structural geology (week 2) Flashcards
what is deformation
- causes rocks to change shape, size, location or orientation
what analysis can be performed on deformed rocks
- descriptive
- kinematic, where changes in position or shape of the rock
- dynamic, where forces/stress acting on rock *rheology
how are things kinematically analysed
- motion of objects
- interpret deformational movements
- translation, distortion, rotation, dilation and dilation
what is stress
- is the force applied to a given area and is defined per unit area
- stress= force/area
what is differential stress
what is stress ellipsoid
- maximum extension occurs when stress=3
what is strain ellipsoid
- when maximum compression occurs towards stress=1
what are the two types of strain and how is it formed
- product of stress
- brittle- cracking/fracturing
-ductile- bending and flowing
co axial vs non co axial
-CO AXIAL
-horizontal stretching/ shortening
NON CO AXIAL
- shear strain
is a pure shear co axial or non-coaxial
co-axial
is a simple shear co axial or non-coaxial
- non co axial
under what conditions does brittle and ductile deformation occur
low temperature= brittle
high temperature= ductile
deformation style is dependant of rheology, what factors come into play
- temperature
- minerology
- grain size
- rock fabric
- fluids
how can strength be quantified in rocks
- a compression rig can be used to yield the strength of rocks and soils
- 3 principal axis of strength
how can the failure envelope be calculated
- based on representative rig compression results
- ## represents the force needed to cause a specific material to fail (fracture)
a very important example of modelled stress in rocks
- the shakespeare cliff
what is a fault
-ma structural break in a rock across which there is notable dispacement
what is a joint
- fractures which have no notable displacement
important in engineering geology
two examples of faults
- highland boundary fault
- moine thrust
fault rock to describe the moine thrust
mylonites
what are the 3 main types of fault movements
- dip slip
- oblique- slip fault
- strike- slip
what are the types of dip slip faults
- normal fault
- reverse fault
what is a normal fault
- hanging wall block moves down relative to the footwall
- extension of the earths crust thins the crust
what are reverse dip-slip and thrust faults
- hanging wall block moves up relative to the footwall
- results in compression of the earths crust= thickens the crust
- ## reverse faults are steeper than thrust faults
how do faults work as mineralisation zones
- precipitation of ore minerals can occur within the fault and surrounding fractures
how do faults operate as conduits
- formation of hydrothermal ore deposits on the seafloor from fluid transport along faults
what are horst and graben structures
- normal fault bounded valleys= grabens
-normal fault bounded ridges=horsts
for example, the basin and range province, in western USA
how are mountain belts formed
- compression- thrust faults- mountain belts
what is the process in which mountain belts build
orogenesis
how do sinistral strike slip faults
- sinistral - (left lateral) strata on the opposite side of the fault plane is displaced on the left
- dextral- (right lateral) - strata on the opposite side of the fault plane is displaced to the right
how do faults operate as conduits
provide natural resources as hydrothermal ore deposits on the seafloor due to fluid transport along faults
how do ores operate as mineralisation zones
- precipitation of ore minerals can occur within the fault and the surrounding fractures
what deposit provides gold to the scotgold resource Limited
cononish
what is strike
- orientation of a horizontal line on a planar structure
what is dip
-angle of inclination on a planar structure
what is dip direction
- the compass direction in which the planar structure is dipping
how do folds form
- caused by compression stress parallel to the bedding planes in a rock body
- ductile deformation process-very slow process (avg= 100,000 years to several mill)
ANATOMY OF A FOLD
- hinge- zone of max curvature
- hinge line- line of maximum curvature
what can be used to quantify tightness
- interlimb angle
- shows how much distrotion a rock has experienced
what is the axial trace
- where the axial plane intersects the earths surface
whats an antiform
- fold closes upwards (angry)
whats a synform
- fold closes downwards (smiley!)
old rocks in the fold core
synformal anticline
young rocks in the core of the fold
antiformal syncline
