chapter three
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Chapter Three. Igneous Activity and Plate Tectonics. 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 - PowerPoint PPT PresentationTRANSCRIPT
Chapter Three Chapter Three
Igneous Activity and Plate Tectonics
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
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
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
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
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
•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
*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 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
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
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
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
CLASSIFICATION OF IGNEOUS ROCKS AND MAGMAS
COMPOSITION TYPE
Si ( % )
OTHER MAJOR ELEMENTS
VISC. OF MAGMA
IGNEOUS ROCKSPRODUCED
FELSIC >65 Al, K, Na HIGH ~ 600 – 800 0C
INTERMEDIATE 55-65 Al, Ca, Na, Fe, Mg MEDIUM ~ 800 – 1000 0C
MAFIC (BASALT) 45 - 55 Al, Ca, Fe, Mg LOW ~ 1000 – 1200 0C
ULTRAMARIC (PERIDOTITE)
< 40 Al, Ca, Fe, Mg VERY LOW > 1200 0C
IGNEOUS ROCK - CHART
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
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: 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 1118 0C AT 100 KM PRESSURE IS 35, 000 TIMES HIGHER–MP 1440 0C
HEAT SOURCES
GEOTHERMAL GRADIENT
MELTING TEMPERT.-DRY
MELTING TEMPERT.-WET
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
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
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
*AFTER BOTH SERIES COMPLETE, HIGH
– SILICA MINERALS FORM EX: K – FELDSPAR MUSCOVITE MICA QUARTZ
CONTD-
HOW MAGMA CHANGES AS IT COOLS:
1.
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
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
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
TABULAR PLUTONS 1. DIKES
2. 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
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
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
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
PLATE SETTINGS & BASALTS
2) OCEANIC 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
BASALTS-OCEAN & LAND
ANDESITE & DIORITE ORIGIN
B) ORIGIN OF ANDESITES & DIORITE
1. PROXIMITY TO SUBDUCTION ZONES
2. FACTORS IN FORMATION a) WATER CONTENT b) ASSIMILATION OF COUNTRY ROCKS c) OCEANIC SEDIMENTS
C) ORIGIN OF RHYOLITES & GRANITES 1. NEARLY ALL FOUND ON CONTINENTS
2. DERIVE FROM PARTIAL MELTING OF LOWER CONTINENTAL CRUST
3. EXIST NEAR MODERN OR ANCIENT SUBDUCTION ZONES
GEOLOGY AT A GLANCE
1. MAGMA, LAVA, DIFFERENCE BETWEEN THEM
2. PROPERTIES TO IDENTIFY IGNEOUS ROCKS
3. FACTOR(S) THAT GOVERN ROCK TEXTURE
4. APHANITIC, PHANERTIC, PLUTONIC, PORPHYRITIC
5. MAJOR ELEMENTS IN IGNEOUS ROCKS
6. CLASSIFICATION OF IGNEOUS ROCKS – BASIS
7. FASTEST COOLING RATE RESULTS
CHAPTER SUMMARY
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