The Ice Peak Formation (IPF) is a stratigraphic unit of Pleistocene age in northwestern British Columbia, Canada. It is the seventh youngest and fifth most voluminous of 13 geological formations comprising the Mount Edziza volcanic complex (MEVC), which consists of volcanic rocks of late Cenozoic age. The IPF is underlain by the 6.3-million-year-old Armadillo Formation, the 4.4-million-year-old Nido Formation and the 1.1-million-year-old Pyramid Formation, all of which are older units of the MEVC. Overlying the IPF are the younger and much less voluminous Pillow Ridge, Edziza, Kakiddi and Big Raven formations of the MEVC; all of these formations were deposited by volcanic eruptions in the last 0.9 million years. The stratigraphic position of the Ice Peak Formation suggests that it is about 1 million years old. The IPF is subdivided into two units informally called the upper and lower assemblages. The upper assemblage consists of randomly oriented alkali basalt, hawaiite, trachybasalt, tristanite, mugearite, benmoreite and trachyte which are in the form of lavas and pyroclastic rocks. This assemblage forms the upper portion of Ice Peak, as well as The Neck, the Camp and Cache hills and the Ornostay and Koosick bluffs. The lower assemblage consists mainly of alkali basalt and hawaiite, but also includes small volumes of trachybasalt, mugearite and tristanite. It forms the bulk of the Ice Peak volcanic pile and occurs on the surrounding Big Raven Plateau.
History The Ice Peak Formation was first defined by Jack Souther, Richard Lee Armstrong and J. Harakal in 1984. It was mapped as one of 15 geological formations of the Mount Edziza volcanic complex, a group of late Cenozoic volcanic rocks in northwestern British Columbia, Canada. In 1988, Jack Souther mapped the IPF in more detail and the number of geological formations comprising the volcanic complex had dropped to 13; the Sheep Track and Kounugu formations were reassigned as members of the Big Raven and Nido formations, respectively, and are no longer recognized.
Stratigraphy Stratigraphically, the IPF is subdivided into two units informally called the upper and lower assemblages. The lower assemblage is the most widespread, having been largely buried under younger rocks and felsenmeer, till, glacial and fluvial outwash, as well as solifluction deposits. Most exposures of this assemblage occur along the western and eastern edges of the Big Raven Plateau in ridges and at the head of valleys. The upper assemblage is exposed along the Mess Creek Escarpment at the southwestern end of the Big Raven Plateau, along the north side of Sezill Creek valley at the western end of the plateau, at the head of valleys at the northwestern end of the plateau, at the southern end of Mount Edziza in the middle of the plateau, and on ridges east of Mount Edziza. The IPF is the seventh-youngest unit of the MEVC and has a volume of 76.7 cubic kilometres (18.4 cubic miles), making it the fifth-most voluminous geological formation of the MEVC. It is also the youngest geological formation of the MEVC that contains more than 70 km3 (17 mi3) of volcanic material. The IPF overlies the 1.1-million-year-old Pyramid Formation, the 4.4-million-year-old Nido Formation and the 6.3-million-year-old Armadillo Formation, all of which are older units of the MEVC. Overlying the IPF are the much less voluminous Pillow Ridge, Edziza, Kakiddi and Big Raven formations; these are younger geological units of the MEVC deposited by volcanic eruptions in the last 0.9 million years.
Lithology Lithologically, the IPF is the most diverse geological formation of the MEVC. It is structurally and petrographically complex, containing a significant volume of volcanic rocks of intermediate composition such as tristanite, trachybasalt, mugearite and benmoreite. The only volcanic rocks of mafic composition are alkali basalt and hawaiite, whereas the main volcanic rock of felsic composition is trachyte. Basalt of the IPF is similar to older basalts throughout the MEVC with the exception of its vesicular texture; it contains open vesicles rather than amygdules filled with calcite or silica. IPF trachyte is similar in composition to the younger Edziza Formation trachyte, but they are separated by an erosion surface. Most of the volcanic rocks comprising the IPF were erupted from Ice Peak, the prominent south peak of Mount Edziza. It is the western rim of a small caldera which formed on the summit of a stratovolcano whose northern flank is buried under the younger, 2,786 m (9,140 ft) high stratovolcano of the Edziza Formation.
Upper assemblage Randomly oriented alkali basalt, hawaiite, trachybasalt, tristanite, mugearite, benmoreite and trachyte lavas and pyroclastic rocks form the upper assemblage. In addition to occurring on the gently sloping surface of the Big Raven Plateau, these rocks also form Camp Hill, Ornostay Bluff, Cache Hill, Koosick Bluff, The Neck and the upper portion of Ice Peak. Camp Hill is a small volcanic cone rising about 180 m (590 ft) above the southwestern portion of the Big Raven Plateau near the Mess Creek Escarpment. About 10 km (6.2 mi) to the southeast, the volcanic cone of Cache Hill rises about 120 m (390 ft) on a ridge between the Big Raven Plateau in the north and the Kitsu Plateau in the southwest. The Ornostay and Koosick bluffs are on the lower western flank of Ice Peak adjacent to the head of Sezill Creek. On the northern side of Sorcery Ridge east of the Big Raven Plateau, the roughly 300 m (980 ft) in diameter volcanic plug of The Neck rises 215 metres (705 feet) above an east–west valley immediately south of Idiji Ridge.
Ice Peak
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