1. Igneous Activity and Plate Tectonics
Chapter Three
Igneous Activity and Plate Tectonics

2. The Rock Cycle
A rock is a naturally formed, consolidated material usually composed of grains of one or more minerals
The rock cycle shows how one type of rocky material gets transformed into another
Representation of how rocks are formed, broken down, and processed in the geosphere
Arrows indicate possible process paths within the cycle

3. 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 :

4. DISTRIBUTION OF MAJOR CONTINENTAL IGENOUS ROCKS

5. 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

6. EFFECT ON THERMAL ENERGY

7. The Rock Cycle and Plate Tectonics
Magma is created by melting of rock
above a subduction zone
Less dense magma rises and cools
to form igneous rock
Igneous rock exposed at surface
gets weathered into sediment
Sediments transported to low areas,
buried and hardened into sedimentary rock
Sedimentary rock heated and squeezed at depth to form metamorphic rock
Metamorphic rock may heat up and melt to form magma
Convergent plate boundary

8. 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

9. Igneous Rocks Magma is molten rock
Igneous rocks form when magma cools and solidifies
Intrusive igneous rocks form when magma solidifies underground
Granite is a common example
Extrusive igneous rocks form when magma solidifies at the Earth’s surface (lava)
Basalt is a common example
Granite
Basalt

10. PEGMATITES: IGNEOUS ROCKS WITH EXCEPTIONALLY LARGE CRYSTALS (QUARTZ, MICA, FELDSPAR ARE COMMON)
EXTRUSIVE OR VOLCANIC ROCKS: WHEN ROCKS SOLIDIFY QUICKLY,
CRYSTALS ARE SMALL
APHANITIC TEXTURE – ROCKS WITH AHANITIC STRUCTURE ARE CALLED
EXTRUSIVE ROCKS
PORPHYRITIC STRUCTURE: LARGER AND SMALLER GRAINS – SLOW
COOLING FOLLOWED ABRUPTLY BY RAPID COOLING

11. VOLCANIC GLASS: WHEN LAVA SUDDENLY COOLS, NO TIME TO FORM CRYSTALS
*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  

12. Igneous Rock Textures
Texture refers to the size, shape and arrangement of grains or other constituents within a rock
Texture of igneous rocks is primarily controlled by cooling rate
Extrusive igneous rocks cool quickly at or near Earth’s surface and are typically fine-grained (most crystals <1 mm)
Intrusive igneous rocks cool slowly deep beneath Earth’s surface and are typically coarse-grained (most crystals >1 mm)
Coarse-grained igneous rock
Fine-grained igneous rock

13. Special Igneous Textures
A pegmatite is an extremely coarse-grained igneous rock (most crystals >5 cm) formed when magma cools very slowly at depth
A glassy texture contains no crystals at all, and is formed by extremely rapid cooling
A porphyritic texture includes two distinct crystal sizes, with the larger having formed first during slow cooling underground and the small forming during more rapid cooling at the Earth’s surface
Pegmatitic igneous rock
Porphyritic igneous rock

14. 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

15. Igneous Rock Identification
Igneous rock names are based on texture (grain size) and mineralogic composition
Textural classification
Plutonic rocks (gabbro-diorite-granite) are coarse-grained and cooled slowly at depth
Volcanic rocks (basalt-andesite-rhyolite) are typically fine-grained and cooled rapidly at the Earth’s surface
Compositional classification
Mafic rocks (gabbro-basalt) contain abundant dark-colored ferromagnesian minerals
Intermediate rocks (diorite-andesite) contain roughly equal amounts of dark- and light-colored minerals
Felsic rocks (granite-rhyolite) contain abundant light-colored minerals

16. CLASSIFICATION OF IGNEOUS ROCKS AND MAGMAS
COMPOSITION
TYPE Si
( % )
OTHER MAJOR ELEMENTS
VISC. OF
MAGMA
IGNEOUS ROCKS
PRODUCED
FELSIC
>65
Al, K, Na
HIGH
~ 600 – 800 0C
INTERMEDIATE
55-65
Al, Ca, Na, Fe, Mg
MEDIUM
~ 800 – C
MAFIC (BASALT)
Al, Ca, Fe, Mg
LOW
~ 1000 – C
ULTRAMARIC (PERIDOTITE)
< 40
VERY LOW
> C

17. IGNEOUS ROCK - CHART

18. ULTRA MAFIC IGNEOUS ROCKS:
* < 40% Si.
* EX: PERIDOTITE & KOMATITE
* OCCURRENCE: RARE AT EARTH’S SURFACE
MAFIC IGNEOUS ROCKS:
* 45 – 55 % Si.
* EX: BASALT & GABBRO
* OCCURRENCE: COMMON ON OCEAN FLOORS AND CONTINENTS
INTERMEDIATE IGNEOUS ROCKS:
* 55 – 65 % Si.
*EX: ANDESITE & DIORITE
* OCCURRENCE: ABUNDANT VOLCANIC ROCK.
FELSIC IGNEOUS ROCKS:
* > 65% Si.
* EX: GRANITE & RHYOLITE
* OCCURRENCE: COMMON ON CONTINENTS

19. CREATION OF MAGMA: THERMAL ENERGY * PARTIAL MELTING
 WHEN ROCKS MELT TO PRODUCE MAGMA  PARTIAL MELTING
 DIFF. MELTING POINT
EX: ALBITE = C
ANORTHITE = C
* MELTING OF ROCKS DEPENDS ON
 HEAT
 PRESSURE
 AMOUNT OF H2O IN THE ROCKS.
THERMAL ENERGY

20. HEAT SOURCES *HEAT: SOURCE OF HEAT IN THE INTERIOR
  * DECAY OF RADIOACTIVE ISOTOPES
*RESIDUAL FROM EARTH’S FORMATION
*FRICTIONAL HEAT FROM PLATE MOTION
*HIGH PRESSURE: THE IONS AND ATOMS IN A CRYSTALLINE SOLID
CLOSER TOGETHER – HIGH TEMP IS REQUIRED TO VIBRATE, WEAKEN,
AND BREAK THEIR BONDS.
*AS PRESSURE INCREASES, THE TEMPERATURE AT WHICH ROCKS MELT
INCREASES
EX: Na – FELDSPAR ALBITE MELTS AT C
AT 100 KM PRESSURE IS 35, 000 TIMES HIGHER–MP C

21. GEOTHERMAL GRADIENT

22. MELTING TEMPERT.-DRY

23. MELTING TEMPERT.-WET

24. 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.

25. 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

26. OCEANIC PLATE SUBDUCTS

27. MAGMA MIXING

28. 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

29. BOWEN’S REACTION SERIES

30. Bowen’s Reaction Series
Minerals crystallize in a predictable order, over a large temperature range
Discontinuous branch
Ferromagnesian minerals (olivine, pyroxene, amphibole, biotite) crystallize in sequence with decreasing temperature
As one mineral becomes chemically unstable in the remaining magma,
another begins to form
Continuous branch
Plagioclase feldspar forms with a chemical composition that evolves
(from Ca-rich to Na-rich) with decreasing temperature

31. EARLY-FORMING CRYSTALS

32. MAGMA & EARLY FORMING CRYSTALS

33. 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

34. CONTD- *AFTER BOTH SERIES COMPLETE, HIGH – SILICA MINERALS FORM
EX: K – FELDSPAR
MUSCOVITE
MICA
QUARTZ

35. HOW MAGMA CHANGES AS IT COOLS:
CRYSTALS CAN
* REMAIN SUSPENDED AND REACT WITH MAGMA
* SINK
* BE PLASTERED TO THE WALLS OR CEILING OF THE
MAGMA
*BE FILTERED OUT AS MAGMA FLOWS ELSEWHERE
OTHER MAGMA CRYSTALLIZATION PROCESSES:
* OTHERS – ASSIMILATION OF ROCK BODIES
* MAGMA MIXING 1.

36. 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

37. PLUTONS: MAGMA THAT COOL UNDERGROUND FORM PLUTONS
CONCORDANT PLUTONS:
DISCORDANT PLUTONS:
TABULAR PLUTONS
PARALLEL TO THE PREEXISTING ROCK LAYERS – CALLED “SILLS”
CUT ACROSS THE PREEXISTING LAYERS – CALLED “DIKES” MASSIVE SIZE BATHOLITHS
RELATIVELY THIN

38. TABULAR PLUTONS DIKES 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.

39. PLUTONIC IGNEOUS FEATURES

40. BATHOLITHS AND LARGE PLUTONS:
1.        LACCOLITHS
2.        LAPOLITHS
          BATHOLITHS
A)DEFINITION
B)EXAMPLES
C)TEXTURE

41. SEMINARY RIDGE TOPOGRAPHIC RIDGE

42. SILLS AND LAVA FLOWS

43. LACCOLITH

44. 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

45. Igneous Activity and Plate Tectonics
Igneous activity occurs primarily at or near tectonic plate boundaries
Mafic igneous rocks are commonly formed at divergent boundaries
Increased heat flow and decreased overburden pressure produce mafic magmas from partial melting of the asthenosphere
Intermediate igneous rocks are commonly formed at convergent boundaries
Partial melting of basaltic oceanic crust produces intermediate magmas

46. Igneous Activity and Plate Tectonics
Felsic igneous rocks are commonly formed adjacent to convergent boundaries
Hot rising magma causes partial melting of the granitic continental crust
Intraplate volcanism
Rising mantle plumes can produce localized hotspots and volcanoes when they produce magmas that rise through oceanic or continental crust
Hawaii is an example

47. PLATE SETTINGS & BASALTS

48. BASALTS-OCEAN & LAND 2) OCEANIC BASALTS 3) CONTINENTAL BASALTS
a) MORBS FROM UPPER MANTLE
b)OIBS ( OCEAN ISLAND BASALTS) FROM DEEPER MANTLE
3) CONTINENTAL BASALTS
a) COMPOSITION VARIES WIDELY
b) BASALTS NEAR CONTINENTAL RIFTS FROM DEEP MANTLE
c)BASALTS NEAR SUBDUCTION ZONES FROM UPPER MANTLE

49. ANDESITE & DIORITE ORIGIN

50. B) ORIGIN OF ANDESITES & DIORITE
PROXIMITY TO SUBDUCTION ZONES
FACTORS IN FORMATION
a) WATER CONTENT
b) ASSIMILATION OF COUNTRY ROCKS
c) OCEANIC SEDIMENTS
C) ORIGIN OF RHYOLITES & GRANITES
NEARLY ALL FOUND ON CONTINENTS
DERIVE FROM PARTIAL MELTING OF LOWER CONTINENTAL CRUST
EXIST NEAR MODERN OR ANCIENT SUBDUCTION ZONES

51. GEOLOGY AT A GLANCE

52. CHAPTER SUMMARY MAGMA, LAVA, DIFFERENCE BETWEEN THEM
MAGMA, LAVA, DIFFERENCE BETWEEN THEM
PROPERTIES TO IDENTIFY IGNEOUS ROCKS
FACTOR(S) THAT GOVERN ROCK TEXTURE
APHANITIC, PHANERTIC, PLUTONIC, PORPHYRITIC
MAJOR ELEMENTS IN IGNEOUS ROCKS
CLASSIFICATION OF IGNEOUS ROCKS – BASIS
FASTEST COOLING RATE RESULTS

53. 8. EXAMPLES OF APHANITIC ROCK, PHANERTIC ROCK
9. WHEN ROCKS MELT UNDER LOWER TEMPERATURE?
10.FACTORS THAT CONTROL MELTING POINT OF A MINERAL.
11. WHAT IS BOWEN’S REACTION SERIES?IT EXPLAINS
WHAT?WHAT IS DISCONTINUOUS SERIES?
12. DIKE, SILL, BATHOLITHS, XENOLITHS
13. OCEANIC CRUST – BASALTS & GABBROS
14. WHAT TYPES OF MAGMA ASSOCIATED WITH WHAT BOUNDARIES