Abstract

The trend of the post-Taconic Appalachian fold-thrust belt changes at the city of Kingston in the New York recess. To the southwest of Kingston, fold-thrust structures trend northeast-southwest, whereas to the north of Kingston, fold-thrust structures trend due north to north-northeast. This paper discusses the structural geometry and origin of this change in trend. Detailed mapping (1:9,600) suggests that the fold-thrust belt in the vicinity of Kingston can be divided into three structural domains (northern, central, and southern). In the northern domain, megascopic folds are open, significant faults do not intersect the present-day ground surface, Ordovician strata below the Taconic unconformity are not extensively thrust over post-unconformity strata, and shortening is less than 5%. In the southern domain, shortening across the fold-thrust belt is 30%, numerous faults intersect the ground surface, and Ordovician strata are significantly thrust over postunconformity strata. In the central domain, there are numerous accommodation faults, there are locally two noncoaxial-spaced cleavages, and strike-slip lineations overprint dip-slip lineations on many slip surfaces. To explain the contrasts between domains, we suggest that the bend at Kingston is an intersection orocline created when northeast-southwest-trending structures of the Kittatiny-Shawangunk segment of the Appalachian fold-thrust belt overprinted and reoriented older north-south-trending structures of the Hudson Valley fold-thrust belt. Calcite twin strain-gauge measurements indicate that there was less than 2% penetrative tangential stretching accompanying the development of this orocline.

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