Chapter 15 Flashcards
pressure
equal squeezing from all sides
compression
squeezing or squashing in a specific direction
tension
stretching or pulling apart
shear
which happens when one part of a material moves relative to another part in a direction parallel to the boundary between the parts
deformation
displacement of rocks on sliding surfaces called faults
folds
bending or warping of layers to produce arch-like or trough-like shapes
Overall change in the shape of a rock body by thickening or thinning
geologic structures
products of deformation such as faults, folds, and foliations
foliation
a fabric caused by the alignment of platy or elongate minerals
block diagram
3D representation of a region of the crust that depicts the configuration of structures on the ground as well as on one or two vertical into the ground
geologic map
represents the earth’s surface as it would appear looking straight down from above, showing the boundaries between rock units and where structures intersect the Earth’s surface.
Cross- section
represents the configuration of structures as seen in a vertical slice through the Earth.
contact
the boundary between two geologic units
trace
line representing the intersection of a planar feature with the plane of a map or cross section
stratigraphic formation
a sequence of sedimentary and/ or volcanic layers that has a definable age and can be identifies over a broad region
unit can be
a stratigraphic formation, intrusive igneous body, interval of a specified type of metamorphic rock
Types of contacts
Intrusive contact
Conformable contact
unconformable contact
fault contact
Intrusive contact
boundary surface of an intrusive igneous body
conformable contact
boundary between successive beds, sedimentary formations, or volcanic extrusions in a continuous stratigraphic
unconformable contact
occurs where a period of erosion and or deposition has interrupted deposition
fault contact
is where two units are juxtaposed across fault
attitude
the orientation of any planar geologic feature
strike
first number, the compass direction of a horizontal line drawn on the surface of the feature
dip
second number, the angle of tilt or the angle of slope of the bed, measured relative to horizontal surface
quadrant notation
when the strike is written as some angle relative to north
azimuth notation
writing strike as a three-digit number
map view
the top of a block
cross-section view
the side of a block
anticline
arch-like fold whose layers dip toward the base of the trough
layers of rock upward
fold limb
side of a fold
fold hinge
the line that separates the two limns
nonplunging fold
hinge of a fold is horizontal
plunging fold
high of a fold has a tilt
basin
a bowl shaped structure
dome
overturned bowl
fault displacement
one body of rock slides past another
hanging wall
rock above the fault surface
footwall
rock below the fault surface
strike-slip faults
tend to be nearly vertical, and displacement on them is horizontal
dip-slip faults
displacement is parallel to the dip direction on the fault
Reverse fault
hanging wall moves up the dip
normal fault
moves down the dip
thrust fault
if a reverse fault has a gentle dip or curved
unconformity
contact that represents a period od non-deposition and or erosion
disconformity
bedding above and below the unconformity is parallel
nonconformity
strata are deposited on a “basement” of intrusive igneous and or metamorphic rock
angular conformity
orientation of the beds above the unconformity is not the same as that below
Tabular intrustion
roughly parallel margins
include dikes which cut across preexisting layers
and sills- sheet-like intrusions
Plutons
irregularly shaped, blob-shaped, or bulb-shaped intrusions
line of section
map view along which you want to produce the cross-section
