Tectonics Notes Topic 1-3

🪨 Tectonics Topic 1.1 Plate Tectonics - Plate Tectonic Theory Tectonic Plate Movement Convection currents Mantle gains heat from core > Less dense Rises towards surface Rising mantle spread beneath the plates > Drag them apart Divergent plate movement) Mantle loses heat and sinks down to core Convection currents collide Convergent plate movement) Material then gain heat again, rising and sinking movement Convection currents) Slab-pull force When 2 plates converge Denser oceanic crust pulled down by gravity T ectonics 1

Subducts beneath less dense plate Crust sinks deeper into mantle under it own weight Pulling the rest of plate in Further convergence Topic 1.2 Tectonics Plates - Seafloor Spreading Seafloor Spreading Plates move away from each other @ Divergent plate boundary Magma from deep within Earth rises and forms mid-oceanic ridge New oceanic crust is formed Evidence of Seafloor Spreading Support Plate Tectonic Theory Age of rocks Nearer to crest of mid-oceanic ridge > Youngest Further away > Older Shows that new oceanic crust is created Then moves laterally on both sides of the mid oceanic-ridge Little sediment accumulation is found @ oceanic trench as older rocks gets destroyed Oceanic crusts younger than continental Topic 1.3 Plate Tectonics - Magnetic Stripping Magnetic Stripping Earth has geographic north and south and magnetic north and south Magnetic north and south shift Normal polarity: Magnetic north points roughly towards geographic north and likewise for south T ectonics 2

Reverse polarity: Magnetic north points roughly towards geographic south and likewise for south Earthʼs polarity constantly flipping multiple times Magnetic stripping is a zebra-like pattern Strips of normal polarity rocks alternating alongside reverse polarity rocks Symmetrical on both sides of mid-oceanic ridge Occurs on Iron-rich lavacools and solidify > Balsamic rocks formed from lava Contain magnetic materials Itʼs magnetic material point towards Earth magnetic North, recording evidence Evidence that supports plate tectonic theory Zebra-like patterns symmetrical > Not random occurrence O plates move away from each other Iron-rich lava erupts from centre of ridge Cools and solidifies > Form new oceanic crust Crust pushed in both directions when process happens again Divergence > Overtime, more lava moves away from ridge due to plate divergence Topic 1.4 Plate Tectonics - Tectonics Processes at Different Plate Boundaries Divergent Plate Boundaries Oceanic-Oceanic Mid-oceanic ridge, submarine volcanos] Convection currents > Two OO plates move apart Decrease overlying pressure > Underlyingmantle to melt Magma formed > Rises thru weak areas in crust Fill gaps caused by sea floor spreading T ectonics 3

Lava cools and solidifies > Basaltic rocks Makes new crust Forms an underwater chain of mountains (mid oceanic ridge) Continental-Continental Rift valley, volcano] Convection currents > 2 CC plates to move apart Rock fracture > Form parallel faults Rocks between faults collapse > Deep rift valley Decrease overlying pressure > Underlying mantle to melt Magma rises thru weak areas in crust Forms volcanoes EQ occurs due to stress and tension released when plates move Convergent plate boundaries Oceanic-Oceanic Oceanic trench, volcano] Convection currents > 2 OO plates collide Denser plate subducts beneath less dense plate Forms a deep depression Oceanic trench) Subducting plate sinks into mantle > High pressure forces water out of crust Lowers MP Melt > Form magma Magma rises thru weak areas in crust Forms volcanos Friction along oceanic plates collide causes EQ to occur Continental-Continental Fold mountains] Convection currents > 2 CC plates collide Subduction does not take place Continental plats too buoyant and less dense T ectonics 4

Huge pressure > Rocks to uplift and buckle EQ occurs due to friction along the convergent plate boundary Oceanic-Continental Oceanic trench, fold mountain, vocalno] Convection currents > Oceanic pate to collide with continental plate Denser oceanic plate subducts beneath less dense continental plate Forms oceanic trench in subduction zone Subducting plate sinks into mantle High pressure forces water put of oceanic crust Lowers MP Mantle melt > Form magma Magma rises thru weak areas in crust Form volcanos Enormous pressure on C plate > Cause it to buckle and get unlifted EQ occur due to friction between subductions plates Topic 2.1 Earthquake and Volcanoes - Tectonics Processes Affecting Magnitude of Earthquakes Earthquakes Occurs when… Rock masses on the side of the fault pushed by tectonic forces Due to friction > They get locked > Stress builds up Stress exceeds strength of fault > Rocks snap/ move to new position Seismic waves released > Ground shaking Focus Depth Point where seismic waves are released Deeper > Weaker , Shallow > Stronger Epicentre Distance] Point directly above focus on surface Closer > Stronger , Further > Weaker T ectonics 5

Energy lost to surroundings Energy lost to surroundings Measurement of earthquakes Using seismometers Richter Scale ML Calculated based on the height of largest recorded wave Measured based on maximum seismic intensity (not total seismic energy released) Inaccurate Moment Magnitude Scale Mw Calculated based on total energy released instead of a single largest one Accurate Topic 2.2 Earthquake and Volcanoes - Tectonics processes affecting the magnitude of volcanic eruptions Volcanoes Parts: Crater Bowl-shaped depression) Vent Opening) Conduit Magma chamber Source of magma) Tectonic process resulting in volcanoes Divergent plate boundary OO Convection currents > Plates move apart > Crust stretches & fractures develop Decrease in overlying pressure > Underlying mantle to melt > Form magma T ectonics 6

Magma contain dissolved gases and is less dense > Rises thru weak areas of crust Erupt as lava > Volcanic eruptions Lava cools > Solidify > Accumulate over time Convergent plate boundary OC Plates move towards each other > Denser plate subduct beneath less dense plate Sinks into mantle > High pressure > Force water out of oceanic crust Water lowers MP of overlying mantle > Melt > Form magma Magma contains dissolved gases and is less dense Rises thru weak areas of crust Erupt as lava > Volcanic eruptions Lava cools > Solidify > Accumulate over time Explositivity of Volcanoes High Silica Lava More viscous magma As magma rises, gases cannot escape easily Pressure builds up until gases escapeexplosively Violent and explosive eruptions Usually stratovolcanoes Low Silica Lava Less viscous magma As magma rises, the dissolvedgasesescape easily Less pressure built up Gentle & effusive eruptions Usually shield volcanoes Stratovolcanoes High viscosity magma rises thru weak areas of crusts > Erupts explosively as lava, ash and rocks Ash and rocks settle on sides, covered up by lava later T ectonics 7

Over successive eruptions… Tall volcano with alternating layers of lava and ash develops with steep sides More viscous lava travel a shorter distance before solidifying Shield volcanoes Low viscosity magma rises thru weak areas of crusts > Erupts effusively Over successive eruptions… Volcano with layers of lava is developed with gentle slopping sides and broad summit Less viscous lava travel a longer distance before solidifying Topic 2.3 Earthquake and Volcanoes - Distribution of Earthquakes, Volcanoes and Tectonic Hazards Distribution of Earthquakes Occur along all type of plate boundaries Largely concentrated at the Pacific Ring of Fire Occur more commonly along convergent plate boundaries at subduction zones as more stress is built up E.g. Common locations of earthquakes Along convergent plate boundary at Pacific Ring of Fire Along divergent plate boundary at Mid-Atlantic Ridge Along transform plate boundary at the San Andreas Fault Pacific Ring of Fire Broad belt around the Pacific Ocean where most EQ and active volcanoes occur Comprises of all types of plate boundaries