Igneous

Question 1

What does igneous mean?

Answer 1

formed from a melt

Question 2

What is the ophiolite suite?

Answer 2

! sediments
! pillow basalt
! sheeted dikes
! more massive gabbro
! ultramafic (mantle)

Question 3

3 types of heat transfer

Answer 3

1. Radiation (heat through air)
2. Conduction (varmeledning)
3. Convection (strømning, mest effektiv)

Question 4

Aphanitic definition

Answer 4

Crystals too small to see by eye

Question 5

Phaneritic definition

Answer 5

Can see the constituent minerals

Question 6

Difference between a laccolith and lopolith?

Answer 6

Laccolith:
- small intrusions
- skubber lagene over op
- flat floor and arched roof

Lopolith:
- larger intrusions
- lagene synker ind
- større

Question 7

Difference in alkaline and subalkaline?

Answer 7

Alkaline = silica-undersaturated
Subalkaline = silica-saturated
-> subalkaline can be divided into tholeiitic and calc-alkaline series

Question 8

What are the two principal types of basalt in the ocean basins?

Answer 8

Tholeiitic Basalt and Alkaline Basalt

Question 9

Where are tholeiites generated?

Answer 9

At mid-ocean ridges

Also generated at oceanic islands,
subduction zones

Question 10

Where are alkaline basalts generated?

Answer 10

At ocean islands

Also at subduction zones

Question 11

What separates the subalkaline from alkaline fields at low pressure?

Answer 11

Thermal divide
Cannot cross this divide, so can’t derive one series from the other

Question 12

What is lherzolite?

Answer 12

Probably fertile unaltered mantle
A type of peridotite with Olivine > Opx + Cpx
Ved opsmeltning vil lherzolit blive til harzburgite

Question 13

How does the mantle melt?

Answer 13

1) Increase the temperature
2) Lower the pressure
3) Add volatiles (especially H2O)

Question 14

Hvad sker der med en smelte ved ændringer i tryk?

Answer 14

Samme kappe, men den går fra at være Si-overmættet til Si-undermættet ved højere tryk

Question 15

What is magmatic differentiation?

Answer 15

Any process by which a magma is able to diversify and produce a magma or rock of different composition

Question 16

Hvad er diversificering af magma?

Answer 16

• Magmablanding - to magmaer blandes
• Afblanding af volatiler
• Fraktioneret krystallisation
• Smeltning og inkorporering af omkringliggende materiale (forurening’)

Question 17

Hvad er Stokes lov?

Answer 17

Lineær sammenhæng mellem stress og strain = viskositet

= Noget med hvordan en partikel synker ned gennem en væske

Vi kender ikke særligt mange sfæriske mineraler, så det her kan aldrig passe 100%

Question 18

What is true for pegmatites?

Answer 18

Late-stage fractional crystallization enriches late melt in incompatible, LIL, and non-lithophile elements

Question 19

When was the Bushveld and Skaergård LMI?

Layered Mafic Intrusion

Answer 19

Bushveld, Precambrian, S. Africa, 66,000 km2

Skaergård, Eocene, East Greenland, 100 km2

Question 20

What are the three types of layering in LMI’s?

Answer 20

Modal layering: variation in modal proportions

Phase layering: variation in primary (cumulus) minerals (appearance/disappearance)

Cryptic layering: variation in mineral composition (called cryptic because it cannot be seen by the eye)

modal = andelen af mineraler (volumen% eller vægt%), summer til 100

Question 21

What kind of layering does the Bushveld and Skaergård LMI’s have?

Answer 21

Bushveld: Uniform modal

Skaergård: Macrorhythmic

Question 22

What is the Sandwich Horizon (in regard to Skaergård LMI)?

Answer 22

Where the latest, most differentiated liquids crystallized

Upper Border Series and the Layered Series meet here

Question 23

Which (Bushveld or Skaergård) has liquid immiscibility?

Answer 23

Skaergård LMI

Question 24

What are the two crystallization models?

Answer 24

• Crystal settling
• In situ crystallization

Question 25

What can crystallization be interrupted by?

Answer 25

- Re-injection of more primitive magma (explain major compositional reversals in phase- or cryptic layering (e.g. Bushveld Complex) - Periodic large-scale density currents

Question 26

What are four problems with the crystal settling process?

Answer 26

- Many minerals found at a particular horizon are not hydraulically equivalent - Size is more important than density in Stokes’Law, but size grading is rare in most LMIs - Dense olivine in the Upper Border Series of the Skaergaard - Plagioclase is in the lower layers of the Skaergaard

Question 27

What is double-diffusive convection?

Answer 27

- Systems with gradients in two or more properties (chemical or thermal) with different rates of diffusion - Especially if it has opposing effects on density in a vertical direction - A series of convecting layers (husk 'pyramide'-diagrammet med en masse små konvektionscirkler i lag)

Question 28

How does rift morphology depend on spreading rate?

Answer 28

Både negativ (graben-struktur) og positiv (upwelling magma) topografi Hurtigtspredende = positiv topo Langsomtspredende = negativ topo

Question 29

What is a “typical” MORB?

Answer 29

A tholeiite with low K2O (< 0.2%) and low TiO2 (< 2.0%)

Question 30

What are the 3 types of MORB?

Answer 30

- N-MORBs tap an upper, depleted mantle - E-MORBs tap a deeper enriched source - T-MORBs = mixing of N- and E- magmas during ascent and/or in shallow chambers

Question 31

What is LLSVPs?

Answer 31

Large Low Shear Wave Velocity Provinces

Question 32

What is expected at the centre of plumes? | Predictions from plume theory

Answer 32

Hot, enriched magmas

Question 33

What is expected away from plume centre? | Predictions from plume theory

Answer 33

Mixed, moderately hot magmas

Question 34

How can the Hawaiian islands be both tholeiitic and alkaline?

Answer 34

Classic explanation: different depth of melting

Question 35

What is the Northern Hemisphere Reference Line (NHRL)?

Answer 35

~linear mixing line between DM and HIMU | DM = depleted mantle HIMU = high my = high 238U/204Pb (høj U, lav Pb)

Question 36

What is the source for EMI, EMII, and HIMU?

Answer 36

EMI = Deeper continental crust or oceanic crust, or sediments thereof EMII = Upper continental crust or ocean-island crust, or sediments thereof HIMU = Subducted and recycled oceanic crust (± seawater)

Question 37

Hvor kommer mange flood basalts fra?

Answer 37

Samlingen af Pangea samt magmatiske provinser da Pangea opsprækkede

Question 38

What does LIP stand for?

Answer 38

Large Igneous Province

Question 39

Hvor findes LIPs?

Answer 39

I forbindelse med grænserne mellem kontinentalplader samt på randen - findes dog også midt på kontinenterne Dannes ved en mantle plume, der har forårsaget opløft

Question 40

What is the definition of LIPs?

Answer 40

Magmatic provinces with areal extents >0.1 Mkm2, igneous volumes >0.1 Mkm3, and maximum lifespans of ∼50 Myr Fun fact: There's a correlation between creation of LIPs and mass extinctions

Question 41

Hvad sker der, når en sill intruderer i et sedimentært bassin?

Answer 41

Kontaktmetamorfose Hydroner brændes af (hvilket frigiver vand og methan) Fluider bevæger sig fra sill og op i sedimenter, hvilket danner vent-komplekser

Question 42

How does density change with temperature and composition of the magma?

Answer 42

Temp. rises = the densities fall no matter the composition Comp. is basaltic = density is highest Comp. is andesitic = density falls Comp. is rhyolitic = density falls even more

Question 43

How does viscosity change with temperature and composition of the magma?

Answer 43

Temp. rises = viscosities fall drastically for both basaltic and andesitic magma. The fall in viscosity for rhyolitic magma is very small. Comp. is andesitic = viscosity is highest Comp. is basaltic = viscosity falls Comp. is rhyolitic = viscosity falls within the same area as the basaltic