Geology 12 Presents Metamorphic Rocks Chp 7 Metamorphic



























































- Slides: 59

Geology 12 Presents

Metamorphic Rocks

Chp 7 Metamorphic Rocks Change Shape • Process by which heat, pressure and fluids change pre-existing rock in the solid state

• Where? : mainly associated with the continents. Sedimentary rocks (& sediments) cover much of the continents, but they are underlain by mainly igneous and metamorphic rocks making up the basement/craton. Not crouton!! • Where the basement is exposed is the shield. • Basement/shield: very stable over the last 600 ma and as 4 ba. million years billion years



Canadian Shield

Agents of Metamorphism: (3) • 1. Heat: increases rate of chemical reactions – 2 sources of heat: • a) Magma body: heats surrounding rock


– b) geothermal gradient: Earth warms up as you descend • Average of 25’C/km • Question: what is temperature at 30 km? T = 30 km x 25’C/km + 10’C T = 750’C + 10’C T = 760’C



• 2. Pressure: – 2 types • A) Lithostatic Pressure = confining pressure = weight of overlying rock – Applied equally in all directions – Increases 0. 25 Kbars/km of depth » (1 Kbar = 14, 700 psi)

• b) Differential Pressure = directed pressure = pressure due to mountain building – Pressure is unequal so rock is distorted conglomerate Meta-conglomerate


• 3. Fluid Activity: water & CO 2 enhance metamorphism by increasing chemical reactions by moving ions through solution Ex: 2 Mg 2 Si. O 4 + 2 H 2 O Mg 3 Si 2 O 5(OH)4 + Mg. O Olivine water serpentine away in sol’n • 3 sources of water: a) Sedimentary rock pore space (sh, sst) b) Released from magma c) Dehydration of water bearing minerals such as gypsum (Ca. SO 4 2 H 2 O)

Types of Metamorphism (3) • 1. Contact Metamorphism: when a hot body of magma alters surrounding rock with increased temperatures and the release of hot fluids (Hi T/Low P + fluids) Aureole = concentric zones of alteration Country rock Igneous intrusion slight metamorphism (rare) intermediate metamorphism (medium) extensive metamorphism (well-done)

rare medium Well done

• The larger the intrusion (more heat + more fluids) = more alteration – Contact Met’ is generally localized (small areas affected) • i) dikes & sills: only rock in immediate contact affected • ii) laccoliths & batholiths: larger area affected • 2 Types of contact Met’ – i) baked (porcelain) clay: HEAT – ii) as magma cools, water is released making new minerals -> hydrothermal alteration – valuable ore deposits

Contact Metamorphism

Country Rock Contact Metamorphism Intrusion


• 2. Dynamic Metamorphism: very localized alteration around fault zones due to differential pressure (Hi P/Low T) Slikensides or fault breccia

Dynamic Metamorphism


Fault breccia

• 3. Regional Metamorphism: results in most metamorphic rocks – Occurs over large areas – Caused by tremendous pressures, temperatures, and deformation, deep in the crust – Usually along convergent plate margins, but… Oceanic crust Upper mantle Low T/Hi P (differential) zone Continental crust Upper mantle Hi T/Hi P (lithostatic) zone

Regional Metamorphism

• …but, sometimes at divergent boundaries (hi T + fluids) ocean Descending sea water Met’ rocks Hot magma High heat flow


n Hand out note helper WS 7. 1 a

Classification of Metamorphic Rocks • 2. 5 types! • 1. Foliated: minerals have arranged in a parallel fashion…result of differential pressure

Foliated Metamorphic Rocks

Rock Parent Rock Appearance Metamorphic Grade Slate sh, volcanic fine grained, low ash splits into flat pieces Phyllite sh fine grained, low-med silvery sheen Schist sh, carbonates flakey micas low-high mafic ign’ rx Gneiss sh, sst, dark & light high felsic ign’ rx bands “Zebra Rock”

Slate



Phyllite

Notice “slight sheen”

Schist



Gneiss = “Zebra Rock”


“Zebras are gneiss”


• 2. Non-foliated: minerals have no orientation, “equidimensional” (no layers, no banding) Rock Marble Parent Appearance Rock Lst sugary, HCl Quartzite Qtz sst sugary, H=7 Metamorphic Grade low-high med-high

Non-foliated Metamorphic Rocks Marble


Quartzite Ford tough


• 2. 5 If nature of original rock can be recognized… Rock Parent Appearance rock congloflattened Metaconglomerate pebbles Metamorphic Grade low – med

Partially Foliated Rock Meta-conglomerate

Metaconglomerate

• Generally, metamorphic grade is indicated by: – 1. increase in crystal size – 2. increase in foliation, mineral segregation, or granitization of minerals – 3. index minerals: reversal of Bowen’s Reaction Series (move up to dark/Ca plag’ Fs minerals)

Pressure increasing DYNAMIC MET’ diamonds graphite REGIONAL Igneous rx granite gneiss Meltin g poin METAMORPHISM t schist phyllite coal slate Sh marble Sedimentary rocks Lst CONTACT METAMORPHISM Temperature increasing

X Y Z Low P/Hi T Contact Meta’ Y Hi P/Low T Regional Meta’ Z Hi P/Hi T Regional Meta’ X

High T Low P

n n n Do Lab 7. 1 Metamorphic Rocks ID Do WS 7. 1 Do Chp 2 -7 Review WS
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Compaction and cementation
Https://geology.com/rocks/
Metamorphic rocks properties
3 types of.rocks
Metamorphic rocks in michigan
Quartzite parent rock
Features of metamorphic rocks
Metamorphic rocks
Characteristics of metamorphic rocks
Characteristics of metamorphic rocks
Metamorphic
Regional metamorphism
Chapter 6 sedimentary and metamorphic rocks answer key
Metamorphic rocks examples
Metamorphic rocks are formed where
Hydrothermal metamorphism
Example of dynamic metamorphic rocks
Relict texture metamorphic rocks
Metamorphic rocks
Rock the concept map
Foliated rock
Metamorphic rock phase diagram
Classification of metamorphic rocks
Foliated metamorphic rocks
Uses of metamorphic rocks
How to identify metamorphic rocks
Chapter 4 lesson 4: metamorphic rocks answer key
Biotite
Metamorphic rocks characteristics
How are metamorphic rocks classified
Nonfoliated
Metamorphic grade
Metamorphic rocks
Metamorphic rocks with a layered or banded look are called
Meta means in metamorphism
Metamorphic rocks
Non foliated metamorphic rocks
Metamorphic rocks drawing
How rocks are formed
Formation of metamorphic rocks
Coquina sedimentary rock type
Characteristics of metamorphic rocks
Common metamorphic rocks
Hydrothermal metamorphic rocks
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Metamorphic rocks renewable or nonrenewable
Esrt rocks
Metamorphic rocks in hawaii
Low grade and high grade metamorphic rocks
How are metamorphic rocks formed
Metamorphic rocks
Sedimentary rocks turn into metamorphic
Phyllite
Metamorphic rocks in texas
Foliated rock
Importance of sedimentary rocks
Metamorphic grade
Luster and streak
Student found a metamorphic rock in the campsite