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Chilcotin Plateau Basalts

The Chilcotin Plateau Basalts, also called the Chilcotin Group, is a medium-sized large igneous province that forms a volcanic plateau running parallel with the Garibaldi Volcanic Belt in south-central British Columbia, Canada.

During Late Oligocene and Pliocene times, one of the largest flood basalts ever to appear on British Columbia's Interior Plateau engulfed 25,000 km² of the Pacific Northwest, forming a medium-sized large igneous province. Volcanism spanned about 16 million years, and occurred in three main magmatic episodes: 15-13 Ma, 9-6 Ma, and 3-1 Ma. Eruptions were most vigorous 6-10 million years ago and 2-3 million years ago, when most of the basalt was released. Less extensive eruptions continued 0.01 to 1.6 million years ago.

These lava flows have been extensively exposed by erosion resulting from the great floods that flowed in this region throughout the past ice ages, which laid bare many layers of the basalt flows along the Fraser Canyon from Soda Creek south to Canoe Creek elsewhere along the Chilcotin, Chilko, Chilanko and Taseko Rivers at Chasm Provincial Park along Upper Deadman River. Prior to Late Pleistocene glacial erosion these centers formed a series of coalesced, low-profile shield volcanoes.

The Chilcotin Plateau Basalts are nearly to and potentially linked to the Columbia River Basalt Group in the United States, which lies across parts of the states of Washington, Oregon, and Idaho. Its morphology is similar to other volcanic plateaus such as the Snake River Plain in Idaho and parts of Iceland.

Formation of the Chilcotin Plateau Basalts

Starting about 16 million years lava flow after lava flow poured out, eventually accumulating to a thickness of more than . As the molten rock came to the surface, the earth's crust gradually sank into the space left by the rising lava. The subsidence of the crust produced a large, slightly depressed lava plain. Strata include crudely columnar-jointed pahoehoe flows, some thick, tiered flows, minor pillow lava and pillow breccia, and rare silicic tephra layers. Individual vents for basalt volcanism include small cinder cones, volcanic plugs, and gabbroic feeders, which locally crosscut lava flows. These form a northwest trend along the axis of the large igneous province.

Transition of flood volcanism

Prior to 16 million years ago, the western Cascade Volcanic Arc stratovolcanoes erupted with periodic regularity for over 27 million years, even as they do today. An abrupt transition to shield volcanic flooding occurred throughout the Miocene and Pliocene. The ultimate cause of this volcanism is still up for debate, however, the most widely accepted idea is that a back-arc basin behind the Cascadia subduction zone initied the widespread and voluminous basaltic volcanism. Some centers erupted along pre-existing brittle fault systems while volcanism along its northern portion is most widely believed to have been related to a center of upwelling magma called the Anahim hotspot (similar to that associated with present day Hawaii), creating the Rainbow, Ilgachuz and Itcha Range shield volcanoes which also in turn form part of the Anahim Volcanic Belt. The exact nature of the relationship between the Anahim hotspot and the Chilcotin Plateau Basalts is, however, unknown.

Notable vents

Volcanoes of the Chilcotin Plateau Basalts include:

References

External links

The Cheslatta Lake suite:Miocene mafic, alkaline magmatism in central British Columbia