Characterizing the nature of the sub-continental lithospheric mantle beneath Prindle volcano, Yukon-Tanana Upland, Alaska

Abstract

Prindle Volcano, an isolated alkali-basaltic cone in eastern Alaska is the northernmost volcanic center within the northern Cordilleran volcanic province (NCVP), a volcanic region along the northwestern region of North America. Prindle contains an ultramafic xenolith suite unlike any volcanic center within the region and perhaps the North American Cordillera. The suite provides an opportunity to examine the sub-continental lithospheric mantle beneath the region. Prindle volcano’s xenolith suite includes various lithologies: lherzolite, harzburgite, olivine-websterite, dunite, and clinopyroxenite. Utilizing petrographical and geochemical analysis, comparisons of mantle xenolith suites within the Cordillera, and suites from similar tectonic settings around the world we can constrain the processes for the Prindle xenolith suite. Textural characteristics within Prindle xenoliths suggest events including shear deformation followed by melt-rock reaction during porous reactive flow. Additionally, the textures and chemistry of the most depleted dunite and harzburgites suggest a supra-subduction zone setting for origination. The lherzolites, websterites, and clinopyroxenites share direct textural and geochemical relationships that suggest an origin through focused, porous reactive flow. Previous studies conducted on other xenoliths within the Cordillera farther south identified a ~100-200°C temperature anomaly in the upper mantle beneath the NCVP due to a subducted slab window. Numerous studies indicate that the anomaly affects volcanic centers in the region. Prindle, however, resides on the margin of the mantle anomaly. With the evidence presented here, we suggest that the Prindle xenolith suite is derived from a localized lithospheric shear zone created by regional uplift above the anomaly located to the southeast. After the shear zone developed, a melt-rock reaction event by focused porous reactive flow with an alkaline fluid/melt occurred. It is surmised that the variability located at Prindle is due to the limited melt volumes during melt-rock interaction compared to those xenolith localities which are located above the regional mantle anomaly.