Meta change
morph body
Can start as any other type of rock:
igneous
sedimentary
metamorphic
Figure 7.1 3.8 BY old metamorphic rock from
Greenland
This is a metamorphosed granodiorite, and provides evidence of the oldest known continent-forming event in Earth history.
Topics covered:
Agents of metamorphism
Changes associated with metamorphism
Examples of metamorphic rocks
Metamorphic grade and facies
Metamorphic
minerals indicate
temperature & pressure conditions
Continents
are underlain by metamorphic rocks
Economically
valuable:
marble
architectural stone
slate (shingles, blackboards, pool tables)
ore deposits: copper, lead, zinc,
iron
Core of the
continent made of very old metamorphic rocks
with granitic plutons
Figure 20.3 Canadian Shield
Figure 20.4 Geologic section
across the craton, showing Precambrian
metamorphic basement and granitic
plutons
Figure 20.5 Satellite image showing the Australian
craton
Really important for the
final outcome
an amphibolite (not enough Fe & Mg) Heat Pressure
Fluid activity How to heat rocks: (1) move the rocks to the heat regional metamorphism (2) bring the heat to the rocks igneous intrusion
and contact metamorphism Geothermal gradients
refer back to Figure 3.15 Typically
about 3ΊC per 100 m down into the crust May be much
higher in volcanic regions and near igneous intrusions Confining, or lithostatic pressure: equal in all directions
For example:
Where do fluids come from?
Figure 7.2
Figure 7.3 Differential pressure can be uneven pressure or
shearing pressure Figure 7.4 A deformed
conglomerate cobbles did not melt, but did squish
Figure 7.5 Orientation of
minerals response to stress
Figure 7.7 Fairly random mineral orientation
Figure 7.7 Preferred mineral orientation
Cover Figure 7.00 Heated, stressed, and bent Non-foliated
granite compared to foliated gneiss
Low
grade Intermediate grade High grade Partial melting
Melting Concept of
index minerals:
A typical sequence of index minerals, from low grade
to high grade: chlorite muscovite biotite garnet
staurolite sillimanite Those four factors, again : Composition (initial composition) Temperature Pressure Fluids And remember: metamorphism
occurs WITHOUT melting
Table 7.1 Parent rocks
& metamorphic rocks Goes
back to initial composition *** know the parent rocks for these
metamorphic rocks *** marble quartzite hornfels Limestone into marble Figure 7.8
CaCO
Figure 7.19 Magma intrusion into
limestone Figure 7.9 Vertical
sequence of metamorphism sediments silt (original sediment)
Slate: Heated
(slightly) and squeezed shale Figures 7.10 & 7.11
Phyllite: Figure 7.12 Newly formed micas, still small grains
Garnet mica schist Garnet a single tetrahedron silicate increasing T
& P
Gneiss Figure 7.14 Light and dark bands or lenses of minerals
Migmatite Figure 7.15 Not quite igneous, but past being a metamorphic
At a convergent plate boundary Figure 7.22 *** Make sure you understand the processes presented in Mid-ocean ridge Figure 7.17 Hydrothermal circulation over a magma
chamber (think Yellowstone) Figure 7.21
Table
7.3 Hydrothermal
processes Ore
bodies
Hydrothermal circulation
concentrates elements into ore bodies in the country rock
Ore veins Figure 7.20 Box 7.4 Figure 1
A, B & C represent different settings
Plate interior normal T & P gradients Volcanic-plutonic complex high T, low P Subduction zone low T, high P
Each piece represents a major collision event, or a series
of related events A field example of metamorphism:
A natural marble outcrop A metamorphic complex Naxos Island, Greece, in the Aegean Sea
Hydrothermal
intrusions into the marble
Initial composition
of rock
Physical factors associated with metamorphism
Heat
Pressure
Fluids
Confining pressure
Foliated metamorphic rock
Metamorphic styles: Contact metamorphism
Depth, heat and metamorphic grade
Metamorphic styles: Regional metamorphism
Hydrothermal systems
Metamorphic facies Temperature & Pressure space
Regional metamorphism Figure 7.22
Core of the North American continent
Creating marble