Dip-Slip Fault in Perry County, Indiana EarthCache
Dip-Slip Fault in Perry County, Indiana
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1. What is the approximate angle of this Slip- Dip Fault?
2. Tell me which type of Slip - Dip fault this is (reverse or thrust), and why you think this? It is because of the answer from question one.
3. A photo of a fossil on the fault if you can find one, or photo of the fault itself. (I request a photo but it is purely optional due to the current Earthcache rules)
*** Please do not put the answers in your log or it will be deleted ***
*** IF YOU BRING YOUR KIDS WITH YOU PLEASE WATCH THEM SINCE THIS IS NEAR A HIGHWAY!! ***
Dip-slip faults
Dip-slip faults can occur either as "reverse" or as "normal" faults. A normal fault occurs when the crust is extended. Alternatively such a fault can be called an extensional fault. The hanging wall moves downward, relative to the footwall. A downthrown block between two normal faults dipping towards each other is called a graben. An upthrown block between two normal faults dipping away from each other is called a horst. Low-angle normal faults with regional tectonic significance may be designated detachment faults.
A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate shortening of the crust. The dip of a reverse fault is relatively steep, greater than 45°.
Cross-sectional illustration of normal and reverse dip-slip faults
A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and foot wall) folds. Thrust faults form nappes and klippen in the large thrust belts.
The fault plane is the plane that represents the fracture surface of a fault. Flat segments of thrust fault planes are known as flats, and inclined sections of the thrust are known as ramps. Typically, thrust faults move within formations by forming flats, and climb up section with ramps.
Fault-bend folds are formed by movement of the hanging wall over a non-planar fault surface and are found associated with both extensional and thrust faults.
Faults may be reactivated at a later time with the movement in the opposite direction to the original movement (fault inversion). A normal fault may therefore become a reverse fault and vice versa.
Fault Rock description
All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any mineralising fluids. Fault rocks are classified by their textures and the implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of detachment faults and major thrust faults.
The main types of fault rock include:
* Cataclasite - a fault rock which is cohesive with a poorly developed or absent planar fabric, or which is incohesive, characterised by generally angular clasts and rock fragments in a finer-grained matrix of similar composition.
o Tectonic or Fault breccia - a medium- to coarse-grained cataclasite containing >30% visible fragments.
o Fault gouge - an incohesive, clay-rich fine- to ultrafine-grained cataclasite, which may possess a planar fabric and containing + Clay smear - clay-rich fault gouge formed in sedimentary sequences containing clay-rich layers which are strongly deformed and sheared into the fault gouge.
* Mylonite - a fault rock which is cohesive and characterized by a well developed planar fabric resulting from tectonic reduction of grain size, and commonly containing rounded porphyroclasts and rock fragments of similar composition to minerals in the matrix
* Pseudotachylite - ultrafine-grained vitreous-looking material, usually black and flinty in appearance, occurring as thin planar veins, injection veins or as a matrix to pseudoconglomerates or breccias, which infills dilation fractures in the host rock.
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