Week 5 Converging Plates

This week we travel to the southern end of the Appalachian Mountain range where Stone Mountain, Georgia is located. The city was a popular destination for weekend hikes for my family due to the mountain also named Stone Mountain in the city. The Appalachians started to form roughly 480 million years ago during the middle Ordovician Period when North America shed its seas and a tectonic highland which corresponded to the mountain range. This happened when the relatively calm Appalachian passive margin became an active plate boundary when it started to collide with a neighboring former ocean plate called Iapetus. I later discovered in our readings that they refer to the formation of the Appalachian Mountains as "one of the oldest mountain ranges on Earth" during a continent-continent convergent boundaries collision. 

I was also able to point out from readings that subduction occurs “when oceanic crust converges with continental crust, the denser oceanic plate plunges beneath the continental plate”. The southern Appalachian Mountains were continually being transformed due to this subduction zone during its initial creation. 

 

What makes Stone Mountain so interesting is the exposed granite rock which originated from the pluton beneath the earth surface in the mantle. It’s estimated to rise to 750 feet and its volume contains one-half billion cubic feet that covers an area of over 583 acres. The mountain has evidence of two distinctive deformations where exfoliation joints occurred when the granite expanded and tension joints. 

 

The mountain trail contains visible evidence of structural fractures where long cracks are exposed along the joints of the mountain. You’d be able to see the visible layers of rock formations where exfoliation slabs are exposed on face of the mountain.

 

Xenoliths are visible in exposed rock fragments which were engulfed by pluton when the mountain was formed. Maltin rock was forced into magma through cracks and dykes in the granite. You can also see pegmatite on the side of the mountain where it cooled faster on the outside than on the inside as you can see the mineralized fractures below from a picture from the 1890s.