H.W. #3 + Read Solar Nebula Theory Study Guide for exam 2 Study Area for lab has practice exam All missed labs must be made up before lab exam All missed homework must be made up before lecture exam 2

Practice Lab Exam Lab Samples Study Area Felmley Hall 203

Metamorphism and Metamorphic Rocks

Rock Cycle Revisited Sedimentary Rocks Igneous Rocks Metamorphic Rocks Magma Sediment Pressure And Cementation Erosion Heat and Pressure Cooling Heat Pressure Erosion

Igneous Aphanitic -glassy -vesicular Phaneritic Sedimentary Nonclastic -biochemical (biogenic) -chemical Clastic Metamorphic Foliated -banded Nonfoliated Rock Textures

Definitions Metamorphism – mineralogical, chemical, and physical changes that occur in solid rocks. Occurs at depths greater than that of sediments and sedimentary rocks Solid state recrystallization – changes that occur without the rock melting (rocks that melt are igneous).

Surface 5 km 30 km 200 o C 600 o C Sedimentary Metamorphic Magma 15 o C

Factors influencing Metamorphism Temperature Pressure Pore Fluid Time

Temperature, Pressure and Rock Type

Factors influencing Metamorphism Temperature below about 200 o C, most minerals are stable (little or no metamorphism) above 200 o C, reaction rate increases as temperature increases, new minerals begin to form above 600 o C, some minerals begin to melt (transition to igneous rocks)

Factors influencing Metamorphism Pressure as pressure increases, pore spaces reduced and density increases, pore fluids are expelled Differential stress pressure is greater in one direction than in another

Differential Stress

Effects of Stress Uniform Differential

Differential Stress Foliation – a metamorphic rock texture due to alignment of minerals as a result of differential stress Slaty cleavage – foliation that develops at low temperature and pressure (metamorphosed shale)

Foliation In this schist, viewed between crossed polarisers, the parallel mica flakes show up in bright colors, and large rounded garnet crystals appear black. Field of view 6 mm, polarising filters.

Burial Mountain Building

Factors influencing Metamorphism Pore fluids (water and carbon dioxide) as pressure increases, pore fluids are expelled Pore fluids increase the rate of metamorphic reactions by: storing ions involved in reactions moving ions from one place to another

Pore Fluids Dissolution / Precipitation

Factors influencing Metamorphism Time solid state recrystallization is a slow process in general, size of minerals increases with time

Preferred Mineral Orientation (Foliation) Ductile (plastic) Deformation Pressure Solution Grain Rotation Growth in Preferred Orientation

Ductile (plastic) DeformationPressure Solution

Grain Rotation

Growth in Preferred Orientation

Foliation

Types of Metamorphism 1. Burial Metamorphism 2. Regional Metamorphism 3. Contact Metamorphism

Types of Metamorphism Burial Metamorphism most common type, occurs where crust is greater than 5 km thick Relatively low temp. and pres. at shallow depths through High Temp. and Press at great depths Maximum stress vertical, foliation parallel to ground surface

Burial Metamorphism

Regional Metamorphism

Types of Metamorphism Regional Metamorphism associated with convergent plate margins folding and faulting increase thickness of the crust occurs over a range of temperatures and pressures low grade to high grade metamorphism

Grades of Regional Metamorphism

Shale sedimentary rock Slate – aligned clay minerals Phyllite – muscovite mica Schist - Biotite mica/ garnet Gniess – quartz/ feldspar (banded) Melting Increasing Hot & Pressure

Metamorphic Grades

Metamorphic rock Protoliths (parent rocks) Parent rock Slate Phyllite Schist Gneiss Marble Quartzite Metamorphic rock Shale unknown Limestone Sandstone

Regional Metamorphism Contact Meta

Types of Metamorphism Contact Metamorphism occurs in rocks around a magma body high temperature (heat from magma) low pressure (occurs at shallow depths in the crust)

Contact Metamorphism

Metamorphic Grade

Low Grade Metamorphism Example: Slate forms at low temperature and pressure microscopic crystals dull luster clay and mica minerals foliated

Low Grade - Slate

Metamorphic Grade

Intermediate Grade Metamorphism Example: Phyllite intermediate temperature and pressure small crystals shiny luster mostly mica minerals foliated

Intermediate Grade – Phyllite

Metamorphic Grade

High Grade Metamorphism Example: Schist high temperature and pressure large crystals mica-rich foliated

High Grade - Schist Side view Top view

Metamorphic Grade

High Grade Metamorphism Example: Gneiss high temperature and pressure large crystals mica-poor foliated

High Grade - Gneiss

Regional Revisited Slate Phyllite Schist, Gneiss

Non-foliated Metamorphic Rocks granular texture interlocking grains composed primarily of one mineral uniform grain size

Nonfoliated - Marble metamorphosed limestone (CaCO 3 ) bedding and fossils obliterated

Nonfoliated - Quartzite metamorphosed quartz-rich sandstone Pore spaces filled with SiO 2