Abstract

Two stock-like plutonic masses belonging to the Cortlandt complex cut foliated isoclinally folded country rocks of probable Cambro-Ordovician age at Stony Point, New York. Two fold systems, an early F1 isoclinal phase and a later F2 phase of axial plane folding about a N. 60° E. axis, are truncated by the earliest pluton of biotite diorite. A later cortlandtitic pluton crosscuts both biotite diorite and the country rocks. From this pluton lamprophyric dikes and sills radiate into the bordering rocks.

Because of the discordant intrusive relationships, the obliteration of the regional axial plane cleavage by contact metamorphism, and the lack of deformed igneous contacts, it is clear that the main deformation in this area preceded intrusion of the plutons. K-Ar age determinations on biotite from the Cortlandt complex indicate a minimum age of 435 m.y. (Long and Kulp, 1962). Acceptance of these data together with the observations presented here indicate that the strong deformational effects now seen in the metamorphosed country rocks were the result of Taconic, not Acadian, orogenesis.

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