Driving Force Behind Plate Tectonics

Criticismcan be fired at all the theories expounded to explain the mechanism ofplatetectonics. Therefore, it is best to choose the theory, which containsonlyminor holes and explains the mechanism in a simple, clear and distinctway.

California K-6 Standards for Plate Tectonics -

mid-Cenozoic era, 45 million years ago
Volcanoes and Other Geosystems
volcanic gas: mainly water vapor; carbon dioxide, sulfur dioxide; traces of nitrogen, hydrogen, carbon monoxide, sulfur, chlorine

can come from deep within core, trapped in earlier rocks, or be recycled ground/ocean water, atmospheric gases

gases can affect climate, ocean/atmosphere creation, and extinction
Volcanism and the Hydrosphere
hydrothermal activity: circulation of water through hot volcanic rocks/magmas--especially intense in spreading centers @ mid-ocean ridges

fumaroles: small vents that continuously emit steam/other gases

geysers: hot-water fountain; spouts intermittently/forcefully

effects: transport of internal heat; seawater chemistry; ore formation


Volcanism and the Atmosphere
volcanism in lithosphere changes composition/properties of atmosphere--affects climate/weather change

sulfurous gases released in eruptions--form aerosols that block sun's radiation--can cause temperature drops
Global Pattern of Volcanism
active volcanoes: 80% at convergent plate boundaries; 15% at divergent plate boundaries; remaining within plate interiors


Mantle Plume Hypothesis
Mantle Plume Hypothesis: intraplate volcanism explanation; mantle plumes (volcanic manifestations of hot/solid material rising from mantle; hotspots)--upward transportation of peridotites through mantle plume, magma produced, penetrates lithosphere and erupts at surface


Hotspot Tracks/Large Igneous Provinces
Hot-spot tracks: worldwide distribution of hotspot volcanic tracks--used to reconstruct absolute plate movements/compute progression of current plate movements

Large Igneous Provinces: large oceanic plateaus caused by flood basalts; hard to explain with mantle plume hypothesis
Volcanic Hazards
eruption clouds: clouds of ash lofted into air traffic lanes by erupting volcanoes

lahars: torrential flows of wet volcanic debris

flank collapse: structural failure resulting in breakage of major part of volcano

caldera collapse: extremely destructive; none in recorded history
Predicting/Controlling Eruptions
Predicting: eruptions can be predicted in many cases; warning signals: earthquakes, swelling, and gas emissions

Controlling: not likely that eruptions can be controlled
Volcanoes form at convergent and divergent plate boundaries
Extrusive rocks form from volcanic eruptions
They are made of
Mineralogy of the source magma influences the type of eruption
Deposition (Sedimentation) occurs when particles settle out or dissolved minerals precipitate.
Continental Environments
Types of Depositional
Environments

Shoreline
Environments
Marine
Environments
A depositional (sedimentary) environment is an area of sediment deposition characterized by a particular combination of climate conditions and physical, chemical, and biological processes.
Usually classified by water depth
determines type of current present
Also classified by distance from land
Dominated by dynamics of waves, tides, and river currents on sandy shores
Sediments are usually siliciclastic
Some (CaCO3) are bioclastic
Diverse due to the wide variety of temperature and rainfall over land masses
Environments build around lakes, rivers, deserts, and glaciers
Alluvial Environments
Desert Environments
Glacial Environments
Lake Environments
Deltas
Tidal Flats
Beaches
Continental Shelf Environments
Organic Reefs
Continental Margin/Slope Environments
Deep-sea Environments
Transport agent: lake currents, waves
Sediments: sand and mud, saline precipitates (when arid)
Climate: arid to humid
Biological processes: freshwater organisms and precipitates
Characteristics of Depositional Environments
Transport agent and medium
Sediments
Climate
Biological Processes
Transport agent: river currents
Sediments: sand, mud, and gravel
Climate: arid to humid
Biological processes: organic matter in muddy flood deposits and wetlands
Transport agent: wind
Sediments: sand and dust
Climate: arid
Biological processes: little biological activity
Transport agent: ice, meltwater
Sediments: sand, mud, and gravel
Climate: cold
Biological processes: little biological activity
Transport agent: river currents, waves
Sediments: sand and mud
Climate: arid to humid
Biological processes: burial of plant debris
Transport agent: tidal currents
Sediments: sand and mud
Climate: arid to humid
Biological processes: organisms mix sediments
Transport agent: waves, tidal currents
Sediments: sand and gravel
Climate: arid to humid
Biological processes: little biological activity
Transport agent: waves and tides
Sediments: sand and mud
Biological processes: deposition of remains of organisms
Transport agent: waves and tides
Sediments: calcified organisms
Biological processes: secretion of carbonates by corals and other organisms
Transport agent: ocean currents and waves
Sediments: mud and sand
Biological processes: deposition of remains of organisms
Transport agent: ocean currents and turbidity currents
Sediments: mud and sand
Biological processes: deposition of remains of organisms
Sedimentary Rocks
Weathering of Sedimentary Rocks
Physical Weathering-
Fragmented by mechanical processes like freezing or wedging by tree roots
Chemical Weathering-
Rocks are chemically altered or dissolved
Categories of Sedimentary Rocks
Clastic Sediments- Produced mainly through the weathering of common rocks.


New evidence from paleomagnetism that led to plate tectonics -

Hypothesis of plate tectonics is proposed -

PlateTectonics is one of the most important geophysical/structural geologysubjectstoday. To determine the cause of the movement of the plates is the moststudiedproblem. The first evidence for plate movement was, of course, found byWegenerin 1925. This was a result of a comparison of the continental edges ofSouthAmerica and South Africa. It was not until the 1950s, however, thatCarey(1954) found the remarkably good fit between the continents using amodeledglobe. Wegener's evidence was primarily geological andpaleo-climatological.