Detailed mapping of Yukon-Tanana Terrane in Glenlyon map area has identified two Carboniferous volcanic successions, and their subvolcanic intrusions. The early-to mid-Mississippian Little Kalzas succession consists predominantly of calc-alkaline volcanic and volcaniclastic rocks which formed in a continental arc setting. Minor alkali basalt occurs stratigraphically below and above the calc-alkaline rocks.The Little Salmon succession, of mid-Mississippian to early Pennsylvanian age, represents a second cycle of continental arc magmatism. It consists of calc-alkaline andesite and volcaniclastic rocks near Little Salmon Lake, but passes laterally along strike to alkali basalt of within-plate affinity. The occurrence of alkaline magmatism within these continental arc sequences suggests episodic rifting of the arc. The occurrence of Mn-rich exhalite within the rifted arc sequence of the Little Salmon succession suggests that this environment may also have been favourable for production and deposition of metal-rich solutions.