1. Major Elements

2. Updates/questions Midterm Topics: 3 component systems continued
Major element compositions

3. Liq/total solids = a-m/Liq-a total Di/Fo = m-Fo/Di-m
Ternary lever w/ 3 phases
Imagine triangular plane X - Di - Fo balanced on bulk a
Liq x a Di m Fo
Liq/total solids = a-m/Liq-a
total Di/Fo = m-Fo/Di-m

4. Pressure Effects

5. Major Elements Measure minerals or glasses: = notes provided
Electron microprobe
Electron beam + element electrons = Xray
Measure whole rocks (multiple minerals)
XRF (XRay Fluorenscence)
Xrays excite inner-shell electrons, on return to ground state emit Xrays
ICP-MS (Inductively-Coupled Plasma Mass Spectrometry)
Measure by “counting” atoms per mass
Few more in book (AA, INAA, Ion Probe)
= notes provided

6. Crustal composition
Abundance of the elements
in the Earth’s crust

7. Data example T a b l e 8 - 3 . C h m i c n y s o f r p t v g u k P d B2 4 6 9 5 7 1 1 5 . 7 4 2 3 9 F e O 6 8 M n g C a N K H + 3 1 . 1 1 . 5 7 T o t a l 9 8 . 7 5 9 9 . 6 9 9 . 3 9 9 . 5 9 9 . 2 3

8. From oxide % to atom %
Mid-Ocean Ridge Basalt

9. Rocks & mineralogy

10. Plotting compositions12 17 22 Al 2 O 3 5 10
MgO
FeO* 4 6 Na 15
CaO 45 50 55 60 65 70 75 1 K
SiO
Based on compiled data by Rick Conrey (unpub)

11. Effect of crystallization
Key:
B=bulk, L=liquid,
P-S=crystals

12. Magma Evolution Harker diagram Smooth trends Model with 3 assumptions:55 65 75 45 2 3 4 8 6 10 14 16
Al2O3
MgO
CaO
Fe2O3
Na2O
K2O
Wt. % SiO2 B BA A D RD R
Harker diagram
Smooth trends
Model with 3 assumptions:
1 Rocks are related
2 Trends = liquid line of descent (mineral control)
3 The basalt is the parent magma from which the others are derived
B=basalt, BA=basaltic-andesite, A=andesite, D=dacite, RD=rhyo-dacite, R=rhyolite

13. Magma Series

14. Alkali vs. Silica -- Hawaiian volcanics:12 10 8 6 4 2 35 40 45 50 55 60 65
%SiO2
%Na2O + K2O
Alkaline
Subalkaline
Figure Total alkalis vs. silica diagram for the alkaline (open circles) and sub-alkaline rocks of Hawaii. After MacDonald (1968). GSA Memoir 116

15. Ternary Variation Diagrams
FeO + Fe2O3
K2O + Na2O
MgO
Skaergaard
Crater Lake

16. Subalkaline subdivisionF A M
Calc-alkaline T h o l e i t c

17. F Tholeiitic Calc-alkaline M A Evolving rocktypes B-A A D R
Rhyolite
Dacite
Andesite
Basaltic Andesite
Ferro-Basalt
Basalt
Calc-alkaline
Tholeiitic
B-A A D R M A

18. Occurrence of different series
After Wilson (1989). Igneous Petrogenesis. Unwin Hyman - Kluwer

19. The Basalt TetrahedronDi Q En
Critical plane of
silica
undersaturation Ne Ab
Plane of
silica saturation Fo Ol Ne Ab
Opx Q
Alkaline field
Subalkaline field
Dividing line
Figure Left: the basalt tetrahedron (after Yoder and Tilley, 1962). J. Pet., 3, Right: the base of the basalt tetrahedron using cation normative minerals, with the compositions of subalkaline rocks (black) and alkaline rocks (gray) from Figure 8-11, projected from Cpx. After Irvine and Baragar (1971). Can. J. Earth Sci., 8,

20. Keeping series separatedOl Ne Ab
Opx Q
Alkaline field
Subalkaline field
Dividing line Ne Ab Q
1070
1060
1713
Ab + Tr
Tr + L
Ab + L
Ne + L
Liquid
Ne + Ab
Thermal
Divide