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

Epidote Group Sorosilicates (paired silicate tetrahedra) Include the mineral Epidote Ca 2 FeAl 2 Si 3 O 12 (OH), Zoisite (Ca 2 Al 3 Si 3 O 12 (OH) and clinozoisite (polymorph)

Garnets Garnet (001) view blue = Si purple = A turquoise = B Garnet: A 2+ 3 B 3+ 2 [SiO 4 ] 3 “Pyralspites” - B = Al Pyrope: Mg 3 Al 2 [SiO 4 ] 3 Almandine: Fe 3 Al 2 [SiO 4 ] 3 Spessartine: Mn 3 Al 2 [SiO 4 ] 3 “Ugrandites” - A = Ca Uvarovite: Ca 3 Cr 2 [SiO 4 ] 3 Grossularite: Ca 3 Al 2 [SiO 4 ] 3 Andradite: Ca 3 Fe 2 [SiO 4 ] 3 Occurrence: Mostly metamorphic Some high-Al igneous Also in some mantle peridotites

Staurolite Aluminosilicate - Fe 2 Al 9 Si 4 O 22 (OH) 2 Similar structure to kyanite with tetrahedrally coordinated Fe 2+ easily replaced by Zn 2+ and Mg 2+ Medium-grade metamorphic mineral, typically forms around 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

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

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?

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

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) Facies Series

Fig 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.

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

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

Meteorite/ Comet Impacts P/T space??

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

Materials indicating Meteorite Impacts Tektites Glass formed from impact

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

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

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

Quartz Polymorphs Coesite and Stishovite found associated with impact craters