FEATURES OF RODINIA BREAK-UP IN THE MINTO INLIER WITH COMPARISONS TO THE NORTHERN CORDILLERA

The break-up of Rodinia spans a warm to cold climatic transition recorded in the Ogilvie, Wernecke, and Mackenzie mountains of the northern Cordillera, and in the Minto Inlier of Victoria Island. In the Ogilvie and Wernecke Mountains, harbingers of break-up are NW-side down syn-sedimentary normal faults and associated olistostromes in carbonate and mixed siliciclastic rocks of the early Neoproterozoic lower Fifteenmile Group. Faults are capped by platformal carbonates of the upper Fifteenmile Group, with olistostromes and slump folds interpreted to result from failed rifting along the NW margin of Laurentia. Subsequent uplift, erosion and deposition of coarse clastic rocks of the Mt. Harper Group in half-graben preserve the most significant phases of extension culminating with eruption of the 717.4 Ma Mt. Harper Volcanic Complex. In the Mackenzie Mountains, initial extension is recorded by warm-climate evaporitic, alluvial and lacustrine deposits of the Coates Lake Group (CLG) deposited in 10-50 km rift basins and capped by allodapic limestone with local km-scale slump folds on tilted fault blocks. Faults cut the unconformably underlying Mackenzie Mountains Supergroup, including plateau basalt and associated sills of the ~780 Ma Gunbarrel magmatic event. The CLG is unconformably overlain by more widespread rift deposits of the glaciogenic Rapitan Group. In the Minto Inlier, rifting was later and less pronounced. Strata of the early Neoproterozoic Shaler Supergroup are correlated for > 1000 km with only subtle facies variations supporting broad-scale thermal subsidence. In the uppermost part of the section, possible mantle plume-related thermal uplift preceding eruption of the ~720 Ma Natkusiak flood basalt is recorded by gradual emergence from marine to terrestrial environments and erosional beveling of these strata toward the NE Minto Inlier, where the basalt overlies small graben filled with coarse epiclastic debris. Along the NW margin of Laurentia, it is clear that the effects of Rodinia break-up began first and were more complex and protracted in the west, and progressed northeastward and up-section, culminating in the widespread rifting and eruption of the Franklin LIP basaltic rocks. Post break-up passive margin deposits of the Windermere Supergroup are preserved only in the northern Cordillera.