Origins of Thin, Hot and Weak Mantle Beneath the North American Plate in British Columbia
Date
2025
Authors
Sparks, Holly
Journal Title
Journal ISSN
Volume Title
Publisher
University Of Victoria
Abstract
The origin of lithospheric mantle underlying the Canadian Cordillera has three proposed models. Two of these models suggest that the lithospheric mantle is a long-lived structure and formed greater than 100Myr ago, while the third proposes recent delamination and subsequent replacement within the past 50Myr. Using foreign fragments of spinel peridotite erupted within basanite to nephelinite lavas at Mount Timothy, British Columbia the thermal history of the mantle can be examined. Geothermometry of Ca-Mg-Fe (TBKN) exchange between co-existing orthopyroxenes and clinopyroxenes was performed, resulting in temperatures ranging from 930°C to 1040°C. Cooling rates of 1°C/Myr-10°C/Myr were then deduced by comparing TBKN temperatures to grain size using Dodson’s relationship for closure temperatures. These cooling rates suggest the mantle lithosphere is ancient, and that if delamination has occurred it would have been upwards of 125 Myr ago. This analysis could be performed on other xenolith localities across the Canadian Cordillera to further conclusions.
Description
Keywords
geology, mantle, xenolith, geothermometry, Canadian Cordillera, peridotite