NWT RESEARCH DATABASE

Tags: physical sciences, geology, geochemistry, paleontology, petrology, mineralogy, acasta gneiss, isotopes

Objective(s): To collect samples from this very ancient and rare set of rocks, while documenting field relationships and structures present in the complex rock outcroppings of the Acasta Gneiss Complex (AGC); and to determine the major- and trace-element composition of the rocks and compare these to published data on broadly similar rocks formed later in Earth's history.

Project Description: This study has the following specific objectives: 1) Collect samples from this very ancient and rare set of rocks, while documenting field relationships and structures present in the complex rock outcroppings of the Acasta Gneiss Complex (AGC); 2) Determine the major- and trace-element composition of the rocks and compare these to published data on broadly similar rocks formed later in Earth history; 3) Determine the oxygen isotope composition of the AGC rocks and minerals with a view to determining if, as is the case in the present-day, surface waters played an important role in the petrogenesis of the rocks. The proposed study will make use of state-of-the-art Cameca 1280 Ion Microprobe recently installed at the U. of Alberta's Canadian Centre for Isotopic Microanalysis. This instrument is capable of isotopic analysis of minerals at very high spatial resolution (<20 micrometers), which is critical to the present study as only such high resolution analyses will enable us to read through later geological events that have obscured but not completely erased a record of the earliest history of the AGC. Collectively, the geochemical and isotopic data obtained in my study will provide insights on the formation of Earth's early continental crust. Previously created maps of the Acasta Gneiss Complex have specific localities where significantly ancient rocks outcrop. These localities will be investigated and portions of the oldest units will be sampled and analyzed at the University of Alberta. Samples will be analyzed using Inductively Coupled Plasma Mass Spectrometry, Secondary Ion Mass Spectrometry in the newly opened Canadian Centre for Isotopic Microanalysis, and a small suite of samples will be analyzed commercially. Copies of publications resulting from this study will be provided to the Northwest Territories Geoscience Office (NTGO). The results of the study will also be presented orally at the Yellowknife Geoscience Forum. The fieldwork for this study will be conducted from July 15, 2011 to August 12, 2011.