evolusi magma.pdf

8/10/2019 Evolusi Magma.pdf

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Fractional crystallization in the Palisades Sill (200 Ma) on theHudsonRiver Fm. Fractionation from an initial homogeneous magma resulted

from the settling of early-formed crystals of olivine and then pyroxene

from the residual melt.


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X

1. For bulk composition X, liquid cools to liquidus at 1600C

P = 1 atm2. Fo begins to crystallize

3. Liquid composition moves

directly away from Fo

4. Liquid composition reaches cotectic;

Di begins to crystallize with Fo

5. Co-precipitation of Fo + Di causes

liquid composition to move down

cotectic curve

6. Liquid composition

reaches ternary eutectic at

1270C; An begins to

crystallize with Di + Fo

7. Liquid is consumed;

An + Di + Fo cool

below 1270C


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Gravity settling

Cool point a olivine layer at

base of pluton if first olivine sinks

Next: ol + cpx layer

Finally: ol + cpx + plag

Cumulate texture:

Mutually touching

phenocrysts with

interstitial crystallizedresidual melt

12

17

22

Al2O3

0

5

10

MgO

0

5

10FeO*

0

2

4

6

Na2O

0

5

10

15

CaO

45 50 55 60 65 70 75

0

1

2

3

4

K2O

SiO2

45 50 55 60 65 70 75

SiO2

Bivariate

(x-y) diagrams

Harker Diagram

major elements

for Crater Lake.

From Winter (2001) AnIntroduction to Igneous and

Metamorphic Petrology.Prentice Hall.


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40 50 60 70 80

0

100

200

300

Ni

SiO2

0

100

200

300

Zr

ppm

wt. %

Note magnitude of trace

element changes

Harker Diagram trace elements

for Crater Lake.

From Winter (2001) An Introduction to Igneous and

Metamorphic Petrology. Prentice Hall.

Bivariate(x-y) diagrams

Ophiolite suite of rocks - range from peridotites (mantle) to gabbro

(deeper ocean crust) to basalt (sheeted dikes and pillows - upper

oceanic crust) to deep-sea sediments.


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Bushveld Igneous Complex (BIC),

South Africa

(65,000 km2, max thickness 7 km) Catatan: Luas Bandung: 1,676 km2

Bushveld Igneous Complex (BIC),

South Africa

(65,000 km2, max thickness 7 km)

http://web.uct.ac.za/depts/geolsci/dlr/301s/bv_field/bv37.jpg


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EVOLUSI MAGMA1. Diferensiasi magma

Fraksinasi kristalisasi (gravity settling, filter pressing)

Liquid immiscibility

2. Magma mixing

3. Asimilasi

Fo-SiO2 system

Liquid Immiscibility


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Some Examples

Late silica-rich immiscible droplets in

Fe-rich tholeiitic basalts

Sulfide-silicate immiscibility (massive

sulfide deposits)

EVOLUSI MAGMA

1. Diferensiasi magma



2. Magma mixing

3. Asimilasi


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MAGMA MIXING

A scoriaceous basalt with bands of rhyolite pumice

incomplete mixing of 2 magmas due to density and viscosity contrasts


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Basalt pillows accumulating at

the bottom of a in granitic

magma chamber, Vinalhaven

Island, Maine

Comingled basalt-Rhyolite Mt.

McLoughlin, Oregon

From Winter (2001) An Introduction to

Igneous and Metamorphic Petrology.

Prentice Hall


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EVOLUSI MAGMA1. Diferensiasi magma



Gaseous transfer

2. Magma mixing

3. Asimilasi

Assimilation Incorporation of wall rocks

(diffusion, xenoliths)

Assimilation by melting is limited by the heat

available in the magma


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ASIMILASI MAGMA

Inclusion of metamorphic rock in lava (xenolith). El Joyazo, SE Spain.


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A gabbro xenolith in a granite body. Donner Pass in the high Sierras.

Gabbro xenoliths in a granite body


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Difer

ensia

sima

gma

Magm

amixi

ng

Asim

ilasi

evolusi magma.pdf

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