STRUCTURAL GEOLOGY  PRIMARY & NON-TECTONIC STRUCTURES 1) PRINCIPLE OF ORIGINAL HORIZONTALITY (NICOLAS STENO ) – LAYERS OF SEDIMENTS ARE ORIGINALLY DEPOSITED HORIZONTALLY. THIS PRINCIPLE IS IMPORTANT TO ANALYSIS OF FOLDED & TILTED STRATA. FIELD OBSERVATIONS REVEAL THAT EARTH IS DYNAMIC THAT LEADS TO SCIENCE OF PLATE TECTONICS; THAT PLATE MOVEMENT CAUSES ROCK DEFORMATION

SEDIMENTS FORMED IN OCEAN & DEPOSITED IN HORIZONTAL LAYERS NOT ALL SEDIMENTARY LAYERS ARE DEPOSITED HORIZONTALLY COARSE SANDS MAY BE DEPOSITED AT 15 0 ANGLE CALLED ANGLE OF REPOSE, EXAMPLE IS SAND DUNES SEDIMENTS MAY COVER OVER PRE-EXISTING INCLINED SURFACE & DEPOSITED UNCOMFORMABLY TO OLDER SEDIMENTARIES ALTHOUGH NOT UNIVERSALLY APPLICABLE, POH IS USEFUL IN STUDY OF SEDIMENTOLOGY, STRUCTURAL GEOLOGY & STRATIGRAPHY

2. PRINCIPLE OF SUPERPOSITION (NICOLAS STENO) - SEDIMENTARY LAYERS ARE DEPOSITED IN A TIME SEQUENCE WITH THE OLDEST AT THE BOTTOM AND THE YOUNGEST AT THE TOP POS APPLIES TO VOLCANIC ROCKS WHICH FLOW ON OLDER ROCKS BY FLOW BANDING

3. THE PRINCIPLE OF LATERAL CONTINUITY – SEDIMENTARY LAYERS EXTEND LATERALLY IN ALL DIRECTIONS COULD BE SEPARATED BY A VALLEY OR BY EROSIONAL FEATURE

3. PRINCIPLE OF CROSS-CUTTING RELATIONSHIP – THE GEOLOGIC FEATURE WHICH CUTS ANOTHER IS YOUNGER OF THE TWO FEATURES. DETERMINATION OF RELATIVE AGES OF STRATA & OTHER GEOLOGIC STRUCTURES A – FOLDED ROCK STRATA CUT BY THRUST FAULT B - LARGE INTRUSION CUTTING THROUGH A

C - EROSIONAL ANGULAR UNCONFORMITY CUTTING OFF A & B ON WHICH ROCK STRATA WERE DEPOSITED D – VOLCANIC DIKE CUTTING THROUGH A, B & C E – EVEN YOUNGER ROCK STRATA OVERLYING C & D F – NORMAL FAULT CUTTING THROUGH A, B,C & E 4. PRINCIPLE OF FAUNAL SUCCESSION – SEDIMENTARY ROCK STRATA CONTAIN FOSSILIZED FLORA & FAUNA AND THAT THESE FOSSILS SUCCEED EACH OTHER VERTICALLY IN A SPECIFIC, RELIABLE ORDER THAT CAN BE IDENTIFIED OVER WIDE HORIZONTAL DISTANCES

ROCK DEFORMATION  DEFORMATION REFERS TO CHANGES IN VOLUME, SHAPE, POSITION OR IN COMBINATION OR ROCK UNDER STRESS  STRESS – APPLIED FORCE ACTING ON THE ROCK  STRAIN – RESPONSE OF A ROCK UNDER STRESS WHICH INVOLVES CHANGE OF VOLUME OR SHAPE OF THE ROCK – RESULTING DEFORMATION  TYPE OF STRESS: 1.LITHOSTATIC (CONFINING) – STRESS IN ALL DIRECTION

5. DIFFERENTIAL (DEVIATORIC) – UNEQUAL STRESS DUE TO TECTONIC FORCES. THERE ARE THREE(3) BASIC KINDS: 5.1 TENSIONAL(EXTENSIONAL) – FORCES ACT IN OPPOSITE DIRECTION; ROCK STRETCHES 5.2 COMPRESSIONAL - FORCES ACT TOWARDS EACH OTHER; SQUEEZES ROCK

5.3 SHEAR – SIDE TO SIDE SHEARING RESULTS TO SLIPPAGE & TRANSLATION THREE KINDS OF DIFFERENTIAL STRESS

 STRAIN – ROCK DEFORMATION IN RESPONSE TO STRESS  CONTROL FACTORS TO ROCK DEFORMATION DEPENDS ON : 1) PRESSURE & TEMPERATURE(DEPTH IN EARTH), 2) ROCK MATERIAL - MINERAL COMPOSITION OF ROCK 3) VOLATILE CONTENTS, 4) TIME  TYPES OF STRAIN/STAGES OF DEFORMATION 1) ELASTIC DEFORMATION – CHANGES IN SHAPE OF ROCK IS REVERSIBLE. 2) PLASTIC DEFORMATION – CHANGES IN SHAPE OF ROCK ARE PERMANENT & NOT REVERSIBLE

3. FRACTURE – ROCK BREAKS  ROCK BEHAVIOR 1) BRITTLE – ROCK BREAKS, 2) DUCTILE – ROCK FLOWS OR BENDS ONCE ELASTIC LIMIT IS SUPASSED, ROCK WILL DEFORM PLASTICALLY IF ROCK IS DUCTILE OR ROCK WILL FRACTURE(RUPTURE) IF ROCK IS BRITTLE

STRESS - STRAIN

 MECHANISM DUCTILE DEFORMATION OCCURS DEPENDING PRINCIPALLY ON TEMPERATURE 1.PLASTIC FLOW OCCURS AT RELATIVELY LOW TEMPERATURE IN THE LOWER CRUST & UPPERMOST MANTLE. ROCK DEFORMS BY GRADUAL CREEP ALONG CRYSTAL GRAIN BOUNDARIES & PLANES WITHIN CRYSTAL LATTICES 2.POWER FLOW CREEP OCCURS WHERE TEMPERATURE IS GREATER THAN 55% OF THE MELTING TEMPERATURE FOR THAT DEPTH(PRESSURE). MOVEMENT OCCURS ALONG CRYSTALLOGRAPHIC PLANES & GRAIN BOUNDARY

3. DIFFUSION CREEP OCCURS WHERE TEMPERATURE IS GREATER THAN 85% OF THE MELTING TEMPERATURE FOR THAT DEPTH(PRESSURE). DEFORMATION/FLOW IS LARGELY BY IONIC/ATOMIC DIFFUSION & CONTINUOUS RECRYSTALLIZATION