Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Structural > Week 19 > Flashcards

Week 19 Flashcards

1
Q

Importance of intrusion

A

Magmatic = abundant rock type in continental crust

Reflects process of thermally-driven differentiation of Earth’s crust

Derived from mantle/lower crust = info on nature of crust

Important mineral deposits

Reflect melting/transport/crystallisation processes associated with tectonic belts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is most continental crust made up of?

A

Large no. of granite plutons
= space problem in emplacement zone/source region

‘Bottle of red ink’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Gabbro glacier model

A

All lower crust crystallises in high level melt lens

Subsides down and away from ridge axis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Multiple sill model

A

Lower crust forms by intrusion of multiple melt lenses throughout lower crust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Gabbro glacier or multiple sill?

A

Hybrid

Can form décollements = thin-skinned deformation = lower orogenic slope

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Upper crustal magmatic system terms

A 
Sill
Dyke
Lopolith
Laccolith
Stepped geometries/fingers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Lopolith

A

Space = erosion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Lacolith

A

Space = source volume withdrawal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why does deformation occur near intrusions?

A

To accomodate intrusions = ‘instantaneous’ localised extension

At intrusion margins

Depends on strength of host rock

= stepped/faulted margin as complex builds up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Moving magma out of the source region

A

G-driven compaction too slow for viscous melts = fracturing is 1’ mechanism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Intrusion and driving forces in magmatic intrusions

A
  1. Melting = source region porous and dilates
    - fluid-absent melting = up to 15% volume increase
  2. = hydraulic overpressure in source
  3. = doming + therefore uplift of Earth’s surface
  4. = radial stress field with vertical tensile cracks/dykes/conduits
  5. Buoyancy forces drive magma up conduit
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Ascent and emplacement in magmatic intrusions

A

Feedback loop set up:

  • initial dyke feeds sill = releases excess mass volume (EMV) in source
  • sill supports roof
    = floor decoupled and subsides back into source
    = expels magma
  • = increase sill size and dilates conduit
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do emplacement-accommodation space mechanisms vary with depth?

A

SHALLOW = doming

DEEPER = laterally

  • overburden too much for doming
  • tectonic forces required

DEEPER STILL = country rocks move down
- = diapirism/cauldron subsidence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Aphantic vs holocrystalline

A

Aphantic = fine grained, surface

Holocrystalline = below surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Intrusion systems

A

Central piston/satellite bodies

Multilayer complex

Multi-feeder laccolith complex

Halle-type

Donnerberg type

Bysmalith

Saucer-shaped sills

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How far can intrusions travel?

A

?! 1000s km horizontal transport

17
Q

Dyke =

A

‘instantaneous’ localised extension

18
Q

Vertical extent of intrusions

A

Stack of tabular shaped intrusions i.e. not ‘bottomless’

- competition between horizontal lengthening and vertical thickening

19
Q

Mud volcanoes =

A

over-pressured shale = intrusion/extrusion

20
Q

Salt intrusion =

A

salt = low viscosity/density

= diapirs/veneers/glaciers

“Allochthonous salt”

CAN OCCUR UNDER COMPRESSION AND EXTENSION

e.g. South Caspian Basin

21
Q

Active salt intrusion

A

Salt pushes up

22
Q

Reactive salt intrusion

A

Faults = buoyancy

23
Q

Passive salt intrusion

A

Sedimentation and loading

Speed of sedimentation affects shape

24
Q

Salt withdrawal minibasin

A

Forms above salt

Subsides as salt flows away from depocentre

25
Q

Salt and seismic sections

A

Does not reflect well

26
Q

Salt intrusions; sedimentary and petroleum implications

A

Sandstone (reservoir) adjacent to salt because deposited same time

= “controlled sedimentary architecture”

27
Q

Salt diapirs in a contractional regime

A

Diapir pre-existing

= pedestal, salt weld and rotated flap

28
Q

Subduction-related magmatism: Cordilleran batholiths

A

Large regions in W N/S America
e.g. Patagonian batholith

Compressional regime = sill favoured rather than dykes = no volcanism

29
Q

Caledonian Late Orogenic granites

A

Emplacement controlled by crustal scale lineaments e.g. transtension
= tectonic-controlled

Intruded late in orogenic cycle

Examples in Ireland

30
Q

Cornubian Batholith

A

Tectonic controls

Variscan convergence = S-S

Post Variscan extension = emplacement of basalt sills

31
Q

Cornwall granites

A

Radioactive (K/U) decay = drill = heat

32
Q

Ketilidian Orogen, South Greenland

A

3 different suites of intrusion:

  1. Cordilleran-style = arc-magmatism (mafic)
  2. Forearc partial melting of sedimentary rocks
  3. Post-orogenic; deep lithosphere alkaline
    - Rapakibi granites - perialkaline
    - >50km2 tabular shaped granite intrusions
    - evidence for floor depression

Structural (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions