generated and not regional, the team will sample outside the crater to >100 km by helicopter. This research will have the added bonus, therefore, of yielding new information about the regional geology of Victoria Island. Objective 3) Ground magnetics Ground magnetic field mapping is an easily deployed and fast technique that may be valuable to identify uplifted basement rocks or hydrothermally altered bodies. Due to the presence of magnetic lithologies in the target rocks (the observed diabase dikes or the possibly magnetic crystalline basement), magnetic field mapping will also constrain the tectonic structures of the area. Continuous measurements along one or two high-resolution profiles spanning from the crater center to outside of the crater (~14 km), as well as discrete measurements will provide a satisfactory coverage of the crater. Objective 4) Gravimetry Ground gravity anomaly mapping, through its ability to image deep structures with contrasted density is particularly adapted to the study of impact craters. Density contrasts are expected between the diabase dikes and the host sedimentary rocks. Like the magnetic field survey, high-resolution (500 m spacing) profiles spanning from the crater center to outside of the crater will be sufficient to characterize a potential gravity low due to the impact. Then additional higher resolution localized profiles (100 m spacing) will be performed over potential buried faults. Objective 5) Seismics Seismics will be used to determine the thickness of glacial deposits and image rocks below them along selected profiles. The research team expects to only apply this method over anomalies, in particular potential faults detected by the gravity and magnetic surveys. This technique will be mostly helpful to image the boundary between glacial deposits and the bedrock. Estimating this thickness will bring crucial constraints for the inversion of other geophysical data. Moreover, if they exist, shallow features of the impact structure (e.g., faults) may also be imaged. Objective 6) Paleomagnetism and impact remagnetization The comparison of the paleomagnetic directions of the sampled rocks with the reference paleomagnetic poles is a valuable dating tool. Paleomagnetic dating may provide an age with an uncertainty of about 10-20 Myr in the 450-200 Ma interval, for instance. The research team will study the paleomagnetism of any melt rock that can be found, but the target rock itself is likely to have been remagnetized. The research team will perform a detailed sampling with a sampling interval of about 1-2 km out to ~20 km. Objective 7) Ground-truthing of remote sensing data In advance of fieldwork, the research team is generating a remote predictive map using Radarsat-2, Landsat 8, ASTER, and other remote sensing data. The research team will characterize the polarimetric SAR signatures and dominant surface scattering mechanisms observed from different types of surficial materials. The team will also quantitatively estimate the physical properties of different geological units, such as the centimeter-scale roughness and dielectric properties. This research will be published in scientific journals and presented at conferences. Copies of these papers will be distributed to interested northern communities and research organizations. The researchers will also have a website with daily updates from the field and use social media and will promote this to local communities. The fieldwork for this study will be conducted from July 8, 2015 to August 3, 2015.