Taconic orogeny

As the mountain chain eroded in the Silurian and Devonian periods, sediment spread throughout the present-day Appalachians and midcontinental North America.

This led to partial melting of the peridotites within the mantle wedge producing magma that returned to the surface to form the offshore Taconic (or Bronson Hill) island arc.

[3] Cameron's Line winds southward out of New England into western Connecticut and passes through southern New York across the Bronx, following the general trend of the East River.

The rocks to the west of Cameron's Line include metamorphosed sedimentary material originally comprising ancient continental slope, rise, and shelf deposits.

Cameron's Line represents the trace of a subduction zone that ceased when the Taconic island arc collided with, and became accreted onto, the eastern margin of North America.

[2] When the Taconic orogeny subsided during the late Ordovician (about 440 Ma), subduction ended, culminating in the accretion of the Iapetus Terrane onto the eastern margin of the continent.

Inland seas covering the midcontinent gradually expanded eastward into the New York Bight region and became the site of shallow clastic and carbonate deposition.

Geologists working in these areas have long puzzled over the "missing" arc terrane typical of Taconic-aged rocks in New England and Canada.

Other lines of evidence supporting a back-arc, Sea of Japan-style tectonic model for the Taconic orogeny in the southern Appalachians include mixing of Ordovician and Grenville (ca.

[12] As the Taconic orogeny subsided in early Silurian time, uplifts and folds in the Hudson Valley region were beveled by erosion.