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Problem 2 (REVISION)
Problem 2 Presentation
Problem 3 - coals
Problem 3 Paper
Problem 4 - Rifting
Problem 4 - Synthesis Paper
Problem 5 - Climate Change
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The CT valley (or rift zone) is a downfaulted crustal segment with dimensions of 5 to 20 by 105 miles. The north-south-trending segment is located between the Eastern and Western Highlands, which are chiefly composed of early Paleozoic metamorphic rocks. It is split into 2 basins, each with their own sedimentary and volcanic records, the Deerfield (smaller basin located in northern Mass) and the Hartford (larger basin located in Southern Mass and CT.)
VERY basic rift model
Rifts: The Making of a Continental Margin.
When a new spreading center forms beneath a pre-existing continent, a rift forms that will eventually, if allowed to proceed normally, divide the original continent into two, with new ocean floor being created to separate them. As the two newly formed plates begin to separate, molten material, mostly basalt, from the mantle beneath will flow upwards into the crack. The heat from this molten material is conducted to the continental material above, reducing its density and causing it to float higher in the mantle, producing a ridge of mountains above the spreading center. As spreading continues, blocks will break loose from the sides of the crack and subside into the void, creating the characteristic "rift valley," such as that in East Africa. As spreading continues, the rift valley will deepen, ultimately subsiding below sea level and allowing ocean water to fill the valley. The now water-covered subsidence blocks will later become the submerged continental shelves.
Depending on the rate of spreading and the amount of heat flowing into the rift, these continental margins may be broad or narrow. Also depending on heat flow, which to a large degree depends on the proximity of plumes, volcanoes may or may not form. Surface fissure flows of basaltic lava may also occur where heat flow is high. (Plumes generally appear to be associated with the formation of new spreading centers, a notion that will be discussed further in a later lesson.)
Continued spreading causes the complete separation of the two land masses, with new sea floor being created beneath the ever-widening ocean. As the continental margins move farther from the heat flow at the spreading, the mountains formed along the continental margins cool and slowly subside back into the mantle. Depending on how much material erosion has removed from their summits, they may sink below the waves and vanish forever.
Freshly rifted continental margins tend to have steep walls, the continental shelves plunging nearly vertically from a few hundred feet deep to the ocean floor, many thousands of feet below. As erosional sediments are washed off the land surface, they first cover the continental shelves, then wash over the precipice to fall on the ocean floor below. Very old continental margins, therefore, tend to have large accretionary wedges on the deep ocean floor piled up against the continental margin.
The rifting process is not always as 'clean' as the above description may sound. Sometimes a segment of spreading center may shift slightly while separation is occurring, causing some of the subsidence blocks to be separated from both daughter continents. These messy remnants may become submerged plateaus or 'banks' on the sea floor, coral atolls, or islands in their own right. New Zealand, for example, is a continental fragment left behind after a long forgotten rifting episode.
Blanchard, Donald L.
The ABC's of Plate Tectonics.
"Sedimentation and Continental Growth."
-Hartford and Newark basins formed together in a "half-graben geometry"?? as symmetrically opposing basins (Manspeizer, 1988).
-Basalt in this region has been labeled as Initial Pangean Rift (IPR) basalt (Puffer, 1994).
-The magma that formed this basalt has the same sills found in the Gettysburg, Culpeper, and Newark basins (Woodruff, 1995).
-This basalt is also present in offshore platforms such as Nantucket and Long Island (Hutchinson, Klitgord, Detrick, 1986).
-Believed to be the same basalt in offshore and onshore basins in Morocco (Bertrand, 1991).
-also something about these basalts being in the Lower Jurassic stratigraphic section...
...running out of battery I will cite this later haha.
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