PERMISSION:
This earthcache was placed with permission from the Blue Ridge Parkway Resource Management Specialist.
EARTHCACHE REQUIREMENTS:
Each cacher must send in their own answers when logging this find. After you arrive at the overlook, enjoy the view and what you will bring home with you through this experience. Review the materials below and answer by message/email the questions to the best of your ability. Enjoy your time at this beautifiul location. Please follow all logging requirements.
MIGMATITE:
Migmatite is a composite rock found in medium and high-grade metamorphic environments. It consists of two or more constituents often repetively layered; one layer was previously paleosome, a metamorphic rock reconstituted subsequently due to partial melting; the alternate layer has a granitic, aplitic, pegmatitic or generally plutonic appearance. Most commonly, migmatites occur below metamorphic rock that is deformed, appearing in the base of eroded mountain chains. This occurred commonly within the Precambrian cratonic blocks. Migmatites form under extreme pressure and temperature during it's prograde metamorphism, when partial melting occurs in the metamorphic paleosome. The components that are exsolved by partial melting are called newsome (new body), which may or may not be herogenous at the micro- to macroscopic scale. Migmatities frequently appear as tight, incoherently folded veins (ptygmatic folds). Segregations form of leucosome, light-colored granitis components exsolved with melasonsome, a dark colored amphibole and biotite rich setting.
HERRIN KNOB OUTCROP:
The migmatitic (mixture of metamorphic rock and igneous rock) mica gneiss is cross-cut by a thick dike of a light-gray, medium-grained igneous trondhjemite (light-colored intrusive igneous rock in which the dominant feldspar is plagioclase). This dike is younger than the gneiss around it because it cuts across the foliation. The Law of Cross Cutting is the logical assumption that a magma protrusion that cuts through horizontal layers at a diaganol or vertical is younger than the layers that it cuts through. Sedimentary rocks are most often found in horizontal or near horizontal layers or strata.
DIP AND STRIKE:
DIP is the acute angle that a rock's surface makes with a horizontal plane. STRIKE is the direction of the line formed by the intersection of a rock's surface with a horizontal plane. Both DIP and STRIKE are perpendicular to each other on a map. Dip and Strike are measurements of the orientation orientation and sloap of a rock. These measurements are used to map geologic structures. Dip and Strike also refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault or other planar feature, is a line representing the intersection of that feature with a horizontal plane. The angle of dip is generally included on a geologic map without the degree sign.
RESOURCE:
A Geologic Adventure Along The Blue Ridge Parkway in North Carolina by Carter/Merschat/Wilson ... 2001
QUESTIONS TO BE ANSWERED:
1, How many dike strikes and dips do you see? Describe their appearance.
2. In observing the cross cuts across the mica gneiss, what line of direction does the dike strike travel?
3. In observing the cross cuts across the mica gneiss, what line of direction does the dike dip travel?
4. What are the colors visible on these dike strikes?
5. Are the dike strikes symmetrical?
6. Post a picture at or near the coordinates (you do not have to be in the picture unless you want to). This is your log signature.
GINGIN'S MESSAGE:
H - Hear the music that fills the air with birds and wind that plays their melodies
E - Enrich your being with the comfort that being "home" is in the mountains
R - Reach for the stars in the cool clear evening sky
R - Richess from the beautiful mountains that fill your senses to overflowing
I - In practing keeping our Earth clean will keep it just as beautiful for those coming after you
N - Never forget that we are stewards of this land, a responsibility not to be taken lightly.
K - Kindness shown through our actions will preserve it for those who have never stepped on it's soil
N - Not to forget, enjoy your time, hold hands with those closest to you, and embrace this time together
O - Only the remnants of your visit should be the tread marks from your shoes or your foot print
B - Because we all love these mountains, come back again and invite someone to share time with you there.
CONGRATULATIONS TO vilstudio/racewalker for being FTF 6-22-21