Geology 11- Lecture Notes 1

1 Geology 11 ‐ Lecture Notes – Gabo (2008)

Dear Class,

These are the lecture notes as I have promised. Again, I have to stress that these are just from the slides and I cannot upload the figures since they do not belong to us. You have to look for some of the figures yourselves (they are usually found in textbooks, too). Maswerte kayo, I put some figures here.

These notes do not and cannot in any way replace listening during the lecture in class. Napansin nyo naman siguro ang dami2x ko sinasabi na wala sa slides :) And the examples I cite are local so you also cannot find them in a basic geology book. For the concepts, though, the books are very helpful :)

The point is, you may have these lecture notes BUT you are not assured of a high score in the exam. Listen and try to participate in the lecture and ask questions when things are not so clear.

Disclaimer lang un hehehe. Ito na ang notes. Ayun, enjoy chickenjoy! ;)

Rakenrol,

Ma’am Jill

Lecture 1 - Introduction to Geology GEOLOGY - study of the earth, its origin, history, materials, processes and resources Geology as a discipline: a. relevance of time, b. issue of scale, c. complexity of replicating natural systems in the laboratory Main Branches: 1. Physical - study of Earth materials and processes > Volcanology, Seismology, Environmental Geology, Engineering Geology, Mining Geology, Petroleum Geology, Mineralogy, Petrology, Geomorphology, Geophysics, Geochemistry, Planetary Geology

2. Historical - study of Earth origin and evolution > Paleontology, Stratigraphy, Geochronology Basic Concepts: 1. Catastrophism

sudden, worldwide catastrophes are the agents of change that alter the physical features of the Earth over time

widely accepted by theologians in the early 1800s due to similarity with Biblical events such as Noah’s Flood


2. Uniformitarianism

proposed by James Hutton (The Father of Modern Geology)

The present is the key to the past.”

advocates the idea that the Earth is continuously modified by geologic processes that have always operated throughout time (at different rates), and that by studying them we can understand how the Earth has evolved through time

Lecture 2 – The Planet Earth

FORMATION OF THE EARTH – offshoot of the formation of the Universe

Formation of the Universe: Big Bang Theory

Formation of the Solar System: Nebular Hypothesis

THE BIG BANG THEORY

contends that the Universe originated from a cosmic explosion (origin unknown) that hurled matter in all directions 15 and 20 billion years ago

first proposed by the Belgian priest Georges Lemaître in the 1920s

Edwin Hubble justified Lemaître’s theory through observations that the Universe is continuously expanding; galaxies are moving away from each other

THE NEBULAR HYPOTHESIS

the solar system originated from a single rotating cloud of gas and dust, starting 4.6 billion years ago, which contracted due to gravity

the idea was first proposed by Immanuel Kant and Pierre Simon de Laplace in the 18th century

THE NEBULAR MODEL

The Big Bang produced enormous amount of matter: rotating cloud of gas and dust.

The rotating gas-dust cloud began to contract due to gravity. Most of the mass became concentrated at the center, forming the SUN.

The remaining matter condensed to form the planets.

THE SUN

mostly made up of hydrogen, the principal product of the Big Bang


sun’s center became compressed enough to initiate nuclear reactions, consequently emitting light and energy (sun became a star)

a middle-aged star

THE PLANETS

composition depended on distance from the sun

planets nearest the sun contained high-temp minerals (e.g. iron) while those that are far away contained lower-temp materials (e.g. methane and ammonia, and some that contained water locked in their structures)

Mercury, Venus, Earth, Mars - inner or terrestrial planets (nearest the sun)

- rocky composition: largely silicate rocks and metals (Si, Fe, O)

Jupiter Saturn Uranus Neptune - giant or Jovian planets (outer planets; far from the sun)

- lack solid surfaces: in gaseous or liquid form

- composition: light elements (H, He, Ar, C, O, Ni)

Pluto - neither a terrestrial or Jovian planet

- similar to the icy satellites of the Jovian planets

SOME INTERESTING FACTS

1. Planets’ revolution = counterclockwise direction.

2. Planets’ rotation direction the same as direction of revolution except for Venus, which rotates in a retrograde direction.

3. Uranus and Pluto rotate about axes that are tipped nearly on their sides.

4. Orbital Speed of the Earth = 30 km/s

THE EARTH

- started as “dust ball” from the nebular gas and dust brought together by gravity (accretion), which was heated (heating) and eventually segregated into layers (differentiation) as it cooled

- when cooling set in, the denser elements (e.g., iron) sank while the lighter ones floated out into the surface, creating a differentiated Earth


CONSEQUENCES OF THE HEATING & DIFFERENTIATION OF THE EARTH

1. formation of atmosphere (mostly gases from volcanic activity)

2. formation of oceans (water released from crystal structure)

* Life started when atmosphere was modified due to the appearance of the blue-green algae.

THE EARTH’S VITAL STATISTICS

Equatorial Radius = 6378 km

Polar Radius = 6357 km

Equatorial Circumference = 40076 km

Polar Circumference = 40008 km

Volume = 260,000,000,000 cu. miles

Density = 5.52 g/cm3

CHEMICAL COMPOSITION (by mass) - 34.6% Iron, 29.5% Oxygen, 15.2% Silicon, 12.7% Magnesium

SHAPE - Oblate spheroid (flattened at the poles and bulging at the equator)

External Features of the Earth

1. Continents 2. Ocean basins

Prominent Features of Continents

1. Mountains – elevated features of continents 2. Mountain ranges – chains of mountains 3. Mountain belts – mountain ranges that run across a vast area

OCEAN BASINS - Oceanic ridges, Trenches, Seamounts/guyots, Abyssal hills/plains

Internal Structure of the Earth

>Crust

1. Oceanic – basaltic composition (SiMa); 3 to 15 km thick; density: ~3.0 g/cm3


2. Continental – granitic composition (SiAl); 20 to 60 km thick; density:~2.7g/cm3

>Mantle – extends to a depth of ~2900 km (Fe, Mg)

1. Upper mantle – extends from the base of the crust 2. Mesosphere – lower mantle; from 660 km depth to the core-mantle boundary

> Core – iron rich sphere with small amounts of Ni and other elements

1. Outer core – 2270 km thick; liquid 2. Inner core – solid sphere with a radius of 1216 km

*Discontinuities/Boundaries

1. Mohorovicic – crust – mantle 2. Gutenberg – core – mantle 3. Lehmann – outer core – inner core

Question: How were these discontinuities discovered?

Mechanical layers

1. Lithosphere

a. Upper crust – brittle; 4-15 km depth

b. Lower crust/uppermost mantle – ductile; 15 to 100 or 200 km depth

2. Asthenosphere – weak sphere; beneath the lithosphere and within the upper mantle

3. Mesosphere – solid, rocky layer

ISOSTASY (it’s very important to understand this concept)

from a Greek word meaning “same standing”

basically concerned with the buoyancy of the blocks of the Earth’s crust as they rest on the mantle

changes in the load over certain regions causes the lithosphere to make adjustments until isostatic equilibrium (i.e., neither rising or sinking) is reached

AIRY’S THEORY (1)

Mountains have “roots” which extend down into the mantle. Thus, elevation is proportional to the depth of the underlying “root”.

http://cache eb com/eb/image?id=73583&rendTypeId=35


PRATT’S THEORY (2)

Elevation is inversely proportional to density. Thus, the higher the mountain, the lower is its density; that is, light rocks “float” higher.

HOW OLD IS THE EARTH? (estimates from different bases)

1. Cooling through conduction and radiation (Lord Kelvin, 1897): ~24 – 40 m.y. 2. rate of delivery of salt to oceans (John Joly, 1901): ~90 – 100 m.y. 3. thickness of total sedimentary record divided by average sedimentation rates (1910):

~1.6 b.y. 4. Amount of evolution of marine mollusks (Charles Lyell, 1800s): ~80 m.y. for the

Cenozoic 5. radioactivity (Henri Becquerel, 1896): ~500 m.y. 6. Radiometric dating: 4.5 – 4.6 b.y. (which is, of course, the accepted age)

Lecture 3 - MINERALS DEFINITION: Naturally occurring, Inorganic, Homogeneous, ,Solid, Definite chemical composition, Ordered internal structure MINERALOID - naturally occurring, inorganic material that is amorphous Ex. glass, opal POLYMORPHISM - ability of a specific chemical substance to crystallize in more than one configuration, which is dependent upon changes in temperature, pressure, or both PHYSICAL PROPERTIES OF MINERALS >Color - caused by the absorption, or lack of absorption, of various wavelengths of light >Streak - the color of a mineral in powdered form; not always identical to the color >Hardness – resistance of mineral to abrasion or scratching Mohs’ Scale of Hardness – 1. Talc; 2. Gypsum; 3. Calcite; 4. Fluorite; 5. Apatite; 6. Orthoclase; 7. Quartz; 8. Topaz; 9. Corundum; 10. Diamond >Crystal Form - the shapes and aggregates that a certain mineral is likely to form (look for pictures showing fibrous, platy, acicular, rhomboid, botryoidal, cubic, tabular, etc)

http://upload.wikimedia.org/wikipedia/commons/d/d3/Isostasy.Airy&Pratt.Scheme.png


>Cleavage - the tendency of a mineral to break in particular directions due to zones of weakness in the crystal structure *Fractures or irregular breakages occur when bond strengths in a crystal structure is equal in all directions. >Luster - the ability of minerals to reflect light (e.g. vitreous, pearly, dull, metallic, etc) >Specific gravity - Ratio of volume of a substance and the weight of the same volume of water Other properties

1. Magnetism – ex. Magnetite (Fe3O4) 2. Fluorescence – ex. CaF2 3. Reaction to chemicals – ex. CaCO3 4. Taste – ex. NaCl 5. Odor – ex. S

CLASSIFICATION OF MINERALS

1. Silicates 2. Non-silicates

Bases for Classification 1. Composition

• Single element (e.g. Cu, Au, S) • 2 elements (e.g. halite, pyrite) • Greater number of different kinds of atoms (e.g. KAl3Si3O10(OH)2)

2. Crystal Structure Relative Abundance of the Most Common Elements in the Crust

ELEMENT % BY WEIGHT

oxygen, O 46.6 silicon, Si 27.7 aluminum, Al 8.1 iron, Fe 5 calcium, Ca 3.6 sodium, Na 2.8 potassium, K 2.6 magnesium, Mg 2.1 all others 1.5

The Silicate Group

- largest group of minerals - compounds containing silicon and oxygen - building block: silicon tetrahedron (SiO4)-4

- structure possessing isolated silicate tetrahedra is called a nesosilicate. derived from the Greek word (nesogaean) that means "island". (e.g. olivine) - structure possessing double island silicate tetrahedra is called a sorosilicate. derived from a Greek word that means "group".


- structure possessing parallel single chains of silicate tetrahedra is called an inosilicate (single chain or double chain). derived from a Greek word that means "chain". (e.g. pyroxene and amphibole) - structure possessing isolated rings of silicate tetrahedra, is called a cyclosilicate. derived from a Greek word that means "ring". - structure possessing parallel sheets of silicate tetrahedra is a phyllosilicate. derived from a Greek word that means "sheet". (e.g. micas) - structure possessing a three-dimensional framework of silicate tetrahedra is called a tectosilicate. (e.g. feldspar and quartz) The Non-Silicates

1. Native metals – gold, platinum, iron 2. Oxides – oxygen is combined with one or more metals (e.g. hematite, magnetite) 3. Sulfides – opaque with distinct colors (e.g. pyrite, galena) 4. Sulfates – SO4 (e.g. barite, anhydrite) 5. Carbonates – carbonate ion plus metal 6. Phosphates – PO4 (e.g. apatite) plus metal 7. Hydroxides – OH plus metal

THE MOST COMMON ROCK-FORMING MINERALS Silicates: Quartz, feldspar (orthoclase and plagioclase), mica (biotite and muscovite), amphibole, pyroxene, olivine Non-silicates: Clay and Calcite Economic importance Non-renewable resource – processes that create the resources are so slow (takes millions of years to accumulate) Ores – useful metallic (and some nonmetallic) minerals that can be extracted and which contain useful substances 1. Mineral resources – sources of metals and other materials 2. Gemstones Lecture 4 – Igneous Rocks ROCKS What is a rock?

• a naturally-occurring aggregate of one or more minerals; may or may not contain mineraloids, natural glass and organic matter.

• Types of rocks vary based on composition, color, texture, structures, etc.


What are igneous rocks?

• Ignis = fire • Formed from solidification of magma (intrusive) or lava which flows out from depths

(extrusive) What is magma?

• Molten material which may contain suspended crystals and dissolved volatiles (gases e.g. water vapor, CO2, SO2)

• Molten rock composed of varying amounts of - Liquid; Silicate (sometimes carbonate or sulfide); Ions of K, Na, Fe, Ca, Mg, Al - Solid; Minerals; Rock fragments - Dissolved gas; H2O, CO2, SO2

• Temperature: 600-1200oC • Generated by increase in temperature, decrease in pressure and addition of volatiles

Sources of heat for melting in the crust

• original heat of the earth at the time of formation • some elements, e.g. U, produce heat through radioactive decay • heat transfer by conduction from a nearby body of magma • hot mantle plumes may upwell into the crust • frictional heat caused by rocks grinding past each other

Origin and Formation of Magma Magma forms at:

• Mid-Oceanic Ridges (MOR) – divergent boundaries • Subduction Zones – convergent boundaries

http://www.washington.edu/uwired/outreach/teched/projects/web/rockteam/WebSite/rc


• Hot spots – mantle plumes Magma is classified according to:

• Silica content - amount of SiO2 • Viscosity - resistance to flow • Temperature - temperature of melt formation

Common Types of Magma Basaltic magma

a. High density b. Low viscosity c. Relatively low silica content d. Crystallize at high temperatures (~1000 - 1200ºC)

Granitic magma

a. Low density b. High viscosity c. Relatively high silica content d. Crystallize at ~600ºC)

basaltic (mafic) andesitic (intermediate) rhyolitic (felsic) Basaltic magma accounts for about 80 percent of all magma erupted by volcanoes. Rhyolitic and andesitic magma accounts for 10 percent each. Classification (chem’l composition)

– Felsic, Silicic or acidic • >63% SiO2 – Intermediate • 52-63% SiO2 – Mafic or basic • 45-52% SiO2 – Ultramafic or ultrabasic • <45% SiO2

* There is a wide variety of igneous rock types but only a few basic types of magma, because the asthenosphere and upper mantle have a fairly uniform composition. Variation in Magma Composition Magmatic Differentiation – process of changing the composition of magma Processes: -Assimilation of country rock – When a molten body moves up through "country rock“, it assimilates rock (melts and incorporates elements from the surrounding rock). This changes the magma composition.


-Magma mixing - If two or more magmas with different chemical compositions come in contact with one another beneath the Earth’s surface, then it is possible that they could mix with each other to produce compositions intermediate between the end members. -Partial Melting – rocks melt incrementally because the minerals that compose them have different melting points. The composition of the resulting magma is different for every melting temperature. -Fractional Crystallization - As a magma crystallizes, the magma becomes depleted in the elements that are entering the crystallizing minerals and so the melt changes composition over time. As a cooling melt changes composition, the minerals that are in equilibrium with it (i.e. that are stable in the melt at the temperature and pressure conditions of crystallization) typically either change composition and/or change to structurally-more complex minerals as in Bowen's Reaction Series Bowen’s Reaction Series (look for a figure showing this) Discontinuous Series – olivine � pyroxene � amphibole � biotite Continuous Series – Ca-rich to Na-rich plagioclase feldspar At the lower temperatures – orthoclase feldspar � muscovite � quartz *As you lower the temperature, the silicate structure becomes more complex Properties of Magma >Viscosity

– property to resist flow – Effects of different factors • ↑ temperature, ↓ viscosity • ↑ SiO2, ↑ viscosity • ↑ dissolved H2O, ↓ viscosity

>Density

– heavier oceanic crust � mafic rocks – lighter continental crust � felsic rocks

Two kinds of igneous rocks Extrusive (volcanic) – molten rock solidified at the surface.

• Ex. Basalt, Andesite, Rhyolite Intrusive (plutonic) – igneous rocks formed at depth.

• Ex. Gabbro, Diorite, Granite Forms of intrusive rocks >Stock – small discordant pluton >Batholith – more than 100 sq. km. in outcrop area >Dike – tabular body cutting across bedding >Sill – concordant tabular body >Laccolith – blister-shaped sill http://www.indiana.edu/~geol105/images/gaia_chapter_5/dike&sill.jpg.gif


Classification of igneous rocks (Based on texture or crystal size) Aphanitic – very fine-grained (<2mm in diameter) as a result of rapid cooling at the surface. - minerals too small to be seen by the naked eye. Phaneritic – coarse-grained (>5 mm) mineral sizes due to magma cooling at depth. Porphyritic – very large crystals (phenocrysts) embedded in smaller crystals (groundmass). Other textures: Vesicular – contains tiny holes called vesicles which formed due to gas bubbles in the lava or magma. Glassy – molten rock quenched quickly as it was ejected into the atmosphere. Pegmatitic – interlocking crystals greater than 1 cm Pyroclastic – formed when volcanic materials are extruded violently. Volcanic ejecta or pyroclasts or tephra: Ash – <2 mm in diameter Lapilli – 2-64 mm in diameter Block or bomb – >64 mm; block is extruded in a solid state while bomb is partially or wholly molten Classification of igneous rocks (Based on shape of crystal faces) Euhedral – well-defined crystal faces Subhedral – intermediate faces Anhedral – no well-formed crystal faces *Suggests rate of cooling undergone by the magma (longer cooling period, more well-formed crystal faces) Classification of igneous rocks (Based on mineral composition) > presence or absence of quartz, composition of feldspars, amount of ferromagnesian minerals COMPOSITION

TEXTURE felsic intermediate mafic ultramafic phaneritic granite diorite gabbro peridotite aphanitic/ porphyritic

rhyolite andesite basalt komatiite

Resources from igneous rocks Metallic Resources

� Produced by igneous processes


� Hydrothermal solutions contain metal ions that eventually precipitate out � Found in:

� Veins � Disseminated deposits � Gold, silver, platinum etc

Epithermal Gold Districts (along Philippine Fault Zone) Baguio-Lepanto, Camarines Norte, Masbate, Surigao, Central, Masara Chromitite, Nickel & PGM Deposits (usually in ophiolite* complexes) Casiguran, Zambales, Camarines Norte, Lagonoy, Mangyan, Antique, Samar, Leyte, Dinagat, Surigao, Central Mindanao, Pujada, Zamboanga, Palawan *Ophiolite – sequence of rock representing oceanic crust-mantle Lecture 5 - VOLCANISM What is a volcano? Etymology - from the Roman god of fire, Vulcan.

Vulcan was said to have had a forge (on Vulcano, an active volcano on the Lipari Islands in Italy.

- place on the Earth's surface (or any other planet's or moon's surface) where molten rock, gases and pyroclastic debris erupt through the earth's crust

- can be a mountain, vent or caldera - Mountainous accumulation of materials resulting from successive eruptions of

lava from a central vent. Why do volcanoes erupt? Due to decompression Magma is lighter than the solid rock around it Types of volcanoes

1. Shield – slopes are gentle (15o or less); shape resembles a Roman shield lying on the ground; made up of successive lava flows

2. Cinder cone – relatively small (<300 m high); steep slopes (30 – 40o); made up of pyroclastic material

3. Composite or strato-volcano – layered structure (tephra and lava flows) Distribution of volcanoes • Pacific Ring of Fire – subduction zones

• Hot spots • Spreading centers – spreading centers

How big are volcanic eruptions? Volcanic Explosivity Index or VEI - is based on a number of things (e.g. plume height, volume, etc.) that can be observed during an eruption.


Volcano eruption types: >Hawaiian - calmest eruption types - characterized by the effusive emission of highly fluid basalt lavas with low gas contents - steady lava fountaining and the production of thin lava flows Magma: fluid Explosive activity: very weak ejection of fluid blobs Effusive activity: then, often extensive flows Ejecta: cow-dung bombs and spatter, very little ash Structure(s): spatter cones and ramparts; very broad, flat lava cones >Strombolian - short-lived, explosive outbursts of pasty lava ejected a few tens or hundreds of meters into the air - no sustained eruption column - episodic explosions with booming blasts Magma: moderately fluid Explosive activity: weak to violent ejection of pasty fluid blebs Effusive activity: thicker, less extensive flows; flows may be absent Ejecta: spherical to fusiform bombs; cinder; small to large amounts of glassy ash Structure(s) cinder cones >Vulcanian - occur as a series of discrete, canon-like explosions that are short-lived, lasting for only minutes to a few hours, often with high-velocity ejections of bombs and blocks. Once the volcano "clears its throat," however, the subsequent eruptions can be relatively quiet and sustained. - more explosive than Strombolian eruptions with eruptive columns commonly between 5 and 10 km high. Magma: viscous Explosive activity: moderate to violent ejection of solid hot fragments of new lava Effusive activity: flows commonly absent, thick and stubby if present Ejecta: essential, glassy to lithic, blocks and ash, pumice Structure(s): ash cones, block cones, block-and-ash cones >Plinian - generate sustained eruptive columns, with some reaching heights of ~45 km. These eruptive columns produce widespread dispersals of tephra which cover large areas with an even thickness of pumice and ash. Magma: viscous Explosive activity: ejection of large volumes of ash; caldera collapse Effusive activity: ash flows, small to very luminous; may be absent Ejecta: glassy ash and pumice Structure(s): widespread pumice lapilli and ash beds; generally no cone-building


>Peleean Magma: viscous Explosive activity: like Vulcanian, commonly with glowing avalanches Effusive activity: domes and/or short, very thick flows; flows may be absent Ejecta: like Vulcanian Structure(s): Ash and pumice cones; domes >Surtseyan or Phreatomagmatic - generated by the intereaction of magma with either groundwater or surface water. - much more explosive; as the water is heated, it flashes to steam and expands explosively, thus fragmenting the magma into exceptionally fine-grained ash. *Why are there many volcanoes in the Philippines? Most Active Volcanoes in the Philippines: 1. Mayon, Albay 2. Taal, Batangas 3. Kanlaon, Negros Oriental Volcano monitoring: seismicity, remote sensing, ground deformation, geophysical measurements, hydrology, gas *Volcanic steam plumes rise from new fumaroles on the north flank of Pinatubo after steam-driven explosions on 2 April 1991; Increase in CO2 and SO2 concentrations

*Why is there an increase in the frequency of volcanic quakes prior to an eruption? As magma rises into the reservoir beneath the volcano, the rising magma and gases exert pressure that causes the rocks to break and trigger earthquakes *Volcanoes change shape before and during eruptions A series of small ground cracks appeared on the crater floor of Mount St. Helens before it erupted. About two days later, the cracks moved and "bent" the line. The crater floor was deformed or changed shape along thrust faults as magma forced its way up the conduit. Within a few days, the rising magma erupted onto the surface of the volcano's lava dome.

*Volcano deformation is measured using electronic distance measurements; The Global Positioning System (GPS) can pinpoint horizontal and vertical movement of the ground.

Precursors of an impending volcanic eruption

• Increase in the frequency of volcanic quakes with rumbling sounds; occurrence of volcanic tremors

• Increased steaming activity; change in color of steam emission from white to gray due to entrained ash

• Crater glow due to presence of magma at or near the crater


• Ground swells (or inflation), ground tilt and ground fissuring due to magma intrusion • Localized landslides, rockfalls and landslides from the summit area not attributable to

heavy rains • Noticeable increase in the extent of drying up of vegetation around the volcano's

upper slopes • Increase in the temperature of hot springs, wells (e.g. Bulusan and Kanlaon) and

crater lake (e.g. Taal) near the volcano • Noticeable variation in the chemical content of springs, crater lakes within the vicinity

of the volcano • Drying up of springs/wells around the volcano

Volcanic hazards 1. Volcanic gases – SO2, CO2 , HCl, etc. 2. Lava flow – streams of molten rock 3. Pyroclastic flow – hot, dry rock fragments 4. Lahar – mixture of water and rock fragments 5. Tephra – volcanic rock that are blasted into the air

Mount Pinatubo eruption - Magmatic explosive eruption on 12 June 1991 forms enormous eruption column of gas and ash above the volcano (Plinian eruption)

Effects • Gases – health problems • Lahars – severe flooding, destruction to lives and property • Lava flows – destruction to lives and property • Tephra – obscure sunlight, impassable roads, infrastructure damages Environmental/climate effects of volcanic eruptions: • Fine ash blocks sunlight • SO2 + H2O produces fine aerosols (fine droplets) that block sunlight • SO2 produces acid rain Benefits: • Fertile agricultural lands • Source of geothermal energy – benign source of electricity

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Geology 11- Lecture Notes 1