ROCKS & ROCK CYCLE ROCKS Three classification of Rocks: 1. Igneous 2. Sedimentary 3. Metamorphic IGNEOUS ROCKS - Formed when molten rocks cool down and hardens Classified by: where they formed; crystal size e.g basalt Intrusive Igneous Rock - cooling down takes place beneath Earth’s surface - e.g granite Extrusive Igneous Rock - cooling down takes place in the Earth’s’ surface - e.g pumice SEDIMENTARY ROCKS - Formed from compaction and cementation of sediments, process is Lithification. - Sediments are: rock pieces, mineral grains, and shell fragments e.g limestone can be also formed in chemical depositing of material that were once dissolve in water. when water evaporates, minerals are left and formed rocks. e.g gypsum How does sediments are formed? - rocks undergo the process of weathering and erosion METAMORPHIC ROCKS - Any rock type is changed into different kind of rocks Due to great heat and pressure e.g gneiis How does rock change? - rocks are heated, squeeze, folded or chemically changed through contact with hot fluid ROCK CYCLE - any type of rocks can change into another Igneous Rock : Rocks melting Magma Cooling and crystallization Igneous rocks … Sedimentary Rocks : Rocks weathering and erosion sediments lithification (compaction and cementation) Sedimentary Rocks … Metamorphic Rocks : Igneous and Sedimentary rocks heat and pressure metamorphic rocks … How does this relate to plate tectonics? - Plate movements drive the rock cycle Subduction : one plate pushed under another plate – re-melts rock Mountain building : folding, faulting, uplift – exposes rock at the surface to be weathered and eroded IGNEOUS ROCKS - Solidification of magma (molten hot-liquid that are formed through partial melting of the upper mantle) Magma is composed of 3 parts : melt; silicate mineral crystals; volatiles MAGMA 1. Melt – liquid component of magma composed of silicon, oxygen, along with lesser Al, K, Na, C, Fe, and Mg. 2. Silicate mineral crystals – solid component of magma. As it cools, the size and number of silicate crystals increases then resemble a crystal mush. 3. Volatiles – gaseous component of magma which is composed of water vapor, CO2, and SO2. - When magma crystallizes at depth it formed Intrusive Igneous Rocks which is also called plutons. When lava (term for magma reaching the surface) solidifies at the surface it formed Extrusive Igneous Rocks which is also called volcanic rocks. PLUTONS (Intrusive Bodies) 1. Sills – concordant plutons; flat, tabular bodies that lies parallel to the host rock 2. Dikes – discordant plutons; cut across the host rock 3. Volcanic Neck – formed in the throat of the volcano 4. Laccoliths - mushroom-shaped plutons 5. Batholiths - enormous, complex rock bodies that covers at least 100 km2 6. Stock – similar to batholiths but smaller in size TYPES OF IGNEOUS TEXTURES a. Aphanitic Texture – extrusive; fine-grained texture and minerals are not visible. Need the use of polarizing microscope b. Phaneritic texture – intrusive; coarse-grained texture; mineral crystals are large and interlocking; visible to the naked eye, uses magnifying lens c. Porphyritic texture – undergo both cooling conditions; large crystals are formed at depth and when magma arises during eruption the remaining melt solidifies at the surface forming: large crystals (phenocrysts) embedded in matrix of smaller crystals (groundmass). d. Vesicular texture – extrusive rocks that exhibit voids called vesicles because of escaping bubbles when they solidify e. Glassy texture – when magma is erupted, it quenched and cool down on the surface forming glassy texture f. Pyroclastic Texture – consolidated rock fragments form volcanic eruption. Can be composed of ashes, molten blobs and large angular blocks How magma forms? - Originate in the upper mantle Greater amount formed in divergent plate boundary, in association with sea-floor spreading Least amounts are formed in subduction zone, where oceanic lithosphere descend in mantle Magma can be generated when: there’s a decrease in pressure called decompression melting, introduction of water that decreases the melting point of the magma, and heating of crystal rocks above their melting temperature IGNEOUS SETTINGS 1. 2. 3. 4. 5. Hotpot zones due to mantle plumes Island arcs Mid Ocean Ridges in divergent zones Continental arcs in convergent zones Rift valleys due to mantle pluming FOR CIVIL ENGINEERS Granite – architectural construction, ornamental stone, monuments, statues Gabbro – crushed stone for concrete aggregate, road metal, rail road Basalt – construction aggregate SEDIMENTARY ROCKS - Constitute 7% of the crust, but covers 75% of its surface Contains the entire fossil record of the earth Retain the chronological record of the past ORIGIN - Involves weathering, mass waste, deposition, lithification, diagenesis Deposition – when transported material settle Compaction – reduction in volume Cementation – important process because it transformed sediments into sedimentary rocks. Lithification – unconsolidated sediments are transformed into solid sedimentary rocks Diagenesis – collective term for the change in physical appearance properties after being deposited, buried and subjected to < 150-200 degree Celsius (higher than this temp leads to metamorphism TYPES OF SEDIMENTARY ROCKS 1. Detrital sedimentary rock – also known as clastic. Classified in their particle sizes. Formed in the lithification of quartz, clasts, and clay. Shale and sandstone are the first and second abundant detrital rock 2. Chemical sedimentary rocks – formed in the precipitate of sediments. Also known as non-clastic. Limestone is the most abundant. Rock salt are example of evaporite. 3. Organic – coal is a unique sedimentary rock because it is made of organic matter EXAMPLES OF SEDIMENTARY ROCKS A. BED – also called as stratum (plural: strata); smallest division of stratified sedimentary rocks B. MUD CRACKS – also called as dessication cracks. Formed from the shrinkage of clay. C. RIPPLE MARKS – agitated water or wind. FOR CIVIL ENGINEERS 1. BUILDING CONSTRUCTION - Sandstone is used in construction of building (e.g. The Cliffe Castle Museum in England and Red Fort building stone in India) - Marble also used in building construction (e.g. Taj Mahal in India, Leaning tower of Pisa is Italy, The Parthenon in Greece) 2. STRUCTURAL WALL CONSTRUCTION - Limestone and sandstone. - Sandstone shall be considered carefully because it is fragile especially for load bearing structures 3. CEMENT PRODUCTION - Limestone is the main source of material for the production of Portland - Cement. Shale is used as a component in cement production. 4. CONCRETE PRODUCTION - Sedimentary rocks are used as aggregate in concrete production because it can withstand pressure. 5. PAVEMENT AND ROAD CONSTRUCTION - Sandstone and limestone - Shale is used as an aggregate Sedimentary rocks are used in highway roadbed. 6. TUNNELING - Sandstone - Shale can also be used because of its softness but proper lining shall be provided 7. BRICK AND TILE MANUFACTURING - Shale 8. ARCHITECTURAL AND MONUMENTAL STONE - Portland Stone (a white-grey limestone) - St. Paul’s Cathedral, Buckingham Palace, Westminster Palace, British museum, the bank of England 9. BUILDING INTERIOR DECORATION - Marbles 10. FACADE CONSTRUCTION - Portland construction 11. FILLER IN PAINT - Shale 12. SHEETROCK AND PLASTER - Gypsum 13. WALLBOARD - Gypsum 14. OTHERS - Construction of the earthen dam, railroad ballast, canals, and as a rockfill METAMORPHIC ROCKS - Alters the minerology, texture, structure and chemical composition of the rocks Occurs at pressure and temp prevailing at the earth surface but below melting temp Metamorphism – process in which pre-existing rocks (parent rocks) are changed by pressure, temp, and chemical condition AGENTS OF METAMORPHISM 1. Heat - most important factor. 2 main reason of heat: Geothermal Gradient and from cooling, intruding magmas 2. - Confining Pressure and Differential Stress Pressure increases with depth because thickness increases Confining Pressure – forces are acquired equally in all directions Differential Stress – deform rocks through unequal forces in diff. direction 3. Chemically Active Fluids - Hot water is released in rocks when magma solidifies and cools at depth. - Clays, micas and amphiboles are hydrated (contains water in their crystalline structure - Metasomatism – when fluid change the chemical composition of the rocks CLASSIFICATION OF METAMORPHIC ROCKS a. Foliated – Foliation refers to any planar or flat arrangement of mineral grains withing rocks. b. Non- Foliated TYPES OF METAMORPHISM 1. Regional Metamorphism – metamorphism of extensive area; associated with intensive compression and mountain building; induced during subduction and collision that produced fold mountain ranges 2. Shear Metamorphism – transformation of rocks within the shear sone which is associated with active fault movement; produce a rock type called mylonite at depths. At shallow depths, rocks are transformed into cataclasites or fault breccias 3. Contact Metamorphism – transformation caused by heat escaping an igneous intrusion. May be accompanied by metasomatism 4. Hydrothermal or Sea Floor Spreading – fractures that develop within the mid ocean ridges. specific metamorphic rocks are associated with specific tectonic environment - Regional at subduction zones Shear at faults Contact is due to rising magma Hydrothermal at the sea floor 5. Shock or Impact Metamorphism – changes in rock and minerals caused by shock waves (meteorites)
