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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

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Chapter Three

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  1. Chapter Three Igneous Activity and Plate Tectonics

  2. The Rock Cycle • A rockis a naturally formed, consolidated material usually composed of grains of one or more minerals • The rock cycleshows 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. 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 rockscool quickly at or near Earth’s surface and are typically fine-grained(most crystals <1 mm) • Intrusive igneous rockscool 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 veryslowly 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. 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 – 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 CLASSIFICATION OF IGNEOUS ROCKS AND MAGMAS

  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: * 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

  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 1118 0C AT 100 KM PRESSURE IS 35, 000 TIMES HIGHER–MP 1440 0C

  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. DISCONTINUOUS SERIES OLIVINE PYROXINE AMPHIBOLE BIOTITE MICA MINERALS WITHOUT Fe, Mg. CONTINUOUS SERIES CALCIUM PLAGIOCLASE SODIUM PLAGIOCLASE SILICATE MINERALS CAN CRYSTALLIZE FROM MAFIC MAGMAS TWO WAYS:

  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

  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   3.        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 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

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