What if we had staurolite and andalusite together? What conditions would that indicate?

1. What if we had staurolite and andalusite together? What conditions would that indicate?

2. Epidote Group • Sorosilicates (paired silicate tetrahedra) • Include the mineral Epidote Ca2FeAl2Si3O12(OH), Zoisite (Ca2Al3Si3O12(OH) and clinozoisite (polymorph)

3. Garnet: A2+3 B3+2 [SiO4]3 • “Pyralspites” - B = Al • Pyrope: Mg3 Al2 [SiO4]3 • Almandine: Fe3 Al2 [SiO4]3 • Spessartine: Mn3 Al2 [SiO4]3 • “Ugrandites” - A = Ca • Uvarovite: Ca3 Cr2 [SiO4]3 • Grossularite: Ca3 Al2 [SiO4]3 • Andradite: Ca3 Fe2 [SiO4]3 • Occurrence: • Mostly metamorphic • Some high-Al igneous • Also in some mantle peridotites Garnets Garnet (001) view blue = Si purple = A turquoise = B

4. Staurolite • Aluminosilicate - Fe2Al9Si4O22(OH)2 • Similar structure to kyanite with tetrahedrally coordinated Fe2+ easily replaced by Zn2+ and Mg2+ • Medium-grade metamorphic mineral, typically forms around 400-500 C • chloritoid + quartz = staurolite + garnet • chloritoid + chlorite + muscovite = staurolite + biotite + quartz + water • Degrades to almandine (garnet at higher T) • staurolite + muscovite + quartz = almandine + aluminosilicate + biotite + water

5. Metamorphic chain silicates • Actinolite and tremolite are chain silicates derived from dolomite and quartz and common in low-mid grade metamorphic rocks • Riebeckite and Glaucophane are also chain silicates – higher grade minerals, often a blue color • These minerals usually lower P, higher T conditions

6. Metamorphic Facies • Where do we find these regimes of P-T ‘off’ of the typical continental isotherms?? • How is the environment that forms a blueschist facies rock different from one forming a hornfels?

7. Metamorphic Facies Table 25-1. The definitive mineral assemblages that characterize each facies (for mafic rocks).

8. Facies Series Miyashiro (1961) initially proposed five facies series, most of them named for a specific representative “type locality” The series were: 1. Contact Facies Series (very low-P) 2. Buchan or Abukuma Facies Series (low-P regional) 3. Barrovian Facies Series (medium-P regional) 4. Sanbagawa Facies Series (high-P, moderate-T) 5. Franciscan Facies Series (high-P, low T)

9. Fig. 25-3.Temperature-pressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

10. Isograds • Lines (on a map) or Surfaces (in the 3D world) marking the appearance or disappearance of the Index minerals in rocks of appropriate compositione.g. the ‘garnet-in isograd’; the ‘staurolite-out isograd’Complicated by the fact that most of these minerals are solid solutions

11. Isograds for a single shale unit in southern Vermont • Which side reflects a higher grade, or higher P/T environment?

12. Meteorite/ Comet Impacts • P/T space??

14. Energy of an impact • Kinetic energy – going from very fast to stopping is a BIG change in energy • What happens to that energy?? • Impactite – any mineral formed as a result of this impact Shatter cone

15. Materials indicating Meteorite Impacts • Tektites • Glass formed from impact

16. Diaplectic Glass • Glass formed through fusion of different minerals – not melted, but fused…

17. What Happens to minerals that are there but not melted? • Shock Quartz • Lamellae retaining evidence of impact

18. Diamonds • Very small diamonds can form from impacts and are found in meteorite impact craters around the world

19. Quartz Polymorphs • Coesite and Stishovite found associated with impact craters