Challis Arc
Encyclopedia
The Challis Arc was an Eocene
volcanic arc
that stretched from southwestern British Columbia
through Washington to Idaho
, United States
. The arc formed 57 million years ago as a result of subduction
of the eastern block of the Kula Plate
ending 37 million years ago. Remnants of the Challis Arc are found as granitic
plutons in the North Cascades, the Okanagan Highland
s and in southcentral Idaho.
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
volcanic arc
Volcanic arc
A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...
that stretched from southwestern British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
through Washington to Idaho
Challis, Idaho
Challis is a city in Custer County, Idaho, United States. The population was 909 at the 2000 census. The city is the county seat of Custer County.-History:...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The arc formed 57 million years ago as a result of subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
of the eastern block of the Kula Plate
Kula Plate
The Kula Plate is an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It is subducting under the North American Plate at the Aleutian Trench and is surrounded by the Pacific Plate...
ending 37 million years ago. Remnants of the Challis Arc are found as granitic
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
plutons in the North Cascades, the Okanagan Highland
Okanagan Highland
The Okanagan Highland is a plateau-like hilly area in British Columbia, Canada, and the U.S. state of Washington . It lies between the Okanagan Valley on its west and the Kettle River on its east, and geologically is more or less an extension of the Thompson Plateau, which lies west of the Okanagan...
s and in southcentral Idaho.