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The nature and sequence of development of the elements of fabric which characterize the metasediments of the Manhattan Formation occurring on Manhattan Island have been investigated. Three phases of deformation have been separated, and the time relations and geometrical form of the three sets of folds and associated planar and linear structures elucidated on the basis of field observations and structural analysis.

Regional metamorphism with the development of the dominant foliation, axial plane to isoclinal folds, was associated with the earliest recognized phase of deformation, termed the Riverside Fold Phase. The most prominent and commonly developed folds were formed during a second phase, the Central Park Fold Phase. Both the banding and dominant foliation were deformed, and the trend of the axes of these folds generally corresponds with the trend of the Appalachian mountain belt. In a third phase of deformation, the Park South Fold Phase, open symmetrical folds were formed. Over most of the Island the effects on pre-existing structures were of a minor nature, but in localized areas deformation was pronounced.

The considerable range shown by the published age dates for the metamorphism of the Manhattan Formation is attributed to the varying effects of the three phases on the potassium/argon and rubidium/strontium isotopic proportions.

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