Geochronologic and Related Studies, Southern and Central New England

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Paleozoic metamorphism and deformation in the southern and central New England Appalachians was complex and polyphaze, and attempts to separate and accurately date tectonic episodes has been difficult. Recent determinations of diffision rates of cations in several common minerals allow a mineral dating method to resolve between protracted slow cooling and discrete later tectonic events in this structurally complex region. The study will obtain Rb-Sr and Sm-Nd isotopic data on coexisting minerals in high grade metaigneous gneisses and amphibolites in order to determine the time of last recrystallization or initiation of cooling following high temperature metamorphism. Detailed analyses employing internal and external comparisons and mass balance considerations will permit stringent evaluation of the technique, which is quite general and potentially applicable to many other orogenic terranes. The results of this study will allow features of middle Paleozoic and late Paleozoic orgination to be separated, yielding a clearer understanding of major culminating events in the tectonic development of the northern Appalachians and a improved information base for the constructure of thermal models.