#schoodic

Pics from Schoodic Point, Acadia National Park, Maine. With and without fog.

Intrusive

This frame was photographed by a student at Otago University on a trip to Maine’s Acadia National Park. There are 2 rock types here; granite and diabase. The larger, pale colored rock is a large granitic pluton. It formed as a massive, slow-cooling magma chamber in the Devonian Period. Granites in this area formed after the collision of an island arc with North America; this collision triggered one of the pulses of mountain-building represented in the Appalachians called the Acadian Orogeny. The dark rock is a diabase, formed almost 200 million years later. After the Acadian Orogeny, North America collided with Europe and Africa to form the supercontinent Pangaea. Then, at the end of the Triassic, those continents pulled apart, opening up cracks in the crust that filled with mafic magmas. The dark rock here is called a diabase – a term for mafic rocks that formed small crystals as they were cooling. It cross cuts the granite, showing that the dike is the younger rock – the granite had to be there fore the dike to fracture it.

The rocks in this area were glaciated until about 10,000 years ago. Note how the dike is eroding more readily than the surrounding granite, shown by the fact that the students need to step down to reach the dike. The dike is slightly more fractured than the surrounding rock and made of minerals that erode more rapidly at the surface.

-JBB

Image credit: Zach Churchill (non-commercial use) http://bit.ly/2DLvMxG