Distribution:

Mount Edziza and northern plateau; Ice Peak, Armadillo Peak and central plateau (Souther, 1988).

Lithology:

The Edziza Formation includes the composite trachyte cone of Mount Edziza and satellitic cones around its flank. The composite cone developed during the final stages of the third magmatic cycle and largely buried the dissected north slope of older Ice Peak. Its circular summit crater, 2 km in diameter and 2,787 m high, has been breached on its east side, exposing alternating sequences of explosion breccia and steeply outward-dipping flows from 30 to 90 m thick. Initial dips of as much as 30° are present in the composite cone, and satellitic domes are bounded by initial slopes of as much as 60°. Rocks of the Edziza Formation are confined to a narrow range of compositions near the pantelleritic trachyte/comenditic trachyte boundary. Sparse phenocrysts of anorthoclase and less commonly of sodic ferrohedenbergite are surrounded by a pilotaxitic groundmass of sodic plagioclase alkali feldspar, arfvedsonite, aenigmatite, kataphorite, and opaques (Souther et al., 1984).

Age Determinations:

Method - K/Ar; Material - Whole Rock; Age - 0.9; Err_Minus - 0.3; Err_Plus - 0.3..

Relationship:

Part of the Mount Edziza Volcanic Complex. It conformably overlies the Pillow Ridge Formation and disconformably overlies the Ice Peak Formation. The upper contact with the Klastline and Kakiddi formations is mostly conformable, but also locally disconformable (Souther, 1988).

Other Citations:

Mihalynuk et al., 1996; Souther, 1992.

References:

Mihalynuk, M., Bellefontaine, K., Brown, D., Logan, J., Nelson, J., Legun, A. and Diakow, L., 1996. Digital Geology, NW British Columbia (94/E, L, M; 104/F, G, H, I, J, K, L, M, N, O, P; 114/I, O, P); Ministry of Energy, Mines and Petroleum Resources, Open File 1996-11.

Souther, J.G., 1988. Geology, Mount Edziza volcanic complex, British Columbia; Geological Survey of Canada, "A" Series Map no. 1623A, 2 sheets.

Souther, J.G., 1992. The Late Cenozoic Mount Edziza Volcanic Complex, British Columbia; Geological Survey of Canada, Memoir 420, 329 p.

Souther, J.G., Armstrong, R.L., and Harakal, J., 1984. Chronology of the peralkaline, late Cenozoic Mount Edziza Volcanic Complex, northern British Columbia, Canada; Geological Society of America Bulletin, March 1984, Vol. 95, Issue 3, pp. 337-349.