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Samenvatting - Magmatische gesteenten (Inleiding tot de petrologie)
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Deze samenvatting omvat alle informatie omtrent de magmatische gesteenten, gezien in het vak 'inleiding tot de petrologie'
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Magmatische gesteenten= stollingsgesteenten
Inhoudstafel
Inhoudstafel........................................................................................................................................... 1
Magmatische gesteenten ....................................................................................................................... 3
Eigenschappen ............................................................................................................................................... 3
Chemische Samenstelling ............................................................................................................................... 3
Genese ............................................................................................................................................................ 4
Soorten ........................................................................................................................................................... 4
Mineralogische samenstelling ........................................................................................................................ 5
Felsische gesteenten ...................................................................................................................................... 6
Mafische gesteenten ...................................................................................................................................... 7
Textuur .................................................................................................................................................. 8
Kristallisatiegraad ........................................................................................................................................... 8
Korrelgrootte .................................................................................................................................................. 9
(Geometrische) kristalvorm ........................................................................................................................... 9
Classificatie en Nomenclatuur............................................................................................................... 10
Klassieke schema’s: ......................................................................................................................................10
IUGS diagram/QAPF diagram .......................................................................................................................11
Plutonische gesteenten ............................................................................................................................12
CIPW-norm (practicumexamen!!) ................................................................................................................15
Magmagenese en evolutie .................................................................................................................... 15
Mantelgesteenten ........................................................................................................................................16
Mechanisme .................................................................................................................................................16
Gefractioneerde kristallisatie ...................................................................................................................17
Kristallisatiereeks van Bowen ...................................................................................................................18
Andere mechanismen (differentiatie) ..........................................................................................................19
Assimilatie ................................................................................................................................................19
Hybridisatie ..............................................................................................................................................19
Ontmenging ..............................................................................................................................................19
Kristallisatiestadia ........................................................................................................................................20
Magmatische reeksen ..................................................................................................................................20
Veldkenmerken en structurren ............................................................................................................. 21
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, Typpes intrusieflichamen .............................................................................................................................21
Concordante intrusieven ..........................................................................................................................22
Discordante intrusies................................................................................................................................23
Eigenschappen intrusies ...............................................................................................................................24
Effusieve erupties................................................................................................................................. 25
Subaërische types.........................................................................................................................................25
subaquatische types: ....................................................................................................................................25
Explosieve erupties .............................................................................................................................. 26
Pyroklastische gesteenten............................................................................................................................26
Classificatie ...................................................................................................................................................27
Types vulkanen .................................................................................................................................... 28
Vulkanische eruptietypes .............................................................................................................................28
Vulkanische bouwwerken (morfologie) .......................................................................................................30
Terminologie ........................................................................................................................................ 32
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,Magmatische gesteenten
Eigenschappen
• Stollen/solidificeren of kristalliseren uit een magma
o Anders: vulkanisch glas
• Fysische eigenschappen: viscositeit – smeltpunt – kristallisatiegedrag
• (Meestal) silicaatmagma: hete vloeistof met silicaatsamenstelling
o Afkoeling: silicaatmineralen
• Magma: smelt + kristallen + opgeloste gassen
o Samenstelling van de 3 toestandsfasen, maar zal zich als geheel als vloeistof
gedragen
o T° (stolling) T° (magma) bij gegeven P (weinig/geen oververhitte magma’s)
▪ Mafische (lage SiO2 c.) magmas zoals basalt 1100-1200°C
▪ Felsische (hoge SiO2 c.) magmas zoals rhyoliet 750-900°C
▪ Oplossen H20: verlaging van het smeltpunt
Chemische Samenstelling
= Vooral O, Si, Al (hoofdelementen)
• Hoofdelem. (>2%) – Nevenelem. (0,1-2%) – sporenelem. (0,1% of <1000 ppm)
o Classificatie: hoofdelementen + nevenelementen (SiO2 gehalte)
o Genese: sporenelementen
• Elementaire oxiden: Vol% O = 93,77, Gew% O = 46,59
• Gabbro – dioriet – syeniet – granodioriet - graniet
• Opgeloste gassen: Oplosbaarheid neemt toe met T en P
o Explosieve eruptie van gas = vulkaanuitbarsting
o Rustig: fumarole (gasbron) – solfatara (zwavelgasbron)
o Externe of atmosferische gassen: H2O, N2, O2 en Ar
o Actieve gassen van zuivere magmatische oorsprong: CO2, NH3, HCl, HF, H2S, SO2
3
, Genese
= Door partieel opsmelten t.h.v. boven mantel en/of onder korst
• → stijgen van magma → stollen aan oppervlakte of in hogere delen van de korst
o Vloeistof lagere dichtheid dan uitgansgesteenten: densiteitsverschil tussen
achterblijvend mantelgesteente en lichtere smeltdruppels. Hierdoor gaan de
smeltdruppels migreren naar boven toe (door zwaktes in de gesteenten)
o Mantel → lithosfeer → aardoppervlak
o Forse daling vd temperatuur: stollen
• Subductie: asthenosferische plaat partieel opsmelten → vorming magmakamers
• Differentiëren van magma’s: veranderen van samenstelling wanneer T en specifieke
mineralen uitkristalliseren
o Gefractioneerde kristallisatie: specifieke chemische samenstelling
bulksamenstelling uitgansmagma
o Bij evenwichtssamenstelling: og samenstelling = uitganssamenstelling
Soorten
• Intrusief/plutonisch/dieptegesteente: magmatisch gesteente gevormd door stagnatie
(stolling) van magma in de korst
o Trage afkoeling = grote kristallen
o Vb) graniet
• Extrusief/vulkanisch/pyroklastisch gesteente: magma bereikt oppervlak. Gassen
ontsnappen door lage druk ➔ ontgaste magma (= lava)
o Snelle afkoeling = kleine kristallen (ook glas)
• Subvulkanisch gesteente: komt in aardekorst, maar niet aardoppervlak
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