Base de données de recherche des TNO

Régions: Sahtu Settlement Area

étiquettes: geology, rock, paleogeology, geochronology

Objectif(s): Earth's oldest rocks, the 4.03 billion year old Acasta gneisses, are found in the Acasta River area 300 km north of Yellowknife, Northwest Territories. An area to the west near Grant Lake contains rocks of similar appearance that have not been thoroughly investigated with respect to age and crustal history. The research team proposes to collect samples from this area and determine, using U-Pb geochronology, the age of various rock units. If Acasta-aged rocks are present, the results will help to determine the extent and geological history of Earth's oldest continental fragment. A demonstrated absence of these rocks will provide equally important information. In both cases, the results will contribute to a broader study of the nature and extent of a large, ancient continental fragment in which the Acasta gneisses occur. The collection of a specimen of Acasta gneiss for public display in the Earth Sciences Gallery of the Royal Ontario Museum will draw public attention to the remarkable geological history of the Northwest Territories.

Description du projet: During the proposed study, transportation of the research team to the field will be by fixed-wing float plane from Yellowknife. From the base camp at Grant Lake, the research team will examine the study area immediately to the east on foot and by inflatable boat. Rock samples up to 20 kg (45 lbs) will be collected for age dating. It is anticipated that only 4-5 samples will be collected for dating. The research team will fly from a base camp to the Acasta River area for 2-3 days of work. In addition to geological mapping, the research team proposes to collect a specimen of 4.03 billion year old Acasta gneiss from the dated locality on the Acasta River. To provide a visually striking specimen for display in the Earth Sciences Gallery at the Royal Ontario Museum, we will collect a sample from the rubble of a previously blasted outcrop. The sample will be transported via Twin Otter aircraft and truck to Toronto where a stone monument company will cut the sample and polish one surface to reveal the gneissic banding characteristic of this rock type. As this is the oldest terrestrial rock ever dated, the sample will provide a reminder of both the tremendous age of the Earth and the important link between NWT geology and ongoing research on the earliest development of the continents. Field equipment will be limited to tents, hammers, cooking gear, zodiac boat, etc. The camp will host either two or three people. The work is scheduled for the third week of August.