Continental Drift, Mountain Building, and Plate Tectonics
Continental Drift-Wegener and Du Toit
Evidence in the early 1900s: fit of continents, Glossopteris plant fossils, glacial deposits,
Mesosaurs and Lystrosaurs.
Two large continental masses: Laurasia and Gondwanaland-together formed Pangea
Paleomagnetism:
Spinning liquid metal core causes electromagnetic field
Magnetic minerals (mainly magnetite) is magnetized and aligned with earth’s mag. Field
below the CURIE POINT.
These fossil magnets reflect changes in the magnetic field through time.
INCLINATION is the angle the magnetic makes with the earth’s surface = latitiude
DECLINATION is the angle between the magnetic and geographic north pole
Sea floor spreading shows a pattern of increasing age of the seafloor and the magnetic reversals
that have occurred in the past 180 million years
Faulting and volcanism along plate boundaries:
Normal fault
Reverse Fault
Thrust Fault
Subduction zones occur where more dense oceanic crust is forced down beneath oceanic or
continental crust
Accretionary Wedges, Forearc basins and the accompanying MELANGE sediments are
characteristic of subduction zones. Deep focus earthquakes also occur
Plates move for 4 reasons:
Convection in the mantle
Magmas pushes the lithosphere upward causing spreading
Cold/dense crust sinks and pulls the slabs down
Slab break and pull (similar to #3)
Rate of subduction/age of crust determines the subduction angle = location of earthquakes and
volcanoes
Plate motion measured by hotspot motion
Continental Rifting and Triple Junctions
Failed rift = aulocogen-often a significant sedimentary basin
Continental Margin Types: PASSIVE MARGINS (cont. margin not plate boundary), ACTIVE
MARGINS (cont. margin = plate boundary)
Folding as plates collide: anticlines and synclines
Mountain building = orogenesis (events often called OROGENIES)
Parts of the continents: Cratons (stable interior) and Mobile belts
Continental Collision can preserve an OPHIOLITE (sequence of ocean lithosphere and assoc.
seds.)
Sequence of Ophiolite
Deep sea fine grained silica or calcareous sediment
Pillow basalts
Dike injected basalt
Gabbro
Peridotite
Mountain Belts often have Paired Metamorphic belts, and Fold and Thrust belts associated with
their uplift and collision
FORELAND BASIN forms inland of the mountain belt as a result of the weight of the thrust
sheets
Sediment shed from mountain belt has a characteristic succession: deeper water turbidites
followed by shallow water and then terrestrial sediment-FLYSCH and MOLASSE
Continental Interiors Warp in response to major mountain building
Domes and Basins: (Himalaya example for Asia, Appalachian example for N. America)