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Metamorphic Facies & Mineral Assemblages Study

Explore metamorphic facies, mineral assemblages, and petrology of rocks & minerals to understand their composition, formation, and transformations. Topics include chlorite, amphibole group, epidote, and more. Dive into the world of rocks and minerals through the lens of metamorphic terranes and facies variations.

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Metamorphic Facies & Mineral Assemblages Study

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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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