Introduction To Plate Tectonics Evolution (Continents, Ocean Basins, Mountains and Continental Margins) Geo 386 (Arabian Shield Course) Dr. Bassam A. A. Abuamarah Mohanna G E O 3 8 6 A R A B I A N G E O L O G Y 1
PRESENTATION OBJECTIVES: What is the geological feature found in the shield, in general. Identify and determine the mechanisms initiating these e geological feature Use a geologic map diagram to construct a cross section and project map features Identify, understand, and illustrate the different geological features associated with the different plate boundaries. N.B.: this lecture is given as an introductory lecture for the Arabian Shield Course
The crust is broken!
Relative Movements of Plates a) Divergent, (b) Convergent-continent/ocean basin, (C) transform, (d) convergent-continent/continent A C D G E O 3 8 6 A R A B I A N G E O L O G Y 5
Plate Margins - Where they Happens.. Divergent Convergent Transform G E O 3 8 6 A R A B I A N G E O L O G Y 6
Divergent plate boundary
Divergent plate boundary 2 plates are moving AWAY from each other Where in the world? Can be Seen in the mid-ocean ridges and rift valleys
Seafloor Spreading at Mid-Ocean Ridges Sediment accumulation increases away from ridge - pelagic rain Depth of crust increases away from ridge Age of crust increases away from ridge G E O 3 8 6 A R A B I A N G E O L O G Y 9
How Do Divergent Margins Develop? DOMING High heat flow, thermal expansion of crust - few km high / 1000 s km across. High, dry climate RIFTING Normal faults accommodate stretch NO ocean crust Possible formation of triple junction High, dry climate: non-marine sandstones, conglomerates in basin East African Rift Zone G E O 3 8 6 A R A B I A N G E O L O G Y 10
Cont d: How Do Divergent Margins Develop? DRIFTING Crust thins and initial intrusion of basalts as new seafloor Shallow ocean; high evaporation Later normal marine sediment Drainage reverses in to the sea. Red Sea (10 Ma). G E O 3 8 6 A R A B I A N G E O L O G Y 11
Mid ocean ridge
Divergent plate boundary Features: 1) Mid ocean ridges 2) Undersea volcanoes may make islands 3) Rift valleys, on land
Types of Convergence: 1- Oceanic versus Oceanic, 2- Oceanic vs Continent, and 3- Continent vs Continent G E O 3 8 6 A R A B I A N G E O L O G Y 14
Convergent plate boundaries
Convergent Boundaries Plate Boundaries where plates are moving together.. or converging, it illustrates : High seismicity to depths of 700 km. Volcanism and/or metamorphism. Areas of continental accretion / growth. Subduction of crust / mountain building Types of boundaries: Ocean to ocean Ocean to continent, and Continent to continent G E O 3 8 6 A R A B I A N G E O L O G Y 16
Subduction Earthquakes are deeper the farther inland you go.
Subduction Accretion some of the lightest oceanic crust joins the continent or Oceanic crust.
Convergent plate boundaries 2 plates move TOWARD each other
What is happening at the plate boundary? Oceanic Plate Oceanic Plate
Which plate is subducting? What is happening to the subducted plate?
Subduction When 2 plates converge, one plate MAY move downwards UNDER the other this is called SUBDUCTION
1- Ocean to Ocean Collision 1. Two plates of same thickness (? Age/temperature). 2. Deep trench on ocean side. 3. Arcuate line of islands ~100 Km land ward from Trench - Island Arc. 4. Zone is long and narrow (1000 s Km x 200-300 Km). 5. High volcanic activity- Andesitic. 6. High seismic activity; earthquake foci 0 to 700 km deep. 7. Marianas Trench (10,860 m deep). 8. Forexample:Tonga Trench south Pacific the deepest point (10,800 m deep) G E O 3 8 6 A R A B I A N G E O L O G Y 23
Ocean-Ocean Components (features): Oceanic plate Trench Fore-arc ridge (melange) Fore-arc basin, Island arc Back-arc basin (down-going plate melts / accom. of spreading) Oceanic Plate G E O 3 8 6 A R A B I A N G E O L O G Y 24
Convergent plate boundaries
2- Ocean - Continent Collision Oceanic crust more dense than continental crust. Continental margin / Volcanic Arc.. Deep trench on ocean side; Fore arc attached to continental crust. Volcanoes - mountain range parallel to / 300-400 km from trench. High volcanic activity- Andesitic. High seismic activity; earthquake foci 0 to 700 km deep. W margin of North / South America Andes and Cascades G E O 3 8 6 A R A B I A N G E O L O G Y 26
Continent to Continent Collision Two pieces of continental crust of equal - light density. Neither subducts slab ; mountain building, continental accretion. India and Eurasia Himalayas. Africa and Europe - Alps (early Mesozoic). Africa and North America - Appalachians (Paleozoic) G E O 3 8 6 A R A B I A N G E O L O G Y 27
G E O 3 8 6 A R A B I A N G E O L O G Y 28
Components Feature Oceanic vs continental crust:: Oceanic plate Trench Fore-arc ridge (melange) Fore-arc basin Continental plate with volcanic arc mountain range (e.g. Andes) G E O 3 8 6 A R A B I A N G E O L O G Y 29
Convergent plate boundaries 1) 2) 3) Features:
Convergent plate boundaries
3-Transform plate boundary Two plates and slide past each other in a lateral horizantal movement. Forming transform faults Pacific Plate North American Plate
Transform Plates
Transform plate boundaries 1) 2) 3) Features:
Transform plate boundaries Features: 1) Major earthquakes 2) Offset linear features 3) Fracture zones, 4) No volcanoes. 5) Earthquakes
WHAT KIND OF BOUNDARY? 1 2 3 4 5
What features do they make? 1 2 3 4 5
Plate Boundary Types
Why do the plates move? 1) 2) 3)
Why do the plates move? 1) Heat 2) Differences in density.
Why do the plates move? Inner core Mantle and outer core are melted Outer core Mantle Crust
1- Heat The Earth was originally molten The heat within the Earth is initiated from then the Decay of Radioactivity elements adds some heat
2- Density D=mass/volume Less dense floats on more dense If you heat an object or fluid, it expands, the density decreases A more dense fluid will force a less dense to rise
The average density of the Earth provides evidence of the relative densities of the different layers of Earth - crust, (lithosphere) -mantle (asthenosphere) and -core. The whole Earth is more dense than the rocks we see
Density Mantle is more dense than crust Oceanic crust is more dense than continental crust
Why do the plates move?
Why do the plates move? Convection happens!
ALL TOGETHER-- Convection happens!
Convection happens! The accepted mechanism for plate motion is: convection in the asthenosphere.
This plate is pulled this way Convection happens!
Convection happens! and this plate is pulled this way.
Wegener s Evidence Wegener supported his hypothesis of continental drift with evidence from: 1. the puzzle fit of the continents, 2. rock units, 3. geologic structures, 4. fossils and glacial evidence.
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. C. D. a. b. c. Seafloor crust shows the direction of the magnetic field when the crust was formed
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. D. a. b. c. Seafloor crust is older farther from the mid-ocean ridge
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. ocean floor topography D. a. b. c. You can see the ridge and the suture zone around it
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. ocean floor topography D. Wegener's evidence. a. b. c. Wegener had none of the above. He had to do it the hard way
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. ocean floor topography D. Wegener's evidence. a. fossils b. c. Tropical fossils show up in polar regions
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. ocean floor topography D. Wegener's evidence. a. fossils, b. jigsaw continents, c. They fit together pretty well
Evidence The modern theory of plate tectonics is supported by evidence from: A. paleomagnetism, B. age of ocean floor sediments C. ocean floor topography D. Wegener's evidence. a. fossils, b. jigsaw continents, c. rock types Similar rocks show up on different continents