Garvies Point Museum
Geologic Terranes and Orogenies of the Northeast
Information on Geologic Terranes and Orogenies of the Northeast

Geologic Terranes and Orogenies of the Northeast

The Saga of Long Island Geologic History

George J. Allgaier, Curator of Geology



Geologic Terranes

A Geologic Terrane is an "exotic" (foreign) piece of the Earth's crust that comes in contact with and becomes part of a continent by way of plate tectonics. This results in the formation of mountains (orogeny); uplift, folding, faulting, and metamorphism... followed by erosion.

KEY: Red area on above image
Proto-North American (Continental) Terrane - Associated with the gathering of Pre-Cambrian cratons, formation of super-continent Rodinia (1100- 750 mya), and the Grenville Orogeny (1250-980 mya). Pre-Cambrian basement domes and arches are present today from the Ozarks to the Adirondacks.


Pink area on above image
Island Arc and Iapetos Sea (Oceanic) Terrane - Closing of the Iapetos Sea and collision with Island Arc resulted in the Taconic Orogeny (440-500 mya) occurring primarily during the Silurian Period which included: Taconic and Berkshire Mountains; Vermont marble and granite; volcanism in northern Maine, northern Quebec, and northern Newfoundland; formation of the Queenston Delta throughout New York, Ontario, Ohio. and Pennsylvania, Caledonian Orogeny active in Greenland and Baltica (Northern Scotland, Scandinavia).


Green area on above image
Avalonian (Continental) Terrane - A piece of Gondwana (Africa) becomes part of Laurentia. Associated with the Acadian Orogeny (375-325mya) occurring primarily during the Devonian Period. Uplift of ancestral Appalachian chain extending from Labrador to Alabama along what is now called the Piedmont. Uplift of the Catskill region and the formation of the Catskill Delta in New York State.


Yellow area on above image
Hartford and Newark (Rift Valleys) Terrane - Basins formed by normal (tension, stretch) faults occurring when North America began to separate from Pangea around 206 million years ago. Triassic - Jurassic basaltic lava flows followed in Northern New Jersey, the Palisade Sill (exposed along the Hudson River), and columnar basalt in the Hartford Basin of Connecticut.



Reference: John Rodgers,1985, Bedrock Geological Map of Connecticut, Connecticut Geological and Natural History Survey, in cooperation with U.S. Geological Survey


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