Chapter Three
Igneous Processes and Igneous Rocks
CHAPTER – 3
IGNEOUS ROCKS
*IGNEOUS ROCKS: ROCKS THAT COOLED AND FIRE
CRYSTALLIZED DIRECTLY FROM MOLTEN ROCK, EITHER
AT THE SURFACE OR DEEP UNDERGROUND
*MAGMA: MOLTEN ROCK WITHIN THE EARTH
*LAVA: WHEN MAGMA REACHES EARTH’S SURFACE
*MOST IGNEOUS PROCESSES ARE HIDDEN FROM VIEW
*REGIONAL EROSION EXPOSES ANCIENT IGNEOUS EVENTS
DISTRIBUTION OF MAJOR CONTINENTAL
IGENOUS ROCKS
MOLTING ROCKS AND CRYSTALLIZING MAGMA
•
MAGMA FORMATION: HEATED UNGERGROUND
MINERALS – BONDS BROKEN- BECOMES MAGMA
– CHEMICAL COMPOSITION OF MAGMA CHANGES
•
MAGMA COOLING AND CRYSTALLIZATION: AS
COOLING PROGRESSES, DIFFERENT MINERALS
CRYSTALLIZE
EFFECT ON THERMAL ENERGY
CLASSIFICATION OF IGNEOUS ROCKS:
•
TEXTURE: SIZE AND SHAPE OF MINERAL CRYSTALS
CRYSTAL GROWTH DURING COOLING
•
MINERAL CONTENT:CHEMICAL COMPOSITION
COOLING HISTORY
•
TEXTURE: RATE AT WHICH MAGMA OR LAVA COOL WHEN 100 – 1000 YRS FOR COOLING
 TIME TO GROW LARGER CRYSTALS  CRYSTALS CAN BE
 VISIBLY SEEN  PHANERTIC TEXTURE
•
INTRUSIVE ROCKS (OR PLUTONIC ROCKS)
SLOW COOLING OCCURS WHEN MAGMAS INTRUDE PREEXISTING SOLID ROCKS
*VOLCANIC GLASS: WHEN LAVA SUDDENLY COOLS,
NO TIME TO FORM CRYSTALS. TEXTURE IS GLASSY.
*PUMICE: FORMS WHEN HIGHLY GASEOUS, SILICA –
RICH LAVA COOLS VERY RAPIDLY
*OBSIDIAN: VERY Si-RICH LAVAS CONTAINING LESS
GAS, COOL VERY QUICKLY
IGNEOUS COMPOSITION
•
MAGMA  O2, Si, Al, Fe, Ca, Mg, Na, K, S.
•
DISSOLVED GASSES  WATER
VAPOR, CO2, SO2.
•
SILICATES ARE THE MAJOR
CONSTITUENTS OF IGNEOUS ROCKS
CLASSIFICATION OF IGNEOUS ROCKS AND MAGMAS
IGNEOUS ROCK - CHART
CREATION OF MAGMA:
* PARTIAL MELTING
 WHEN ROCKS MELT TO PRODUCE MAGMA  PARTIAL MELTING
 DIFF. MELTING POINT
EX:
ALBITE = 1118 0C
ANORTHITE = 1553 0C
* MELTING OF ROCKS DEPENDS ON
 HEAT
 PRESSURE
 AMOUNT OF H2O IN THE ROCKS.
•
THERMAL ENERGY
HEAT SOURCES
GEOTHERMAL GRADIENT
MELTING TEMPERT.-DRY
MELTING TEMPERT.-WET
LITHOSPHERIC THINNING
L. THINNING-CONTD
THINNING-CONTD.
FLUIDITY AND VISCOSITY OF MAGMA:
MAGMA RISES BECAUSE
 IF IT IS LESS DENSE THAN SURROUNDING ROCK
 EXPANDING GASES DRIVE IT UPWARD
 IT IS SQUEEZED UPWARD BY SURROUNDING ROCKS
VISCOSITY: FLUID RESISTANCE TO FLOW
A) INCREASES WITH DECREASING TEMPERATURE
B) MINERAL (SILICA) CONTENT INCREASES VISCOSITY VALUE.
CRYSTALLIZATION OF MAGMA:
*MINERALS MELT AT THE SAME TEMPERATURE
AT WHICH THEY CRYSTALLIZE
 FIRST TO MELT  LAST TO CRYSTALLIZE
* AT EACH STAGE OF COOLING,
CRYSTAL/LIQUID RATIO CHANGES
OCEANIC PLATE SUBDUCTS
MAGMA MIXING
BOWEN’S REACTION SERIES:
A)
BOTH MAFIC AND FELSIC ROCKS CAN CRYSTALLIZE FROM AN
ORIGINALLY MAFIC MAGMA
B)
EARLY – FORMING CRYSTALS REMAINING IN CONTACT WITH
THE STILL – LIQUID MAGMA REACT WITH IT TO EVOLVE INTO
DIFFERENT MINERALS
BOWEN’S REACTION SERIES
EARLY-FORMING CRYSTALS
MAGMA & EARLY FORMING CRYSTALS
SILICATE MINERALS CAN CRYSTALLIZE FROM MAFIC MAGMAS TWO WAYS:
DISCONTINUOUS SERIES
•
•
•
•
•
OLIVINE
PYROXINE
AMPHIBOLE
BIOTITE MICA
MINERALS WITHOUT Fe, Mg.
CONTINUOUS SERIES
• CALCIUM PLAGIOCLASE
• SODIUM PLAGIOCLASE
CONTDHOW MAGMA CHANGES AS IT COOLS:
INTRUSIVE ROCK FORMATION:
•
RISING MAGMA MAY FORCE OVERLYING ROCKS TO BULGE
UPWARD  RESULTING ROCK APPEARS AS A DOOMED INTRUSION
WITHIN OTHER ROCKS  THIS STRUCTURE IS KNOWN AS DIAPIR
•
XENOLITHS: WHEN PREEXISTING ROCK IS ASSIMILATED IN A
MAGMA, THEY APPEAR IN THE SOLIDIFIED ROCK AS DISTINCT
BODIES – XENOLITHS
PLUTONS: MAGMA THAT COOL UNDERGROUND FORM PLUTONS
TABULAR PLUTONS
o
DIKES
o
SILLS – DISTINGUISHED FROM EXTRUSIVE FLOWS BY
A)EVIDENCE OF HEATING OF ADJACENT ROCK SURFACES
B)EVIDENCE OF INCLUSIONS OF COUNTRY ROCK IN BOTH UPPER & LOWER SILL
SURFACE
C)LACK OF VESICLES ( HOLES FROM GAS BUBBLES ) ON UPPER SURFACE
D)LACK OF WEATHERING OF LARGE SURFACE.
PLUTONIC IGNEOUS FEATURES
BATHOLITHS AND LARGE PLUTONS:
1.
LACCOLITHS
2.
LAPOLITHS
3.
BATHOLITHS
A)DEFINITION
B)EXAMPLES
C)TEXTURE
SHIPROCK PEAK
SEMINARY RIDGE TOPOGRAPHIC RIDGE
SILLS AND LAVA FLOWS
LACCOLITH
PLATE TECTONICS AND IGNEOUS ROCKS:
A) THE ORIGIN OF BASALT & GABBROS
1) INTRODUCTION
* UPPER MANTLE LACKS LIGHT ELEMENTS
*DEEPER MANTLE POSSESSES SOME LIGHT ELEMENTS
*PRESENCE OR ABSENCE OF LIGHT ELEMENTS IN GABBRO &
BASALT IDENTIFIES SOURCE OF PARENT MAGMA
PLATE SETTINGS & BASALTS
BASALTS-OCEAN & LAND
ANDESITE & DIORITE ORIGIN
B) ORIGIN OF ANDESITES & DIORITES
ORIGIN OF FELSIC ROCKS
IGNEOUS ************
A)
ROCKS OF THE HIGHLANDS
1. 4 – 4.5 * 109 YRS OLD
2. PRINCIPALLY ANORTHOSITE –
COMPOSED OF Ca – PLAGIOCLASE ANORTHITE
3. NO WATER – CONTAINING MINERALS
4. NO RELATIONSHIP TO PLATE TECTONICS
5. NO RELATIONSHIP TO MOON’S INTERNAL HEAT
GEOLOGY AT A GLANCE
CHAPTER SUMMARY