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Flashcards in Magma Deck (21)
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1
Q

magma basics

A
  • molten rock - a very hot viscous liquid (1100 = 800 degrees celcius)
  • Found at depths of the earth
  • Lava = magma that’s reached the surface of earth
2
Q

chemical/mineral composition of magma

A
  • Typical magmas are high in Si and O as well as Al, Ca, Na, Mg, Fe, and K -> form silicate minerals
  • Magmas cool and crystallize to form igneous rocks
  • Can be felsic, mafic, or intermediate
3
Q

intrusive vs. extrusive

A
  • Different names for exact same chemicals/composition depending on whether or not they made it to the surface
  • extrusive = “volcanic”
  • intrusive = “plutonic”
  • Intrusive has large crystals because it cools quickly, extrusive has small crystals because it cools slowly
4
Q

mafic magmas

A
  • more ferromagesian minerals – Ca, Fe, Mg
  • darker in colour
  • Volcanic (extrusive): basalt
  • Plutonic (intrusive): Gabbro
5
Q

felsic magmas

A
  • more K, Na, and Silica
  • lighter in colour
  • Volcanic (extrusive): rhyolite
  • Plutonic (intrusive): granite
6
Q

intermediate magmas

A
  • Volcanic (extrusive): andesite

- Plutonic (intrusive): diorite

7
Q

Bowen’s reaction series

A
  • The order in which minerals crystallize out of a magma
  • Mafic magmas are high temperature: ~1100 degrees Celsius
  • Felsic magmas are low temperature: ~800 degrees Celsius
  • 2 branches:
  • Discontinuous branch: ferromagnesian minerals - olivine -> pyroxene -> amphibole -> biotite -> potassium feldspar (from hottest to coolest)
  • Continuous branch: plagioclase feldspar – calcium rich -> sodium rich -> quartz (from hottest to coolest)
8
Q

magma components

A
  • Liquid components (the melt)
  • Solid components (crystallized silicate minerals)
  • Gaseous component (volatiles – either dissolved in the melt or exsolved as bubbles)
9
Q

how do magmas form/how does solid rock melt? (and 3 ways to melt them)

A
  • Geothermal gradient increases with depth and pressure (the further you go into the earth, the hotter it is, yet the harder it is to melt the rocks)
  • The deeper you are in the earth, the harder it is to melt rocks because it requires a lot more energy
  • Temperature always helps melt rocks, but pressure of the earth’s depths prevents melting
  • 3 ways to melt rocks (how to get above the geothermal gradient):
  • Increase temperature
  • Reduce pressure (“decompression melting”)
  • Add water/volatiles (decompresses/reduces the melting point -> like adding salt to ice)
10
Q

magma generation in a plate tectonic setting (3 ways)

A
  1. Introduction of volatiles at subduction zones
    - Lowers the melting temperature of overlying mantle material
    - Causes partial melting in the mantle generating magma with a new composition
  2. Heat is added (eg. A magma body from a deeper source intrudes cyrstal rock and the additional heat melts a portion of the rock)
    - Increases temperature by “underplating”
    - Again, partial melting causes generation of new magma
  3. Convective upwelling in the asthenosphere results in decrompression melting
    - The asthenosphere rises up close to the surface of the earth, where the pressure is lower
    - Like taking the lid off a Coke bottle -> decreases pressure
11
Q

different magma types: plate tectonic setting

A
  • Mafic magmas:
  • Mid-ocean ranges (divergent plate margins) and hot spots
  • Partial melting of mantle peridotite (ultramafic rock) produces mafic magma
  • Intermediate and felsic magmas:
  • Subduction zones (convergent margins)
  • Partial melting of lithosphere/crust generates magma that is richer in silica
12
Q

magma evolution (differences in composition over time) (3 ways)

A
  1. Crystal settling (magmatic differentiation): As minerals crystallize out of the melt while magma is cooling, they can settle and remove themselves from the melt, changing its chemical composition
  2. Assimilation of host rock: Magma will crack/partially melt its way through another rock
  3. Magma mixing: Silicic magma moves upward slowly, while the mafic magma moves rapidly upwards and connects with it -> some mafic material crystallizes in silicic magma, resulting in black blobs
13
Q

intrusive igneous rocks

A
  • Ex. Granite, diorite, gabbro
  • Form from slow cooling of molten rock (magma)
  • This occurs deep below the earth’s surface
  • May take 100’s-100 000’s years to cool
  • Slow cooling = large crystal size. Coarse-grained (macroscopic)
  • Terms associated with intrusive rocks: country rock, contact metamorphism, xenolith, diapirs, pluton, batholith, dykes/dikes, sills
  • Intrusive bodies get exposed by uplift and erosion of both overlying and surrounding material
14
Q

country rock

A

older rock that igneous body is intruding into

15
Q

contact metamorphism

A

alteration of surrounding country rock by increased T

16
Q

xenolith

A

fragment of surrounding country rock incorporated into the magma

17
Q

diapirs

A

rising bodies/blobs of magma

18
Q

pluton

A

large igneous bodies that crystallize at depth within the Earth’s crust

19
Q

batholiths

A
  • large (>100km^2 igneous bodies formed by coalescence/joining together of plutons)
  • Ex. Chief
20
Q

dykes/dikes

A
  • thinner sheet of igenous rocks
  • usually high angled, cross-cut existing strata (vertically)
  • Ex. Found on Chief, Ship Rock
21
Q

sills

A
  • thinner sheet of igenous rocks

- moves in between strata (concordant with it); unzips it rather than cross-cuts it (horozontally)