Nd-Sr Isotopes and the Tectonic Significance of the Paleo- zoic Acatlan Complex, Southern Mexico

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The proposed research is aimed at understanding tectonic history of the southern N. American craton and the Caribbean region - especially the relations between the Paleozoic (?) Acatlan metamorphic complex (related to closure of a Paleozoic ocean) and the Grenville age (1Ga) Oaxacan crystalline complex (high-grade granulite terrane). These complexes are analogous to the Appalachian-Caledonian and Grenville orogenic belts of eastern N. America except that they have 'reversed polarity' (i.e. Acatlan is west of Oaxacan, whereas appalachian-Caledonian is east of Grenville). One goal is to determine if these belts actually correlate (in which case tectonic reorganization is implied in Mexico) or if Acatlan is an accreted Pacific terrane unrelated to Appalachia. Emphasis will be on detailed Rb-Sr and Sm-Nd geochronology of acatlan, and on its isotopic evolution relative to the crust below north-central Mexico.