Bowen's reaction series A2

Question 1

Types of pyroxene

Answer 1

Augite and Diopside

Question 2

Types of olivine

Answer 2

Forsterite and Fayalite

Question 3

what is the most common type of amphibole

Answer 3

Hornblende

Question 4

2 sections Bowens reaction series

Answer 4

discontinuous
continuous

Question 5

discontinuous series minerals/rocks

Answer 5

high temp olivine UM

                    pyroxene     
                                            M
                   amphibole    

                   biotite              I    low temp

Question 6

Continuous series minerals/rocks

Answer 6

High temp Ca rich (UM)

                 (plagioclase feldspar)

low temp Na rich (I)

Question 7

whole Bowen’s reaction series

Answer 7

olivine Ca rich

pyroxene

amphibole
(hornblende)

biotite Na rich

            orthoclase 
           
            Muscovite 
              
             Quartz 

As we move down temp and silica content decrease

Question 8

Discontinuous reaction series explanation

Answer 8

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

Question 9

continuous reaction series explanation

Answer 9

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

Question 10

Eutectic systems

Answer 10

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

Question 11

eutectic point

Answer 11

point at which all 3 phases exist

liquid, solid and mix

Question 12

liquidus

Answer 12

Phase boundary

everything above this line is melt

below some crystal and some melt- partial melt

Question 13

2 different types of Eutectic phase diagrams

Answer 13

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

Question 14

solidus

Answer 14

phase boundary

shows temp when the rock first begins to melt

anything below = solid

Question 15

differences between binary and solid solution eutectic diagrams

(how to read them)

Answer 15

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

Question 16

Zone crystals

Answer 16

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

Question 17

forsterite vs fayalite

Answer 17

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

Question 18

Minerals at low temps of Bowens reaction series

Answer 18

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

Question 19

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

Answer 19

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)

Question 20

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

Answer 20

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

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

Question 21

How can magma become contaminated with diff rock

Answer 21

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

Question 22

3 types of magma differentiation

Answer 22

fractional crystallisation

gravity settling

filter pressing

Question 23

fractional crystallisation

Answer 23

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

Question 24

Gravity settling

Answer 24

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

Question 25

Filter pressing

Answer 25

during crystallisation there is a point when liquid + crystals together = slushy mess

mass of overlying crystals squeezes liquid out
forms layer above = more silicic

Question 26

chem analysis of rocks

Answer 26

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)

Question 27

Examples of where magma differentiation occurred

Answer 27

Palisade sill

Skaergaard intrusion

Hekla volcano

Bushveld igneous complex

Question 28

palisade sill description and explanation

see diagram in booklet

Answer 28

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

Question 29

Skaergaard intrusion description and explanation

see diagram in booklet

Answer 29

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

Question 30

Helka volcano description + explanation

see booklet for diagram

Answer 30

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

Question 31

Bushveld igneous complex
description

Answer 31

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

Question 32

mineral dep of platinum group elements

Answer 32

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)