A group of hydrothermal breccias, collectively known as Wernecke breccia, formed at approximately 1.60 Ga in Yukon. The breccias consist of a hydrothermally precipitated matrix that cements clasts derived mainly from the metasedimentary Wernecke Supergroup. Locally, clasts and megaclasts of the Bonnet Plume River intrusions, the Slab volcanics, and other volcanic rocks are also present within the breccias. This paper describes a volcano-sedimentary succession interpreted as a megaclass within Wernecke breccia. The succession consists of pyroclastic and epiclastic rocks that formed in a volcanic environment in a region of evolved crust. This finding adds detail to the character of a postulated Proterozoic terrane that may have collided with the northwestern margin of ancestral North America toward the end of the Paleoproterozoic.
