Geology: Sedimentary, Metamorphic, and Plate Tectonics Fundamentals

sedimentary rock

sedimentary- unsolicited grains from erosion & transport

sediment rx- deposited, compacted, cemented sediment

lithification=compaction+cementation

sedimentary processes

porosity- % of open space btw. grains

permeability- connectivity of pore spaces

clastic processes- uplift->transport->deposition->compaction->lithification

clastic classification

shale-clay sized

siltstone- silt sized

sandstone- sand sized

conglomerate- gravel sized

maturity

texture- more rounded, smaller grains=more mature

composition- near source=mixed minerals, far from source=quartz rich (stable)

chemical and biogenic rocks

chemical: direct precipitation from water (salts)

biogenic: formed by organisms (limestone)

depositional environments

setting where sediments accumulate, each produces unique textures

(rivers, deltas, beaches, deep sea)

metamorphic rocks

forms: pre-existing rx under increased P/T

causes: mechanical deformation+new minerals form

metamorphic grade

low grade: shale->slate->phyllite; sandstone->quartzite

medium grade: schist (string foliation, new minerals muscovite, tourmaline

high grade: gneiss (mineral segregation into bands, just below melting)

types of metamorphism

contact: high T only, near igneous intrusions, localized

regional: high P&T over larger areas (mnt building)

rock cycle: rx can transform btw. igneous, sed, meta

Wegener's continental drift

fit of continents, fossils distribution, paleoclimate evidence

initially rejected-no mechanism for movement

modern evidence of continental drift

-seafloor topography: mid-ocean ridges, trenches

-seafloor spreading (Hess): new crust at ridges, destroyed at trenches (subduction)

-age of seafloor: youngest ridges, oldest near continents

-paleomagnetism: magnetic reversals recorded in basalt

-driving forces: mantle convection+ridge push+slab pull

divergent plate boundaries

(<- ->)

-mid-ocean ridges, rifting

-voluminous basalt volcanism, minimal earthquakes

transform

(<-->)

-plates slide past

-shallow, frequent earthquakes

-no volcanism

convergent

(-> <-)

-oceanic-continental: subduction, volcanic arcs (Andes, Cascades)

-oceanic-oceanic: volcanic island arcs (Japan, Aleutians)

-contential-contential: mountain building, large quakes, no volcanism

mantle hotspots

stationary heat sources (Hawaii, Yellowstone)

earthquake hazards

ground motion: shaking, surface waves

-avoid faults, building codes,

ground failure:

-landslides (slope failure)

-Liquefaction (water-saturated sediments lose strength)

tsunamis: caused by seafloor uplift, travel across ocean basins at high speed, small offshore huge near coast

prediction attempts

-seismic gap (quiet zones=future quakes likely)

-precursors: uplift/tilt, well water, animal behavior

-periodicity: repeating intervals

hazards areas in U.S

-west coast (San Andreas-transform)

-Alaska (subduction)

earthquake waves

p-waves: (compressional, fastest, travel thru solids+liquids)

s-waves (shear, slower, solids only)

surface waves: (slowest, most destructive)

seismic shadow zones

P-waves shadow zone: mantle-core boundary

S-wave shadow zone: liquid outer core

interior structure confirmation: solid inner core, liquid outer core, mantle above