EOSC 210 (Lecture 1-8)

Layers of Earth

Inner core, outer core, mantle, crust

Mantle

Solid but flows

Less dense than core

Silicate minerals (Fe, Mg)

Lower & uppermost = rigid 

Mesosphere + Asthenosphere

Crust

Least dense, rigid (solid)

Silicate minerals (quartz, feldspar, Na, K)

Igenous and sedimentary rocks

Oceanic and Continental

Oceanic Crust

Thinner but denser

Continental Crust

Thicker but less dense

Lithosphere

Uppermost mantle and crust

Rigid, flows, on top of asthenosphere

Oceanic and Continental 

Continental Drift

Wegener

Less dense continents move bc Earth’s rotation

Wrong, rejected

Plate tectonic observations

Map, rocks and mountains, fossils, sea floor

Plate tectonic observations: map

Edges of continents match

continental shelves (no big rivers) match even better 

Plate tectonic observations: rocks and mountains

Seem to continue across continents

same types, ages, structures

Plate tectonic observations: fossils

same across continents

Plate tectonic observations: sea floor

Harry Hess: sonar and ocean profiles, floor isnt flat

Marie Tharp: maps sea floor, symmetrical volcanic mtn range

Plate tectonics

surf of Earth broken into rigid plates that move relative to ea other

Types of plate margins, boundaries

Divergent, convergent, transform, passive

Divergent margins

Plates spread, move apart

Continent-continent: first valley

ocean-ocean: mid ocean ridge, spreading center 

Features: under sea, little shallow earthquakes, lots of udnerwater volcanoes, symmetrical, cant curve

Convergent margins

Plates move towards ea other

Diff densities and 1 is oceanic: Subduction

Denser plates move under (eldest under)

Features: lots of earthquakes, large mtn ranges, subduction gives destructive volcanoes, no subduction no volcanoes

Transform boundaries

Plates move past ea other

Features: lost of small medium earthquakes, no volcanoes, coastlines = eldest, mid ocean ridge = youngest

Passive margins

continental lithosphere is connected to oceanic lithosphere with no movement

Features: thick layers of sediment on ocean side, very little geological activity

Driving forces, mechanisms for plate tectonics

mantle convection, slab pull, ridge pull

mantle convection

Circulating heat from the core being brought up

asthenosphere drags on lithosphere, pulling it along

slab pull

where earth subducts, increased pressureand heat causes mineralogical/chemical changes, increases densitym pulls plate down

ridge pull

mid ocean ridges are spreading centers, high heat flow, hotter material is less dense, float higher than oceanic lithosphere.

Slope causes forces away from ridge

Mineral

Naturally occuring, inorganic solid, orderly internal structure, characteristic chemica composition, crystal form, and physical properties

Mineral structure

thru bonds elements form a crystal structure

repeated 3D arrangement of atoms 

regular geometric shape, the external expression of its internal structure

ways minerals form

cooling and crystallizing from magma or lava (small vs large crystals)

precipitation from a fluid (evaporate)

chemical changes (new conds new minerals)

precipitation from biogenic activity (biomineralization)

mineral groups

based on their anions and hv similar properties

mineral group: silicates

SiO4, silica tetrahedra, olivine, feldspar

ENG: binding btwn sheets is weak, easily weather to clay, easily uptake water

mineral group: carbonates

CO3

Karst topography: distinct landscape where bedrock dissolves (caves, depressions, sinkholes), calcite

ENG: Dissolve in rainwater

mineral group: sulfides

S

primary for many important minerals 

Galena, pyrite

ENG: economic, environmenta, acid mine drainage, pH acidic

mineral group: native elements

think carbon and diamond (polymorphs)

Rock

agglomeration of minerals, attached, complicated mineral definition

types of rocks

igneous, sedimentary, metamorphic

Rock cycle

magma solidifies to igneous, igneous erodes to sediment, lithities to sedimentary rock, metamorphs into metamorphic rock (this can also happen from igneous)

Lava

extrusive, volcanic, cools quickly, glassy, non crystaline

Magma

intrusive, plutonic, slow coolingm crystaline

Extrusive

quick cooling, smaller crystals (aphanitic)

Aphanitic

fine grained crystals, cannot be distinguished without a microscope

cooled rapidly

Porphyritic

mix of fine and coarse grained crystals, visible crystals (phenocrysts) with non-visible ones

part of material cooled slowly other quickly (two stage cooling)

Phaneritic

coarse grains, visible crystals

cooled slowly, km in depth

Intrusive

slow cooling, large visible crystals

ENG: strong foundations, impermeable, resistant to weathering, BUT fractures

Felsic

light colors, silica, feldspar

Mafic

dark colors, magnesium and iron, gabbro

Bowens reaction series

describes which minerals will form from the melt, depends on temp of cooling, diff compositions can form from same magma

How to make magma…

Increase temp

descrease pressure (decompression)

add water or volatiles (lower melting temp)

Where does magma form

hot spots, divergent margins, subduction zones

Magma: Hot spots

hot material from deep in the mantle brought to surface

Magma: divergent margins

pulling apart plates reveals materials below and lowers pressure

Magma: subduction zones

water goes down in the plate, releases, mantle melts

Intrusive magma bodies

plutons, batholith, dykes, sills, laccolith

intrusive magma bodies: plutons

Mass of igneous rock that cools and crystalizes, rising magma (diapirs), cool at depth, brought to surf by plate tectonics

intrusive magma bodies: Batholith

large >100km2

igneous bodies formed by several plutons formed tgt 

intrusive magma bodies: dykes

flat intrusive bodis that cut thru layers or follow fractures, can form near surf, vertical, sometimes look like extrusive rocks (small crystals)

intrusive magma bodies: sills

flat intrusive bodiees, follow bedding and tend to be horizontal 

intrusive magma bodies: Laccolith

mushroom shaped body, magma is injected btwn layers, inflates or puffs them up

Volcano

Conical mtn, forms above source of magma

Volcano viscosity

the measure of a fluids resistance to flow

high, thick slow flow

low, runny, quick flow

Affected by: temp of magma, hotter = less viscuous. 

Composition of magma: silicate minerals = sticky, higher silica = higher viscosity

Volcano gas content

1-10%, if magma viscous gases get trapped,gasexpand near surface, pressure increases

Explosive volcano

high gas content and viscous magma

scary and hazardous

Effusive volcano

low gas content and runny magma

tame volcano with lots of lava flows

fewer hazards

mafic magma

45-55 silica (lower), high temp, low viscosity, effusive

intermediate magma

55-65 silica (int), avg temp, avg to high viscosity, explosive

felsic magma

65-75 silica (high), cool temp, high viscosity, highly explosive, gen doesnt make volcanoes and just explodes

Shield volcano

mafic, effusive, hot spots

Composite volcano

Strato, intermediate, explosive, subduction

Hazards: fluid material

lava flows: low viscosity (basalts) can flow and spread laterally, erupt at 1200-1400C, road and property damage, not dangerous to humans

gases: can erupt from volcanoes without warning, suffocate entire regions

Hazards: pyroclastic material

Ash: <2mm diameter, form due to bubble formation and magma fragmentation

Pyroclastic flows: lateral flows off a turbulent mixture of hot gases and pyro material, travel far, 500-700C

Hazard: Lahars

not alws associated w eruptions

Volcanic debris flow: mixture of water, pyro material, and debris, travel fast with little warning, follow river channels, thing glaciers melting

Extrusive igneous rocks and construction

typically less uniform than intrusive rocks, more prone to weathering and breaking down, subject to slope failure and provide weaker foundation support, fractures and potential for lava tubes problematic for tunneling or reservoir site.

metamorphic rocks

a change in form for minerals and rock caused by pressure, temp, fluids, time, NO melting 

Where: not at surf, in convergent and transform margins

country rock

original rock around a metamorphic rock

parent rock

parent material or protolith of meta rocks

Agents of metamorphism

temp, pressure, fluid activity, time

metamorphism: temp

geothermal gradient 25C/km, highest in divergent boundary, intrusions, mid ocean ridges, deeper is hotter

metamorphism: pressure

lithostatic: equal in all directions, increases w depth 

differential: directed stress, compressive or shear, result of plate tectonics

rocks confined to greater pressure are typically denser and recrystallize high density materials 

meta: Foliation

due to compressive differential stress, looks like horizontal laters.  Mineral recrystallize perpendicular to pressure. Always horizontal regardless of initial orientation

metamorphic grade

intensity of metamorphism

metamorphism: fluid activity

water and other fluids in pore spaces of rock facilitates transfer of ions within rocks and mineral, water increases rates of reactions and metamorphism

metamorphism: time

chemical rxns take time to happen, minerals 1mm growth per 1 million yrs

what changes occur in rocks during metamorphism

new minerals, less stable to more stable in new context, recrystallization, foliation, rock density increases

non-foliated

formed without pressure or of mineral that dont produce foliation

grade change w/ depth, increasing temp and pressure

slate, phyllite, schist, gneiss, migmatite

slate

product of low grade metamorphism, minerals start to align, rock breaks into sheets

phyllite

foliation can be wavy, minerals grow larger, gives a sheen on foliation

schist

micas and minerals are clear, minerals visible to the eye

gneiss

no mica since temp too high, visible big crystals w alternating layers of mafic and felsic material

migmatite

mix of both metamorphed and igneous material, rock begins to melt, creates a mixed rock w veins and patches of granite

ENG properties of meta rocks

higher grade = better for safety 

non foliated: generally stronger

foliated: tend to fail along the foliation planes

contact metamorphism

high temp, low pressure

magma moves to uppercrust, heat is added to the country rock

size of the aureole relates to type of country rock, magma temp, size

regional metamorphism

high temp, high pressure

occures over large regions of the continental crust due to increased pressure and temp, at more than 5 km

forms foliated rocks

dynamic metamorphism

low temp, high pressure

occur around fault zones

rocks grind agaisnt ea other create some friction and lost of pressure

foliated rocks

metasomatism

mostly fuild activity, magma body releases fluids and also heaats surrounding groundwater, correction occurs, circulates for thousands of yrs, altering the composition of surrounding rocks, hydrothermal alteration

weathering

refers to breakdown of rocks and mineralson surf without moving them, caused by various factors such as temp change, water, and chem rxns

erosion

removal and transportation of rocks and soil from their og locations, by agents

agents of erosion

wind, water, ice

physical and mechanical weathering

split large rocks into smaller ones by exerting forces that exceed the strength of the rock

changes the surf area to volume ratio

physical weathering: frost wedging

water inside fractures in rocks freezes, expands, and exceeds tensile strength of the rock, causing it to split

frequent freeze thaw cycles

produces large angular blocks of rock called talus 

physical weathering: salt wedging

pressure created by cristallization of salt particles in pore spaces or fractures

as water evaporates, minerals are left behind to grow and exert pressure on the surrounding rock

common in coastal areas, arid climate, and polluted air

physical weathering: pressure release, exfoliation

At depth, rocks subjected to elastic compression from the overlying rocks

removal of overburden releases forces and rock expands

results in fracture parallel to ground surf

physical weathering: root wedging

plant or tree roots grow in existing cracks, as root grows, forces cracks to expand, can cause damage to infrastructure

chemical weathering

disintegration of rock forming minerals by chem rxns w water or other atm gases