Ice Peak Formation

Unit Name: Ice Peak Formation
Unit Type: Lithostratigraphic
Rank: Formation
Status: Formal
Usage: Currently in use
Age Interval: Pleistocene - Holocene (1.806 - 0 ma)
Age Justification: Geochronology. The oldest dated sample from the Ice Peak (3.7 ± 1.0 Ma) has a large error due to atmospheric argon and consquently is disrgarded. The remaining dates fall into two groups: 2.8 Ma, and between 1.6 and 1.2 Ma. The younger dates are from samples with the highest potassium content and are least susceptible to fractionation or contamination errors. The Ice Peak Formation is structurally and petrographically complex, and the range of dates may reflect real age differences within the Ice Peak pile. The discrepancy between the Ice Peak dates, all greater than 1.5 Ma, and concordant dates from the underlying Pyramid, all less than 1.2 Ma, suggests that the Ice Peak data are systematically biased toward Older, anomalous results. The presence of excess argon is a likley explanation. Correcting for a common excess of ~0.05 x 10*-6 cc/gm, which is the same magnitude as the solubility of Ar in magma at 1 atmospheric pressure, would reduce all of the Ice Peak dates to about 1 Ma and bring them in line with dates from the underlying Pyramid and overlying Edziza Formations. The problem of excess argon may have affected individual dates for several older formations, but a comprehensive and systematic bias appears to be unique to the Ice Peak. The Ice Peak is the only formation that includes a significant volume of intermediate rock types. Ice Peak rocks also contain an exceptional ecess of 87Sr, which suggest crustal contamination. The Pillow Ridge Formation, which is probably comagmatic with the upper Ice Peak, is alos contaminated with crustal material (Souther et al., 1984).
Province/Territory: British Columbia

Originator: Souther et al., 1984.

Distribution:

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

Lithology:

Ice Peak rocks include picritic and alkali olivine basalt, hawaiite, benmoreite comenditic, and pantelleritic trachyte. Despite this compositional diversity, the formation represents a single composite cone that developed around a vent or cluster of vents near Ice Peak. The salic end members and some of the highly porphyritic hawaiites make up thick flows of the central edifice, whereas aphyric and moderately feldsparphyric basalts predominate in the distal parts of the surrounding shield. There is a transition from aphyric basaltic flows in the lower part of the Ice Peak Formation to more porphyritic and salic rocks in the upper part. Locally, trachyte and benmoreite flows are interstratified with basaltic sequences. Ice Peak activity culminated with an effusion of thick trachyte flows. Ice Peak basalt is similar to older basalts except that it commonly has open vesicles, rather than calcite- or silica-filled amygdules. Ice Peak trachyte and benmoreite flows are interstratified with basaltic sequences. Ice Peak activity culminated with an effusion of thick trachyte flows (Souther et al., 1984).

Age Determinations:

Method - K/Ar; Material - Whole Rock; Age - 1.2; Err_Minus - 0.1; Err_Plus - 0.1..

Method - K/Ar; Material - Whole Rock; Age - 1.5; Err_Minus - 0.4; Err_Plus - 0.4..

Method - K/Ar; Material - Whole Rock; Age - 1.5; Err_Minus - 0.1; Err_Plus - 0.1..

Method - K/Ar; Material - Whole Rock; Age - 1.6; Err_Minus - 0.2; Err_Plus - 0.2..

Method - K/Ar; Material - Whole Rock; Age - 2.8; Err_Minus - 0.1; Err_Plus - 0.1..

Method - K/Ar; Material - Whole Rock; Age - 2.8; Err_Minus - 0.2; Err_Plus - 0.2..

Method - K/Ar; Material - Whole Rock; Age - 3.7; Err_Minus - 1; Err_Plus - 1..

Relationship:

The Ice Peak is the oldest formation erupted during the third magmatic cycle of the Mount Edziza Complex. It rests directly on the Pyramid rhyolite but is much more extensive and is commonly underlain by till or glacial-fluvial gravel. The period of glaciation during which these deposits were laid down is probably coeval with ice-contact assemblages in the Pyramid Formation (Souther et al., 1984). The central edifice of Ice volcano was superimposed on the southern part of the Pyramid pile. Flows descending the eastern and western sides of Ice volcano spread far beyond the limits of the Pyramid pile, across the old surface of Nido basalt and locally onto pre-Tertiary basement rocks beyond the edge of the eroded shield (Souther, 1992). There is a possible conformable contact with the overlying Pillow Ridge Fromation and a discontinuous contact with the overlying Edziza Formation (Souther, 1988).

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.

Source: GSC file of geological names; T.E. Bolton and J. Dougherty (compiler)
Contributor: Michael Pashulka
Entry Reviewed: No
Name Set: Lithostratigraphic Lexicon
LastChange: 02 Feb 2011