The
land that became New England was added to the
core of North America between about 465 to 400
million years ago.
Two island arcs, the
Taconic and Avalonian, which had been moving
northward from their places of formation near the
juncture of South America and Africa impacted
with Laurentia (Proto-North America). These long
island chains also added land in Canada and
Greenland and as far south as the Carolinas.
Orogeny
is a geological term for the process of
mountain-building. Orogenies are driven by
collision of land masses.
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| These two drawings, one
schematic and one pictorial, are adapted
from a set of paleographic views of Earth
history by Dr.
Ron Blakely, Northern Arizona
University. They provide an overview to
the multi-step processes that added New
England to Proto North America and added
land to the coast as far south as the
Carolinas. The pictures show the
eastern coast of Proto North America
about 430 million years ago,
with Greenland nestled against northern
Canada. Part of Siberia is visible at
upper right (in the drawing on the
right). Note that Proto North America is
straddling the equator, the present
"east coast" is closer to being
a "south coast", and much of
the US and Canada was covered by shallow
seas. Baltica, the core of
western Europe, moving westward, has made
impact against Greenland.
Mountains are being raised on both
continents.
The Taconic island chain (TAC)
began to collide with Proto North America
about 40 million years earlier (470
to 450 million years ago). The
energy of ongoing impacts was still
raising mountains from Canada to Virginia
430 million years ago. The
Iapetus Ocean, which had been the
shoreline for Proto North America, is
closing as Western and Eastern
Avalonia (WAV and EAV), following behind
the Taconic arc, are heading for
collision with the recently-extended
coast of Proto North America. A
wide swath of Iapetus Ocean seabed
material will be pushed onto Proto North
America as the Avalonian islands push
against and onto Proto North America.
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The Taconic
Orogeny - Circa 450 Million Years Ago
Prior to the Taconic
orogeny, the "east" coast of what is
now the United States was located near the Hudson
River valley, Philadelphia, Washington, DC and
extended to western South Carolina. The Taconic
Orogeny added land to Proto North America that
is now the western portions of New England and
the Canadian Maritime provinces. This collision
added land and raised mountains southward
through northern New Jersey, south-eastern
Pennsylvania, Virginia
and North Carolina. The
orogeny ended about 445 million years ago.
The first set of pictures show
the world between 500 and 460 million years ago. Note
the movement of an arc of small
islands (the Taconic Arc, located just above the
symbol T__T
in the right hand panel) as they moved
northward, away from the South American coast
(near present-day Colombia) toward Proto North
America. The Taconic island arc bumped
into Laurentia starting about 470 million years
ago.
The first impact was
against what is now Greenland and eastern Canada.
Moving southward, the collision zone moved
through New York, near the present Hudson River
valley. The Taconic mountain chain was created as
the arc rode up and onto the Laurentian land
mass, a part of which was subducted (drawn under)
the Taconic arc. (Outside of New York state these
mountains may have many different names, and are
often heavily eroded).
The oval drawings were
derived from an animation
sequence by Christopher R. Scotese and the
Paleomap Project. J
indictates the approximate location of
present-day Jamestown. The closeup artist
renderings on this page are derived from a series
by Dr.
Ron Blakely, Professor of Geology, Northern
Arizona University. For a more detailed
description of the geology of this event, see the
Taconic
Orogeny page developed by SUNY Stony Brook.
Avalonia Collides with Proto
North America
The Acadian Orogeny - Circa 400 Million Years Ago
In the sequence of drawings
below, you can see that, about 460
million years ago, the eastern end of the
Avalonian arc was approaching Baltica (Proto
Western Europe). Around 440 million years ago,
these two land masses had "docked".
The Acadian Orogeny
started about 430 to 425 million years ago, when
the Avalonian arc, moving northwest, and Baltica,
moving west, impacted against the
southward-moving Proto-North America.
The eastern (northern)
portion of Avalonia was sandwiched between both
eastern Canada and parts of Baltica. Contact
between Avalonia and Proto North America
progessed to the south and west over the next 40
million years.
Ongoing collisions
created the Northern Appalachian mountains. The
event is known as the Acadian orogeny
(or sometimes the
Appalachian or Avalonian orogeny)
| As Avalonia advanced,
the basaltic bed of the Iapetus
Ocean was pulled under Laurentia
(subducted) and melted. Volcanos formed
in and near the narrowing ocean. The
Northern Appalachians rose as
the land was compressed and bent. |
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Large volumes of volcanic
material and Iapetus Ocean sediments were
pushed onto the margin of Laurentia
as the land masses converged, forming a
band of younger terrane between the older
Laurentian and Avalonian terranes. This
now-metamorhosized material is found in
the present states of Maine, New
Hampshire and Vermont plus major parts of
Massachusetts and Connecticut. In this
sketch of the New England states, Iapetus
Terrane is colored light grey.
It typically contains schist, phyllite,
gneiss and granite. Avalon
Terrane is shown in dark grey. All of Rhode
Island's foundation rocks were part of
Avalonia itself. "Avalon
terrane" is also found in eastern
Maine, Massachusetts and Connecticut.
South Carolina also contains Avalonian
Arc material (sometimes called Carolina
Terrane). It is also found in New
Brunswick, Newfoundland and Nova Scotia;
as well as Morocco, Portugal, Spain,
Ireland, Wales, southern England and the
northern coasts of France, Belgium,
Holland and Germany.
|
The SUNY Stony Brook Acadian
Orogeny page presents more detailed
information on the geology of this event.
| By about 360
million years ago the Northern
Appalachian mountains had become greatly
eroded. |
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Life was beginning
to move onto land as well as sea.
Vascular plants appeared that could grow tall.
Ferns, reeds and horsetails evolved. Insects and
amphibians appeared. Tall conifer trees developed
and forests appeared.
Continue with the next
installment of this narrative
Alleghenian
Orogeny
North
America collides with
Africa, pushing the
Appalachians higher,
forming the
supercontinent Pangaea,
and creating the
Narragansett Basin
|
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