STRUCTURAL GEOLOGYPRIMARY & NON-TECTONIC STRUCTURES1) PRINCIPLE OF ORIGINAL HORIZONTALITY (NICOLAS STENO 1638-1686) – 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 150 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 FAULTB - 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 & CE – EVEN YOUNGER ROCK STRATA OVERLYING C & DF – 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 DEFORMATIONDEFORMATION REFERS TO CHANGES IN VOLUME,

SHAPE, POSITION OR IN COMBINATION OR ROCK UNDER STRESS

STRESS – APPLIED FORCE ACTING ON THE ROCKSTRAIN – 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 BREAKSROCK BEHAVIOR 1) BRITTLE – ROCK BREAKS, 2) DUCTILE – ROCK FLOWS OR BENDSONCE 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