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The Columbia River Basalt Group is a large igneous province that lies across parts of the Western United States. It is found in the U.S. states of Washington, Oregon, Idaho, Nevada, and California. The Basalt group includes the Steen and Picture Gorge basalt formations. ==Introduction== During the middle to late Miocene epoch, the Columbia River flood basalts engulfed about of the Pacific Northwest, forming a large igneous province with an estimated volume of . Eruptions were most vigorous from 17–14 million years ago, when over 99 percent of the basalt was released. Less extensive eruptions continued from 14–6 million years ago.〔, p.2; , p..〕 Erosion resulting from the Missoula Floods has extensively exposed these lava flows, laying bare many layers of the basalt flows at Wallula Gap, the lower Palouse River, the Columbia River Gorge and throughout the Channeled Scablands. The Columbia River Basalt Group is thought to be a potential link to the Chilcotin Group in south-central British Columbia, Canada.〔(Igneous rock associations in Canada 3. Large Igneous Provinces (LIPs) in Canada and adjacent regions: 3 )〕 The Latah Formation sediments of Washington and Idaho are interbedded with a number of the Columbia River Basalt Group flows, and outcrop across the region. Absolute dates, subject to a statistical uncertainty, are determined through radiometric dating using isotope ratios such as 40Ar/39Ar dating, which can be used to identify the date of solidifying basalt. In the CRBG deposits 40Ar, which is produced by 40K decay, only accumulates after the melt solidifies.〔, p.〕 Other flood basalts include Deccan Traps (late Cretaceous period) that cover an area of 500,000 km2 (193,051 sq mi) in west-central India and Siberian Traps (late Permian) that cover (800,000 sq mi) in Russia. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Columbia River Basalt Group」の詳細全文を読む スポンサード リンク
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