Northern Cordilleran Volcanic Province - Geology - Geologic Features

Geologic Features

Hot springs are present throughout the Northern Cordilleran Volcanic Province, indicating magmatic heat is present under the Northern Cordilleran Volcanic Province. They are formed if water percolates deeply through the crust and heats up from the primal magmatic heat under the surface. After the groundwater is heated, the heated groundwater rises to the surface as a hot spring. In some cases, the heated groundwater may rise along extensional faults related to rifting in the Northern Cordilleran Volcanic Province. The Lakelse Hot Springs near Lakelse Lake Provincial Park in northern British Columbia is interpreted to be one such example. With a temperature of 89 °C (192 °F), the springs are the hottest in Canada. It is also possible the magma associated with the Nass Valley eruption 250 years ago to the north rose along the same north trending fault lines fueling the Lakelse Hot Springs. Hot springs are also present in Iskut River Hot Springs Provincial Park and Choquette Hot Springs Provincial Park in northwestern British Columbia.

Xenoliths, rock fragments that become enveloped in a larger igneous rock, are widespread in the Northern Cordilleran Volcanic Province. Xenoliths that originated in the Earth's crust include rich metamorphic rocks and felsic intrusive rocks. Granulite xenoliths exist mainly at the Fort Selkirk Volcanic Field in central Yukon, Prindle Volcano in easternmost Alaska and at Castle Rock and the Iskut River in northern British Columbia. Felsic intrusive xenoliths are a lot more common and usually originate from adjacent granitic intrusions, including those that form the Coast Mountains. More than 14 volcanic zones throughout the Northern Cordilleran Volcanic Province comprise xenoliths that originated from the Earth's mantle and are located mainly at the Yukon-Tanana Terrane, the Cache Creek Terrane and at volcanoes occupying the Paleozoic and Mesozoic Stikinia terrane. They consist of lherzolite, harzburgite, wehrlite, dunite, websterite and garnet composed pyroxenite. The highest and lowest temperatures recorded by mantle xenoliths increase to the south and decrease to the north. Mantle xenoliths at Prindle Volcano in easternmost Alaska record the minimum temperature of 860 °C (1,580 °F) and mantle xenoliths from the Fort Selkirk Volcanic Field in central Yukon record the minimum temperature range from 960 to 1,050 °C (1,760 to 1,922 °F). At Castle Rock in northern British Columbia, mantle xenoliths record the maximum temperature of 1,260 °C (2,300 °F), as well as the maximum temperature range from 1,000 to 1,260 °C (1,832 to 2,300 °F). The minimum xenolith temperatures indicate that the boundary between the Earth's crust and mantle is shallowest beneath the northern portion of the Northern Cordilleran Volcanic Province. Therefore, the temperature ranges for the northernmost xenolith series is about one-half the temperature range found in xenoliths at the southern portion of the volcanic province.

Megacrysts, crystals or grains that are considerably larger than the encircling matrix, are commonly found in lava flows throughout the Northern Cordilleran Volcanic Province. They consist of three different groups, including kaersutitic amphibole megacrysts, clinopyroxene megacrysts and plagioclase megacrysts. Megacrysts made of kaersutite are known to be found mainly at Llangorse Mountain in northern British Columbia. Black glassy clinopyroxene megacrysts are widespread throughout the Northern Cordilleran Volcanic Province, suggesting their creation is independent of lithosphere structure. In contrast, clear glassy plagioclase megacrysts are found largely at the southern end of the Northern Cordilleran Volcanic Province and largely within the boundaries of the Stikinia terrane. This suggests the plagioclase megacrysts have a source that is sensitive to the Earth's lithosphere, including contamination or magma ponding. Megacrysts made of plagioclase and clinopyroxene regionally show significant evidence of reaction with the associated magma, including sieve-textured cores and random, resorbed and embayed outer margins wherever they are located.

Lava tubes are widespread in the Northern Cordilleran Volcanic Province, and are typically basaltic in composition. At the Level Mountain Range, lava tubes reach diameters of 1 m (3.3 ft) to 2 m (6.6 ft). These owed their origin to highly fluid lavas with temperatures of at least 1,200 °C (2,190 °F). In Nisga'a Memorial Lava Beds Provincial Park of northwestern British Columbia, lava tubes are present that were formed during one of Canada's most recent volcanic eruptions in the 18th century. Lava Fork at the British Columbia-Alaska border is influenced by lava flows from a recent volcanic eruption that later collapsed into underlying lava tubes after the lava solidified. Sections of these collapsed lava tubes now form volcanic pits.

Extensive areas of nearly flat-lying lava flows throughout the Northern Cordilleran Volcanic Province can cover areas of at least 100 km2 (39 sq mi) and are generally composed of highly-fluid basaltic lava. However, lava plains that pre-date the last glacial period have been eroded and overridden by glacial ice, affording a less distinctive form to these older landforms. For example, lava beds at least a million years old in central Yukon contain unconsolidated glacial deposits that were deposited when glacial ice rode on top of the lava flows comprising the lava beds.

Subvolcanic intrusions in the Northern Cordilleran Volcanic Province are exposed in areas of high relief. This includes volcanic plugs found at the Mount Edziza volcanic complex, the Level Mountain Range, Hoodoo Mountain and in the Atlin and Maitland areas. Volcanic plugs in the Atlin and Maitland areas consist of olivine nephelinite and basanite magmas. Minor plugs made of gabbroic and granitic magma are associated with volcanic stratigraphy at the Mount Edziza volcanic complex and Level Mountain Range.

Read more about this topic:  Northern Cordilleran Volcanic Province, Geology

Famous quotes containing the word features:

    It is a tribute to the peculiar horror of contemporary life that it makes the worst features of earlier times—the stupefaction of the masses, the obsessed and driven lives of the bourgeoisie—seem attractive by comparison.
    Christopher Lasch (b. 1932)