Born of Fire and Ice..... EarthCache
Born of Fire and Ice.....
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Welcome to the Lucerne Granite that is exposed along this road-cut. This granite is not only beautiful but tells a story of the past. Enjoy your visit to this unique roadside lesson.
This exposed granite is a section of what is known as the Lucerne Pluton. A pluton in geology is an intrusive igneous rock body that crystallized from a magma below the surface of the Earth. How deeply it is buried can be determined by the grains size. The slower it cools the larger the grain size indicating that it was formed when it was deep underground. If it cools near the surface the grain is much smaller. Plutons can include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies. In practice, "pluton" usually refers to a distinctive mass of igneous rock, typically kilometers in dimension. The term originated from Pluto, the ancient Roman god of the underworld. The use of the name and concept goes back to the beginnings of the science of geology in the late 1700s. While the word granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.
The Lucerne Granite is a massive, coarse-grained, late Devonian granite located in central Maine within what is known as the Coastal Maine Magmatic Province. These magma chambers form through some combination of processes including, but not limited to, partial melting of the crust, fractional crystallization, reactions caused by volatile components present, and the mixing and mingling of higher temperature mafic melts with lower temperature chamber material. Scientists in 1993 proposed partial melting of the crust and fractional crystallization as two processes involved in the formation of the Lucerne Granite. The composition of the granite is noteworthy for its large crystals of pinkish feldspar. Each nestes within a halo of black crystals of hornblende and biotite mica.
After the igneous rocks deep within the earth cooled and formed granites the erosion process began. Over long periods of time the overburden and rocks were removed. The granite that you see today was finally shaped and exposed by the most recent glacial episode in Maine began about 25,000 years ago, when the Laurentide ice sheet overspread New England and Eastern Canada. During its peak development evidence of the direction of the glacier movement is preserved in the northwest-southeast striations and grooves visible in the bedrock in surrounding areas. Approximately 17,000 years ago, the ice reached its maximum extent, which extended beyond the current coastline onto the continental shelf. The slowly flowing ice was thick enough to cover Maine's highest mountains. It swept away much of the evidence of earlier glaciations, even removing the bedrock in many places. The weight of this glacier was so great that it depressed the underlying land mass. The ice began to retreat from the shelf between 17,000 and 15,000 years ago. As the ice withdrew, the land remained depressed due to the previous weight of the glacier, it began to rebound until approximately 12,000 years ago when the present coastline was exposed above sea level leaving many of the cracks that you see before you.
At the coordinates listed above you will be on a viewing a roadside granite outcrop. Take some time to look at how the granite has formed and the size of the grain. To log this Earthcache send an email to me through my profile with the following information: What is the size of the grain in the granite? You are looking for the large white box type crystal which is what ive this granite its value. Make sure to use metric measures because this is science at its best. If you don’t have a ruler that’s OK because you can use coin to make the measurements, a dime is 1 millimeter thick and a nickel is 2 centimeters (20 millimeters) across the face. Remember the deeper the granite was formed the larger the grain will be once it is exposed. Please begin your email with the name of the earthcache. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.
According to Caldwell in Geology of Maine once a large section of this granite was used for the doorstep of a brothel used by lumberman in Bangor. It was closed about 1971, when the log drives ceased on the Penobscot River. The step was rescued by logger during demolition and incorporated into the loggers memorial on Chesuncook Lake.
Reference information used can be found at (visit link)
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
Additional Hints
(Decrypt)
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