1st part of paper due 3/10/06 1” margins, 12 pt type, double spaced, ~ 1-2 pages Geologic Setting

Location (generally provide geologic location map) Basic geology: rock units and their distribution

Previous Work Focus on structural research May be included in Geologic Setting or be a separate

section with its own subheading Reference list

Geological Society of America Bulletin format Use RefWorks!

Thrust and Folds

Extension may also occur locally in association with subduction zones

…Or in association with continent-continent collisions, where ‘orogenic collapse’ is one way that mountain systems achieve isostatic equilibrium

Mechanical paradox Thrust movement on low-

angle surface with ‘typical’ coefficient of friction of rock requires stresses high enough to break the rock

To understand how this motion takes place, we need to think about concepts of displacement, stress, and fault mechanics

OLDOLD

YOUNGYOUNG

Three descriptions of mechanical interactions Displacement describes the movement of

particles with respect to an external reference frame

Deformation can be described by a displacement field Translation Rotation Shape change (distortion) = strain

Stress is force per unit area

Stress ≠ strain

Components of Deformation

Deformation

Three categories of displacement

Relative particle motion can be described even if part of the system is fixed in space

Three descriptions of mechanical interactions Displacement describes the movement of

particles with respect to an external reference frame

Deformation can be described by a displacement field Translation Rotation Shape change (distortion) = strain

Stress is force per unit area

Fault movement depends on magnitude of fault perpendicular versus fault parallel forces on fault plane

Classes of forces on rocks Body forces (gravity)

depend on amount of material

Surface forces are ‘pushes and pulls’

Combination of forces result in deformation where they are unequal in different directions

Normal and shear components of stress Force is a vector

quantity Stress is force/unit

area, thus is not a vector, since there is area dependence

We can, however, ‘decompose’ stress into surface normal and parallel components

Geologic sign conventions