Geology of the Quartet Mountain lamprophyre suite, Wernecke Mountains, Yukon

The Early Cambrian Quartet Mountain lamprophyres are volatile-rich ultramafic alkaline dikes that crosscut the Wernecke and Mackenzie mountains supergroups in the Wernecke Mountains of northern Yukon. Their emplacement may have been triggered by Early Paleozoic extension of the Cordilleran miogeocline. Numerous small-volume alkalic igneous rocks that range in age from Cambrian to Devonian occur elsewhere in the miogeocline and may reflect a similar tectonic setting. The Quartet Mountain lamprophyres contain phenocrysts of phlogopite ± diopside ± olivine within a dark-grey aphanitic groundmass and were likely generated by low-percentage melting of mantle at depths >90 km. One of the lamprophyres contains abundant pseudomorphed olivine xenocrysts and xenoliths of inferred crustal and mantle affinities. Although this dike resembles kimberlite because of its abundance of mantle xenoliths and xenocrysts and its ultramafic composition, it differs from kimberlite in its abundance of phlogopite phenocrysts. It is best described as an ultramafic lamprophyre with kimberlitic affinity. The lamprophyres have modest potential to host diamonds.