Paul Karabinos
Professor
of Geosciences
127 Bronfman Science Center
(413)
597-2079
Dramatic tectonic thinning and omission of lithologic units around the Chester Dome in southeastern Vermont suggests that a ductile, normal-sense shear zone affected the region during the Devonian Acadian orogeny. Chester Dome Fieldguide (2002)
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The Shelburne Falls arc in western New England formed ca.
485 to 470 Ma above an east-dipping subduction zone. Collision of the Shelburne
Falls arc with Laurentia during the Ordovician resulted in the Taconic orogeny.
After collision, a flip in subduction polarity produced a west-dipping subduction
zone near the Laurentian margin. The Bronson Hill arc formed above this new
subduction zone ca. 455 to 440 Ma. Plate convergence along this new west-dipping
subduction zone ended the Taconic orogney. Shelburne
Falls Arc Fieldguide (2003)
The Berkshire massif in western Massachusetts is cored by Middle Proterozoic Grenvillian crust typical of the Laurentian margin. Numerous felsic sills occur along both the eastern and western borders of the massif and in the interior, and they were interpreted as Ordovician syn-tectonic intrusives into Taconic thrust faults. In an effort to constrain the timing of Taconic deformation we used the SHRIMP to date five of the sills and discovered that there are two distinct groups of sills, neither of which are related to Taconic deformation. Sills in the interior of the massif and along its western margin crystallized at ca. 1 Ga during an intense thermal event. Granitic sills along the eastern margin of the massif formed ca. 432 Ma during the Silurian, at approximately the same time that extension began to open the Connecticut Valley trough.
Amerian Journal of Science Article (2008)
Berkshire Massif Fieldguide (2008)
Berkshire Massif Fieldguide (2003)
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The Day Mountain thrust sheet contains a spectacular quartz-pebble conglomerate, part of the Neoproterozoic Dalton Formation, that records strain during Paleozoic deformation. A detailed strain study is underway to investigate deformation and the role of strain partitioning during thrusting.
Day Mountain Fieldguide (2008)
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