Search

Heat generated from the decay of K, Th, and U plays a fundamental role in the differentiation and stabilization of Earth's continental crust. This is particularly important in the construction of Archean cratons that form the nuclei of Earth's continents. The Kapuskasing uplift is a rare exposure of an Archean‐age crustal cross‐section that provides a snapshot of crustal melting, differentiation, and compositional stratification. We integrate field observations, whole‐rock compositions, thermodynamic equilibrium and accessory mineral modelling with heat production and latency time modelling to provide insights into the partitioning of heat‐producing elements between residue and melt during anatexis of metabasites as well as the resulting effects on metamorphic timescales and the production of tonalite–trondhjemite–granodiorite (TTG) suites. We model six metabasite compositions ranging from relatively fertile greenschist facies metabasites to melt‐depleted residual mafic (upper‐)amphibolites to granulites. Heat‐producing elements are modelled to be partitioned between melt and residue; the dominant minerals in the residue that host these elements are apatite, hornblende, K‐feldspar, and epidote. At 800–850°C epidote is no longer stable, and the melt fraction is predicted to contain roughly half of the heat production capacity for the system. Apatite and melt are expected to be the dominant repositories for Th and U during anatexis; zircon is predicted to be completely consumed by 850°C, whereas apatite persists to higher temperatures and allanite is expected only in minor modal abundances at high‐P, low‐T conditions. The partitioning of heat‐producing elements into relatively low‐density melt decreases the heat production of the residual system during anatexis. Due to their high density and affinity for U and Th, epidote and apatite retain heat production capacity in the residue during metabasite melting. Thermal latency modelling of metamorphism suggests that enriched metabasite compositions require 38–46 My to increase the temperature from ~650 to 850°C (solidus temperature to peak metamorphic temperature of the Kapuskasing uplift), whereas estimates are considerably shorter for depleted compositions (7–25 My). Four of the six samples modelled require 60–70 My to reach 1000°C from the solidus. Our modelling of heat‐producing element partitioning and predicted proportions of melt suggest that enriched basaltic compositions are the most reasonable source of TTG magmas and our heating time modelling indicates the mantle as an equal to dominant source of heat for metabasite anatexis compared with radiogenic heat production. [ABSTRACT FROM AUTHOR]

The cold, remote, northern regions of Canada constitute a challenging environment for the provision of reliable energy and food supply to communities. A transition from fossil fuels to renewables-based sources of energy is one positive step in reducing the greenhouse gases from the energy supply system, which currently requires long-distance transport of diesel for electricity and heating needs. Geothermal energy can not only displace diesel for part of this energy need, it can provide a base-load source of local energy to support food production and mitigate adverse impacts of food insecurity on communities. In this proof-of-concept study, we highlight some potential benefits of using geothermal energy to serve Canada's northern communities. Specifically, we focus on food security and evaluate the technical and economic feasibility of producing vegetables in a "controlled environment", using ground sources of heat for energy requirements at three remote locations—Resolute Bay, Nunavut, as well as Moosonee and Pagwa in Ontario. The system is designed for geothermal district heating combined with efficient use of nutrients, water, and heat to yield a diverse crop of vegetables at an average cost up to 50% lower than the current cost of these vegetables delivered to Resolute Bay. The estimates of thermal energy requirements vary by location (e.g., they are in the range of 41 to 44 kW of thermal energy for a single greenhouse in Resolute Bay). To attain adequate system size to support the operation of such greenhouses, it is expected that up to 15% of the annually recommended servings of vegetables can be provided. Our comparative analysis of geothermal system capital costs shows significantly lower capital costs in Southern Ontario compared to Northern Canada—lower by one-third. Notwithstanding high capital costs, our study demonstrates the technical and economic feasibility of producing vegetables cost-effectively in the cold northern climate. This suggests that geothermal energy systems can supply the heat needed for greenhouse applications in remote northern regions, supplying a reliable and robust source of cost-competitive sustainable energy over the long-term and providing a basis for improved food security and economic empowerment of communities. [ABSTRACT FROM AUTHOR]

The article provides information on a study on biogenic carbon in pink corundum found in the southern part of West Greenland. Topics discussed include rutile inclusions based on uranium-lead geochronology, analysis of the carbon isotope composition of graphite to determine its origin, and finding on the chemical conditions necessary for corundum growth.