Английская Википедия:Fish Canyon Tuff

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Шаблон:Infobox eruption The Fish Canyon Tuff is the large volcanic ash flow or ignimbrite deposit resulting from one of the largest known explosive eruptions on Earth, estimated at Шаблон:Cvt.[1] (see List of largest volcanic eruptions). The Fish Canyon Tuff eruption was centred at the La Garita Caldera in southwest Colorado; the caldera itself would have formed by collapse, as a result of the eruption. Studies of the tuff show that it all belongs to one eruption due to its uniform bulk-chemical composition (SiO2=bulk 67.5–68.5% (dacite), matrix 75–76% (rhyolite) and consistent phenocryst content (35–50%) and mineralogical composition (plagioclase, sanidine, quartz, biotite, hornblende, sphene, apatite, zircon, Fe-Ti oxides are the primary phenocrysts). This tuff and eruption is part of the larger San Juan volcanic field[2] and the Oligocene Southern Rocky Mountain ignimbrite flare-up.[3]

The Fish Canyon Tuff eruption occurred around 28 Million years ago. Sanidine crystals from the Fish Canyon Tuff (FCTs) are used as a reference mineral in 40Ar-39Ar dating, and the current 'astronomically calibrated' age for the FCTs is 28.175 Ma.[4]

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References


Шаблон:Colorado-geo-stub