Transcript clastic rocks-composition - Cal State LA

CLASTIC ROCKSCOMPOSITION
Clastic Components
► detrital
grains
► f. grained matrix
► authigenic minerals
Mineral Abundance
► Depends
on:
 source rk
 mechanical/chemical stability
Chemical Stability
► qtz,
zircon,
tourmaline
most stable:
► least
stable
pyroxene,
olivine;
feldspars in
between
Mechanical Stability
► depends
on hardness
& if cleavage present
► qtz hard, rk frags=
weak
http://cmsc.minotstateu.edu/Labs/web%20minerals/Albite.html
TYPES OF DETRITAL GRAINS
TYPES OF DETRITAL
GRAINS
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C. Quartz
 most common, most stable
 average s.s. = 65% qtz; some
up to 100%
 source =
plutonic/gneisses/schists
 have mono/polyxline; undulose
vs nonundulose
 difficult to tell source rk from
qtz
 qtz volcanics--nonundulose,
monoxline
 polyxline= meta source-many
xls
 hydrothermal-much inclusions;
mono or coarse polxline
 monoxline qtz w/undulose ext
& polyxline least stable
Petrographic Textures of Detrital Polycrystalline Quartz as an Aid to
Interpreting Crystalline Source Rocks Steven W. Young (2) Journal of
Sedimentary Research Volume 46 (1976)
http://plaza.snu.ac.kr/~lee2602/atlas/quartz.html
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FELDSPAR
s.s. avg. 10-15%, arkoses up to
50%
destroyed during transport:
felds to sericite, clays
(kaol./illite)
felds common from
granite/gneiss
humid climate= felds
dissolution; arid= felds survive
humid & rapid uplift--felds
survive
Elemental Mobility in Sandstones Duping Burial: Whole-Rock
Chemical and Isotopic Data, Frio Formation, South Texas K.L.
Milliken, L.E. Mack, L.S. Land Journal of Sedimentary Research
Volume 64a (1994)
http://www.endeeper.com
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Micas & Clays
 common in matrix and mudrocks
 biotite & chlorite may form large grains on bedding
plane
► Heavy
Minerals
► Other
Minerals
 usually 1 %
 provenance-garnet, epidote,staurolite-metamorphic
terrain
 rutile, apatite & tourmaline-most common ig. rocks
 Carbonate fossils; oolites, pellets, intraclasts
 phosphate, glauconite
Classification of Sandstones
► Over
50 proposed
► Based on:
 texture
 composition/mineralogy/ presence or absence
of matrix
Textural Classification
► congl/breccia,
ss,
mudrocks
(siltstones,
mudstones,
claystones)
► use sand, silt, clay
as end members,
also gravel
Compositional/
mineralogical
classification
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qtz, felds, rk frags
common in ss
matrix may be present
most use trangular
QFL/QFR plots
qtz arenites, arkoses,
lithic arenites matrixfree
wackes greater than 5%
matrix
Graywacke problem
 matrix-rich ss, chlorite
matrix
From F.J. Pettijohn, P.E. Potter, and R. Siever, Sand and Sandstone (1987), 2nd
ed., Springer-Verlag, Berlin
Provenance
► Mineralogy
clue to eroded source
 rk fragments most important
 K felds mostly alkalic ig/met rks
 fresh angular felds = high relief source or arid
or cold climate
 small, rounded weathered = low relief or warm
humid climate
 be ware of diagenesis
Tectonic Setting
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What is tectonic setting of source rocks?
3 major tectonic settings
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continental block provenances
magmatic arc provenances
recycled orogen provenances
Continental Block
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In continental
masses
May have
passive/active
margins
Composed of
plutonic, meta, and
sed rocks, few
volcanics
Generate qtzose
sands, high K to Ca
felds ratios
Meta and sed rk
frags
http://csmres.jmu.edu/geollab/Fichter/SedRx/Clastic.html
Recycled orogen
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Plate collision zones
with uplift at suture
Have sed and met
rks present prior to
collision
Produce:
 sed/met rk frags
 moderate qtz, high
qtz, felds ratio
 If have magmatic
arc/cont collision
have:
 volcanics,
ultramafics, chert,
argillite, lithic ss,
and ls.
Magmatic Arc
Plate
convergence
zone with arc
► Have volcanic
highlands
► Produce:
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 volcaniclastic
debris
 qtz & K felds
rare except at
arc dissection
 deposition in
trench