TREMADOCIAN TO PRIDOLIAN ACCRETIONARY ARC, COLLISIONAL, AND POST-COLLISIONAL ASPECTS OF THE TACONIDE ZONE, NORTHEASTERN US

Integrated field studies by many workers over the last thirty years have established that the Taconian orogeny, in its broadest definition, extends from the latest Cambrian or Tremadocian (502 + 4 Ma) arc volcanics in Moretown and Cram Hill Formations of Vermont to the recently recognized syn- to post- collisional Caradocian and Landoverian(443 to 434 Ma) migmatite-granite complexes along the eastern margin of the Berkshire/ Housatonic massifs and the mantle-derived igneous stitching plutons of the Hodges-Cortlandt type in Connecticut and New York. Along- strike differences in the nature of emplacement of Taconic allochthons, the degree of reactivation of Laurentian basement and intensity of metamorphism associated with Caradocian collision suggest that irregularities in the Laurentian margin produced these different responses. These changes are well expressed in the Caradocian through Pridolian tectonics in the New York recess southward into Pennsylvania. Resolved synmetamorphic right-slip thrusting increases southward, consistent with structural inversion (destruction) of a cratonic promontory centered on western Massachussetts Coeval features from Massachussetts to Vermont however suggest incomplete tectonic filling of the Quebec reentrant, left-slip thrusting during crustal imbrication and late Caradocian- Landoverian relaxation tectonics. Extensional diorites of the Braintree pluton(419 + 0.39 Ma, Black and others, 2004) crosscut Taconian structures and foliations in the Moretown Formation in central Vermont and establish the minimum age for cessation of the Taconian orogeny in New England, as does the imperfectly dated( Silurian?) Beemerville intrusive complex in the foreland of the Taconides in New Jersey.