--> Abstract: Cleavage Pattern Used to Determine the Structural/Topographic Framework of the Taconic Orogeny in Western Massachusetts and Eastern New York, by Rachel V. Shaak and Donald M. Fisher; #90078 (2008)

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Cleavage Pattern Used to Determine the Structural/Topographic Framework of the Taconic Orogeny in Western Massachusetts and Eastern New York

Rachel V. Shaak and Donald M. Fisher
Department of Geosciences, The Pennsylvania State University, University Park, PA

The Taconic wedge in eastern New York and western Massachusetts reveals a regional cleavage fan that varies from west to east that may reflect variations in the orientation of maximum compressive stress across a doubly vergent wedge model, with a dramatic change across the synorogenic divide. There is a contrast in the orientation and number of cleavages from west to east across the Taconic allochthon. A single slaty cleavage exists in the Taconic allochthon in the Hudson Valley, whereas there is a crenulation cleavage front near the New York-Massachusetts border where the map pattern indicates folding of thrust sheets and development of windows and klippes. These observations are consistent with predictions of doubly vergent wedge mechanics and are similar to observations in the active arc-continent collision in Taiwan, a modern analog for the Taconic orogeny that displays a regional cleavage fan relative to the synorogenic divide, with a single cleavage in the continent-facing prowedge and refolding and crenulation cleavage development in the arc-facing retrowedge. Cooling histories from radiometric dating of biotite confirm that the fabrics are Taconic age and have not been reset by later deformation during the Acadian or Alleghenian mountain building events suggesting that the greatest crustal thickening and most of the deformation is likely Taconic. Thus, the NY-Massachusetts border may approximate the paleodivide, and the multiple fabrics observed in Western Massachusetts may have initially formed in a single orogenic event.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas