THE CONNECTICUT VALLEY: RIFTING AND VOLCANISM

Amy LombariZoe Gentes

Andew InfanteJennifer Sullivan

Dennis Titterton

Pangaea

The breakup of Pangaea is estimated to have occurred around 200 million years ago during the Mesozoic era (early Jurassic period) (Tarbuck, 2002)

Rifting started in the late Triassic period and continued to completely separate Pangaea to form two separate masses known as Laurasia and Gondwana

Basaltic oceanic crust forms between continents that are separating

Pangaea continued

The breakup of Pangaea took place over four stages

The first stage is relevant to our subject and the Connecticut rift valley:

The rifting between Laurasia and Gondwana during the Late Triassic. By the end of the Triassic, the expanding Atlantic Ocean separated North America from Africa. (Wicander and Munroe, 2002)

Region of Interest

http://sahallquist.files.wordpress.com/2008/07/ctgeomap_big.jpg

Connecticut (CT) rift valley Region of continent-continent riftingType of sedimentsVolcanism due to rifting

Amongst many other areas, a large record of this rift can be found in the Central Valley area of Connecticut.

The CT valley is a down faulted crustal segment with dimensions of 5 to 20 by 105 miles.

It is split into 2 basins, each with their own sedimentary and volcanic records

Rift Valleys The central valley of CT is one of the

areas affected by the continental rift between the North American craton and the African cratonContinental Rifting:

○ Convection and mantle plumes are two mechanisms involved in the cause of the continental rift

○ Pangaea acted as an insulation for the mantle plume which resulted in a significant change in convection beneath the supercontinent

Basic rift model Divergent plate boundary

Progressive formation of a rift valley through extension of the lithosphere and continental crust

The crust responds by brittle fracture.

Early rift sediments are downfaulted into the developing rift .

Erosion takes place on the sides of the rift valley

http://www.le.ac.uk/geology/art/gl209/lecture3/lecture3.html&usg

Sediments The Harford basin is one of several rift basins in the

eastern United States that formed during the breakup of Pangaea.

Over millions of years, the Hartford basin accumulated clastic sediments as well as basaltic lava

Early Devonian rocks consist of marine clastic deposits with subordinate carbonates, lava flows and terrestrial deposits

These sediments are located here due to the once lacustrian environment

Paleoenvironments Plant fossils and the presence of evaporites

provide evidence for a climate that repeatedly altered between humid and arid (Prothero and Dott, 2002)

The basin contains imprints of leaves, bark and wood that tells us that in Mesozoic times, Connecticut had a tropical climatePlants found included; conifers, horsetails, giant

club mosses and cycads

Volcanisim

In a Rift Valley volcanoes are not as explosive

Mafic lava High viscosity, high volatile content in felsic

lava makes the volcano more explosive Dikes and sills are very common in the

Central Valley of CT. They were formed when cracks in the

lithosphere/crust were filled with lava from beneath the rift.

Volcanism continued We can use paleomagnetic stratigraphy to

determine that there were different volcanic events that occurred in the late Triassic period (Tremblay and Pinet, 2005)

Basalt is found in the rift valley because of volcanism

As lava flowed into lakes it formed pillow basalts

http://3dparks.wr.usgs.gov/nyc/mesozoic/connecticut.htm

http://www.vincentsapone.com/ctoutdoors/trips/target/target.html

References Alain Tremblay and Nicholas Pinet, 2005, Diachronous

supracrustal extension in an intraplate setting and the origin of the Connecticut Valley–Gaspé and Merrimack troughs,

northern Appalachians. Geological Magazine, 142 , pp 7-22

Donald R.Prothero and Robert H. Dott, 2002, Evolution of the Earth, Edition 6, McGraw Hill, New York, New York, p. 384

Tarbuck, Edward D., Frederick K. Lutgens, and Tasa Dennis, 2002 Earth: An Introduction to Physical Geology. 7th ed. Upper Saddle River, NJ: Prentice Hall

Wicander, Reed; Monroe, James S., 2000, Historical Geology: Evolution of Earth and Life Through Time, 3rd ed., Brooks/Cole, pp.348-354.

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