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Major Elements

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

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Major Elements

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  1. Major Elements

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

  3. 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. Measure minerals or glasses: • 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 Major Elements

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

  7. T a b l e 8 - 3 . C h e m i c a l a n a l y s e s o f s o m e r e p r e s e n t a t i v e i g n e o u s r o c k s P e r i d o t i t e B a s a l t A n d e s i t e R h y o l i t e P h o n o l i t e S i O 2 4 2 . 2 6 4 9 . 2 0 5 7 . 9 4 7 2 . 8 2 5 6 . 1 9 T i O 2 0 . 6 3 1 . 8 4 0 . 8 7 0 . 2 8 0 . 6 2 A l 2 O 3 4 . 2 3 1 5 . 7 4 1 7 . 0 2 1 3 . 2 7 1 9 . 0 4 F e 2 O 3 3 . 6 1 3 . 7 9 3 . 2 7 1 . 4 8 2 . 7 9 F e O 6 . 5 8 7 . 1 3 4 . 0 4 1 . 1 1 2 . 0 3 M n O 0 . 4 1 0 . 2 0 0 . 1 4 0 . 0 6 0 . 1 7 M g O 3 1 . 2 4 6 . 7 3 3 . 3 3 0 . 3 9 1 . 0 7 C a O 5 . 0 5 9 . 4 7 6 . 7 9 1 . 1 4 2 . 7 2 N a 2 O 0 . 4 9 2 . 9 1 3 . 4 8 3 . 5 5 7 . 7 9 K 2 O 0 . 3 4 1 . 1 0 1 . 6 2 4 . 3 0 5 . 2 4 H 2 O + 3 . 9 1 0 . 9 5 0 . 8 Data example 3 1 . 1 0 1 . 5 7 T o t a l 9 8 . 7 5 9 9 . 0 6 9 9 . 3 9 9 . 5 0 9 9 . 2 3

  8. From oxide % to atom %

  9. Rocks & mineralogy

  10. 22 10 Al O MgO 2 3 17 5 0 12 15 10 FeO* 10 CaO 5 5 0 0 4 6 3 Na O 2 K O 4 2 2 2 1 0 0 45 50 55 60 65 70 75 45 50 55 60 65 70 75 SiO SiO 2 2 Plotting compositions

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

  12. B BA D A RD R 16 Al2O3 14 10 Fe2O3 6 8 2 MgO 4 0 8 4 CaO 4 0 Na2O 3 2 4 K2O 2 0 55 65 45 75 Wt. % SiO2 Magma Evolution 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. 12 10 Alkaline 8 %Na2O + K2O 6 4 2 Subalkaline 55 65 40 60 35 45 50 %SiO2 Alkali vs. Silica -- Hawaiian volcanics:

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

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

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

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

  19. The Basalt Tetrahedron Di Ol Opx Critical plane Plane of of silica silica saturation undersaturation Ab Q Ne Subalkaline field Alkaline field En Fo Ab Q Ne Dividing line Figure 8-12. Left: the basalt tetrahedron (after Yoder and Tilley, 1962). J. Pet., 3, 342-532. 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, 523-548.

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

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