The Capricorn Assemblage, also known as the Capricorn Formation, is a

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 central portion of the

Mount Meager massif The Mount Meager massif is a group of volcanic peaks in the of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located north of Vancouver at the northern end of the ...

in southwestern

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 Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. It is named after

Capricorn Mountain Capricorn Mountain is one of the several volcanic peaks of the Mount Meager massif in southwestern British Columbia, Canada. The slopes of Capricorn Mountain appear to be more gentle than other volcanic peaks of the massif. The mountain consists o ...

, the third highest subsidiary peak of Meager. The assemblage was formed during a period of volcanic activity about or less than 90,000 years ago. Weathered

rhyodacite Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

is the main

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...

comprising the Capricorn Assemblage. It forms the final of Capricorn Mountain and

Mount Job Mount Job is one of six named volcanic peaks of the Mount Meager massif in British Columbia, Canada. It is a pile of rubble held together by volcanic ash and sand. The main summit of Mount Job is hard to climb because of difficult access and its ...

. The rhyodacite is characterized by

phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

s of

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

and

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...

. Capricorn Assemblage rhyodacite underlies

Plinth Assemblage The Plinth Assemblage, also known as the Plinth Formation, is an accreted terrane of igneous rocks in southwestern British Columbia, Canada, located just north of the Lillooet River and on the northern flank of the Mount Meager massif. It is named ...

rhyodacite on the south flank of

Plinth Peak Plinth Peak, sometimes called Plinth Mountain, is the highest satellite cone of the Mount Meager massif, and one of four overlapping volcanic cones which together form a large volcanic complex in the Garibaldi Volcanic Belt of the Canadian Cascad ...

References

{{coord missing, British Columbia Mount Meager massif Volcanism of British Columbia Geologic formations of British Columbia Pleistocene volcanism

See also

References