•Litoshpere..Crust & Rigid upper mantle

•Astenosphere – weak and capable of flow

•Oceanic and Continental crust

•Oceanic – 6-12 km thick, dense heavy, basalt, SIMA

•Continental – 40-60km thick, less dense, granite, SIAL

• Made up of 7 major and several minor plates each with indep. movt.

Cause of Movt… Thermal convection currents hot material rises, cools & sinks. The lateral movt. drags the plates.Continental plate…lighter Oceanic plate….. heavier

Continental Drift.. Wegener 1912.. Pangaea.. One super continent. 225 million yrs ago200m yrs ago split…. Laurasia.. Europe, Nth America & Asia.Gondwanaland.. Sth. Am, Africa, India, Australia, Antartica.

1963 (Harry Hess) Theory accepted… discovered Mid Atlantic Ridge which was proof of ocean floor spreading.

Proof: Continental Fit .. Like a jigsaw,

Matching fossils;

matching rocks (structure & type) Mt. ranges…Appalachion Mts of U.S. & Caledonian of Irl & Br. both fold mts.Matching glacial deposits in S. America, Africa and Australia

Sea floor spreading and Age of ocean floor: oil drilling shows edge of ocean rock 200m yrs older than the Mid Atlantic ridge.

Satellite measurements show Sth Am. & Africa moving 2.5cm apart each year.

Continental drift.swf

Plate Boundaries: Constructive

A) Diverge.. Move apart causes cracks fills with magma.

Result: (i) New ocean floor…

(ii) Mt. range/ridge e.g. Mid Atlantic Ridge … cont. move apart.

(iii) Islands form…. e.g. Iceland.

East African Rift Valley

6000km long

2 new African plates – Nubian Plates & Somali Plates

Red Sea is a part of the Rift Valley

Western and eastern Rift Valley

Contains some of the deepest lakes in the world

Lake Tanganyika – 1,470 metres deep

Lake Victoria – 2nd largest lake in the world

Eastern Africa- divergent platesEurasian & African plates collided 25m yrs ago -- fractures.Magma plumes warped the surface upwards, making it brittle. It fractured and moved apart.This gave rise to 3 active rift zones

Gulf of EdenEast African RiftRed Sea

The Arabian Peninsula split off from Africa & opened up the Red sea and the Gulf of Eden.East Africa in 50m yrs will detach itself and form a new continent & sea.

DestructiveDestructive

B) Converge.. B) Converge.. Meet one plate sinks = subduction zone…. Meet one plate sinks = subduction zone…. Crust destroyed.Crust destroyed.

1.1. Oceanic & OceanicOceanic & Oceanic … older heavier plate descends under lighter … older heavier plate descends under lighter plate plate

(i) Narrow trench e.g Mariana Trench where Pacific & Phillipi(i) Narrow trench e.g Mariana Trench where Pacific & Phillipinnnes nes plates meet.plates meet.

(ii) Volcano … Crust melts & produces magma.(ii) Volcano … Crust melts & produces magma. (iii) Island arcs…hotspots as magma melts the crust…plates move (iii) Island arcs…hotspots as magma melts the crust…plates move

eg. Japan.eg. Japan. (iv) Earthquakes… caused by collision stress(iv) Earthquakes… caused by collision stress

2. Oceanic & Continental… collide oceanic sinksResult trench, volcano, earthquake, E.g. Andes Mts. (Sth. Am.)

3. Continental & Continental….. Collide buckle & fracture.

Result Mts. & earthquakes e.g. Himalayan mts. Where Indian and Eurasian plates met…. Contain sea fossils… proof that they were once in the sea.

Passive

Plates slide past each other (sheer) -- (i) transform fault… San Andreas Fault… Pacific & American plates.

(ii) Earthquakes

ConstructiveConstructive Rising current of magma splits continentRising current of magma splits continent

Move apart – water rushes in – oceanMove apart – water rushes in – ocean

Mid-ocean ridge above plume of magmaMid-ocean ridge above plume of magma

Volcanoes along ridgeVolcanoes along ridge

Some islands e.g. Iceland might appearSome islands e.g. Iceland might appear

DestructiveDestructive Ocean-ocean – subducted plate melts Ocean-ocean – subducted plate melts

and rising magma creates line of and rising magma creates line of volcanoes called island arcvolcanoes called island arc

Ocean-continent – heavier ocean Ocean-continent – heavier ocean plate sinks, buckles and folds, plate sinks, buckles and folds, islands, extinxt volcanoes pushed islands, extinxt volcanoes pushed against continent edge making it against continent edge making it widerwider

Sinking magma creates volcanoesSinking magma creates volcanoes

Continent- continent- Large Fold MtsContinent- continent- Large Fold Mts

Passive- Mostly along mid ocean Passive- Mostly along mid ocean ridgesridges

Sometimes on dry land – San Sometimes on dry land – San Andreas faultAndreas fault

EarthquakesEarthquakes

Irelands past shows evidence of desert & tropical climates.Geology: Croagh Patrick, MayoQuartzite… Sugarloaf, Wicklow formed at opposite ends of an ocean.

Limestone…. Central plain - formed at bed of tropical ocean.

Fold Mts. Nth west they run sw/neMunster they run e/w

Why? Different rock types. Plates have drifted from 30˚ south of equator to 54˚ north ... Drifted 9,000 miles in 500 million years.

Million Years ago 400 Nth & sth Irl join(20˚ sth) …. Causing folding and

faulting. 380 Move Nth… desert area… only nth. section above

sea level Erosion & deposition in sth. - old red sandstone,

Munster350 Rise in sea level- Irl. submerged in tropical seas. Result in limestone of the Burren.250 European & African plates collide - Fold mts. Of

Munster.251 Erosion & marine sediments form into oil & gas.100 Uplift… land rises above sea level-- more limestone

& chalk65 Volcanic bursts & rifting-- detach from America &

form Atlantic ocean & Antrim Plateau.