Tipping the Clown: Changing Density in the Deer Isle Granite

When I was young I had an inflatable clown with weights on the bottom, so you could administer whatever childhood battering you cared to, and the clown would bob back upright.  I recently read about a feature of the Deer Isle Granite that got me thinking about that clown.

Deer Isle Granite: Naskeag Point

The granite that underlies Deer Isle is long.  It extends from Flye Point on the Blue Hill Peninsula to the southern tip of Stonington in the south.  While the rock is all clearly Deer Isle Granite, it is not homogenous.  Going to Naskeag Point on the mainland presents a deep pink, while a visit to Stonington displays a much wanner stone.  The middle ground of Oak point shows something in between.  The source of the redness may lie in oxidized (rusty) iron that replaces aluminum ions typically present in a mineral called feldspar.

Deer Isle Granite: Oak Point

Liquid rock under the surface cools to form solid granite.  As a result of 4.6 billion years of sorting by density, most granite bodies tends to have fairly uniform consistency.  Deer Isle Granite is different.  For some reason, during its formation, two types of magma were mixed together.  Imagine a nice Italian dressing, shaken before being added to salad. The vigorous mixing swirled everything together, but before it could harden there was time to settle.  Less dense materials, high in silicon content drifted to the top, while the more dense, high aluminum content stuff sank to the bottom.  The aluminum portion took on its iron and its rusty hue.

Deer Isle Granite: Stonington

Under normal conditions the weighted bottom of the clown would remain pointed downward.  The Acadian mountain building event was not normal conditions.  A small continent, and the tectonic plate it rode upon, glided across the fluid mantle toward the prehistoric Maine coast and rammed the landmass.  The collision was not a child's smack, but a match full of heavyweight boxer's jabs.  This impact was enough to permanently tip the clown on its side, revealing the changing color.

Dietrich, Richard Vincent, and Brian J. Skinner. Rocks and Rock Minerals. New York: Wiley, 1979. Print.

Hooke, Roger Leb.. "A Geologic History of Deer Isle, Maine." College of the Atlantic, Serpentine Ecology Conference. July 2007. Web. 14 Oct. 2013. <www.coacommunity.net/downloads/serpentine08

A Trip to Baxter Four Hundred Million Years Ago

To visit Baxter State Park during Devonian time would have been quite an experience.  Devonian time extends from 419 million years ago, when fish were just starting to widen their grip as rulers of the ocean, to 359 million years ago, when amphibians were testing their new toes on continental soil.  It is during this period of prehistory when almost the entirety of Baxter's bedrock was lain down.

419 million years ago, to travel the path that one takes to the north entrance of the park from Patten would require a boat.  Paddling north on the route that 159 takes, you'd hit land not far south of Shin Pond and a long portage would take you over the island arc and continue you on your way.  The island extends into the realm of the park only in so much as the rains tearing apart the island, at a snails pace, were delivering the islands sedimentary fragments into the surrounding ocean.  The heavier sand dropped first in a wide delta, while the smaller silt and clay drifted farther into the ocean, only to be dropped when the stream's energy had been almost fully spent.  The sandstone that was once the delta can be found along the eastern edge of the park, while the old ocean bottom wraps the northern and western sides.

The trip up Katahdin would have, in fact, been a descent.  While the portage island was being torn apart, southern Maine was plunging beneath northern. As the ocean bottom sank, it melted.  As it melted it rose, creating an upside down tear drop of magma not far from the surface, but still a ways down from Baxter Peak's current stature.  As the magma cooled, minerals formed creating the small, but visible crystals of the Katahdin granite.  The magmatic elements paired off, leaving behind the ingredients of water vapor.  The bubbling gas rose to the top of the magma chamber.  As the magma hardened around the bubbles it left cavities in which different minerals could form.  The change from the liquid magma chamber which formed the base of Katahdin to the frothy top, which formed the peaks is visible today as the white, even grained granite evolves into reddish, multi-textured granite.

While the Travelers are smaller in stature now, they literally rose out of Katahdin during the Devonian.  The Traveler Rhyolite was the volcano to Katahdin's magma chamber.  A trip there means braving molten lava, but also burning ash.  A hellish expedition to be sure, but at least there wouldn't be any black flies.  The drifting ash interbedded with the lava and then flowed down slope.  In modern times the flow is visible because the gray ash is flattened amidst the white rhyolite.

Later in the Devonian, a trip down the South Branch Pond Brook, geologically, wouldn't have been too much different than it is now.  The towering volcanoes, like the mountains that now stand, would have provided a prime environment for raging rivers powerful enough to break apart and then round the edges of chunks of rhyolite.  Smaller particles would be taken farther off to sea.   This order is preserved in the sequence of rocks below the falls - rhyolite, conglomerate, finer-grained sedimentary rock.

With current technology as a limit, an adventure in Devonian Baxter State Park is of course an impossibility.  The current landscape becomes our only time machine through which to view this exciting period in Maine's history.

Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000

Rankin, Douglas W., and Dabney W. Caldwell. A Guide to the Geology of Baxter State Park and Katahdin. Augusta, Me.: Maine Geological Survey, Dept. of Conservation, 2010. Print.

"Maine Geologic Map Data." Maine Geologic Map Data. 05 Apr. 2013. Web. 03 July 2013.