Overview:
This is an Earthcache, there is NOT a container to find at the posted coordinates. To log a 'Found It' for this cache you will need to visit GZ and email me the answers to the questions below.
Edit 1/29/2017: Capitalized the TR in intrusion, to avoid confusion with inclusion. I made the decision for revision so all can envision with precision.
The cache is located in Lakeside Park, one of my favorite in-town playgrounds. This 400+ acre park lies at the foot of Lake Winnebago (which is what Fond du Lac means) one of the largest natural freshwater lakes in the world. There is plenty to do here year round: walking, biking, observation tower, playgrounds, fishing, boating, flower and bird viewing, snowshoeing, baseball, soccer, volleyball, fitness stations, shelters for picnics and get-togethers, petting zoo, canoe/ bike/ pedal boat rental, carousel and mini train rides, firework and Christmas light displays, Walleye Weekend, Art on the Island, and new in 2016 a free mini zip line.
Summary:
Sedimentary rock is created by the deposition of minerals and organic particles which are later cemented together. Sedimentary rock is found only on a thin veneer of the Earth's surface.
Igneous rock is created through the cooling and solidification of liquid magma. The magma can be made up of rock from the Earth’s mantle or crust.
Metamorphic rock is created by the transformation of sedimentary or igneous rock. They are often squished, intruded upon, and folded. Metamorphic rock can form from tectonic processes such as continental collisions or it can be formed when it is heated up by molten magma from the Earth's interior.
Determining the Relative Age of rocks:
The Principle of Cross-cutting states that any geologic feature that crosses other layers or rock must be younger then the material it cuts across. Using this principle any fault or igneous inTRusion must be younger than all material it crosses.
The Principle of Inclusions states that once a rock is lithified (finished forming), no other material can be incorporated within its internal structure. In order for any foreign material to be included within the rock, it must have been present at the time when the rock lithified (became solid). Therefore, the foreign piece, or inclusion, must be older than the material it is included in.
Igneous InTRusions:
The diagram shows the ways magma may move within the Earth. The magma is under extreme pressure and forces it way through existing native rock. These magma formations, when cooled, create igneous inTRusions and there are three basic types: batholith, sill, and dike. A batholith is a large underground pool of magma that may feed the other two types. A sill forms when magma pushes between native rock layers and may appear as a horizontal "vein" in a host rock. A dike forms when magma pushes upward through cracks and faults of the native rock and may appear as a vertical "vein" in a host rock.
It may be easier to visualize thinking on a smaller scale. Imagine the rock we see here at Lakeside Park is under extreme pressure and heat. Partial melting occurs around it and magma is created. The under pressure magma then found a weakness and injected into our host rock and cooled, this process is called an igneous inTRusion.
Conclusions about our rock on-site:
Our specimen is a metamorphic rock made up of different igneous rocks. It was subjected to extreme heat and (varying) directed pressure at different stages of its formation. First our host rock (became foliated, which means it) was squished down from a single direction and formed the horizontal “layered” appearance. Using the Principles of Relative Age, we know in addition to the squishing into “layers”, three more kinds of metamorphism events happened to our host rock (Listed in order of prevalence):
The host acquired (pinkish) igneous inTRusions.
The rock "layers" became folded (light gray, look at west facing side of rock, Wow!).
(Dark gray) foreign rock inclusions became embedded in the host rock.
This is an Earthcache so there is no container to find. To log a 'Found It' for this cache you will need to visit the coordinates and email me the answers to the following questions. Please do not write your answers in your log. See the geocache 'Hint' section for help with where to look for the answers.
1. Fill in the blanks (with younger or older):
1a. The material of the foreign rock inclusions we see is ________ than the host rock.
1b. The igneous inTRusions, and their material, we see are ________ than the host rock.
2a. Two types of igneous inTRusions exist in our rock: Name them.
2b. At least two igneous inTRusion events occurred. (Use your answers from 2a.) : Which type of inTRusion happened first and which type of inTRusion happened after? How can you tell?
3. Which occurred first: the igneous inTRusions or the folding (of the “layers”)? Explain: what can you see, or not see, that is evidence for your answer?
Thanks to a certain Fondy High School teacher who pointed me in the right (geological) direction!
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