STRUCTURES Flashcards
types of stress
compression, tension, shear.
causes: * Tectonic forces, gravity, and the pressure form overlying rocks
compression
shortening
folding, reverse fault
tension
stretching
thinning crust
normal fault
shear
parallel forces, on opposite side of a plane [twisting laterally]
* Bending horizontally, strike-slip fault
o Strain (deformation): change in shape or size due to stress. Observed in a material (rocks) is a function of
Types of stress
How stress is applied
Temperature
Material properties
Speed at which stress is applied
Strain is how rocks respond to stress, expressed in rocks by: folding (bending), or faulting (breaking)
- Distinguish between the 3 types of deformation
elastic, plastic, brittle
Elastic deformation
- Temporary change in shape or size
- Recovers when stress is removed
- Stores energy
Plastic deformation
- Permanent change in shape or size- results in folding
Brittle deformation
- Loss of cohesion due to stress
- In ricks results in faults and fractures
o Syncline:
strata slope upward away from the axis of folding
o Anticline :
strata slop downward away from the axis
These can create domes and basins
the hinge
is the horizontal line that defines the part of the fold with he sharpest curve
folded landscapes
o A synclinal ridge is formed when the differing composition of strata resulting in different weathering responses
o Faulting:
occurs when rocks on either side of the fracture shift relative to the other side. Fault zones are areas where fractures in the rock demonstrate crustal movement
o Folding vs faulting
Fold- strain involves plastic deformation to accommodate for stress
Fault- strain involves brittle failure to accommodate stress
o Normal
Tension
One side slips up (footwall) and one slides down (hanging wall)
A fault scarp identifies the displacement of the ground
reverse
Compression
Hanging wall moves up relative to the footwall
Thrusts low angle reverse faults – can result in overthrusting (old rock lying nearly horizontal with young)
o Strike-slip
Shear stress
Side to side movement
Transform fault – san andreas fault
o Faulted landscapes produce
Horst: upward faulted block
Graben: downward faulted block
Normal faulting - extension
o Crustal formation
Magma less dense = rise
o Three uplift crustal regions
Tectonic mountains and landforms – produced by foding, faulting, and crustal movement
Volcanic feature, formed by surface accumulation of molten rock from eruptions of subsurface materials
Residual mountains and stable continental cratons, formed from inactive remnant of ancient tectonic activity
o Craton
Craton: Old stable part of continental crust
* Compatible with diamonds
Continental shield- region w/ craton that is exposed
* Untouched by tectonic process, away from boundaries
Platform: continental area covered by relatively flat or gently tilted sedimentary strata
Basement/ crystalline basement- region below sedimentary platform/cover
- Understand how mountains are built
volcanic eruptions, uplift and erosion compression of plates/ thrust faults, crustal extension
Volcanic eruption
- Lava piles up, convergent margins, hot spots, divergent margins (most under the sea)
Uplift (and erosion)
- Floating lithosphere is subject to gravitational forces and buoyancy
- Occurs due to the internal heat and thickness of the root
Compression of plates/ thrust falls
- Regional compression over large areas
- Orogeny at convergent margins
o Oceanic plate- continental plate collision orogenesis
o Oceanic plate- oceanic plate collision orogenesis
o Continental plate- continental plate collision orogenèses
Crustal extension
- Basin and range extension – thins crusts but also makes local topographic high
o Oceanic- continental example
Andes mountains (south America)
continental- continental example
Himalayan mountains
- Explain how accretion of terranes are related to the geological history of BC
o Accretion of terranes
Continents can be extended through the process of adding terrains as volcanic island arcs
BC is a result of accretion of material like micro continents and islnd arcs being added to the west coast