Download 17 ppt

Chain silicates
JD Price
Silicate Structure
Silicate Structure
(SiO2)
Inosilicates (singles)
Pyroxene
Orthopyroxene - hypersthene
Enstatite Mg2Si2O6
Orthoferrosilite Fe2Si2O6
Clinopyroxene - Augite
Diopside CaMgSi2O6
Hedenbergite CaFeSi2O6
Image from mineral.galleries.com
Image from Klein and Hurlbut, 1985
Pyroxenoids
Wollastonite CaSiO3
Rhodonite Mn2+0.9Fe2+0.02Mg0.02Ca0.05SiO3
Pyroxmangite Mn2+0.8Fe2+0.2SiO3
Image from mineral.galleries.com
Image from Klein and Hurlbut, 1985
Inosilicates (doubles)
Amphiboles
Anthophyllite (Mg,Fe,Al)6[(Al,Si)8O22](OH)2
Cummingtonite (Mg,Fe,Al)6[(Al,Si)8O22](OH)2
Actinolite Ca2(Mg,Fe)5[Si8O22](OH)2
Hornblende Ca2(Fe,Mg)4Al(AlSi7O22)(OH,F)2
Tremolite (CaAl.Si7O22)(OH,F)2
Image from mineral.galleries.com
Sodic amphiboles
Arfvedsonite Na3Fe2+4Fe3+(Si8O22)(OH, F)2
Glaucophane Na2Mg3Al2(Si8O22)(OH, F)2
Riebeckite Na2Fe2+3Fe3+2(Si8O22)(OH, F)2
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Arfvedsonite italianminerals.com
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Glaucophane in blueschist USF
Asbestos (part 1)
There is no single
mineral called asbestos.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Asbestos is a term used
for any fibrous mineral
or rock that is soft and
pliable.
A number of amphiboles
may be asbestosforms crocidolite, fibrous
riebeckite is on
example.
Crocidolite, although rare in the
US, is the asbestos mineral
that is demonstrably
carcinogenic.
More asbestos next time…
Image from Blackburn
and Dennen, 1988
Breaking inosilicates
Images from Klein and Hurlbut, 1985
Metamorphic Facies
P kbar
All of these
conditions are
relevant to
metamorphism on
Earth. Note that
some rocks will
melt at lower T
than others
Grade - the degree
of advancing
metamorphic
conditions
Spear, 1993
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Diagram by Brad Hacker, UCSB
Metamorphic series
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Thermal metamorphism
The heat and fluids from igneous
bodies may substantially alter
the country rock they intrude.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
These are the high-T, low-P
grades (in many cases).
Thermal metamorphism rarely
produces lineated fabrics in the
resulting rocks.
Diagram by Jim Rice, UOregon
Valentine Wollastonite
Calcite, wollastonite, and graphite
Proterozoic (1.1 billion years)
Hot, silica-rich fluids from the Diana Complex (quartz
syenite) invaded adjacent calcite marble rocks.
CaCO3 + SiO2 = CaSiO3 + CO2
(calcite + silica = wollastonite + carbon dioxide)
Blue color calcite from the scattering of light uranium-decay
defects in the crystal structure. Both the defects and the
blue color disappear when heated to 250oC (482 oF).
Wollastonite has been mined throughout the Adirondacks
for use as welding flux, as a component in ceramic
materials, and as a strengthener in plastics.
A
G
E
S
Shield
Platform
Orogen
Extended
Basin
oldest rocks, 2.5 - 3.9 Ga
oldest sediments, 2.5-0.6 Ga
compressed,< 0.6 Ga
<0.6 Ga
<0.2 Ga
Divergent Boundary Oceanic Rift
Divergent Boundary Continental Rift
http://jsc.nasa.gov
STS-32
Example: the East African Rift
Hot spot
Pacific plate
motion
Example: Hawaiian chain
Hawai’i
Transform margin
Example: San Andreas Fault
© Cornell Geology
Continental Collision
Example: the Himalaya
Grade space
Collisions produce
orogens. Because the
pressure on the crust is
variable, exposed
orogens reveal mapable
regions of rocks at the
same grade.
The center, known as a
core complex,
experiences the highest
grade (note the minerals
listed).
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Amphibolite
Conditions: high P & T
Minerals: amphibole and whatnot (usually feldspar and
quartz)
Origin: clastic - Fe,Mg rich (shale), mafic (basalt,
gabbro)
Greenschist Facies
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Granulite
Conditions: very high T & high P
Minerals: pyroxene, olivine, garnet
Origin: mafic (basalt, gabbro)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Subduction: Continental arcs
Example: the Cascades
Subduction: Island arcs
Example: Indonesia
Gunung Semaru and
Bromo Caldera, Java
Blueschist facies
High pressure and
relatively lower
temperatures.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Photomicrograph of garnet-lawsoniteglaucophane blueschist from Sivrihisar,
Turkey.
Subducted materials relatively cold rocks
taken deep into the
earth.
Na-amphibole schists
may be part of the
package.
Eclogite
Conditions: high to very high P & T
Minerals: pyroxene, olivine, garnet
Origin: mafic (basalt, gabbro)
Univ. of North Carolina Web atlas of
metamorphic textures
Retrograded eclogite
Univ. of North Carolina Web atlas of metamorphic textures
Mg3Al2Si3O12 + 2CaMgSi2O6 + H2O + 0.5O2
= Ca2Mg5 Al2Si6O22(OH)2 + SiO2
Important point - the subducted slab doesn’t melt to produce
the volcanism seen in the arc. It simply doesn’t get warm
enough.
Permeability and q
k  d 2f 2 / 1600
k in m2
d = 1 mm
from von Bargen & Waff, 1986
Faceting
Waff and Faul, 1992
Faceting
Amphibolite
Faceting
Extensive faceting substantially
lowers permeability for a given
fluid fraction
d = 1 mm
6 µm
Price et al. (in review)
Melting under subduction volcanoes is most likely related to
fluid release deep in the mantle. Fluids move through
networks to flux mantle, promotes melting at 1200ºC.