The Little Iskut Formation is a
stratigraphic unit
A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize ...
of
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
age in northwestern
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, Canada.
Naming
The Little Iskut Formation takes its name from the
Little Iskut River, a
tributary
A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drai ...
of the
Iskut River
The Iskut River, located in the northwest part of the province of British Columbia is the largest tributary of the Stikine River, entering it about above its entry into Alaska.
From its source at Kluachon Lake the Iskut River flows south and wes ...
which flows southeast from the southern end of the
Mount Edziza volcanic complex
The Mount Edziza volcanic complex is a large and potentially active north-south trending complex volcano in Stikine Country, northwestern British Columbia, Canada, located southeast of the small community of Telegraph Creek. It occupies the sou ...
.
Geology
The Little Iskut Formation has a volume of , making it the seventh most voluminous
geological formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
comprising the Mount Edziza volcanic complex.
It occurs at the northeastern end of the
Spectrum Range
The Spectrum Range, formerly called the Spectrum Mountains and the Rainbow Mountains, is a subrange of the Tahltan Highland in the Stikine Country of northwestern British Columbia, 20 km west of the Stewart-Cassiar Highway, south of Mount ...
where it covers a roughly wide area. A small portion of the Little Iskut Formation is exposed in the
Mess Creek Escarpment to the west.
The Little Iskut Formation consists of
trachybasalt
Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides. Minerals in trachybasalt include alkali feldspar, calcic plagioclase, olivine, clinopyroxene and li ...
flows and
breccia
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.
The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
. It ranges in thickness from on Stewpot Ridge to about near the middle of Artifact Ridge. The Little Iskut Formation originally formed a small symmetrical
shield volcano during the Miocene.
The Little Iskut Formation conformably overlies the
Raspberry Formation south of Bourgeaux Creek. Little Iskut trachybasalt is overlain by
rhyolite of the
Armadillo Formation and
basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
of the Nido Formation. Two subunits comprise the Little Iskut Formation. The upper unit consists entirely of trachybasalt lava flows while the lower unit consists of abundant breccia.
K–Ar dating
Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium ...
has yielded an age of 7.2 ± 0.3 million years for Little Iskut trachybasalt.
See also
*
Volcanism of Western Canada
Volcanism of Western Canada has produced lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, greenstone belts, submarine volcanoes, calderas, diatremes and maars, along with examples of more less common v ...
References
{{Northern Cordilleran volcanoes
Geologic formations of British Columbia
Mount Edziza volcanic complex
Miocene Canada
Miocene shield volcanoes
Shield volcanoes of Canada