Part 1: Geology of Our Vineyard in Connecticut

Earlier this year I blogged about the Geology of Champagne and its ancient geological origins that lead to the formation of the chalk that is so important in the growing of grapes for making champagne.
I was spurred on this quest for learning about the geology of our area in southeastern Connecticut since I should know this because wine geeks associate the soil type with the wine that is produced. It took a while to understand how our state was formed but it is an interesting and enlightening journey into geologic history.
First, let me begin with what I knew after living in Connecticut for 35 years. I knew that we were part of Avalonia. Avalonia is a terrane, or a section of the earth's crust that has it's own history. The terranes that constitute the state of Connecticut are arranged, by and large in a north-south direction. The Avalonia terrane, part of the Eastern Uplands is shown colored in pink in this illustration.

The question that I was seeking to answer was how did Connecticut get to be like this, comprised of (from west to east), the Western Uplands, the Central Valley and the Eastern Uplands.
From the beginning of the formation of our earth, land masses have continually been moving in a process called plate tectonics. Going back 500 million years to the Ordovician Period, the arrangement of land masses looked like the illustration below. Instead of the modern Atlantic Ocean, there was the Iapetos Ocean. Laurentia (proto North America) and Baltica (proto Western Europe) had drifted away from Gondwana. Avalonia, located in the southern hemisphere, had separated from Gondwana, resulting in the birth of the Rheic Ocean.

Here is another view of the land masses as they were arranged 500 million years ago. This view shows the land mass of Avalonia and its relationship with Laurentia and Baltica as well as the Iapetus ocean.

Then about 300 million years ago, several crustal plates, including Africa and Eurasia collided with Laurentia, the proto North American plate to create the Appalachian Mountains and the supercontinent Pangaea. Plates composed of oceanic crust and plates composed of continental crust met and the lighter, thicker continental plate rode over the thinner, denser oceanic plate causing the oceanic crust to sink toward the interior of the earth (subduction).
During this collision Avalonia, a small continent believed to have been part of the African plate, was caught in the crunch when Baltica and Laurentia collided closing and collapsing the lapetos Ocean.

Here is another look at Pangaea which places Connecticut right in the rift zone which is an extensive system of fractures and faults. As the land mass collided and was heated by the east-west compression, the rocks became pliable and tended to fold along a north-south axes.
This tremendous heat generated by the colliding land masses altered the primary rock-forming elements. Forces exerted on the primary elements of silicon, oxygen, aluminum, calcium, sodium, iron, potassium, magnesium created new minerals that became stable under these new conditions. Clay metamorphosed into mica and grit changed into quartz. These forces lead to the creation of the metamorphical origins of the schists and gneisses in Connecticut.

For the moment, we will leave the continents stuck together in the supercontinent Pangaea. Stay tuned for my next blog about the break up of Pangaea.
References:
1. Illustrations from C. R. Scotese from The Paleomap Project.
2. Murphy, J & Pisarevsky, Sergei & Nance, R & Keppie, John. (2001). Animated history of Avalonia in Neoproterozoic - Early Proterozoic. Journal of The Virtual Explorer. 3. 10.3809/jvirtex.2001.0009
Animated history of Avalonia in Neoproterozoic - Early Proterozoic
3. Online: Avalonia - Geologic History exerpted from WRITTEN IN STONE: A GEOLOGICAL HISTORY OF THE NORTHEASTERN UNITED STA TES, ©1989 by Chet Raymo and Maureen E. Raymo.