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last chapter of geology
49
Geology
Undergraduate 1
11/26/2009

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Term
Strike
Definition
a horizontal line in the place of bedding expressed as a compass direction.
Term
Dip
Definition
represented as a direction and an angle.
Term
Angle of dip
Definition
angle between a horizontal plane and a bedding plane. (measured in degrees).
Term
Direction of dip
Definition
compass direction in which the layer is inclined from horizontal (90 degrees from strike) and is given as the "down dip" direction.
Term
Ductile
Definition
occurs when rocks bend, forming Folds.
Term
Brittle
Definition
occurs when rocks break, forming Faults.
Term
Folds
Definition
bent or folded rocks at convergent plate boundaries.
Term
Faults
Definition
fractures in the Earth's crust along which displacement has occurred; rocks break under stress in any tectonic environment.
Term
Fault plane
Definition
the plane along which the rock or crusted material has fractured.
Term
Hanging wall block
Definition
the rock material which lies above the fault plane.
Term
Footwall block
Definition
the rock material which lies below the fault plane.
Term
Displacement
Definition
amount of movement along a fault.
Term
Dip-slip faults
Definition
movement is predominantly vertical (some lateral). Characterized by upwards or downwards.
Term
Horst
Definition
raised by the fault block bounded by 2 normal faults.
Term
Graben
Definition
lowered fault black bounded by 2 normal faults.
Term
Strike-slip faults
Definition
high angle faults in which the sense of displacement is horizontal in that it is parallel to the strike of the fault plane. Occurring along transform boundaries, crust is conserved.
Term
Right lateral fault
Definition
movement of the opposite block is to the right.
Term
Left lateral fault
Definition
movement of the opposite block is to the left.
Term
Limbs
Definition
sides of a fold.
Term
Axial plane
Definition
imaginary plane that divides a fold into 2 equal halves.
Term
Axis (hinge line)
Definition
trace of the axial plane on the Earth's surface.
Term
Monocline
Definition
horizontal beds are modified by simple step-like folds.
Term
Anticline
Definition
Up-arched strata with the limbs dipping away from center.
Bed gets older toward the center.
Term
Syncline
Definition
Troughs with the limbs dipping toward the center.
Beds get younger toward the center of the fold.
Term
Asymmetrical fold
Definition
a fold without a mirror image in respect to the axial plane.
Term
Overturned fold
Definition
one of the limbs is overturned (upside down)
Term
Plunging folds
Definition
fold axis plunges into the ground.
Term
Dome
Definition
An up-arched series of strata with beds on all sides dipping away from the center.
Rocks become progressively younger away from the center of the structure.
Term
Basin
Definition
A down-arched series of strata with beds on all sides dipping towards the center.
Rocks become progressively older away from the center of the structure.
Term
Batholith
Definition
a very large body of intrusive igneous rock, usually granite, that has been exposed by erosion of the overlying rock.
Term
Dike
Definition
A sheet-like body of igneous rock that cuts across layering or contacts in the rock into which it intrudes.
Term
Half Grabens
Definition
develop when parallel listric normal faults on either side of a block develop. The block becomes tilted instead of dropping down as in a graben.
Term
Detachment fault
Definition
a low angle normal fault --generally has greater displacements.
Term
Listric normal fault
Definition
a normal fault with a curved fault trace. They often merge into a detachment fault.
Term
Metamorphic Core Complex
Definition
a dormal uplift of intensely metamorphosed and plutonic rocks overlain by a tectonically detached, less metamorphosed cover.
Term
Arroyos
Definition
ephemeral desert creeks are common in the southwest desert.
Term
Collapsed Caldera
Definition
The caldera in Saguaro West was carried on a detachment fault many miles to the southwest to its present location.
Term
Pluton
Definition
a large body of intrusive igneous rock that solidified within the crust.
Term
Stock
Definition
>100>10 km2 masses of igneous rocks.
Term
Spheroidal weathering
Definition
occurs when corners of a rock weather faster causing the rocks to become rounded.
Term
Boulder Arch
Definition
forms when boulders are perched in precarious positions.
Term
Exfoliation
Definition
similar to spheroidal weathering, but on a larger scale . Large curved sheets or slabs of rock peel off.
Term
Releasing bend
Definition
a bend in a strike slip fault in which extension causes a graben to form. (called a pull apart basin.)
Term
Restraining Bend
Definition
a bend in a strike slip fault in which compression causes mountain building. The faults associated with these are usually not exposed at the surface. (Called blind thrusts.)
Term
Thrust
Definition
low-angle reverse fault.
Term
Alluvial Fan
Definition
an outspread sedimentary deposit that forms in an arid or semi-arid region where a stream issues from a narrow canyon onto a plain or valley floor.
Term
Fanglomerates
Definition
cemented gravels originally deposited on alluvial fans.
Term
Fault scarp
Definition
a steep slope or cliff formed directly by movement along a fault and representing the exposed surface of the fault before modification by erosion and weathering.
Term
Wineglass Canyon
Definition
resembles a wine glass in that they have a narrow canyon at the base and wider canyon further up slope. Alluvial fan is at the base.
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