Plate Margins

Question 1

Constructive Sub-Plate

Answer 1

Dominated by convection currents

Heat escape core - move through mantle - heats asthenosphere rock - flow upwards towards lithosphere

Rising part cc reach bottom lithosphere it heats it, becomes less dense and stretches and deforms upwards

Question 2

Constructive Plate Processes

Answer 2

Dominated by sea floor spreading

Lithospherr heated by cc less dense s and d upwards - form ocean ridge

As ridge rises above abyssal plain
Increasingly rugged towards centre - series eroded subridges running parallel to main

Question 3

Constructive Resultant Landforms

Answer 3

Centre of ocean ridge features Central Rift Valley
1.5km deep up to 30km wide

Inner slopes - steep and relatively straight

Outer slopes - gentler gradient marked by series stepped terraces parallel to main ridge

Over Time raised sides slide down sideways under gravity as they cool slightly and become more dense.
During this deformation fracturing of rock allows magma to intrude into lithosphere- cool and harden to form dykes - help displace rock laterally away from margin

Question 4

Conservative Processes

Answer 4

Plates curve across ocean floor
Avoid margin twisting S shape it fractures perpendicular to it
- Creates Transform Faults bisecting the cons margin - zigzag pattern along ridge

Question 5

Conservative Sub plate

Answer 5

Convection currents - same as constructive

Question 6

Collision Sub Plate

Answer 6

As continents approach oceanic lithosphere between subducts below one of continents

Eventually two continent lithosphere collide and subducting oceanic detaches - continues down asthen slowly melts and becomes assimilated fully into asthen

Eventually all subduction stops

Question 7

Collision Plate Process

Answer 7

As converge, sediments laid down on sea floor.
From rivers flowing off edge of continents
As oceanic subducts sediment ontop is scraped off and builds up on surface (resists subduct less dense)

Question 8

Collision Landforms

Answer 8

Continental too buoyant to subduct so plates collide and litho compressed. Sea floor sediments folded upwards creating fold mountains

Process of deformation causes multiple faults and fractures in mountains. mtns have deep root below surface

Question 9

Destructive Processes

Answer 9

Oceanic litho thousand miles away from place created = cold and denser

Litho subduct down into asthen

Oceanic and Continental more dense oceanic subduct below

Oceanic and oceanic litho colder and denser subducts

Question 10

Destructive Sub plate

Answer 10

Dominated by subduction aided by sinking of convection currents

Subducting segment - Benioff Zone

Subduction Melting ~ As subduct surface lithosphere melts as it comes into contact with asthen

Hydration Melting ~ sea water carried down by sub plate lowers mp of litho also mixes with melted material reducing viscosity - 80km

Subduction stops 600-700km
-fully assimilated

Question 11

Destructive Landforms

Answer 11

Fold mountains - similar to collision margins but may be further built up by volcanoes

Deep sea trenches - 50-100km wide 5-10km deep
2 oceanic meet subduction = compression forces that cause plate to buckle and deform producing DST - non-sub deform downwards

Island Arcs - plate subduct surface melt aided by sea water. Partial melting create magma less dense than surrounding asthen.
Rises upward through lithosphere melts and erupts to form volc
Over time volc build upwards above ocean surface - arc of islands parallel to trench

Distance islands depends on angle benioff zone