Types of Metamorphism Regional metamorphism Large scale – large volume of rock is affected Associated with convergent plate margins and mountain building Folding and faulting increase thickness of the crust Occurs over a range of temperatures and pressures Fluids are also present Low grade to high grade metamorphism Will have zones of contact metamorphism

Regional Metamorphism

Metamorphic Grade

The following diagram illustrates the rock cycle The following diagram illustrates the rock cycle. Match the lettered responses to the blank ovals on the diagram. (Note: some letters are used more than once.) Magma 1 2 Metamorphic rock 3 Igneous rock a) Cementation & Compaction (lithification) b) Heat and Pressure c) weathering, transportation, deposition d) Cooling and solidification e) Melting E D B C A Start with 10 points – for each wrong answer subtract 1. 4 6 5 7 Sedimentary Rock Sediment 8

Rock Cycle

Geologic Structure

Rock Deformation Stress Rock Strength Force applied to an area Pressure Differential stress – magnitude of stress is greater in one direction Rock Strength Rock’s resistance to deformation (stress)

Rock Deformation Cont. Strain Elastic deformation Plastic deformation A rock’s response to stress Deformation resulting in change of shape or position Elastic deformation Deformation is reversible, after stress is removed, materials return to original shape, i.e. A rubber band Plastic deformation Deformation is permanent Rock flow in response to stress Need high pressures and temperatures, generally deep in earth’s interior, i.e. Taffy

Rock Deformation Cont. Brittle deformation Deformation is permanent Rock break (fracture) or lose cohesion Generally low temperature and low pressure, common in shallow crust, i.e. Peanut brittle

Types of Stress Tensional (Extension) Stress Compressional Stress Shear Stress

Tension or Extensional Stress Stress move away from each other (pull apart) Rock lengthens Common in divergent boundaries, but not sole locale Ductile deformation – stretching and thinning of rock Brittle deformation – fracturing and faulting

Compressional Stress Stress presses (squeezes) rock together Rock shortens Common at convergent boundaries Ductile deformation – shortening and thickening of rock – rock folds Brittle deformation – fracturing and faulting

Shear Stress Stress creates a lateral shift in the rock Rock slides past other rock Common at transform boundaries Results in faults

Folds Ductile deformation Compressional stress Horizontal rocks are deformed

Fold Terminology Limb – the sides of the fold Axial plane (hinge plane) – imaginary plane that divides the fold into two equal parts, marks location of maximum curvature Fold axis (hinge line) – the line formed by the intersection of the hinge plane and a bedding plane

Syncline A fold with the youngest beds in the middle Generally trough shaped, with limbs dipping toward the center

Anticline A fold with the oldest beds in the middle Generally arched shaped, with limbs dipping away the center

Monocline Folds with only one limb Often Associated with faults

Fold Symmetry Symmetrical fold – limbs of the fold dip at the same angle Asymmetrical fold – limbs of the fold dip at different angles

Overturned Fold Fold where one limb has been tilted beyond vertical

Plunging Fold The hinge line or fold axis is inclined

Daily Exercise-Complete the concept map 1 2 3 Applied to a causes 1 2 3 At low T & P or high stress rate At high T & P or low stress rate 5 4 The material The material no displacement 7 6 8 Joints Deformation Folds Normal Anticline Reverse Tension Rock Faults Compression Break Plastic deformation Syncline Brittle deformation Force/stress displacement Defined by youngest rock in middle Defined by oldest rock in middle 11 1 – j 2 – n 3 – k 4 – g 5 – I 6 – f 7 – a 8 – b 9 – h 10 – c 11 – e Start with 10 points and subtract accordingly. 9 10 Each letter can be used only once, and it is possible that it will not be used.

Faults A results of brittle deformation Fractures in the Earth's crust where displacement has occurred

Fault Terminology Hanging wall – block that lies below the fault plane Footwall – block that lies above the fault plane

Classes of Faults Dip-Slip Strike Slip Oblique-Slip Movement is primarily vertical Strike Slip Movement is along strike Oblique-Slip Movement is both vertical and along strike

Dip-Slip Fault – Normal Fault Extensional Stress Hanging wall moves down with respect to footwall

FOOTWALL HANGINGWALL

Normal Fault Horst – raised block of material bounded by two normal faults Graben – trough (valley) bounded by two normal faults

Dip-Slip Fault – Reverse Fault Compressional Stress Hanging wall moves up with respect to footwall

Dip-Slip Fault – Thrust Fault Compressional Stress Low-angle reverse fault (fault plane < 45o) Displacement can be 100’s km (~60 miles) Typically associated with folds

Strike-Slip Fault Shear Stress No vertical movement Left-lateral strike-slip faults: movement of opposite plate is to the left Shear Stress No vertical movement Movement parallel to fault plane Right-lateral strike-slip faults: movement of opposite plate is to the right

Joints Brittle deformation at low pressure Tension fractures with NO DISPLACEMENT