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EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11

EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18. Metamorphic Petrology. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18.

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EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11

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  1. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Metamorphic Petrology

  2. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Metamorphic facies – metabasites (mafic protoliths) A suite of mineral assemblages found repeatedly in metamorphic terranes of all ages around the world, with a regular relationship between mineral composition and bulk composition. P-T ranges of major metamorphic facies

  3. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Mafic protoliths at greenschist facies Characteristic mineral assemblage = epidote + chlorite + actinolite + albite Additional phases = quartz, calcite, titanite, Fe-Ti-oxides A = alkalis (Na2O+K2O) C = CaO F = ferromagnesian (FeO+MgO) Epidote = Ca2Al3Si3O12(OH)2 Chlorite = (Mg,Fe)3Al4Si6O20(OH)16 Albite = NaAlSi3O8 Actinolite = Ca2(Fe,Mg)5Si8O22(OH)2

  4. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18

  5. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Epidote mineral group Zoisite = Ca2Al.Al2O.OH.Si2O7.SiO4 Clinozoisite-epidote series = Ca2(Al,Fe3+).Al2O.OH.Si2O7.SiO4 Si2O7 isolated double tetrahedra SiO4 isolated single tetrahedra AlO6 isolated single octahedra AlO4(OH)2 isolated single octahedra

  6. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Chlorite (Mg,Al,Fe)12[(Si,Al)8O20](OH)16 Layered structure of alternating talc-like Y6Z8O20(OH)4 and brucite Y6(OH)12 layers. Z = Si, Al; Y = Mg, Fe, Al Chlorite is the most characteristic mineral of the greenschist facies, common in low grade, hydrothermal alteration of ferromagnesian minerals. Y in brucite layer Z in talc layer Y in talc layer Z in talc layer

  7. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 16 Amphibole group Double chains of SiO44- tetrahedra linked together by intermediate cations. Unit cell formula therefore based on [Si4O11]6- units WX2Y5Z8O22(OH)2

  8. Amphibole group EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 16 Amphibole group WX2Y5Z8O22(OH)2 • Chemical garbage can – almost anything that doesn’t fit into other minerals goes into amphibole • Hydrous mineral – structurally bound water as (OH)- [hydroxyl] group.

  9. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 16 Amphibole group WX2Y5Z8O22(OH)2 Types include tremolite, tschermakite, pargasite, edenite, hornblende, glaucophane Hornblende – one of the Ca-rich amphiboles – common in intermediate plutonic rocks, and in basic or ultrabasic rocks : W = (Na,K)0-1 X = Ca2 Y = (Mg,Fe2+,Fe3+,Al)5 Z = Si6-7Al2-1 (Na,K)0-1Ca2(Mg,Fe2+,Fe3+,Al)5Si6-7Al2-1O22(OH,F)2

  10. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Tremolite – ferroactinolite (part of the Ca-amphibole group) WX2Y5Z8O22(OH)2 Ca2(Mg,Fe2+)5[Si8O22](OH,F)2 (1) W-site is empty (2) Solid solution with hornblende, but if Si=Al replacement is <0.5 atoms pfu, it is tremolite Can form by hydration reactions involving pyroxenes such as…. 3MgSiO3 + 2CaMgSi2O6 + SiO2 + H2O = Ca2Mg5Si8O22(OH)2

  11. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Greenschist to amphibolite facies for mafic rocks

  12. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Greenschist to amphibolite facies for mafic rocks Epidote and chlorite decrease in abundance, eventually disappearing. Hornblende, almandine-rich garnet and plagioclase increase in abundance 3(Mg,Fe)10Al4Si6O20(OH)3 + 12Ca2Al3Si3O12(OH)2 + 4SiO2 = chlorite epidote quartz 10Ca2(Mg,Fe)3Al4Si6O22(OH)2 + 4CaAl2Si2O8 + 2H2O hornblende anorthite The anorthite combines with existing albite to form oligoclase (Ab70-Ab90) Thus, amphibolites are essentially hornblende + plagioclase assemblages, sometimes with minor Fe-rich garnet.

  13. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 18 Greenschist to amphibolite facies for mafic rocks

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