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High-grade Precambrian (Proterozoic Y) granulite gneisses, paragneiss and rusty gneisses (metasedimentary/metavolcanic, ?) in the Hudson Highlands of southeastern New York State are intruded by plutons of Storm King granite gneiss and Canada Hill granite. The metasedimentary/metavolcanic (?) gneisses were deformed multiply during the Grenvillian dynamothermal metamorphism in three phases of deformation (D1, D2, D3). Plutons of Storm King granite gneiss contain S1 planar and L2 linear fabrics and were deformed in all phases of deformation with the metasedimentary/metavolcanic (?) gneisses. This indicates a pre-tectonic to early syntectonic age for intrusion of the Storm King granite gneiss. Plutons of Canada Hill granite cut D1 and D2 fabric elements in both Storm King granite gneiss and the metasedimentary/metavolcanic (?) gneisses. Canada Hill granite contains a weak S3 planar fabric and was deformed during D3. This indicates a late-tectonic age for the Canada Hill granite.

Plutons of Canada Hill granite are for the most part confined to and have migmatitic borders with paragneiss. A closed system metasomatic process is indicated for formation of the Canada Hill granite. Rather than a magmatic episode, formation of Canada Hill granite may represent a time of regional granitization brought about by redistribution of chemical components within the host paragneiss. This mechanism is supported by Rb-Sr systematics for the paragneiss and Canada Hill granite.

The age determinations for paragneiss (Rb-Sr whole-rock age = 1147 ± 43 m.y.) and Canada Hill granite (Rb-Sr whole-rock age = 913 ± 45 m.y.), when examined in conjunction with reported radiometric data for the Hudson Highlands, provide evidence for two distinct metamorphic-plutonic episodes within the Grenvillian event. The first episode occurred at about 1140 m.y. and is recorded in the age for paragneiss. This episode was characterized by Storm King plutonism, metamorphism of the Storm King granite and metasedimentary/metavolcanic (?) gneisses, and development of D1 fabric elements. The Storm King granite gneiss intruded as sheets and sills prior to and during the early stages of D1. The second episode at 1000 m.y. was characterized by hornblende granulite metamorphism, plutonism, Canada Hill granitization, and the development of coaxial D2 and D3 fabric elements.

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