NH Swirling Migmatite EarthCache
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This is an Earthcache. It was APapROVED on Earthcaching's 10th anniversary! Because this is an Earthcache no matter how hard you search there is absolutely NO container present. Instead you will have to turn on your critical thinking and hone your observation skills. BYOP and a piece of paper!
For paperless cachers I have listed the Logging Requirements first so that they do not get truncated.
Logging Requirements:
1. Describe what portion of the rock wall is Migmatite.
2. Observe the oxidation (rust) in the Migmatite. What geological factors could have caused this patterning? Would you consider this rust wide-spread or limited in this roadcut?
3. Notice the pegmatite (white quartzish) vein at GZ. Is there a greater percentage of Migmatite or pegmatite at GZ? why? (see description for hints.)
Geology:
The dominate bedrock exposed in this roadcut belong to the early Devonian Littleton Formation and the late Devonian New Hampshire plutons that intrude the Littleton. The Littleto rocks are schists and gneisses and micaceous quartzites. They contain the mineral sillimanite, which indicatets high=grade metamorphism. Many of the old area roadcuts have even become rusty because of the iron-rich rocks that have "rusted" in contact with the air.
Rocks:
Migmatite -- gneiss with granitic veinings that come about becase of the partial melting during extreme metamorphism
Pegmatite - an igneous rock with extremely large grains, usually more than a centimeter in diameter. There is no veining, but instead a granitic appearance because of its granitic origins.
Because the rocks are dated as early Devonian because of the fossils present, the metamorphism is considered to have happened in the middle-to-late Devonian Acadian mountain-building period. Some of the gneisses contain many very pale, granitic layers, veins, and lenses. The magma probably formed through partial melting during the extreme metamorphism of the host rock. Those rocks full of small bodies of granite are called migmatite (see logging requirement), a descriptive term for an intimate mixture of igneous ad metamorphic components; they are very common in regions of high-grade metamorphism, such as those here!
"Several roadcuts in the Littleton formation also contain dikes of extremely coarse white pegmatite (logging requirement) or very fine-grained aplite, both varieties of granite. The dikes are especially numerous near new Hampshire series plutons and probably originate by intrusion of magma from those bodies into country rock fractures."
Resource: VanDiver, Bradford B. "New Hampshire 9 COnord N.H. -- Brattleboro Vt." Roadside Geology of Vermont and New Hampshire. Missoula: Mountain Pub., 1987. 179-81. Print.
Additional Hints
(No hints available.)