Beyond Pangea: The Chain Lakes' Long History

Every middle schooler hears about Pangea.  You look at the world map and envision the ocean closing and that land before time re-forming.  And that's the end.  You don't think about what happened before because no one ever told you that there was a before.  Well, I am here to set you straight.

Don't get me wrong.  Pangea is old.  When Pangea was THE place to be, dinosaurs had not yet set foot on this Earth.  In fact, the dry center of the giant continent set the stage for water loving amphibians to evolve into drought tolerant reptiles.  Later, these reptiles gave birth to the generations that would become the feared lizards we call dinosaurs.  Here in Maine, however, you will find no trace of dinosaurs, because nearly every rock was formed before the oceans that collapsed to make way for Pangea produced their parting waves.

What's important to realize is that the formation of whole Earth continents, like Pangea, is a cycle.  These so-called supercontinents occur occasionally throughout Earth history.    Six hundred million years ago, the supercontinent of the day, one that we call Pannotia, would have filled much of the space taken up by the modern day western Pacific Ocean, and a large hunk of Antarctica, too.  About 1.3 billion years ago, Rodinia was gathering all the Earth's land masses at the equator.  This is the point at which we will begin our journey back to the future.

The Chain Lakes Massif, an elevated hunk of land just north of Sugarloaf, may be the best perch from which to watch the story unfold.  A supercontinent is formed when an ocean closes.  The weighty seafloor rock descends into the Earth beneath the lighter continental shoreline. The diving rock melts, and then reascends, forming a chain of volcanoes, not unlike the modern Andes.  The larger the colliding continents, the larger the mountain chain - and Rodinia was big!  The billion year old mountain chain is now the core of North America, running the 3000 miles from Newfoundland, Canada to Veracruz, Mexico.  Big mountains fall fast, and as rain and ice dragged sediment from the peaks it dropped it into the closing ocean.  Some scientists think it was this sediment that would become the Massif.  As the ocean closed, the sediment may have changed from mud to stone.

A billion years ago Rodinia was formed, but this, too, must pass.  The mega-continent shattered.  While the 3000 mile backbone, called the Grenville Province, stayed intact, the sedimentary shorelines drifted away.  While the cycle continued, the sedimentary island moved along the Earth's surface, but 400 million years after it started its journey, the Massif came home.  As its ocean closed, and Pannotia gathered, the piece of land that would become the Chain Lakes became nestled in the heart of the new supercontinent.  Nestled may be an understatement, because the crushing force of the continent forming squeezed, buried, and roasted the rock, altering it from a simple sedimentary rock to a banded metamorphic one called gneiss.

Pannotia didn't last long, and when the proto-Pangea split, the Massif hung on to what would become North America.  In fact at that time it would have been coastal property, but that would change as oceans closed one more time.  The Iapetus Ocean (Iapetus was the father of Atlas, and the Iapetus was the predecessor of the Atlantic) closed in stages.  The first impact was a set of Carribean-like islands, the next a small continent called Avalon.  Each collision provided more heat and more pressure, driving the gneissic metamorphism of the once sedimentary rock even further; and making the geologic puzzle harder to solve.

The final crunch came as Africa found its place in the Pangeaic landscape.  The world, different than the one in which we now reside, would at least be familiar to our geographic sensibilities.  South America cuddled up with western Africa, and northern Africa spooned by New England.  Pangea may be the first chapter in our middle school geology texts, but it was one of the last in this corner of Maine.

DiPietro, Joseph A. Landscape Evolution in the United States: An Introduction to the Geography, Geology, and Natural History. Burlington, MA: Elsevier, 2013. Print.

Landing, Ed. "Vestiges of Rodinia: Adirondack and Hudson Highlands." New York State Geological Survey. New York State Museum, n.d. Web. 11 Nov. 2013. <http://www.nysm.nysed.gov/nysgs/nygeology/tectonic/02.html>.

Meert, Joseph . "A History and Preview of Supercontinents through Time." Gondwana Research. N.p., n.d. Web. 11 Nov. 2013. <http://gondwanaresearch.com/hp/supercon.pdf>.