Introduction to Tectonics and Folds

Question 1

Tectonics

Answer 1

The branch of geology which deals with the large scale structures of the Earth and the processes that have produced them

Question 2

In plate tectonics which of the Earth’s layers are moving and in response to what

Answer 2

Lithosphere moves horizontally over the hotter, semi-plastic asthenosphere in response to gravity and friction

Question 3

What are the three types of plate boundaries

Answer 3

• Divergent boundaries
• Transform boundaries
• Convergent boundaries

Question 4

What happens at divergent boundaries and what are they characterised by

Answer 4

Plates move away from each other and they are characterised by mid-ocean ridges and continental rift zones

Question 5

Process of ocean forming at divergent boundaries - beginning

Answer 5

the thick continental crust insulates the mantle causing partial melting of the mantle and the rise of more buoyant material which is the cause of continental breakup

Question 6

Process of ocean forming at divergent boundaries - Stage 1

Answer 6

Stage 1: rising magma causes crustal upwarp which stretches and thins the crust leading to basaltic magma from the mantle erupting at the surface forming an incipient rift

Question 7

Process of ocean forming at divergent boundaries - Stage 2

Answer 7

A rift develops leading to the continental crust breaking and basaltic lava fills the rift

Question 8

Process of ocean forming at divergent boundaries - Stage 3

Answer 8

A narrow sea develops which is the beginnings of a new mid-ocean ridge. The oceanic crust is more developed and the continents are still relatively close

Question 9

Process of ocean forming at divergent boundaries - Stage 4

Answer 9

An ocean basin is formed in the well developed mid-ocean ridge as the continents are widely separated

Question 10

What happens at drivers

Answer 10

• ridge push at elevated ridge
• slab pull at trench - old, cold, dense lithosphere
• convection

Question 11

What happens at transform boundaries and what are they characterised by

Answer 11

• plates move past each other
• characterised by large faults or faults along mid-ocean ridges
• intense seismic activity

Question 12

What happens at convergent boundaries and what are they characterised by

Answer 12

• earth isn’t expanding so creation of lithosphere must be balanced by destruction
• subduction occurs as plates move towards each other and old lithosphere is consumed
• characterised by ocean trenches, volcanism, earthquakes and metamorphism

Question 13

Oceanic - Oceanic subduction

Answer 13

• subduction zone where two plates of oceanic lithosphere converge
• one plate dives into mantle
• characterised by ocean trenches and volcanic island arcs
• Produces basalt (& andesite) (mafic)

Question 14

Oceanic - Continental subduction

Answer 14

• subduction zone where one plate of oceanic lithosphere and one plate of continental lithosphere converge
• oceanic plate dives into mantle - more dense
• characterised by oceanic trenches, volcanic mountain range and metamorphism
• produces andesite (intermediate)

Question 15

Continental - Continental subduction

Answer 15

• subduction zone where two plates of continental lithosphere converge
• continental lithosphere cannot be subducted - too thick, low density
• plate motion taken up by intense deformation
• characterised by mountain ranges, plateaus, intrusions and metamorphism
• produces granite (intrusions) and rhyolite

Question 16

What are the three major forms of stress and what do they lead to

Answer 16

• compression: stresses along the same line but converging; causes shortening
• tension: stresses along the same line but diverging; causes extension
• shear: stresses parallel but in opposite directions; causes transverse breaks

Question 17

Folds

Answer 17

• folds are rock layers that have been bent or crumpled in response to compression
• most folding occurs at depth in the crust
• rocks deform plastically (ductile): hot and confined

Question 18

Anticline

Answer 18

• strata folded upwards to form an arch-shaped structure
• strata on opposite sides of axial plane dip away from each other
• oldest strata at core

Question 19

Syncline

Answer 19

• strata folded downwards to form a trough shaped structure
• strata on opposite sides of the axial plane dip towards each other
• youngest strata at core

Question 20

Dams and shit

Answer 20

look in book