Rock Basics: Background to Understand Earth’s Landscapes

The Wave –Western Australia

The Wave – Utah

Composition of the Continental Crust

• O- Oxygen 47%• Si- Silicon 28%

These together = 75% of continental crust • Al- Aluminum 8.1%• Fe- Iron 5.0%

• Ca- Calcium 3.6% - nutrient• Na- Sodium 2.8% - nutrient• K - Potassium 2.6% - nutrient• Mg- Magnesium 2.1% - nutrient

Examples

Silicates: have Si as base, Quartz (Si02)obvious 75%

Feldspars: have Si and Al, and when add (Ca, K, Na) = Feldspars

Clay minerals stick to your boot and have layered structures

Colorado & Minerals

Basic Rock TypesIGNEOUS SEDIMENTARY METAMORPHIC

Igneous (made by “fire”) - Solidified from molten rock (i.e., magma).

Sedimentary - Deposited (strata) and buried close to Earth’s surface.

Metamorphic (“changed form”) - Transformed from preexisting rocks under high pressure, temperature & fluids.

Rock TypesSedimentary

rocks are most abundant near Earth’s surface- poor preservation

Igneous and Metamorphic rocks make up most of the crustal volume

- limited exposure!

Sediments make up only 5% by

volume

Sediments make up

75% surface area

Entire classes on rock minerals…but for us…

• Minerals crystallize from melt, derived from deep within Earth’s crust or mantle

– High temperatures, 700° C & more

– Crystal size depends on cooling rate• Small = rapid; large = slow (millions of years)

• Intrusive rocks cool slowly within deep magma chambers:

– Coarse, interlocking crystals

• Extrusive rocks cool rapidly at (or near) the surface of the earth:

– Fine-grained, often “glassy”

Details on Igneous Rocks

Igneous Rocks

Common in volcanic areas & plate boundaries

Basalt

• Loose particles (sand, silt, marine shells) accumulate on shorelines, basins, rivers, etc.,

–Clastic Sediments (clast = “little”)

• Minerals precipitate from dissolved chemicals in water

–Chemical & Biochemical Sediments

• All are the products of Weathering—the breaking apart & decaying processes, and Erosion—the transportation processes from source to point of deposition

Details on Sedimentary Rocks (strata)

Lithification

Shale

Sandstone

Conglomerate

Breccia

Large to Small

• High temperatures and pressures at depth cause changes in mineralogy, texture, and composition (very complex…lots of ways to squish rocks)

– Changes take place in Solid State by recrystallization and chemical reactions

– Temperatures greater than 250° C, less than 700° C

• Regional Metamorphism - High pressures and temperatures derive from regional collision, deformation and mountain building (tectonics)

• Contact Metamorphism - Locally high temperatures, adjacent to intrusions

– Igneous body touching & “cooking” surrounding area

Details on Metamorphic Rocks

Mafic & felsic minerals align…

Metamorphic Rocks

Common at convergent

plate boundaries

Notice alignment of minerals = foliation

Metamorphic Rocks Fig 4.6

• Foliations - Planar fabric defined by

– Alignment of platy minerals (micas & clays)

– Alternating bands of mineral types

• Indicative of high pressures and deformation during formation

– Pressure-Temperature-time paths

• Not Foliated

• Distinct low- pressure minerals

Typical Rock Types Seen by Geologic Origin

Grain

Aspects

Clastic Solution (carbonate)

Foliated Non-Foliated

Intrusive Extrusive

Coarse Conglomerate

Breccia

Limestone & Dolomite

Gneiss Marble Granite

Gabbro

Diorite

Medium Sandstone

Siltsone

Limestone

& Dolomite

Schist

Phyllite

Quartzite

Fine Shale

(Mudstone)

Calcareous Mudstone

and Chert

Slate Amphibolite Basalt

Rhyolite

Obsidian

Sedimentary Types

Metamorphic Igneous Types

The Rock Cycle

-Melting & Intrusion-Solidification of melt-Mountain Building-Uplift & Exposure-Weathering-Erosion-Deposition & Burial-Metamorphism-Melting & Intrusion

Large blocks of time represented by changes in evolution

Geologic Time

Animation about Geologic Time

Geologic Time as Football Field: click here to see the animation

Plate Tectonics

Rearranging Earth’s Surface

Alfred Wegener and how a scientific paradigm operates

“Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence...It is only by combing the information furnished by all the earth sciences that we can hope to determine ‘truth’ here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw.Alfred Wegener. The Origins of Continents and Oceans (4th edition)

Field work: Atlantic once closed

Shape MatchRocks MatchFossils Match

Lifetime of work

Theory of Continental Drift

Meteorologist proposesto change geology

1st edition 1915

Until 1960s – Utter Rejection by Geologists

Dr. Rollin T. Chamberlin of the University of Chicago said, “Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories.”

“Utter, damned rot!”W.B. Scott, President of the American Philosophical Society

American Association of Petroleum Geologists organized a symposium specifically in opposition to the continental drift hypothesis.

Today: We Map Tectonic Plates

See animation

Today: We accept that most Earthquakes and Volcanoes occur along boundaries of

Tectonic PlatesSee animation

Today: We Accept Plate Movement

Today: We Accept Pangaeaand its breakup

Why the Opposition & Shift?

• Opposition:– An example of how a discipline can get “locked into” a

pathway of mental thinking for decades (paradigm)– An example of how a discipline protects its “turf” –

rejecting the thoughts of a meteorologist• Shift:

– Enough time for the opponents to die, and a bunch of new geologists in the 1960s to challenge “the establishment”

– Reminder throughout this class that ideas shift and much depends on the mental framework of the scientist

Structure of Earth allows continents to move

Wegener could not answer a fundamental question of HOW continents could move.

But geology advanced to the point to begin to understand Earth’s internal structure & how it allows continental drift...

Earth’s Structure

Brittle Crust Floats on Flowing, Plastic-like Asthenosphere

Different Crusts: 5/6th submerged(isostatic balance)

Ocean Crust Continental CrustMore Dense (sima) Less Dense (sial)

Isostacy crust adjusts to create a balance

(equilibrium)

Peep the ani...

Two continental plates under Tibet

To reach isostatic balance, Tibet Plateaurises

Too thick, so get uplift

Reason for Movement(we think…)

Excess heat from radioactive decay creates liquid outer core (and magnetic field), and forces mantle to have convection

TYPES OF PLATE INTERACTION

Stream Systems onDynamic Earth

Type of Plate Interactions:Divergent Boundaries

Mid-oceanridges areplaces of

plate divergence

Mid-Atlantic Ridge is the Icon

EastPacific

Rise

MidAtlantic

Ridge

Mid Indian

Ridge

Sea Floor Spreading:Key to Rejecting the Old Ways

• “Plate Tectonics” = continental drift + sea-floor spreading

• Rename the theory with new evidence:1. Potassium-Argon dating2. Paleomagnetism

Age of the Ocean Crust

Animation showing ages of ocean crust getting older away from spreading

Always New Details Being Added

Submarine Volcano erupting!

Paleomagnetism

Animations – Click on the PicturesVisualizing reversals of magnetic field and how this creates a mirror image on the two sides of a spreading center

Lava has minerals that “record” the magnetic field

Paleomagnetism in Symmetry

Conclusionwas thatsea floorsspreadingapart

Don’t Worry!

Hollywood movie “The Core” – silly

It will take thousands of years to shift that extreme

Source for Latest Info:

Website

Obvious question:With making new sea floor, why isn’t

Earth expanding?

Old ocean plates undergo “subduction”

Type of Plate Interactions:Convergent Boundaries

Oceanic-Continental Convergence

Denser Oceanic Crust SubductsTrench Forms

Volcanoes FormLithosphere Subducts Into AsthenosphereEarthquakes Common All Along Boundary

Andes

Nazca plate collide with South American Plate

Cartoon

Latest Research from Nature

Ocean – ContinentConvergencein PacificNorthwest

Oc-Co Convergence...

Island Arcs from Ocean – Ocean Convergence

Oc-Oc Converg ani...

Continent – Continent Collision

Example of Himalaya

Himalaya Formation

Formation of Appalachian Mountains resulted from the collision of the African and European Plates with North American Plate prior to 300 million years ago.

Ural Mountains

Formation of the Ural Mountains related to collision tectonics prior to 300 Ma ago.

Convergence & Tsunami

Effects Of Plate Locking

EQ (or landslide or volcanic eruption) Movement Generates the Wave that travels about 500

mph

AnimationsShows how Tsunami can be made from subduction

Shows time sequence in Tsunami destroying coastal city in Alaska

Mega-Quake set off 2004

Tsunami & will happen again

Energy ripple

Sumatra UpliftSri Lanka

Type of Plate Interactions:Transform Boundaries

Side-by-side motionalong San Andreas zone

Transform motion of the San Andreas Fault can be seen by offset of streams that cross the fault zone.

California Won’t Fall into the Ocean

Continent is 5/6ths submerged, so it is anchored very tight

Other Transform Boundaries

Hot Spots

Often in the middle of a plate

Focus here on Hawaii & Yellowstone

Hawaiian Hotspot

Animation of Hawaii as moves over Hot Spot

Trail of the Hot Spot

Note change in direction 43 myr agoChange in direction 43 myr ago

Alternative Hypothesis

Yellowstone Hot Spot