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
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.
Continents2.
Ocean basinsProminent Features of Continents
1.
Mountains – elevated features of continents2.
Mountain ranges – chains of mountains3.
Mountain belts – mountain ranges that run across a vast areaOCEAN BASINS - Oceanic ridges, Trenches, Seamounts/guyots, Abyssal hills/plains Internal Structure of the Earth
>Crust
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 crust2.
Mesosphere – lower mantle; from 660 km depth to the core-mantle boundary > Core – iron rich sphere with small amounts of Ni and other elements1.
Outer core – 2270 km thick; liquid2.
Inner core – solid sphere with a radius of 1216 km*Discontinuities/Boundaries
1.
Mohorovicic – crust – mantle2.
Gutenberg – core – mantle3.
Lehmann – outer core – inner coreQuestion: 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”.
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 Cenozoic5.
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 - MINERALSDEFINITION: 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. CaF23.
Reaction to chemicals – ex. CaCO34.
Taste – ex. NaCl5.
Odor – ex. SCLASSIFICATION OF MINERALS
1.
Silicates2.
Non-silicatesBases 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, iron2.
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 metal6.
Phosphates – PO4 (e.g. apatite) plus metal7.
Hydroxides – OH plus metalTHE 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.
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
• 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 densityb.
Low viscosityc.
Relatively low silica contentd.
Crystallize at high temperatures (~1000 - 1200ºC) Granitic magmaa.
Low densityb.
High viscosityc.
Relatively high silica contentd.
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
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
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
