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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 20. Metamorphic Petrology. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21.

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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 20 Metamorphic Petrology

  2. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 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 21 Granulite facies and mafic protoliths Most granulites are in Archean crustal regions (cratons) and involve a variety of protoliths (mafic to felsic, sedimentary Rocks).

  4. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Granulite facies and mafic protoliths Essential mineralogy Low pressure (lower granulite facies) plagioclase + cpx + opx ± hornblende ± olivine Medium pressure (middle granulite facies) plagioclase + cpx + opx + garnet ± hornblende High pressure (upper granulite facies) plagioclase + cpx + garnet + quartz ± hornblende

  5. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Granulite facies and mafic protoliths Continuous reactions in the transition from amphibolite facies to granulite facies NaCa2(Mg,Fe)5AlSi2O22(OH)2 + 3SiO2 = NaAlSi3O8 + 2Ca(Mg,Fe)Si2O6 + 3(Mg,Fe)SiO3 + H2O hornblende quartz albite diopside enstatite NaCa2(Mg,Fe)5AlSi2O22(OH)2 = Ca(Mg,Fe)2Al2Si3O12 + CaAl2Si2O8 + (Mg,Fe)SiO3 + H2O hornblende garnet anorthite enstatite Progressive dehydration during transition from amphibolite facies to granulite due to prograde Reactions similar to those above, extraction of hydrous partial melts, or influx of CO2-rich fluids that dilute the H2O concentration.

  6. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Mafic granulites

  7. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Granulite facies and quartzo-feldspathic protoliths (intermediates and granitoids) Alkali feldspar + plagioclase + garnet ± kyanite + opx± cpx ± hornblende ± magnetite ± ilmenite

  8. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Kyanite, andalusite and sillimanite Allotropes of Al2SiO5 (same chemical formula but different atomic structures) kyanite sillimanite andalusite

  9. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Kyanite, andalusite and sillimanite Univariant reactions Invariant triple point ANDALUSITE

  10. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Kyanite, andalusite and sillimanite – atomic structures All 3 minerals are “island silicates” as they have isolated SiO4 tetrahedra They have chains of AlO6 octahedra cross-linked by SiO4 tetrahedra and by additional Al polyhedra with various co-ordination numbers… - octahedral in kyanite [CN=6] - tetrahedral in sillimanite [CN=4] - triangular bipyramidal in andalusite [CN=5]). kyanite andalusite sillimanite

  11. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Metamorphic textures and classification • Classification is fairly flexible and contextual! • Main factors that can be used are • Fabric – the most important – schist, gneiss, phyllite, slate etc • Protolith – if it can be determined – mafic, pelitic etc • Chemical composition – mafic, pelitic, quartzo-feldspathic etc • Special mineralogical names – amphibolite, marble (calcite), quartzite, serpentinite etc • Metamorphic grade – high, medium or low

  12. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Metamorphic names based on fabric This essentially means how well the foliation is developed and the type of foliation. Foliation is like cleavage in minerals, particularly the mica minerals. Strongly foliated = slate, phyllite, schist (break readily into slabs or plates) Weakly foliated = gneiss (foliation can be seen but does not have a mechanical expression) Non-foliated = greenstone, amphibole, eclogite, serpentinite, quartzite, marble, hornfels (isotropic fabric).

  13. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Types of foliations a. Compositional layering b. Preferred orientation of platy minerals c. Shape of deformed grains d. Grain size variation e. Preferred orientation of platy minerals in a matrix without preferred orientation f. Preferred orientation of lenticular mineral aggregates g. Preferred orientation of fractures h. Combinations of the above Turner and Weiss (1963) and Passchier and Trouw (1996).

  14. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Strongly foliated rocks (slate, phyllite, schist) Slate = aphanitic, dull lustre, pervasive cleavage, often graphitic Protolith is usually shale (organic material, clay and quartz) recrystallised to chlorite and micas or other fine-grained sediment

  15. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Strongly foliated rocks (slate, phyllite, schist) Phyllite = aphanitic, but coarser grains than slate, lustrous or silky sheen on cleavage surfaces, micaceous Transitional between slate and schist

  16. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Strongly foliated rocks (slate, phyllite, schist) Schist = phaneritic, sometimes porphyroblastic, segregation layering of felsic and mafic minerals parallel to fabric. Coarser than slate or phyllite Biotite schist Garnet quartz mica schist

  17. EMSC2017 - ROCKS AND MINERALS – Semester 1, 2012 – Lecture 11 EMSC2017 - ROCKS AND MINERALS – Semester 1, 2013 – Lecture 21 Weakly foliated rocks (gneiss) Gneiss – low or no chlorite or micas, quartz and feldspar are main minerals, but ferromagnesian minerals also present, foliation caused by mineral segregation into layers usually. Quartz biotite gneiss Pyroxene gneiss

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