Distribution:

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

Locality Data:

Thickness(m): Maximum 100.

Lithology:

The Armadillo Formation includes both felsic and basic lavas and pyroclastic rocks that issued from separate centres during a long period of biomodal volcanism. The felsic rocks, which include comenditic rhyolite and trachyte flows, domes and pyroclastic deposits, were erupted from a cluster of vents on and around Armadillo Peak. The basic centres are less clearly defined, but major, long-lived basaltic volcanoes must have been developed both north and south of the felsic lava complex and spread thick lobes of flows west into the Mess Creek lowlands (Souther, 1992). It consists chiefly of comendite, interlayered with lesser amounts of comenditic and panelleritic trachyte and minor basalt. By far the largest volume of material issued as domes and viscous flows, erupted during the culmination of the first magmatic cycle. Some of the flows are as much as 100 m thick and more than 10 km long. Moderately to strongly welded pyroclastic flows and air-fall pumice deposits, although volumetrically small, form a widespread distal facies that serves as an important marker horizon. The Armadillo comendites and trachytes have similar mineralogy except for more quartz in the comendites. Most flows have a quenched, vitreous base of flow-banded obsidian from 1 to 3 m thick. Above this, the rock is holocrystalline, commonly with 5% to 10% phenocrysts of sanidine and hedenbergite and less commonly of fayalite, arfvedsonite, and aenigmatite (Yagi and Souther, 1974). The groundmass minerals, alkali feldspars, quartz, acmitic pyroxene, aeenigmatite, arfvedsonite, and kataphorite commonly occur in radiating spherulitic clusters (Souther et al., 1984).

Age Determinations:

Method - K/Ar; Material - Whole Rock; Age - 6.1; Err_Minus - 0.1; Err_Plus - 0.1..

Method - K/Ar; Material - Whole Rock; Age - 6.1; Err_Minus - 0.2; Err_Plus - 0.2..

Method - K/Ar; Material - Whole Rock; Age - 6.5; Err_Minus - 0.2; Err_Plus - 0.2..

Method - K/Ar; Material - Whole Rock; Age - 6.8; Err_Minus - 0.3; Err_Plus - 0.3..

Method - K/Ar; Material - Whole Rock; Age - 6.2; Err_Minus - 0.1; Err_Plus - 0.1..

Method - K/Ar; Material - Whole Rock; Age - 6.3; Err_Minus - 0.5; Err_Plus - 0.5..

Method - K/Ar; Material - Whole Rock; Age - 7.1; Err_Minus - 0.3; Err_Plus - 0.3..

Method - K/Ar; Material - Whole Rock; Age - 10.2; Err_Minus - 1.4; Err_Plus - 1.4..

Relationship:

The Armadillo is the oldest salic formation in the Mount Edziza Volcanic Complex. South of Raspberry Pass, distal Armadillo ash flows rest directly on the unmodified surface of the Little Iskut shield. Elsewhere, Armadillo rocks rest on moderately eroded Raspberry basalt, from which they are commonly separated by a colluvial layer (Souther et al., 1984). The top of the Armadillo Formation is defined by an erosion surface that separates it from the overlying Nido and Kounugu basalt successions (Souther, 1992).

Other Citations:

Mihalynuk et al., 1996.

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.

Yagi, K. and Souther, J.G., 1974. Aenigmatite from Mount Edziza, British Columbia, Canada; American Mineralogist, v. 59, p. 820-829.