Structural Geology Lecture

• Stress – a directed pressure which may lead to strain (change in shape/deformat ion) • 

Topo Maps vs Geologic Maps • Geologic maps – formations, members, beds, contacts  

Outcrops

Things we see: Faults • Occur along breaks  movement • Faults are from three types of stress:  

Tension

 

Compression



     

Shear

 

From stresses we get: Faulting • Normal Faults • Reverse Faults • Thrust faults • Sense of motion of the top block relative to the bottom block (REGARDLESS of which one has actually moved!)

Normal Fault • From tensional stress • ‘Normal’ referring to normal response to g • Hanging wall black moves down relative to footwall block 

Reverse Faults

• Hanging wall block moves up in relation to footwall • Can happen at a high angle (reverse fault) or low angle (thrust fault)

Strike Slip Faults • Also known as lateral faults • Motion relative to an observer standing on one side • Right lateral or left lateral strike-slip fault

Left-lateral strike-slip fault

Right-lateral strike-slip fault

Transform Faults (Strike-Slip) • Occur on plate boundaries

Folded Structures

• Anticline – convex fold, oldest rocks in the middle • Syncline – concave fold, youngest rocks in the middle • Both bend around a fold axis within the axial plane

• Folds have limbs – one on each side of axial plane – If one limb is under the other  overturned fold

• Fold axis may not be horizontal  plunging fold – Plunge = angle between fold axis and horizonal – Trend = the plunge bearing (compass direction) 

– 

A 3 D A n ticlin e  D o m e

-The oldest rocks at center of the dome!

A 3D Syncline 

-Oldest rocks are at the center of the basin!

Basin

Mysteries….(aka uncomformities!) • Discomformity – Unconformity between relatively parallel strata • Angular unconformity - ….between nonparallel strata • Noncomformity – unconformity between sedimentary rock and non-sedimentary rock

Unconformities

How do we map this stuff? • Strike – compass bearing of line formed by the intersection of a horizontal plane to an incline layer D ip – a n g le b e tw e e n a h o rizo n ta lp la n e a n d th e tilte d stra tu m ( w a te r ru n s d o w n a lo n g d ip d ire ctio n )

Check out Fig 10.1!