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Kosco, D.G., 1981

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Bibliographic Reference

Kosco, D.G., 1981, Part I, The Mount Edgecumbe volcanic field, Alaska, an example of tholeiitic and calc-alkaline volcanism; Part II, Characteristics of andesitic to dacitic volcanism at Katmai National Park, Alaska: University of California, Berkeley, Ph.D. dissertation, 258 p., illust., maps.


Whole rock and isotopic composition data for lava samples have been collected from the Holocene stratovolcano Mt. Edgecumbe in southeastern Alaska. Results indicate that a wide variation in chemical compositions exists and the suite may be divided into two series on the basis of chemical, mineralogical, and isotopic characteristics. The Tholeiitic Series lavas consist of generally phenocryst-poor olivine basalts whose chemical and isotopic compositions are transitional between 'normal' MORB and LREE-enriched lavas of atypical areas such as the Azores platform. The Calc-alkaline Series lavas are 'typical' andesites and are believed to represent a second, independent magmatic episode. Mageik, Trident, Katmai and Griggs are andesitic stratovolcanoes that encircle the 1912 ash flow in Katmai National Park, Alaska. Over 100 whole rock analyses have been performed and indicate a range of 54 to 68% SiO2 with a pronounced concentration of samples between 61 and 65% and, combined with the data of Hildreth and Grunder (1979) and Bordet et al. (1963), an absence of samples between 68 and 77%. The chemical composition of the KNP samples are compared to whole rock analyses of volcanoes from elsewhere on the Alaska Peninsula and the Aleutian Islands. When the trends of the calc-alkaline volcanoes are compared at 60% SiO2 the Alaska Peninsula and Aleutian Islands volcanoes show virtually indistinguishable chemical compositions. This suggests that the continental crust of the Alaska Peninsula does not affect the magmas generated in this area. This conclusion is supported by Pb and Sr itotopic data (Kay et al. 1978). However, the bulk composition of the Aleutian Islands lavas appear to be 5 to 8 wt.% SiO2 less silicic than the lavas of the Alaska Peninsula. This difference is attributed to the presence of continental crust in the Alaska Peninsula. This crust, because its density is similar to or lower than the density of many basic to intermediate lavas, causes the stagnation of many rising magmas. These ponded magmas then evolve, giving rise to the intermediate and silicic compositions that are seen on the Peninsula.

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