The Rock Cycle, Isostasy, and the Dynamics of the Lithosphere · The Rock Cycle, Isostasy, and the...
Transcript of The Rock Cycle, Isostasy, and the Dynamics of the Lithosphere · The Rock Cycle, Isostasy, and the...
The Rock Cycle, Isostasy, and the Dynamics of the Lithosphere
Siccar Point, Scotland
Rock - aggregates of mineralsRock cycle - movement and transformations of rock in the lithosphere
What is the ultimate origin of rock in the lithosphere?Molten magma from the
Earth’s mantle.
Basic geology on Mars would be easy to learn - almost all of the rocks are basalt. Mars has volcanism.
Mars does not have:• Plate Tectonics• Oceans• Water-rich atmosphere
The Rock Cycle
Igneousrock
Cooled frommolten rock
Magma / Lava
Igneous Rocks
(from the L. ingnis – fire)
• rocks that have crystallized (solidified) directly from a molten state.
•Molten rock - magma / lava•Composed of randomly interlocked crystals of silicate minerals.
Physical Geology - Rock Cycle and Isostasy
Dry mantle(basalt, gabbro)
Wet mantle(andesite)
Continental crust(rhyolite, granite)
Plate Tectonic Setting
The Rock Cycle
Igneousrock
Cooled frommolten rock
Magma / Lava
uplift and weathering
GravelSandMudDissolved ions
Physical Geology - Rock Cycle and Isostasy
Weathering / Erosion • the physical and chemical breakdown
of rock.• occurs at the Earth’s surface.
Physical Geology - Weathering
Weathering does several very important things:
• Breaks down rock to make sediments.
• Forms soils.• Forms economic mineral
deposits.• Removes CO2 from the
Earth’s atmosphere.
Physical Geology - Weathering
Mechanical Weathering physical disintegration of rock
• jointing• sheeting• wedging
Physical Geology - Weathering
Vertical jointing - tectonic stress + gravity
Lysefiord, Norway
Passed geology 1CFailed geology 1C
Physical Geology - Rock Cycle and Isostasy
Sheeting of Granite bedrock
Enchanted Rock, Texas
Physical Geology - Weathering
Ice and Frost Wedging
• caused by freeze - thaw cycles.• water expands when it freezes.• ice has 9% more volume than liquid
water.
Physical Geology - Weathering
Chemical WeatheringThe chemical reaction of minerals with air and water.
• hydrolysis (acid attack)• oxidation• dissolution (leaching)
CO2 + H2O = H+ + HCO3
-
H+ + feldspar = Ca++ clay + silica
Chemical Weathering
HCO3-, Ca+, silica
to the ocean
Physical Geology - Weathering
Minerals prone to chemical
weathering• feldspars• pyroxenes• amphiboles• micas
• quartz • clay minerals (e.g.
kaolinite)• iron oxides (e.g.
hematite)• carbonate (calcite)
Stable mineral products of chemical
weathering
Common in Igneous Rocks Common in Sedimentary Rocks
Sedimentary Rocks (from the L. sedimentum– to settle)
•Grains produced by the weathering of other rock.
•Layers form at the Earth’s surface.•Layers preserve fossils and other information about past environments.
• Composed of layers of mineral grains.
Alluvial fan depositional environment, Death Valley, California
River System depositional environment, New Zealand
Fossils are organic remains buried in sediments and preserved in sedimentary rock.
These Cape Buffalo carcasses are on their way to becomming fossils.
Ankylosaur skeleton being excavated from sandstone, Mongolia.
Ankylosaur skeleton being excavated from sandstone, Mongolia.
Coal - carbon derived from plant matter
Tar, oil, natural gas - hydrocarbon from marine algae
Fossil Fuels are found in Sedimentary Rock
Plants Peat CoalLignite
coal
Fossil Fuels
oil
Igneousrock
Cooled frommolten rock
The Rock Cycle
Magma / Lava
SedimentaryRock
Deposited inlayers on thesurface.
Uplift and
Erosion
Redeposition
burial and subsidence
uplift and erosion
Metamorphic Rocks (from the G. meta– to change, and morphos– form, shape)
• Changes texture and mineral composition.
• Usually happens when rock is buried beneath mountain ranges during plate collisions.
• Rocks altered by heat and pressure.
Physical Geology - Rock Cycle and Isostasy
Sedimentary Rock
Low Grade Metamorphic Rock
High Grade Metamorphic Rock
Migmatite
Magma
200° C 3000 ATM
600° C
Slate Phyllite Schist
Low Grade High Grade
Progressive Metamorphism
Igneousrock
Cooled frommolten rock
The Rock Cycle
Magma / Lava
Uplift and Erosion
SedimentaryRock
Deposited inlayers on thesurface.
Uplift and
Erosion
Redeposition
burial and subsidence
MetamorphicRock
Changed by heat and pressure.
melting
uplift and erosion
Burial and subsidence
Uplift - the movement of the crust upward.
Subsidence - the movement of the crust downward.
The crust can move because it is floating on the asthenosphere.
changes in density of the crust.changes in thickness of the crust.
What causes the lithosphere to float higher or lower on the underlying asthenosphere?
What changes the density of rock?
•Heating - rock expands, becomes less dense.
•Cooling - rock contracts, becomes more dense.
•Changes in density cause the lithosphere to float higher or lower on the asthenosphere.
What changes the thickness of the crust?
•Plate collisions• Shortening and thickening of the
crust in the collision zone.• Thrusting of one plate on top of
another.•Erosion
• Thinning of the crust exposed above sea level.
Physical Geology - Rock Cycle and Isostasy
Isostasy - equilibrium position of lithosphere “floating” on asthenosphere.
oceanic lithosphereoceanic lithospherecontinental lithosphere
Asthenosphere
Isostacy
oceanic lithosphereoceanic lithospherecontinental lithosphere
Asthenosphere
Rock at earth’s surface.
IsostacyCrust is “loaded” with rock, increasing its thickness.
Surface rock is buried.
Loaded crust subsides.
Loaded crust subsides.
New isostatic equilibrium is achieved.
Surface rock is now deep in the Earth’s interior.
Surface topography erodes.
Crust rebounds to new isostatic equilibrium.
Rebound
Once deeply buried rock has been uplifted back to the surface
Igneousrock
Cooled frommolten rock
The Rock Cycle
Magma / Lava
Uplift and Erosion
SedimentaryRock
Deposited inlayers on thesurface.
Uplift and
Erosion
Redeposition
burial and subsidence
MetamorphicRock
Changed by heat and pressure.
melting
uplift and erosion
Burial and subsidence