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Poole, A.R., 1996

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Poole, A.R., 1996, Age and geochemical constraints on ridge subduction for igneous rocks of the eastern Chugach Mountains, Alaska: Houston, Texas, Rice University, M.A. thesis, 83 p., illust.


Igneous rocks in the Chugach metamorphic complex (CMC) of southern Alaska form part of the Sanak-Baranof belt, a series of forearc plutons believed to have been formed by subduction of a spreading ridge. Trace-element and Nd-Sr isotopic data suggest that magmas were derived from the mixing of two sources: Melted accretionary wedge sediments and mafic material underplated at the base of the wedge as the ridge was subducted. Metabasaltic amphibolites at Yakutat Bay found to be derived directly from material of MORB composition are further evidence that this underplated mafic source existed. Ridge migration along the Alaskan margin was generally towards the east. However, new U-Pb and 40Ar/39Ar geochronology data show that within the CMC this movement was probably complicated by the subduction of a transform, causing the locus of magmatism to appear to jump from Van Cleve Glacier to Yakutat Bay at 54 Ma.

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