Transcript ppt - SOEST

Review
Today
Review of the material covered so far
About the Midterm -- Wednesday
- Essay questions
- Lectures including major elements (part I covered)
- Book chapters 1-8
Ask questions today or during office hours
The Earth’s Interior
Crust:
Crust
Depth (km)
Upper Mantle
Transition Zone
Mantle
60
220
410
660
Lower
Mantle
Granite/Andesite (felsic)
Mantle:
Peridotite (ultramafic)
2898
Outer
Core
Core:
(liquid)
Metal alloy/liquid
Core
5145
Inner
Core
(solid)
6370
Most important elements
Si
14.4%
Al Ca
S
3.0% 1.4% 1.0%
O
50.7%
Fe
15.2%
Mg
15.3%
Figure 1-5. Relative atomic abundances of the seven most common elements that
comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic
Petrology, by John Winter , Prentice Hall.
P and T rise with depth
0
Pressure (GPa)
30
10
20
40
1000
Mantle
2000
3000
4000
Core
5000
6000
What Gradient was this?
Geotherm and solidus: how to melt
Since the
geotherm is
too cold, how
do you melt
the mantle?
Ternary diagrams
Know how to classify a rock
Textures: result of nucleation+growth
minor undercooling (Ta):
rapid growth and slow
nucleation
=> fewer coarse-grained
crystals.
more undercooling (Tb):
slower growth and rapid
nucleation
=> many fine-grained
crystals.
very rapid cooling: little/no
nucleation or growth (Tc) =>
glass
Textures
Grain size: matrix vs. phenocryst
Grain shape: euhedral, subhedral, anhedral
Speed in growing: dendritic, skeletal, swallow tailed
Zoning: normal, reversed, oscillatory
Resorbtion
Growth order: mineral with inclusions, WHICH WAS FIRST?
Intergrowths: granophyric or graphic
Twinning: know and recognize: Carlsbad, albite, tartan twins
Replacement and exsolution: Myrmekite, (anti-)perthite

Networks
O atoms on corners can be shared:
•2 shared O => chain (spaghetti)
•3 shared O => sheet (lasagna)
•4 shared O => lump of
dough/ravioli?
Connecting Si tetrahedra makes
polymers (like plastic)
http://visionlearning.com/library/modules/mid140/Image/VLObject-3539060516120522.jpg
Effect of volatiles
•Adding H2O or CO2 changes polymers:
H2O breaks polymers
CO2 combines polymers
Polymerization and Viscosity
•
What will move more easily:
a) Shorter chain polymers?
b) 3D networks?
•
What does that mean w.r.t. rock types?
Ease with which the melt moves relates to viscosity
=> Viscosity related to composition
Types of volcanoes
What composition goes with what volcano again?
Does that make sense with viscosity?
Terms to remember
Central vent: main path: crater eruptions
Rift/fissure vent: main vent can get plugged up, easy way out to the side;
common in flood basalts, Kilauea/Hawaii
Pyroclastic systems: different cone types
Domes: when after main eruption?
Lava flows: 2 types
Rhyolite flows: slow, blocky, glassy (obsidian) WHY SLOW?
Caldera: What is the eruption sequence/how to form one?
Fissure eruptions: what are they, associated with what?
What are pillow lavas and columnar joints?
Pyroclastic material: tephra vs. pyroclastic flows
Ring dikes and cone sheets
The Phase Rule
F=C-f+2
F = # degrees of freedom
The number of intensive parameters that must be specified in
order to completely determine the system
things like temperature and pressure
NOTE: if pressure = fixed => F = C - f + 1
Can also think of this as “how many parameters can be
varied independently from each other”
Crystallization in binary diagram
Cool to 1455oC (point b) -- F = C - f + 2
Composition of melt and crystals?
WHAT LEVER?
1600
a
Liquid
1500
b
T oC
1400
c
Anorthite + Liquid
1392
1300
1553
Diopside + Liquid
1274
1200
Diopside + Anorthite
Di
20
40
60
Wt.% Anorthite
80
An
Crystallization: eutectic
at 1274oC f = 3 so F = 2 - 3 + 1 = 0 invariant
 (P) T and the composition of all phases is fixed
o
 Must remain at 1274 C as a discontinuous
reaction proceeds until a phase (which?) is lost
1600
a
Liquid
1500
b
T oC
1400
c
Anorthite + Liquid
1392
1300
1553
g
Diopside + Liquid
1200
d
h
Diopside + Anorthite
Di
20
40
60
Wt.% Anorthite
80
An
1274
Crystallization & solid solution
F=2-2+1=1
(“univariant”)
Must specify only one
variable from among:
T
X
X liq
An
liq
An
X
liq
Ab
X
plag
An
plag
An
and X
are dependent upon T
a
1500
X
plag
Ab
1557
b
Liquid
c
Plagioclase
1400
o
T C
+
1300
Liquid
Plagioclase
1200
The slope of the solidus
and liquidus are the
expressions of this
relationship
1118
1100
Ab
20
40
60
80
An
Cool X = n
o
 At 1960 C hit solvus
exsolution
 2 liquids o and p
f=2 F=1
Immiscible Liquids
n
Liquid
2000
o
p
both liquids follow solvus
At
1695oC
Two Liquids
1800
get Crst also
T oC
Liquid +
Forsterite
Reaction?
Cristobalite + Liquid
1600
1557
1543
c
1695
Mafic-rich
liquid
Forsterite
+ Enstatite
Crst
Silica-rich
liquid
1713
1695
Enstatite + Cristobalite
1470
Enstatite + Tridymite
1400
Mg2SiO4
20
40
MgSiO2
60
Wt.% X2
80
SiO2
Effect of PH O on Ab-Or
2
Figure 6-17. The Albite-K-feldspar system at various H2O pressures. (a) and (b) after
Bowen and Tuttle (1950), J. Geol, (c) after Morse (1970) J. Petrol.
a
Liquid
Fo + Liq
Di + Liq
Di + Fo
f = 2 (Fo + Liq)
 F=3-2+1=2
System determined:
liq
 T and X
or
An
 X liq and X liq
An

Fo
Pure Fo forms
Just as in binary
An
Ternary phase
diagrams
Ternary lever w/ 3 phases
 Imagine
triangular plane X - Di - Fo balanced on bulk a
Liq x
a
Di
m
/
/
total Di/Fo = m-Fo/Di-m
Liq total solids = a-m Liq-a
Fo
Major
elements:
x-y plots
22
10
Al2O3
MgO
17
5
0
12
15
Harker diagram
for Crater Lake
FeO* 10
10
5
Notice curves and
kinks
CaO
5
0
0
4
6
3
Na2O
4
2
2
0
45
1
0
50
55
60
SiO2
65
70
75 45
50
55
60
SiO2
65
70
75
K2O
Effect of crystallization
Key:
B=bulk, L=liquid,
P-S=crystals


Balance liquid and
crystals to bulk
composition
Crystals
CONTROL liquid
path