page_title: Itcha Range
section_title: Volcanic history
hierarchical_section_title: Itcha Range / Geology / Volcanic history
caption_attribution_description: English: Geology of the Itcha Range in British Columbia, Canada
context_page_description: The Itcha Range, also known as the Itchas, is a small isolated mountain range in the West-Central Interior of British Columbia, Canada. It is located 40 km northeast of the community of Anahim Lake. With a maximum elevation of 2,375 m, it is the lowest of three mountain ranges on the Chilcotin Plateau extending east from the Coast Mountains. Two mountains are named in the Itcha Range; Mount Downton and Itcha Mountain. A large provincial park surrounds the Itcha Range and other features in its vicinity. More than 15 animal species are known to exist in the Itcha Range area, as well as a grassland community that is limited only to this location of British Columbia. The Itcha Range is within territory which has been occupied by aboriginal peoples for millennia. This area has a relatively dry environment compared to the Coast Mountains in the west.
  In contrast to most mountain ranges in British Columbia, the Itcha Range represents an inactive shield volcano. This highly dissected volcanic edifice consists of a variety of rock types, including basanite, hawaiite, trachyte, rhyolite, phonolite and alkali olivine basalt.
context_section_description: Two stages of volcanic activity constructed the Itcha Range. The first stage, referred to as the felsic shield-building stage, occurred between 3.8 and 3.0 million years ago. Three phases comprise this stage; a pre-explosive phase, an explosive phase and a post-explosive phase. Analysis of the first trachyte magmas to erupt during the pre-explosive phase suggest they were relatively fluid as shown by their areal extent. Eruptions became more viscous during the explosive phase, followed by more viscosity during the post-explosive phase. As a result, the volume of erupted material became smaller over time. The increasing viscousness of felsic lava during the shield-building stage suggests a maturing plumbing system underneath the Itcha Range, which may have consisted of multiple, isolated, cupola-type magma chambers.
  A 900,000‑year‑long period of quiescence followed after the felsic shield-building stage, during which time erosion ate away at the shield's gentle slopes. This quiescence was followed by a mafic capping stage between 2.2 and 0.8 million years ago, but renewed activity might have occurred in the last 340,000 years. Alkali olivine basalts of the mafic capping stage were derived from the fractionation of a clinopyroxene, olivine and oxide assemblage. However, the associated hawaiite lavas may have derived from an alkali olivine basalt parent by the fractionation of a clinopyroxene-dominated assemblage at higher pressures. As volcanic activity waned during the mafic capping stage, lava flows became more viscous and decreased in volume. This suggests that parental magmas may have been derived by increasingly smaller degrees of partial melting with time. If volcanic activity of the Itcha Range is related to a hotspot, this temporal and spatial evolution would suggest a waning heat source.
  The main body of the shield erupted over an area of about 300 km² (120 sq mi). Volcanic activity associated with the Itcha Range extended 20 km (12 mi) south to the Satah Mountain area where lavas erupted along a north-northwest trending fault system and covered an additional area of 250 km² (97 sq mi). Although the Satah Mountain volcanic field is not part of the Itcha Range, it is linked to the range by a volcanic ridge.
caption: Geologic map of the Itcha Range showing stages of development
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