Bowen's reaction series A2 Flashcards

1
Q

Types of pyroxene

A

Augite and Diopside

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2
Q

Types of olivine

A

Forsterite and Fayalite

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3
Q

what is the most common type of amphibole

A

Hornblende

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4
Q

2 sections Bowens reaction series

A

discontinuous
continuous

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5
Q

discontinuous series minerals/rocks

A

high temp olivine UM

                    pyroxene     
                                            M
                   amphibole    

                   biotite              I    low temp
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6
Q

Continuous series minerals/rocks

A

High temp Ca rich (UM)

                 (plagioclase feldspar)

low temp Na rich (I)

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7
Q

whole Bowen’s reaction series

A

olivine Ca rich

pyroxene

amphibole
(hornblende)

biotite Na rich

            orthoclase 
           
            Muscovite 
              
             Quartz 

As we move down temp and silica content decrease

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8
Q

Discontinuous reaction series explanation

A

Left hand branch

crystallisation of minerals rich in Mg and Fe

in M magma olivine first to form
> 1500 degrees

as temp decreases:
pyroxene—>amphibole—>biotite

slow cooling allows high temp minerals to react with remaining magma to form low temp minerals

if fast cooling e.g. eruption
olivine may be preserved

if one reaction is incomplete may see a reaction rim of old mineral

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9
Q

continuous reaction series explanation

A

right hand branch

crystallisation of P feldspar from Anorthite (Ca rich) to albite (Na rich)

in-between there are intermediate versions of P feldspar (mix of Ca and Na)

Ca rich only really seen in UM/M rocks
Na rich only really seen in IM/ maybe S rocks

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10
Q

Eutectic systems

A

melt looks/is homogenous (ratio of comp determines which crystal forms first)

temp decreases
crystallisation simultaneous on cont and discont

when crystals form they are immiscible (non homo) from 2 solid planes

2 solid planes are known as eutectic system
+ can be seen in eutectic phase diagram

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11
Q

eutectic point

A

point at which all 3 phases exist

liquid, solid and mix

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12
Q

liquidus

A

Phase boundary

everything above this line is melt

below some crystal and some melt- partial melt

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13
Q

2 different types of Eutectic phase diagrams

A

binary e.g. diopside-Anorthite
and
solid solution e.g. anorthite-Albite
and Forsterite-Fayalite

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14
Q

solidus

A

phase boundary

shows temp when the rock first begins to melt

anything below = solid

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15
Q

differences between binary and solid solution eutectic diagrams

(how to read them)

A

binary:
discont series
looks like 2 hills

To see which crystals precipitate in different comps you go up from comp and see which hill

to consider og melt composition you have to go across at the temperature and down to the comp when u hit the liquidus of the relevant crystal

solid solution:
cont series
onle 1 region

when reading this diagram you must go horizontally across the blob
e.g. if you were trying to figure out what comp crystals would first form you would drop down at the melt till you hit the liquidus
move along till you hit the solidus and then move down to the comp

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16
Q

Zone crystals

A

when crystals form at high temp it will be mafic

magma cools more layers added to crystals

outer layers must be less mafic

e,g, with plagioclase feldspar
more Ca rich inside and Na rich outside
drawn as squares inside squares

17
Q

forsterite vs fayalite

A

both olivine
Zoomed in look at Bowens reaction series

high temp Mg rich-Forsterite
e.g. 1500

Low temp Fe rich-Fayalite
e.g. 1400

as temp decreases Fe subs for Mg

18
Q

Minerals at low temps of Bowens reaction series

A

2 series converge at low temp

final group of minerals don’t react with remaining liquid

they are Silicic

orthoclase–> muscovite–>Quartz
as temp decreases

19
Q

Why do large igneous intrusions display a range of diff rock types

A

magma may not be homogenous

diff cooling rates

stoping or assimilation of C rock (changes comp)

as magma cooled injection of new magma from below (change comp)

20
Q

How can magmas mix +why don’t they usually?

A

don’t usually as:
diff densities, diff temps, diff viscosities

can mix if there is a strong mixing mechanism = strong convection current required

21
Q

How can magma become contaminated with diff rock

A

stoping and assimilation of C rock
change comp

begin with xenolith, melts, changes comp

assimilation changes bulk comp e.g. M magma + s country rock = inter magma

22
Q

3 types of magma differentiation

A

fractional crystallisation

gravity settling

filter pressing

23
Q

fractional crystallisation

A

diff mineral crystals form at diff temps

e.g. olivine/pyroxene form at higher temp
these incorp a lot of Fe and Mg

remaining Magma is more silicic
becomes increasingly more silicic

24
Q

Gravity settling

A

solid nearly always denser than liquid

crystals form = denser than melt

first crystals form are Mafic = most dense

gravity causes minerals to settle at bottom of magma chamber

forms cumulate layers with mafic layers at bottom

if they stay in melt instead then they cont bowens reaction series

25
Filter pressing
during crystallisation there is a point when liquid + crystals together = slushy mess mass of overlying crystals squeezes liquid out forms layer above = more silicic
26
chem analysis of rocks
rocks contain many diff chemicals e.g. SiO2 MgO FeO Al2O3 etc. proportions are dependent on S vs I vs M vs UM e.g. less silicic= less SiO2 more mafic = more MgO (also more FeO but less diff)
27
Examples of where magma differentiation occurred
Palisade sill Skaergaard intrusion Hekla volcano Bushveld igneous complex
28
palisade sill description and explanation see diagram in booklet
C rock = sandstone sandstone-metaquartizite-basalt-dolerite-gabbro-dolerite-olivine-basalt-metaquartzite-sandstone metaquartzite = baked margin basalt= cooled margin dolerite= fractionation results comp lower in M minerals + richer in S Gabbro= coarse cooled slowest olivine- first crystals to form as high MP (fractionation), denser, sink, gravity settling
29
Skaergaard intrusion description and explanation see diagram in booklet
upper border rock- mirrors zoned layers but thinner as early formed minerals stuck to roof of M chamber contains section of S rock (formed from last part of melt which was highly S due to fractionation) upper zone layer mid zoned layer lower zoned layer l----------v----------l layered series shoes rhyming layers crystal settling interrupted by large scale convection gravity settling filter pressing > expulsion of L > convection mixes > repeat > each time more evolved (more s) each layer has plagio on top of pyroxene and olivine Marginal border zone- chilled margin + contaminated by C rock (Gneiss)+ alternating hot fluids
30
Helka volcano description + explanation see booklet for diagram
Expected to be mafic as Iceland + D plate margin yet is inter/ Rhyolite longer between eruptions= more S fractionation: mafic min crystalise at higher temps > gravity settling > silicic at top > eruption get progressively more mafic
31
Bushveld igneous complex description
South Africa layered Igneous intrusion 400KM * 800Km vol= 1000000 Km^3 varied thickness up to 8 km formed 2 million years ago contains rich deps- largest reserve of platinum
32
mineral dep of platinum group elements
e.g. Pt Pd Ag Cu rare in crust as mostly react with Fe and in outer core the one that don't react with Fe react with sulphur react with Fe= siderophile (outer core) react with S= chalcophile (crust)